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Age anatomy and physiology. Cheat sheet: briefly, the most important

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Table of contents

1. Accepted abbreviations
2. Patterns of growth and development of the child’s body (Basic patterns of growth and development. Age periodization. Acceleration of growth and development. Age-related anatomical and physiological characteristics. Hygiene of the teaching and educational process at school. Hygienic foundations of students’ daily routine)
3. The influence of heredity and environment on the development of the child’s body (Heredity and its role in the processes of growth and development. Man and plants. Man and animals. The influence of viruses on the human body. Hygiene of clothing and footwear)
4. Patterns of ontogenetic development of the musculoskeletal system (Features of the functions and structure of the musculoskeletal system. Types and functional characteristics of muscle tissue in children and adolescents. Growth and work of muscles. The role of muscle movements in the development of the body. Peculiarities of growth of the skull bones. Growth of the spine. Spine of an adult and a child. Development of the chest. Features development of the pelvis and lower extremities. Skeleton of the lower extremities. Development of bones of the upper extremities. The influence of furniture on posture. Hygienic requirements for school equipment)
5. Development of the body's regulatory systems (The significance and functional activity of the elements of the nervous system. Age-related changes in the morphofunctional organization of the neuron. Properties of excitation impulses in the central nervous system. Bioelectric phenomena. Processes of excitation and inhibition in the central nervous system. Structure and functioning of the spinal cord. Structure and functioning of the brain. Functions of the autonomic department nervous system. Endocrine glands. Their relationship and functions. Development of the child’s genital organs. Puberty)
6. Analyzers. Hygiene of the organs of vision and hearing (Concept of analyzers. Organs of vision. Structure of the eye. Light and color sensitivity. Light-perceiving function. Light regime in educational institutions. Auditory analyzer. Vestibular apparatus)
7. Anatomical and physiological features of brain maturation (Development of the cerebral hemispheres and localization of functions in the cerebral cortex. Conditioned and unconditioned reflexes. I.P. Pavlov. Inhibition of conditioned reflexes. Analytical-synthetic activity of the cerebral cortex. First and second signaling systems. Types of higher nervous activity)
8. Age-related features of blood and circulation (General characteristics of blood. Blood circulation. Heart: structure and age-related changes)
9. Age-related characteristics of the respiratory system (Structure of the respiratory organs and vocal apparatus. Respiratory movements. Acts of inhalation and exhalation. Gas exchange in the lungs. Hygienic requirements for the air environment of educational institutions)
10. Age-related features of digestion (Structure of the digestive canal. Digestion process)
11. Age-related features of metabolism and energy (Characteristics of metabolic processes. Main forms of metabolism in the body. Age-related characteristics of energy metabolism)
12. Hygiene of labor training and productive work of students

Accepted abbreviations

ATP - adenosine triphosphate

н - nano... (10-9)

Topic 1. PATTERNS OF GROWTH AND DEVELOPMENT OF CHILDREN'S ORGANISM

1.1. Basic patterns of growth and development

The general biological properties of living matter are the processes of growth and development, which begin from the moment of fertilization of the egg and represent a continuous progressive process that takes place throughout life. The organism develops in leaps and bounds, and the difference between the individual stages of life is reduced to quantitative and qualitative changes.

Growth is an increase in the size and volume of a developing organism due to the reproduction of body cells and an increase in the mass of living matter. The changes relate primarily to anthropometric indicators. In some organs (such as bones, lungs), growth is carried out mainly due to an increase in the number of cells, in others (muscles, nervous tissue), the processes of increasing the size of the cells themselves predominate. It must be said that this definition of height does not affect changes due to fat deposition or water retention.

Absolute indicators of body growth are an increase in the total amount of protein in it and an increase in the size of bones. General growth is characterized by an increase in body length, depending on the growth and development of the skeleton, which, in turn, is one of the main indicators of the health and physical development of the child.

Growth and physical development occur simultaneously. In this case, there is a complication of the structure, which is called the morphological differentiation of tissues, organs and their systems; the shape of the organs and the whole organism changes; functions and behavior are improved and complicated. There is a mutual natural dependence between growth and development. During this process, quantitative changes accumulate, which leads to the emergence of new qualities. It is impossible to consider the presence of age-related features in the structure or activity of various physiological systems as evidence of the inferiority of the child's body at individual age stages, because each age is characterized by a complex of such features.

The relationship between the physical and mental development of children. Famous teacher and anatomist P.F. Lesgaft put forward a position on the relationship between the physical and mental development of children: physical education is carried out by influencing the psyche of children, which, in turn, affects the development of the psyche. In other words, physical development determines mental development. This is especially clearly detected in congenital underdevelopment of the cerebral hemispheres, which manifests itself in dementia. Children who have such a defect from birth cannot be taught to speak and walk; they lack normal sensations and thinking. Or another example: after removal of the gonads and with insufficient function of the thyroid gland, mental retardation is observed.

It has been established that mental performance increases after physical education lessons, a small set of physical exercises in general education lessons and before homework.

Speech and physical and mental development of children. The role of speech for the physical and mental development of children cannot be overestimated, since the speech function has a leading influence on their emotional, intellectual and physical development. At the same time, the role of speech in the formation of the student’s personality and consciousness, as well as in his learning to work and physical exercises, increases. With the help of speech, thoughts are formed and expressed; through speech, children are taught and raised. As children grow and develop, their ability to reflect objective reality in concepts, abstractions and generalizations, in the laws of nature and society increases.

Initially, concrete, visual-figurative and practical-effective thinking predominates in primary school age. Specific images and actions develop a specific memory in younger students, which, in turn, has a significant impact on their thinking. For middle school age, the predominance of verbal abstract thinking, which becomes the leading one among older students, is characteristic. At this age, verbal, semantic memory predominates.

With the help of oral speech, children learn written speech, and the improvement of the latter entails an even greater development of oral speech and the process of thinking. As the ability to generalize, abstract thinking develops, there is a transition from involuntary attention to arbitrary, purposeful attention. In the process of mental and physical activity of children, the upbringing and training of voluntary and involuntary attention take place.

Speech and thinking develop in parallel in the process of verbal communication with other people, during games, physical exercises and labor activities of children. Speech has a great influence on the mental development of children.

Age-related psychology. Developmental physiology is closely related to developmental psychology, which studies the patterns of emergence, development and manifestations of the psyche of children. Its subject is the study of the content of the psyche, i.e., what exactly and how a person reflects in the world around him.

The psyche is the result of the reflex, or reflective, activity of the human brain. Physiology deals with the study of only the physiological mechanisms of the brain. It is especially important to study the functions of the labor activity of the human body and his speech, which are the physiological basis of the psyche.

Basic patterns of development of the human body. Throughout the entire life cycle, from birth to death, the human body undergoes a number of consistent and natural morphological, biochemical and physiological (functional) changes. A child is not a reduced copy of an adult, therefore, for teaching and raising children, one cannot simply quantitatively reduce the properties of an adult in accordance with the age, height or weight of the child.

A child differs from an adult in specific features of the structure, biochemical processes and functions of the body as a whole and individual organs, which undergo qualitative and quantitative changes at various stages of his life. To a large extent, these changes are due to hereditary factors, which mainly predetermine the stages of growth and development. At the same time, such factors as education and upbringing, behavior (activity of skeletal muscles), nutrition and hygienic living conditions, and puberty are of decisive importance for the manifestation of hereditary factors and new qualities of the body, the formation of age-related characteristics of children.

Heterochrony and systemogenesis. According to S.I. Halperin, the growth and development of individual organs, their systems and the entire organism occur unevenly and non-simultaneously - heterochronically. The outstanding Russian physiologist P.K. proposed the doctrine of heterochrony and substantiated the resulting doctrine of systemogenesis. Anokhin. In his opinion, a functional system should be understood as “a broad functional unification of variously localized structures based on obtaining the final adaptive effect necessary at the moment (for example, a functional respiratory system, a functional system that ensures the movement of the body in space, etc.).

The structure of a functional system is complex and includes afferent synthesis, decision making, the action itself and its result, back afferent from effector organs and, finally, the action acceptor, comparison of the effect obtained with the expected one. "Afferent synthesis includes processing, generalization of various types of information As a result of the analysis and synthesis of the received information, it is compared with past experience.A model of the future action is formed in the action acceptor, the future result is predicted, and the actual result is compared with the previously formed model.

Various functional systems mature unevenly, they turn on in stages, gradually change, creating conditions for the body to adapt to different periods of ontogenetic development. Those structures that together will constitute a functional system of vital importance by the time of birth are laid down and mature selectively and accelerated. For example, the orbicular muscle of the mouth is innervated at an accelerated rate and long before other muscles of the face are innervated. The same can be said about other muscles and structures of the central nervous system that provide the act of sucking. Another example: of all the nerves of the hand, those that provide contraction of the muscles - the flexors of the fingers, which carry out the grasping reflex, develop the earliest and most fully.

The selective and accelerated development of morphological formations that make up a full-fledged functional system that ensures the survival of the newborn is called systemogenesis.

Heterochrony is manifested by periods of acceleration and deceleration of growth and development, the absence of parallelism in this process. A number of organs and their systems grow and develop non-simultaneously: some functions develop earlier, some later.

Higher nervous activity. Heterochrony is determined not only by phylogenesis and its repetition in ontogeny, which is a biogenetic law; it is determined by the conditions of existence, which change at all stages of children's ontogenesis. Since the unity of the organism and its living conditions is ensured by the nervous system, a change in the conditions of existence of the organism entails a change in the functions and structure of the nervous system. Thus, in the growth and development of the body, its individual organs and systems, the main role belongs to conditioned and unconditioned reflexes.

Conditioned and unconditioned reflexes constitute the highest nervous activity, provide life in a constantly changing world around. All functions of the body are caused and changed by a conditioned reflex. Congenital, unconditioned reflexes are primary, they are transformed by acquired, conditioned reflexes. At the same time, conditioned reflexes do not repeat unconditioned ones, they differ significantly from them. While maintaining the same conditions of life in a number of successive generations, some conditioned reflexes become unconditioned.

In the implementation of higher nervous activity, the metabolism of the nervous system changes, therefore, over the course of many generations, its structure has also changed. As a result, the structure of the human nervous system (especially his brain) is fundamentally different from the structure of the nervous system of animals.

Metabolism. Higher nervous activity plays a leading role in onto- and phylogenesis. In the current reactions of the body, mutual transitions of excitation and inhibition, as well as shifts in the relationships of the endocrine glands, are of great importance.

Studies have shown that in animals the metabolism directly depends on the size of the body surface. The doubling of body weight in mammals occurs due to the same amount of energy contained in food, regardless of whether the animal grows quickly or slowly, that is, the length of time required to double the weight is inversely proportional to the metabolic rate (Rubner's rule. Specified This rule is also observed in relation to the human body, but both during growth and after the end of this period, the quantitative and qualitative differences in the metabolism of the human body do not completely depend on this rule.After growth, mammals consume the same amount of energy per 1 kg of body weight, For a person, this figure is almost four times higher.This is due to the social conditions of a person's life, mainly with his work activity.

muscle activity. Skeletal muscles play an exceptional role in human ontogenesis. During the period of muscle rest, 40% of the energy is released in the muscles, and during muscle activity the energy release increases sharply. Famous physiologist I.A. Arshavsky formulated the energy rule of skeletal muscles as the main factor that allows us to understand both the specific features of the physiological functions of the body at different age periods and the patterns of individual development. The rule states that “the characteristics of energy processes in different age periods, as well as changes and transformations in the activity of the respiratory and cardiovascular systems in the process of ontogenesis depend on the corresponding development of skeletal muscles.”

Human movement is a necessary condition for its existence. They make up his behavior, are made in the process of labor, in the course of communication with others through speech, while satisfying physiological needs, etc. Movements are the key to good health and positive emotions. This means that a person's motor activity is due to social and physiological necessity and needs, and not to a subjective factor - love for muscle sensations (kinesophilia).

During muscular activity, the amount of information that comes from the environment through external sensory organs - exteroreceptors - increases significantly. This information plays a leading role in the reflex regulation of physical and mental performance. The nerve impulses coming from the exteroreceptors cause changes in the functions of all internal organs. This leads to a change (increase) in the metabolism and blood supply of the nervous system, motor apparatus and internal organs, which ensures the strengthening of all body functions, accelerating its growth and development during muscle activity.

The nature, intensity and duration of the muscular activity of children and adolescents depend on social conditions: communication with other people through speech, training and education, especially physical, participation in outdoor games, sports and work activities. The behavior of children and adolescents at school, outside of school, in the family, their participation in socially useful activities are determined by social laws.

When the nature of the functioning of skeletal muscles changes, reflex changes in the structure and functions of the nervous system occur, age-related differences arise in the structure and development of the skeleton and locomotor apparatus, innervation of internal organs, their growth and development (primarily for the organs of the cardiovascular, respiratory and digestive systems). ). The physiological mechanism of this action is that with the tension of the skeletal muscles and their contractions, special receptors, proprioreceptors, which are present in them, in the joints and tendons, are irritated. The main functions of proprioceptors are:

a) irritation during muscular activity is a prerequisite for regulating movements by the nervous system, correcting their coordination, and forming new motor reflexes and skills;

b) ensuring, as a result of the influx of centripetal impulses from proprioreceptors into the nervous system, its high performance, especially the brain (motor-cerebral reflexes);

c) reflex regulation of the work of internal organs - provides coordination of movements and changes in the functions of internal organs (motor-visceral reflexes).

Thus, muscular activity is the main condition for mental and physical performance.

Irritation of proprioreceptors, the action of metabolic products that are formed during muscle activity, and the entry of hormones into the blood as a result of a reflex enhancement of the functions of the endocrine glands - all this changes the metabolism and leads to age-related changes in the growth and development of the body as a whole and its individual organs.

First of all, those organs grow and develop that bear the greatest load during contractions of skeletal muscles, as well as those whose muscles function more. The accumulation of substances and energy in the structure of the body due to growth ensures further growth and development, increases the efficiency, and the improvement of the physiological mechanisms of metabolism regulation contributes to a more economical use of substances and energy, leads to a decrease in the level of metabolism per unit body weight. The development of inhibition in the nervous system directly depends on the functions of the skeletal muscles: the onset of inhibition coincides with the appearance of skeletal muscle tone, which ensures static immobility or movement of the body in space.

Critical periods of growth and development largely depend on changes in the nature of the tone of the skeletal muscles and its contractions. Thus, the transition from the infantile period of development to the preschool (or nursery) is associated with the development of a static posture, walking, and the beginning of mastering speech. This activity of the skeletal muscles causes changes in the structure of the nervous system and the improvement of its functions, the structure of the skeleton and skeletal muscles, the regulation of the cardiovascular and respiratory systems, an increase in the volume and weight of the heart, lungs and other internal organs. Termination of breastfeeding, changes in the consistency and composition of food and the appearance of milk teeth lead to a restructuring of the digestive canal, changes in its motor and secretory functions and absorption. The level of metabolism per 1 kg of body weight increases significantly due to the participation of tone and contractions of skeletal muscles not only in the movement of the body, but also in heat production at rest. By the end of the preschool period, running mechanisms are formed, and speech functions continue to develop.

In the preschool period, the maintenance of a relative constancy of body temperature at rest by tension of the skeletal muscles ceases; with the onset of preschool age, the skeletal muscles at rest completely relax. The motor neurons of the brain acquire a shape characteristic of an adult, the weight of the brain increases significantly (it becomes three times larger than that of a newborn). Improving the functions of the brain (especially the mechanism of inhibition) leads to a decrease in the level of metabolism per 1 kg of body weight, the appearance of an inhibitory effect of the nervous system on cardiac and respiratory activity, an increase in the period of wakefulness and a decrease in the period of sleep.

During the period of transition to primary school age, the muscles of the hands develop rapidly, the simplest labor and household motor skills are formed, small precise hand movements begin to be developed. Changes in motor activity are associated with the beginning of schooling, especially with learning to write and the simplest work.

As a result of the complication and increase in the number of movements and great mobility, by the beginning of primary school age, the development of brain neurons basically ends, and its functions are improved. First of all, this applies to braking, which ensures the coordination of subtle and precise movements. Basically, by this age, the formation of the inhibitory effect of the nervous system on the heart is completed, the weight of the heart and lungs increases, and the improvement of the regulation of metabolism entails a decrease in its level by 1 kg of body weight. When changing milk teeth to permanent ones, a further restructuring of the digestive canal occurs, which is associated with the consumption of food corresponding to an adult.

The transition to middle school or adolescence is characterized by the onset of puberty, a change in the functions of skeletal muscles, their increased growth and development, and the mastery of motor skills of labor and physical exercise. There is a completion of the morphological maturation of the motor apparatus, which has almost reached a fairly perfect level of functioning, characteristic of adults. At the same time, the formation of the motor zone in the brain practically ends, the frequency of the pulse and respiration decreases, and there is a further decrease in the relative level of metabolism, which, nevertheless, is even more than in an adult. The change of milk teeth to permanent ones is completed.

The transition to adolescence is characterized by increased muscle growth and the formation of massive muscle fibers, a sharp increase in their strength and a significant complication and expansion of the motor apparatus. The weight of the brain and spinal cord almost reaches the level of an adult. The process of ossification of the sesamoid bones begins.

There is another proof of the dependence of the growth and development of children on the activity of skeletal muscles: in cases where, due to a disease (for example, inflammation of the motor nerves), movement is restricted, there is a delay in the development of not only skeletal muscles and the skeleton (for example, the development of the chest), but also a sharp slowdown in the growth and development of internal organs - the heart, lungs, etc. Children who have had poliomyelitis and therefore are significantly limited in movement differ from non-sick children in a higher frequency of heartbeats and respiratory movements of the chest. In children deprived of the opportunity to perform normal dynamic work, inhibition of the work of the heart and respiration is observed, therefore, the frequency of respiration and heart contractions is the same as in younger children.

Reliability of biological systems. On the general laws of individual development, the famous Soviet physiologist and teacher A.A. Markosyan proposed to include the reliability of biological systems, which is usually understood as “a level of regulation of processes in the body that ensures their optimal course with the urgent mobilization of reserve capabilities and interchangeability, guaranteeing adaptation to new conditions, and with a rapid return to the original state.”

In accordance with this concept, the entire path of development from conception to death takes place in the presence of a supply of life opportunities. This reserve ensures the development and optimal course of life processes under changing environmental conditions. For example, in the blood of one person there is such an amount of thrombin (an enzyme involved in blood clotting) that is enough to clot the blood of 500 people. The femur is able to withstand a 1500 kg stretch, and the tibia does not break under the weight of a load of 1650 kg, which is 30 times the usual load. A huge number of nerve cells in the human body is also considered as one of the possible factors for the reliability of the nervous system.

1.2. Age periodization

Passport age, where the inter-age interval is equal to one year, differs from biological (or anatomical and physiological) age, covering a number of years of a person's life, during which certain biological changes occur. What criteria should be put in the basis of age periodization? To date, there is no single point of view on this issue.

Some researchers base periodization on the maturation of the gonads, the rate of growth and differentiation of tissues and organs. Others consider the so-called skeletal maturity (bone age) to be the starting point, when the time of the appearance of ossification sites and the onset of a fixed connection of bones is determined radiologically in the skeleton.

As a criterion for periodization, such a sign as the degree of development of the central nervous system (in particular, the cerebral cortex) was also put forward. The German physiologist and hygienist Max Rubner, in the theory of the energy rule of the surface, suggested using the features of energy processes occurring in different age periods as a criterion.

Sometimes, as a criterion for age periodization, the method of interaction of the organism with the corresponding environmental conditions is used. There is also an age periodization based on the allocation of periods of newborn, toddler, preschool and school age in children, which reflects the existing system of child care institutions rather than age characteristics.

The classification proposed by the Russian pediatrician, the founder of the St. Petersburg school of pediatricians, who studied the age-related anatomical and physiological characteristics of children, N.P. Gundobin. In accordance with it, they distinguish:

▪ period of intrauterine development;

▪ newborn period (2-3 weeks);

▪ infancy period (up to 1 year);

▪ pre-school (from 1 year to 3 years);

▪ preschool age (from 3 to 7 years, period of baby teeth);

▪ junior school age (from 7 to 12 years);

▪ middle, or teenage, age (from 12 to 15 years);

▪ senior school, or youth, age (from 14 to 18 years for girls, from 15-16 years to 19-20 years for boys).

Developmental and educational psychology more often uses periodization based on pedagogical criteria, when periods of preschool age are divided according to kindergarten groups, and at school age three stages are distinguished: junior (I-IV grades), middle (IV-IX grades), senior (X -XI classes).

In modern science, there is no single generally accepted classification of periods of growth and development and their age limits, but the following scheme is proposed:

1) newborn (1-10 days);

2) infancy (10 days - 1 year);

3) early childhood (1-3 years);

4) the first childhood (4-7 years);

5) second childhood (8-12 years old for boys, 8-11 years old for girls);

6) adolescence (13-16 years for boys, 12-15 years for girls);

7) adolescence (17-21 years for boys, 16-20 years for girls);

8) mature age:

I period (22-35 years for men, 22-35 years for women);

II period (36-60 years for men, 36-55 years for women);

9) old age (61-74 years for men, 56-74 years for women);

10) senile age (75-90 years);

11) centenarians (90 years and above).

This periodization includes a set of features: the size of the body and organs, weight, ossification of the skeleton, teething, the development of endocrine glands, the degree of puberty, muscle strength. The scheme takes into account the characteristics of boys and girls. Each age period is characterized by specific features. The transition from one age period to another is called a turning point in individual development, or a critical period. The duration of individual age periods is largely variable. The chronological framework of age and its characteristics are determined primarily by social factors.

1.3. Acceleration of growth and development

Acceleration, or acceleration (from the Latin acceleratio - acceleration), is the acceleration of the growth and development of children and adolescents compared to previous generations. The phenomenon of acceleration is observed primarily in economically developed countries.

The term "acceleration" was introduced into scientific use by E. Koch. Most researchers understood acceleration as the acceleration of mainly the physical development of children and adolescents. Subsequently, this concept was significantly expanded. Acceleration began to be called an increase in body size and the onset of maturation at an earlier date.

Traditionally, body length, chest volume and body weight were considered as the most important signs of physical development. But, given that the morphological features of the body are closely related to its functional activity, a number of authors began to consider the vital capacity of the lungs, the strength of individual muscle groups, the degree of ossification of the skeleton (in particular, the hand), eruption and change of teeth, the degree of sexual intercourse as signs of physical development. maturation. In addition, the proportions of the body began to be attributed to the essential features.

At present, the concept of acceleration has become so broad that, referring to acceleration, they speak of both the acceleration of the physical development of children and adolescents, and the increase in the size of the body of adults, the later onset of menopause. Therefore, such a concept as a secular trend (secular trend) is often used, understanding it as a trend that has been observed for about a century, to accelerate the physical development of the whole organism - from the intrauterine period to adulthood.

The acceleration was most noticeable in children in the second half of the 1965th century. So, body weight began to double at an earlier age (in 1973-4 - at 5-1940 months, in 1941-5 - at 6-1984 months). There was an earlier change of milk teeth to permanent ones (in 5 - from 6-1953 years old, in 6 - from 7-10 years old). The timing of puberty has shifted. So, the age of menstruation in the twentieth century. decreased every 1974 years by about four months and in 12,7 averaged 1930 years. There was an acceleration in the development of secondary sexual characteristics. In children and adolescents, earlier morphological stabilization was observed. The whole process of ossification ended in boys two, and in girls three years earlier than in the XNUMXs.

In connection with acceleration, growth also ends earlier. At 16-17 years old in girls and at 18-19 years old in boys, ossification of long tubular bones is completed and growth in length stops. Over the past 13 years, Moscow boys of the age of 80 have become 1 cm taller, and girls - by 14,8 cm. Thus, as a result of the accelerated development of children and adolescents, they have achieved higher rates of physical development.

It must be said that there is also information about the lengthening of the childbearing period: over the past 60 years it has increased by eight years. In women in Central Europe, over the past 100 years, menopause has shifted from 45 to 48 years; in Russia, this time is on average 50 years, and at the beginning of the century it was 43,7 years.

Reasons for acceleration. To date, no single generally accepted point of view has been formed on the origin of the acceleration process, although many hypotheses and assumptions have been put forward.

So, most scientists consider the determining factor in all shifts in the development of changes in nutrition. They associate acceleration with an increase in the content of high-grade proteins and natural fats in food, as well as with a more regular consumption of vegetables and fruits throughout the year, enhanced fortification of the body of the mother and child.

There is a heliogenic theory of acceleration. In it, an important role is given to the effect of sunlight on the child: it is believed that children are now more exposed to solar radiation. However, this argument does not seem convincing enough, since the process of acceleration in the northern countries is no less rapid than in the southern ones.

There is a point of view on the connection of acceleration with climate change: it is believed that humid and warm air slows down the process of growth and development, and a cool dry climate contributes to the loss of heat by the body, which supposedly stimulates growth. In addition, there are data on the stimulating effect on the body of small doses of ionizing radiation.

Some scientists cite a general decline in morbidity in infancy and childhood, coupled with improved nutrition, as an important reason for the acceleration due to advances in medicine. It is also obvious that the development of science and technological progress contribute to the emergence of many new factors affecting humans, and the properties of these factors and the features of their effects on the body are still poorly understood (we are talking about chemicals used in industry, agriculture, everyday life, new medicines and etc.). Some researchers assign a significant role in acceleration to new forms and methods of upbringing and education, sports, and physical education.

Acceleration is also associated with the negative impact of the pace of modern urban life. This and abundant artificial lighting (including advertising); stimulating effect of electromagnetic oscillations arising from the operation of television and radio stations; city ​​noise, traffic; the influence of radio, film and television on early intellectual, especially sexual, development.

Technological progress in economically developed countries has led to the concentration of the population in large cities. The development of transport and communications has shortened distances that previously seemed very significant. Increased migration of the population. The geography of marriage has expanded, genetic isolation is collapsing. This creates fertile ground for changes in heredity. The younger generation grows taller and matures earlier than their parents.

Acceleration is a subject of study not only in biology and medicine, but also in pedagogy, psychology and sociology. Thus, experts note a certain gap between the biological and social maturity of young people, while the first comes earlier. In this regard, a number of questions arise before medical theory and practice. For example, there was a need to define new norms for labor and physical activity, nutrition, standards for children's clothing, shoes, furniture, etc.

1.4. Age anatomical and physiological features

Each age period is characterized by quantitatively determined morphological and physiological parameters. The measurement of morphological and physiological indicators that characterize the age, individual and group characteristics of people is called anthropometry. Height, weight, chest circumference, shoulder width, lung capacity and muscle strength are all the main anthropometric indicators of physical development.

Growth, development and their changes in certain age periods. Children grow and develop constantly, but the rates of growth and development differ from each other. In some age periods growth predominates, in others - development. The unevenness of growth and development rates and their undulation also determine the division into age periods.

So, up to 1 year of life, growth predominates in a child, and from 1 year to 3 years - development. From 3 to 7 years old, the growth rate accelerates again, especially at 6-7 years old, and the rate of development slows down; from 7 to 10-11 years old, growth slows down and development accelerates. During puberty (from 11-12 to 15 years), growth and development accelerate sharply. Age periods of growth acceleration are called stretching periods (up to 1 year, from 3 to 7, from 11-12 to 15 years), and some slowdown in growth - rounding periods (from 1 to 3, from 7 to 10-11 years).

Separate parts of the body grow and develop disproportionately, that is, their relative sizes change. For example, the size of the head relatively decreases with age, while the absolute and relative length of the arms and legs increases. The same can be said about the internal organs.

In addition, there are also gender differences in the growth and development of children. Until about 10 years old, boys and girls grow almost the same. From 11-12 years old girls grow faster. During puberty in boys (from 13-14 years old), the growth rate increases. At the age of 14-15, the growth of boys and girls is almost equal, and from the age of 15, boys grow faster again, and this predominance of growth in men persists throughout life. Then the growth rate slows down and basically ends by the age of 16-17 in girls, by 18-19 in boys, but slow growth continues until 22-25 years.

The length of the head of young men is 12,5-13,5%, torso - 29,5-30,5%, legs - 53-54%, arms - 45% of the total body length. In terms of growth rate, the shoulder is in the first place, the forearm is in the second place, the hand grows more slowly. The greatest increase in the length of the trunk occurs about a year after the greatest increase in the length of the legs. As a result, the length of the body of an adult is approximately 3,5 times greater than the length of the body of a newborn, the height of the head is twice, the length of the body is three times, the length of the arm is four times, the length of the leg is five times.

Due to the discrepancy in the rates of growth and development, there is no strictly proportional relationship between height and weight, but, as a rule, at the same age, the greater the height, the greater the weight. The rate of weight gain is greatest in the first year of life. By the end of the first year, the weight has tripled. Then the weight gain averages 2 kg per year.

Like height, the weight of boys and girls up to 10 years old is approximately the same, with a slight lag in girls. From 11-12 years old, the weight of girls is more associated with the development and formation of the female body. This predominance of weight remains with them until about 15 years of age, and then, due to the predominance of growth and development of the skeleton and muscles, the weight of the boys increases, and this excess of weight persists in the future.

Age differences in the increase in the absolute and relative weight of individual organs are also significant. For example, the circumference of the chest from the age of 7 is greater in boys, and from the age of 12 in girls. By the age of 13, it is almost the same in both sexes (girls have a little more), and from the age of 14, the circumference of the chest is larger in boys. This difference persists and increases in the future. The width of the shoulders in boys from 6-7 years old begins to exceed the width of the pelvis. Generally speaking, the width of the shoulders in children increases annually, especially between 4-7 years of age. This annual increase is greater for boys than for girls.

1.5. Hygiene of the educational process at school

School education is the result of the joint activity of the teacher and the student. In this regard, it is necessary to distinguish between the hygiene requirements for both the teacher and the student. This helps, on the one hand, to develop a system of individual actions of the student, which includes planning all stages of educational activities, preparation and maintenance in order of the workplace, performing tasks in accordance with the principle from easy to difficult, from simple to complex, etc. on the other hand, the rational distribution of the teacher's workload during the day, the elimination of breaks between lessons, taking into account the difficulty of the subject when scheduling, providing the maximum opportunity for expanding knowledge are included in the concept of the scientific organization of the teacher's work. The hygiene of pedagogical work also includes the regulation of the activities of each teacher (taking into account the increase in fatigue throughout the working day), the possibility of daily rest, rest on weekends, a change of activity during the holidays, a good rest in the summer.

Scientific and hygienic principles of children's labor. Mental work is a product of the activity of cells in the cerebral cortex, which in children is usually accompanied by motor activity - muscle work. Muscular work, in turn, is associated with the activity of the central and peripheral nervous system. Thus, the student’s work is the product of a mandatory combination of mental and physical labor.

The scientific and hygienic organization of the work of a schoolchild includes the organization of the educational and educational process, as well as recreation, taking into account the physiological capabilities of the child. This includes the creation of optimal conditions that contribute to the preservation of the child's working capacity, his normal growth and development, and the strengthening of his health. Consequently, all aspects of the education and upbringing of children (observance of the daily routine, age regulation of the load on the nervous system and muscular apparatus, proper organization of life, good rest) should be closely interconnected. Insufficient satisfaction of the physiological needs of the child leads to the suppression of normal life functions, a decrease in resistance to adverse factors, an increase in susceptibility to infectious diseases, a disruption in the relationship between body systems, and a negative effect on higher nervous activity.

In hygiene, considerable attention is paid to the observance of physiological norms that affect the child's abilities. The main limiting factors are fatigue and overwork.

Fatigue and overwork. The result of any sufficiently long work is fatigue of the body due to the fact that in the process of activity the energy reserves accumulated in the cells and necessary for work are gradually depleted. The gradual increase in mental fatigue is expressed in a decrease in performance: the quantity and quality of what is done decreases, interest in work decreases, the coordination of individual operations is disrupted, attention is scattered, memory is weakened, and uncertainty appears. A temporary decrease in the performance of brain tissue cells and the entire body as a whole is called fatigue. This is a natural physiological phenomenon.

The physiological nature and nervous mechanisms of mental fatigue are explained by the classical reflex theory of Sechenov-Pavlov, according to which the source of the feeling of fatigue is "exclusively in the central nervous system", and not in the muscles, as previously thought. Fatigue of cortical cells I.P. Pavlov considered them as their "functional destruction", and the inhibition that occurs in them - as a process that prevents further destruction and enables cells to restore their normal state.

Thus, fatigue is a natural temporary physiological state of the body. It cannot be avoided, but the skillful use of the method of work and the timely unloading of the body make it possible to delay fatigue for some time.

Signs of fatigue in children usually appear by the end of the fourth or fifth lesson: lethargy, absent-mindedness, drowsiness occur, attention is poorly concentrated, discipline violations are possible. If the fatigue that has arisen is not replaced by rest, then overwork occurs, which is very harmful to the body, since it is associated with an excess of the functional capabilities of the cortical cells and is prohibitive. Overfatigue of schoolchildren is associated with excessive workload, combining academic work and classes in circles, music, sports schools, violation of the daily routine and rules of personal hygiene.

Usually, overwork appears immediately after overload, but it can also occur after a while. For example, if during the summer holidays the child’s rest is organized incorrectly, then at the beginning of the school year this may not affect academic performance, however, the performance of such a student will decrease much earlier than that of a normally rested child.

To eliminate acute (quick and single) fatigue, as a rule, it is enough to get enough sleep at night. Systematic fatigue and overwork is not eliminated by one normal sleep. This requires rest for at least two weeks, high-calorie nutrition with an abundance of vitamins, water procedures, appropriate organization of sleep. The use of tonics and drinks is undesirable.

To prevent fatigue, it is necessary to properly and rationally organize the work of the student. This is ensured by the efforts of the teacher, since the children themselves are not yet capable of this due to age characteristics.

The concept of a child’s “school maturity”. In Russia, compulsory schooling for children is introduced from the age of 6-7 years. As a rule, by this time the child’s body is morphologically and functionally prepared for learning. Nevertheless, a child’s entry into school is a turning point in his life, breaking the stereotype developed in preschool institutions and the family.

The most difficult for most students are usually the first 2-3 months of study. It is even possible the occurrence of such a condition, which is defined by doctors as an adaptive disease (it is also called "school stress" or "school shock"). The task of the teacher is to facilitate the period of adaptation of the child to new conditions, that is, to reduce the neuropsychological trauma of the transition period from preschool to school life.

The concept of school maturity, i.e., the child's functional readiness for learning, is one of the important problems of age-related physiology, pedagogy, psychology, and school hygiene. It is associated with a characteristic of the level of physical, mental and social development at which the child becomes receptive to systematic training and education at school. Teachers, doctors, psychologists must take into account the degree of school maturity, since children who have not reached this level become unsuccessful students.

To determine the degree of school maturity, they use the test proposed in 1955 by the German psychologist A. Kern and improved by I. Irasek in 1966. The Kern-Irasek test consists of the following tasks: the child is asked to draw a person and points arranged in a certain order, according to memory after their demonstration and copy the phrase written in cursive. The work is evaluated on a five-point system - from 1 (best mark) to 5 (worst mark). The sum of points for individual tasks is a general indicator. Children who have received from 3 to 5 points for completing three tasks of the test are considered ready for systematic learning. Getting 6-8 points indicates the need for additional preparation of children for school (these are the so-called middle-aged children). A score of 9 or more points indicates unpreparedness for schooling.

Individual approach to children. Whether students will become interested in the lesson depends on the skill of the teacher, on his ability to present the material taking into account the age characteristics of the students, as well as on the physical condition of the children, the type of their higher nervous activity and functional capabilities.

Most often, the composition of students in the class is heterogeneous: there are children with poor health and a lower level of training, who need individual treatment and the selection of special material for homework, consultations, and additional classes.

For children suffering from chronic diseases (rheumatism, tuberculosis intoxication), there is one day a week free from school, when they work at home on the instructions of teachers. The decision to grant the child a day off from school is made by the teachers' council on the basis of medical documents. First of all, children who live at a distance of 500 m and further from the school apply for such a benefit.

1.6. Hygienic basics of the daily routine of students

The daily routine is a dynamic system of load distribution and rest, which ensures the conservation of strength and energy for the normal functioning of the body. The daily regimen of the child is based on a comprehensive consideration of the characteristics of his growth, development, living conditions and is designed to establish the physiological balance of the body with the environment in which education and upbringing are carried out. Thus, the mode is the basis of the health-improving and preventive effect on the body of all factors of educational work.

Justification for students' daily routine. The regimen should take into account the age characteristics of the child, include the normal duration of sleep for him, his stay in general education and special (music, art, sports) schools. Any element of a schoolchild’s daily routine should be carried out in favorable conditions (for example, you need to prepare for lessons in a cozy and hygienically properly equipped place, sleep in a well-ventilated room, etc.).

To help the child and his parents draw up a scientifically based student's daily routine, the class teacher at the parent meeting informs about the approximate daily routine, explaining the purpose of each element of the routine for the student's progress and health. Here are some of those recommendations.

The child should get up after a night's sleep at 7-7.30 in the morning. This is acceptable for first and second shift students. Then the child does morning exercises, goes to the toilet, has breakfast and goes to school, where he must come 10-15 minutes before the start of classes to prepare for the lesson.

The child should return home at about the same time, this brings up punctuality and saves time. The student should go home slowly so as not to waste extra energy and be able to be in the fresh air.

At home, the student changes clothes, washes his hands and has lunch. After that, younger students (especially first-graders and children who have had illnesses) should sleep for 1-1,5 hours, which is necessary to restore strength and strengthen the nervous system.

Healthy students, starting from the second grade, after lunch can relax in the fresh air, for example, skiing, skating, sledding, playing outdoor games, etc. After that, the child starts doing homework (primarily of medium and advanced difficulty).

1,5-2 hours before bedtime, children have dinner.

schedule of lessons. The alternation of academic disciplines in the lesson schedule ensures a switch in the activity of the cerebral cortex and therefore prevents children from becoming tired and meets pedagogical requirements.

There are four lessons in grades I-III. In grade IV, it is allowed (no more than twice a week) to increase the number of lessons to five. In grades V-IX there are five lessons daily, in grades X-XI - six lessons each.

The performance of schoolchildren during the school day is different. Initially, it increases and reaches a maximum (in the second lesson in the lower grades and in the third in the older grades), and then begins to decline due to the onset and increase of fatigue. The last (fifth or sixth) lesson is the most difficult for many children. The teacher should organize it in such a way as to keep the students working longer.

The working capacity of students also differs during the week: in the first days it is higher, by the end of the week it decreases. Thus, when drawing up a schedule, it is necessary to alternate objects so that the degree of mental stress corresponds to the working capacity of the body. The largest study load should be in the middle of the week, the smallest - on Monday and Saturday. In order for the children to fully rest, students of grades I-IV are recommended not to give assignments at all on weekends and significantly reduce them to students of middle school age. The same goes for vacations.

Duration of the academic year. The academic year in secondary schools begins on September 1. It consists of four academic quarters, which are separated by holidays of varying lengths.

Analyzing the fatigue of children during a quarter and a year as a whole, scientists noticed that the decrease in working capacity is especially noticeable towards the end of these periods. However, properly organized rest contributes to its restoration.

It is recommended that on the first day after the holidays, the lessons begin with a repetition of the material covered. Thus, a kind of bridge is created from the known, but forgotten, to the unknown, which has to be known and learned. This principle has a physiological and hygienic basis - the breaking of conditioned connections and the prevention of fatigue.

Physiological and hygienic justification for lesson duration and breaks. The educational process at school varies according to age. A lesson in a general education school lasts 45 minutes, but as a result of studying performance, scientists came to the conclusion that for first-grade students this load significantly exceeds the norm and the lesson for them should be reduced to 35 minutes. Research on the duration of active attention confirms this. For example, for seven-year-old children, the period of active attention is 10-12 minutes, for ten-year-olds - 16-20 minutes, for eleven- to twelve-year-olds - up to 25 minutes, for older schoolchildren - up to 30 minutes. It follows that the duration of explanation of new material in each age group should not exceed the duration of the period of active attention.

In the course of studying the dynamics of the productivity of students' work, it was found that in the classroom (especially in the primary grades) it is impossible to use only one type of activity in working with children, it must be diversified, switching children from one type of work to another. This is due to the fact that when changing the type of activity, the nature of the stimuli changes, as a result of which various analyzers and, consequently, different parts of the cerebral cortex are excited, giving the possibility of inhibition to previously functioning cells and thereby prolonging the working capacity of schoolchildren.

In addition, a special place in the change of activity is occupied by physical culture pauses conducted by the teacher. They also help relieve fatigue. In the lower grades, physical education pauses are carried out from the second lesson, and in the older ones - from the third. The signal for their implementation is the beginning of a decrease in working capacity: in the lower grades this happens after 25-30 minutes from the beginning of the lesson, and in the older ones - after 30-35 minutes. For students of grade I in the first quarter, physical culture breaks are recommended twice per lesson - after 15-20 and 30-35 minutes. The duration of the pauses is determined by the teacher leading the lesson.

It should be noted that in students of grades I-II, the first signal system prevails over the second. In this regard, when organizing a lesson, it is necessary, relying on the sensory perception of the subject, to use visual aids, to involve visual, auditory and motor analyzers in the field of activity, and if possible, also touch.

An important role in the organization of the lesson is played by the observance of hygiene standards and rules for seating students at their desks (tables), the creation of an air-thermal regime, etc.

The breaks between lessons are designed to allow students and teachers to relax, as well as to allow students to move to the classrooms, laboratories and classrooms in which the next lessons will be held. Proper physiological and hygienic change is a prerequisite for full-fledged work in the next lesson.

Changes last 10 minutes, and after the second lesson - 30 minutes. In some cases, instead of one thirty-minute break, two twenty-minute breaks are allowed (after the second and third lessons). Other reductions are unacceptable because they increase the workload on students and predispose to the development of overwork and, therefore, neuroses.

During the break, children rest from mental activity. Breaks should not be used to prepare for the next lesson. Pupils go to a ventilated recreational room or to an open sports ground (depending on the weather). Hot breakfasts are offered at the big break.

Topic 2. INFLUENCE OF HEREDITY AND ENVIRONMENT ON THE DEVELOPMENT OF CHILDREN'S ORGANISM

2.1. Heredity and its role in the processes of growth and development

Heredity is the transmission of parental traits to children. Some hereditary qualities (nose shape, hair color, eyes, facial contours, ear for music, singing voice, etc.) do not require the use of any devices for their fixation, others associated with the cytoplasm and nuclear DNA (metabolism, blood type, the usefulness of the set of chromosomes, etc.), require quite complex studies.

The growth and development of the child depend on the received hereditary inclinations, but the role of the environment is also great. It is customary to distinguish between favorable and unfavorable (or burdened) heredity. The inclinations that ensure the harmonious development of the abilities and personality of the child belong to favorable heredity. If the appropriate conditions are not created for the development of these inclinations, then they fade away, not reaching the level of development of the giftedness of the parents. For example, a singing voice, ear for music, drawing abilities, etc. do not develop.

A burdened heredity cannot always ensure the normal development of a child, even in a good upbringing environment. Usually it is the cause of anomalies (deviations from the norm) and even deformities, and in some cases the cause of prolonged illness and death. In addition, the cause of anomalies in children may be the alcoholism of parents and the harmfulness of their profession (for example, work related to radioactive substances, pesticides, vibration).

However, heredity, especially unfavorable, should not be considered something inevitable. In some cases, it can be corrected and managed. For example, methods have been developed for the treatment of hemophilia - the introduction of a specific blood protein.

The birth of children with unfavorable heredity can be avoided by consulting geneticists. In particular, such consultations contribute to the prevention of closely related marriages, which are the cause of the birth of abnormal children.

Timely detection of inherited traits in children makes it possible to send some children to special schools for the gifted, and others to auxiliary schools. Children with mental and physical disabilities (mentally retarded, deaf, blind) in auxiliary schools are involved in socially useful work, acquire literacy and improve their intellectual development. A huge merit in correcting unfavorable heredity in children belongs to oligophreno-, deaf- and typhlopedagogy.

Qualified teachers in special schools improve the mathematical, musical and other inclinations of children, which is associated with a huge amount of work for their development. The teacher should be aware that parents often see extraordinary abilities in their child, although in fact he may have very modest inclinations. Therefore, it is very important to tell parents in time how to develop in the child that tendency that is revealed in him and which he, perhaps, inherited from his grandfathers, and not from his parents. Such a manifestation of abilities is associated with a feature of heredity: its long-term stability, when signs are transmitted over many generations and do not always appear in the first generations (this is the so-called recessive heredity).

Relationship between the body and the environment. The founder of Russian physiology I.M. Sechenov wrote that “an organism without an external environment that supports its existence is impossible, therefore the scientific definition of an organism must also include the environment that influences it.” Consequently, outside of nature and the social environment, in essence, there is no human being.

I.P. Pavlov, developing this position, came to the conclusion that it is necessary to speak of a person as an integral organism, which is closely interconnected with the external environment and exists only as long as a balanced state of him and the environment is maintained. In this regard, all reflexes were considered by Pavlov as reactions of constant adaptation to the outside world (for example, a person's adaptation to different climatic conditions or different habitats).

Thus, the development of a person cannot be adequately assessed without taking into account the environment in which he lives, is brought up, works, without taking into account those with whom he communicates, and the functions of his body - without taking into account the hygienic requirements for the workplace, home environment, without taking into account the relationship of man with plants, animals, etc.

2.2. man and plants

The world of flora is a huge pantry that gives a person the necessary nutrients that are synthesized by plants. From vegetable raw materials, a person makes medicines, clothes, builds dwellings, etc. Due to the specifics of life, plants purify the air of carbon dioxide and make up for the loss of oxygen in the atmosphere.

But the plant world cannot be fully appreciated without studying its representatives such as bacteria, fungi, yeast, which play a special role in the life processes of all organisms. Unlike green plants, they lack chlorophyll, which is necessary for the synthesis of carbohydrates, but they have the ability to cause fermentation processes (this is due to the production of alcohols, souring of milk, etc.). Among them there are both useful and necessary for a person microorganisms, and harmful, which include pathogens.

Microscopic representatives of the plant world are diverse in form and biological properties. For example, some of them are spherical in shape, which is why they are called cocci (from the Greek kokkos - grain). Under a microscope, they can be seen lying either in groups, like bunches of grapes (staphylococci), or in chains, like beads (streptococci), or in pairs (gonococci). The former are less dangerous than the latter, but they are all disease-causing.

A number of representatives of microorganisms have the form of sticks. They are called bacilli, or bacteria (from the Greek. bakterion - stick). Some rod-shaped microbes in the course of evolution turned into corkscrew-like ones - spirilla, or spirochetes (for example, the causative agent of syphilis). Other rod-shaped bacteria, over time, under the influence of certain factors, bent in the form of a comma. In a living culture, they make oscillatory movements. These are vibrios (for example, vibrio El Tor - the causative agent of cholera).

Regarding humans, microorganisms are divided into saprophytes (these are microbes that do not harm the body, feeding on dead epithelial cells or undigested food residues in the intestine) and parasites - microbes that destroy the body. Pathogenic microorganisms can enter the human or animal body. This process is called infection or infection. Parasitic microbes, entering the body, can affect it slowly (like staphylococci) or sharply and suddenly (acutely), therefore the diseases caused by them are called acute (for example, diphtheria, dysentery, etc.).

A person fights microbes, uses disinfection, destroying pathogens in the external environment by physical methods (high temperature, steam under pressure, ultraviolet rays, etc.), mechanical, chemical (solutions of acids, salts, alkalis, etc.) and biological means (antibiotics and etc.). These measures prevent infection of the body, increase its resistance. Thus, in interaction with the microcosm, a person must comply with the norms and rules developed by hygiene (school, communal, food hygiene, etc.).

2.3. Man and animals

Human life is impossible without relationships with higher and lower animals. Most of the higher animals are a source of meat, milk, raw materials for the manufacture of clothing and footwear, etc. But they can also cause significant harm to humans. For example, a sick animal becomes a carrier of infectious agents.

Diseases that humans contract from animals are called zoonotic diseases. To destroy their pathogens, they carry out disinfection and disinsection (destruction of insects, rodents, etc.). Domestic animals infected with such dangerous diseases as glanders, plague, and rabies are subject to destruction.

Microscopic animals are rickettsia, which are visible only in an electron microscope. Rickettsia are the causative agents of a number of diseases called rickettsiosis. Of these, typhus is the most dangerous for humans.

Of the simplest unicellular animals that parasitize in humans, one can name dysenteric amoeba and Plasmodium, the causative agent of malaria. The carriers of the first are flies and a sick person, Plasmodium is spread by malarial mosquitoes.

Some diseases are caused by various types of worms. They are called helminths, and diseases are called helminthiases.

To combat anthroponotic (affecting only humans) diseases, the causative agents of which belong to the world of animals and plants, sera and vaccines are used.

Serum is a blood product of a person or animal, which is devoid of formed elements and some proteins, but contains specific substances against a particular disease.

A specially prepared culture of killed or weakened pathogens (for example, against poliomyelitis, tuberculosis, etc.) is called a vaccine.

2.4. The effect of viruses on the human body

Viruses form a large group of parasites of humans, animals and plants. They can cause a number of serious diseases, such as natural and chicken pox, poliomyelitis, etc. Viruses are studied by a special science - virology.

Viruses are peculiar living beings, intracellular parasites of plants, animals, humans and microorganisms. They do not have a cellular structure and autonomous metabolism. A unit (or individual) of a mature virus is called a vibrio; its genetic material is one molecule of nucleic acid (RNA or DNA) protected by a protein sheath. Viruses reproduce only in the cells of the host organism, i.e., where they parasitize.

In medicine, for the prevention of viral diseases, sterilization (treatment with high temperature, chemical solutions), irradiation with ultraviolet rays of natural and artificial origin, and x-rays are used.

Sources of pathogens. Ways of transmission of the disease. Sick people or animals can spread many diseases. Pathogens spread through exhaled air, sputum, feces and vomit, discharge from purulent wounds, ulcers and hair loss. Those pathogens that are released by the source into the external environment are kept alive or die. Having penetrated the body, they begin to multiply and parasitize, causing harm.

In the chain of movement of pathogens from a diseased organism to a healthy one, the duration of their stay in the external environment, as well as the degree of their resistance to its various factors, play an important role. Being outside the body, pathogens die after a few days or hours, and are susceptible to disinfectants, but some of them (for example, anthrax, etc.) can remain viable for several years.

The following ways of transmission of pathogens from a diseased organism to a healthy one are distinguished.

1. A contact route of transmission is possible as a result of contact with the patient. Contact can be direct (bite, kiss, etc.) and indirect, including contact with objects used by the patient (for example, dishes, food, etc.). Diphtheria, smallpox natural, Botkin's disease, and other diseases are transmitted in this way.

There may be cases when pathogens are transmitted through caregivers who do not comply with sanitary and hygienic requirements. This type of transfer of pathogens is called transfer to a third party.

To avoid infection, you should not enter the room of a contagious patient, kiss him and maintain other types of contact (for example, use his things, etc.).

2. The airborne route is the transmission of microbes through the air and with droplets of saliva when coughing and sneezing. Influenza, diphtheria, measles and other infections are transmitted in this way. Constant ventilation of rooms (classrooms, apartments), systematic cleaning with the use of disinfectants, exposure to ultraviolet rays help prevent infection.

3. The most dangerous is the water-food way of spreading infectious diseases, when pathogens enter the body with contaminated water or food. This route of infection is the most widespread; pathogens of gastrointestinal diseases (dysentery, infectious jaundice, etc.) are transmitted through it.

To prevent gastrointestinal diseases, in addition to the rules of personal hygiene, it is necessary to thoroughly wash vegetables, fruits and berries with hot boiled water before use. Particular attention should be paid to the quality of drinking water and cooked food.

4. The transmission route involves the transmission of pathogens with the help of insects. At the same time, some insects carry pathogens on their bodies and limbs (for example, flies), others excrete pathogens with saliva when bitten (for example, lice). Some animals carry parasites (for example, mice and rats - fleas infected with plague). Ways to combat the spread of infection are deratization, disinfestation and disinfection, as well as treatment of sick animals and people (including bacillus carriers); medical control over meat and dairy products and farms, places of sale of prepared food and foodstuffs.

2.5. Hygiene of clothes and shoes

Hygienic requirements for clothing depend on the conditions of its operation and the characteristics of human activity. For the manufacture of clothing, the use of materials that emit chemicals in quantities exceeding the maximum permissible limits is prohibited. Polymeric materials for clothing must have chemical stability, i.e., do not release various ingredients toxic to the body into the environment. Clothing materials may contain non-polymerized monomers, as well as components of various auxiliary substances used for processing natural and synthetic fabrics (impregnations, dressings, etc.).

Research methods. During the hygienic assessment of clothing, the materials from which it is made are examined and a physiological and hygienic study of experimental and prototypes is carried out.

To determine the content of toxic substances, the latest methods of quantitative analysis are used, including chromatographic, spectrophotometric, etc. If there is no information about the toxic properties and the nature of their effects on the body, a toxicological study is carried out on experimental animals (mice, rats, guinea pigs). Using modern biochemical, physiological, immunological, pathomorphological and other research methods, local irritating, allergenic, resorptive effects are studied. When evaluating materials intended for children's clothing, toxicological experiments are carried out on growing animals, taking into account their age-related reactivity.

Giving an assessment of the material for the manufacture of clothing from a hygienic point of view, they analyze heat and moisture conductivity, hygroscopicity, breathability. In addition, the mechanical properties of materials are determined, i.e. thickness under load, elasticity, extensibility. In connection with the widespread use of polymers, it became necessary to hygienically evaluate textile materials for the level of electrostatic field strength and the time for the charge to drain from it.

Hygienic requirements for certain types of clothing. Separate hygiene requirements are developed for each layer of clothing. Thus, summer clothing should not impede heat transfer and sweat evaporation. Therefore, for its manufacture, materials with good hygroscopicity (at least 7%), air permeability (at least 330-370 degrees per 1 cubic dm), low thermal resistance (0,09-0,11 degrees per 1 kcal) and electrostatic field strength.

It has been established that the lighter the clothing, the more rays it reflects, the less it absorbs them and the less it heats up. Therefore, light-colored clothes are good for summer, and dark ones, which absorb more heat, are good for winter. The best materials for summer clothes are cotton, natural linen and artificial (viscose, silk) fabrics, which have good breathability and moisture conductivity and have little thermal resistance.

Another important indicator of the properties of clothing is its water capacity, i.e., the ability of a fabric to be saturated with water: the more air present in the pores of the clothing fabric is replaced by water, the lower its breathability and the greater its thermal conductivity. As a result, sweat and gases emitted by the skin (carbon dioxide, carbon monoxide, etc.) accumulate under clothing, heat loss increases significantly, which worsens health and reduces performance. In addition, soaking clothing with water increases its weight.

Woolen fabric has the least water capacity and the greatest air permeability when wet. For example, the water content of woolen flannel is 13%, cotton flannel - 18,6%, cotton tights - 27,2%, silk tights - 39,8%, linen tights - 51,7%. Based on this, at low air temperatures and during rain or snow, physical work is best done in clothes made of woolen fabric, and in summer - in clothes made of linen. It is acceptable to use materials from a mixture of natural, viscose artificial fibers with synthetic polyester, while the share of the latter should be no more than 30-40%.

Materials for winter clothing should have high thermal insulation properties, and its top layer should have a little breathability to provide protection from the wind. In the cold season, clothing made of dense, porous fabrics with good heat-shielding properties (woolen, half-woolen, etc.) is rational. It is advisable to wear clothes made from a mixture of viscose with natural (wool) and synthetic fibers, the content of which should be approximately 40-45%.

Outerwear (suits, coats) are sewn from materials of considerable thickness and porosity (drape, cloth). The necessary wind protection is provided by pads made of materials with low air permeability. In addition, synthetic materials are used for the top layer, which reduces the weight of clothing by 30-40%. Clothes are more hygienic the less they weigh.

For the top layer, the best fabrics are those that absorb moisture poorly and give it away quickly, i.e., fabrics that have a faster rate of moisture evaporation and a shorter drying time. Of the synthetic materials, lavsan, nitron and capron have the highest rate of evaporation from the surface. In order to impart water-repellent properties, many of these fabrics are treated with special impregnations and latexes.

The main role in heat transfer belongs to the thermal conductivity of clothing, which depends on porosity, i.e., on the air content in the fabric. Since air is a poor conductor of heat, the greater the porosity of the fabric, the less it conducts heat, therefore, the less heat transfer. The porosity of fur averages 95-97%, wool - up to 92%, flannel - 89-92%, tights - 73-86%, linen fabrics - 37%. It is clear that fur and woolen clothing retains heat better than linen, so it is more suitable for winter, and linen for summer.

Underwear should be light, soft, light and have great breathability and hygroscopicity. The most practical and appropriate knitted underwear made of knitwear or thin cotton (or linen) fabric. This linen washes well. Woolen underwear irritates the skin and is washed worse. Underwear should be changed at least once a week, as dirt, waste products and germs accumulate on it. In summer, as well as during intensive muscular work, underwear is changed more often. Cotton or linen fabric is suitable for bed linen. Bed linen also needs to be changed and washed once a week.

A headdress for summer should be light, comfortable, light, breathable, not put pressure on the head and protect it from direct sunlight. A winter headdress should, on the contrary, be dark, light and contain a lot of air in the pores.

Hygienic requirements for children's clothing. Since children's skin has a relatively large surface area, it is thinner and more delicate and, in addition, contains up to one-third of the body's total blood, heat transfer through the skin in children is greater than in adults. In this regard, the hygienic requirements for children's clothing are much stricter than for adult clothing.

The outerwear of children and adolescents should be light in summer, dark in winter, freely fit the body, do not interfere with breathing, blood circulation, do not restrict movement, that is, correspond to the size of the body. The size of the child's clothing increases as it grows. Clothing that is not tailored to fit can cause injury to children because it tends to hit the surroundings. It is necessary to avoid tightening the body with belts, elastic bands. In winter, you can not wrap up children, wear clothes that do not correspond to the air temperature. On the contrary, given the great mobility of children, their winter clothes should be slightly less warm than necessary to maintain body temperature at rest. Children should not wear heavy coats that restrict movement. Children's clothing should be comfortable and light, because heavy clothing contributes to the appearance of scoliosis in a child and the formation of an incorrect posture; in such clothes, children quickly get tired. In addition, tight clothing can interfere with blood circulation and breathing.

For clothes of young children, it is best to use materials made from natural fibers (cotton, wool). The use of synthetic fibers, as well as materials treated with various impregnations, should be avoided.

Hygienic requirements for shoes. The design of the shoes and the material from which they are made must meet hygienic requirements. First of all, shoes should ensure the physiological functions of the foot, correspond to its anatomical and physiological characteristics, not squeeze it, not disrupt blood and lymph circulation, innervation, and not cause abrasions. Shoes should be 10-15 mm longer than the foot. It is not recommended to wear tight and narrow shoes, as this can lead to foot deformation, limited joint mobility, and impaired blood circulation and innervation.

Heel height is one of the design features of shoes that affect the musculoskeletal system of the foot. Wearing shoes with high heels (7 cm or more) leads to shortening of the calf muscles, relaxation of the anterior muscles of the lower leg and ligaments of the foot. As a result, the leg becomes extremely unstable due to the movement of the center of gravity forward, and the center of support - on the bent toes and heel. This is due to the fact that the footprint of shoes with high heels is 30-40% less than that of shoes with low heels. Often this leads to tucking of the foot, sprains, and dislocations of the ankle joint. Such shoes are especially dangerous in winter. High-heeled shoes contribute to scoliosis, change the normal shape of the pelvis, and lead to displacement of internal organs and the appearance of pain. The rational height of the heel, which provides optimal muscle balance between the flexors and extensors of the foot, cushioning when walking and maintaining the arch of the foot, is 20-30 mm for men, 20-40 mm for women, and 10-30 for children (depending on age). XNUMX mm. In this case, the toe of the shoe must correspond to the width and outlines of the front edge of the foot.

Shoes should be soft, light, water-repellent, not change shape and size after wetting and drying. In the conditions of a cold and average climatic zone, you need to wear shoes made of low heat-conducting materials.

The foot of an adult during 1 hour at rest releases up to 3 ml of sweat, and during physical work - about 8-12 ml. Moisture, accumulating in shoes, irritates the skin, contributes to the appearance of scuffs, maceration of the epidermis, the occurrence of various skin diseases. Therefore, shoes intended for the summer period should provide ventilation of the intra-shoe space due to the physical properties of the materials (breathability, hygroscopicity, etc.), as well as due to design features (perforation of the top, the presence of open areas, etc.), which helps to avoid overheating feet and accumulations of sweat. The best material for summer shoes is genuine leather. Shoes are also made from artificial and synthetic materials.

The child's shoes should not hamper the movement of the foot, especially the fingers. Tight shoes retard the growth of the foot, deform it, cause scuffs, and impede normal blood circulation. Shoes that are too loose can also cause scuffs. Therefore, when designing shoes for children, it is necessary to take into account the features of the children's foot: the footprint should be ray-shaped with a wide toe, raised top, a straight inner edge and a recess for the heel and metatarsophalangeal part. Shoes for young children should be well fixed on the foot.

The correct formation of the foot depends on the heel part of the shoe (heel and heel), so the heel of children's shoes is made especially strong, hard and stable.

Topic 3

3.1. Features of the functions and structure of the musculoskeletal system

The organs of movement are a single system, where each part and organ is formed and functions in constant interaction with each other. The elements that make up the system of organs of movement are divided into two main categories: passive (bones, ligaments and joints) and active elements of the organs of movement (muscles).

The size and shape of the human body is largely determined by the structural basis - the skeleton. The skeleton provides support and protection for the entire body and individual organs. The skeleton has a system of movably articulated levers, set in motion by muscles, due to which various movements of the body and its parts in space are performed. Separate parts of the skeleton serve not only as a container for vital organs, but also provide their protection. For example, the skull, chest and pelvis serve as protection for the brain, lungs, heart, intestines, etc.

Until recently, the prevailing opinion was that the role of the skeleton in the human body is limited to the function of supporting the body and participating in movement (this was the reason for the appearance of the term "musculoskeletal system"). Thanks to modern research, the understanding of the functions of the skeleton has expanded significantly. For example, the skeleton is actively involved in metabolism, namely in maintaining the mineral composition of the blood at a certain level. Substances included in the skeleton, such as calcium, phosphorus, citric acid and others, if necessary, easily enter into exchange reactions. The function of the muscles is also not limited to the inclusion of bones in movement and the performance of work, many muscles, surrounding the body cavities, protect the internal organs.

General information about the skeleton. Bone Shape. The human skeleton is similar in structure to the skeleton of higher animals, but has a number of features that are associated with upright posture, movement on two limbs, and high development of the arm and brain.

The human skeleton is a system consisting of 206 bones, of which 85 are paired and 36 unpaired. Bones are the organs of the body. The weight of the skeleton in a man is approximately 18% of the body weight, in a woman - 16%, in a newborn - 14%. The skeleton consists of bones of various sizes and shapes.

According to their shape, bones are divided into:

a) long (located in the skeleton of the limbs);

b) short (located in the wrist and tarsus, i.e., where greater strength and mobility of the skeleton are simultaneously required); c) wide or flat (they form the walls of cavities in which internal organs are located - the pelvic bone, the bones of the skull); d) mixed (have different shapes).

Bone connections. Bones articulate in a variety of ways. According to the degree of mobility, joints are distinguished:

a) motionless;

b) sedentary; c) movable bone joints, or joints.

An immovable joint is formed as a result of the fusion of bones, while movements may be extremely limited or completely absent. For example, the immobility of the bones of the brain skull is ensured by the fact that numerous protrusions of one bone enter the corresponding recess of the other. This connection of bones is called a suture.

The presence of elastic cartilage pads between the bones provides little mobility. For example, such pads are available between individual vertebrae. During muscle contraction, the pads are compressed, and the vertebrae are drawn together. During active movements (walking, running, jumping), cartilage acts as a shock absorber, thereby softening sharp shocks and protecting the body from shaking.

Movable joints of bones are more common, which is provided by the joints. The ends of the bones that form the joint are covered with hyaline cartilage 0,2 to 0,6 mm thick. This cartilage is very elastic, has a smooth shiny surface, so the friction between the bones is significantly reduced, which greatly facilitates their movement.

From a very dense connective tissue, an articular bag (capsule) is formed, which surrounds the articulation area of ​​\uXNUMXb\uXNUMXbthe bones. A strong outer (fibrous) layer of the capsule firmly connects the articulating bones. Inside the capsule is lined with a synovial membrane. The joint cavity contains synovial fluid, which acts as a lubricant and also helps to reduce friction.

Outside, the joint is reinforced with ligaments. A number of joints are strengthened by ligaments and inside. In addition, inside the joints there are special devices that increase the articulating surfaces: lips, discs, menisci from connective tissue and cartilage.

The joint cavity is hermetically closed. The pressure between the articular surfaces is always negative (less than atmospheric), and therefore the external atmospheric pressure prevents their divergence.

Types of joints. According to the shape of the articular surface and the axes of rotation, joints are distinguished:

a) with three;

b) with two; c) with one axis of rotation.

The first group consists of spherical joints - the most mobile (for example, the joint between the scapula and the humerus). The joint between the innominate and the thigh, called the walnut, is a type of ball and socket joint.

The second group consists of elliptical (for example, the joint between the skull and the first cervical vertebra) and saddle joints (for example, the joint between the metacarpal bone of the first finger and the corresponding bone of the wrist).

The third group includes block-shaped (joints between the phalanges of the fingers), cylindrical (between the ulna and radius) and helical joints (forming the elbow joint).

Any loose body has six degrees of freedom, because it produces three translational and three rotational movements along the coordinate axes. A fixed body can only perform rotations. Since all links of the body are fixed, joints with three axes of rotation are the most mobile and have three degrees of freedom. Joints with two axes of rotation are less mobile, therefore they have two degrees of freedom. One degree of freedom, which means that joints with one axis of rotation have the least mobility.

Bone structure. Each bone is a complex organ consisting of bone tissue, periosteum, bone marrow, blood and lymphatic vessels and nerves. With the exception of the connecting surfaces, the entire bone is covered with periosteum - a thin connective tissue membrane rich in nerves and vessels that penetrate from it into the bone through special openings. Ligaments and muscles are attached to the periosteum. The cells that make up the inner layer of the periosteum grow and multiply, which ensures the growth of the bone in thickness, and in the event of a fracture, the formation of a callus.

Sawing a tubular bone along its long axis, one can see that a dense (or compact) bone substance is located on the surface, and under it (in depth) - spongy. In short bones, such as vertebrae, spongy matter predominates. Depending on the load experienced by the bone, the compact substance forms a layer of different thickness. The spongy substance is formed by very thin bony crossbars oriented parallel to the lines of the main stresses. This allows the bone to withstand significant loads.

The dense layer of bone has a lamellar structure and is similar to a system of cylinders inserted into each other, which also gives the bone strength and lightness. Bone tissue cells lie between the plates of bone substance. Bone plates make up the intercellular substance of bone tissue.

A tubular bone consists of a body (diaphysis) and two ends (epiphyses). On the epiphyses are the articular surfaces, which are covered with cartilage involved in the formation of the joint. On the surface of the bones are tubercles, tubercles, grooves, ridges, notches, to which the tendons of the muscles are attached, as well as holes through which the vessels and nerves pass.

Chemical composition of bone. Dried and defatted bone has the following composition: organic matter - 30%; minerals - 60%; water - 10%.

The organic substances of the bone include fibrous protein (collagen), carbohydrates and many enzymes.

Bone minerals are represented by salts of calcium, phosphorus, magnesium and many trace elements (such as aluminum, fluorine, manganese, lead, strontium, uranium, cobalt, iron, molybdenum, etc.). The skeleton of an adult contains about 1200 g of calcium, 530 g of phosphorus, 11 g of magnesium, i.e. 99% of all calcium present in the human body is contained in the bones.

In children, organic substances predominate in the bone tissue, so their skeleton is more flexible, elastic, easily deformed during prolonged and heavy load or incorrect body positions. The amount of minerals in the bones increases with age, and therefore the bones become more fragile and more likely to break.

Organic and mineral substances make the bone strong, hard and elastic. The strength of the bone is also ensured by its structure, the location of the bone crossbars of the spongy substance in accordance with the direction of the forces of pressure and tension.

Bone is 30 times harder than brick and 2,5 times harder than granite. Bone is stronger than oak. It is nine times stronger than lead and almost as strong as cast iron. In a vertical position, the human femur can withstand the pressure of a load of up to 1500 kg, and the tibia - up to 1800 kg.

Development of the skeletal system in childhood and adolescence. During prenatal development in children, the skeleton consists of cartilage tissue. Ossification points appear after 7-8 weeks. The newborn has ossified diaphysis of the tubular bones. After birth, the ossification process continues. The timing of the appearance of ossification points and the end of ossification varies for different bones. Moreover, for each bone they are relatively constant; they can be used to judge the normal development of the skeleton in children and their age.

The skeleton of a child differs from the skeleton of an adult in its size, proportions, structure and chemical composition. The development of the skeleton in children determines the development of the body (for example, the musculature develops more slowly than the skeleton grows).

There are two ways of bone development.

1. Primary ossification, when bones develop directly from the embryonic connective tissue - mesenchyme (bones of the cranial vault, facial part, partly the clavicle, etc.). First, a skeletal mesenchymal syncytium is formed. Cells are laid in it - osteoblasts, which turn into bone cells - osteocytes, and fibrils impregnated with calcium salts and turn into bone plates. Thus, bone develops from connective tissue.

2. Secondary ossification, when the bones are initially laid down in the form of dense mesenchymal formations that have the approximate outlines of future bones, then turn into cartilaginous tissues and are replaced by bone tissues (bones of the base of the skull, trunk and limbs).

With secondary ossification, the development of bone tissue occurs by replacement both outside and inside. Outside, the formation of bone substance occurs by osteoblasts of the periosteum. Inside, ossification begins with the formation of ossification nuclei, gradually the cartilage resolves and is replaced by bone. As the bone grows, it is resorbed from the inside by special cells called osteoclasts. The growth of bone substance comes from the outside. Bone growth in length occurs due to the formation of bone substance in the cartilage located between the epiphysis and diaphysis. These cartilages are gradually shifted towards the epiphysis.

Many bones in the human body are not formed entirely, but in separate parts, which then merge into a single bone. For example, the pelvic bone first consists of three parts, merging together by the age of 14-16. The tubular bones are also laid in three main parts (ossification nuclei in the places where bone protrusions are formed are not taken into account). For example, the tibia in the embryo initially consists of a continuous hyaline cartilage. Ossification begins in the middle part at about the eighth week of intrauterine life. Replacement on the bone of the diaphysis occurs gradually and goes first from the outside, and then from the inside. At the same time, the epiphyses remain cartilaginous. The nucleus of ossification in the upper epiphysis appears after birth, and in the lower epiphysis - in the second year of life. In the middle part of the epiphyses, the bone first grows from the inside, then from the outside, as a result of which two layers of epiphyseal cartilage remain separating the diaphysis from the epiphyses.

In the upper epiphysis of the femur, the formation of bone trabeculae occurs at the age of 4-5 years. After 7-8 years, they lengthen and become uniform and compact. The thickness of the epiphyseal cartilage by the age of 17-18 reaches 2-2,5 mm. By the age of 24, the growth of the upper end of the bone ends and the upper epiphysis fuses with the diaphysis. The lower epiphysis grows to the diaphysis even earlier - by the age of 22. With the end of ossification of tubular bones, their growth in length stops.

Ossification process. General ossification of the tubular bones is completed by the end of puberty: in women - by 17-21 years, in men - by 19-24 years. Because men reach puberty later than women, they are taller on average.

From five months to one and a half years, that is, when the child gets on his feet, the main development of the lamellar bone occurs. By the age of 2,5-3 years, the remnants of coarse fibrous tissue are already absent, although during the second year of life, most of the bone tissue has a lamellar structure.

Decreased function of the endocrine glands (anterior pituitary, thyroid, parathyroid, thymus, genital) and lack of vitamins (especially vitamin D) can cause delayed ossification. Acceleration of ossification occurs with precocious puberty, increased function of the anterior part of the adenohypophysis, thyroid gland and adrenal cortex. Delay and acceleration of ossification most often appear before the age of 17-18, and the difference between "bone" and passport ages can reach 5-10 years. Sometimes ossification occurs faster or slower on one side of the body than on the other.

With age, the chemical composition of bones changes. The bones of children contain more organic matter and less inorganic matter. With growth, the amount of salts of calcium, phosphorus, magnesium and other elements increases significantly, the ratio between them changes. So, in young children, calcium is retained in the bones the most, but as they grow older, there is a shift towards greater retention of phosphorus. Inorganic substances in the composition of the bones of a newborn make up one-half of the bone weight, in an adult - four-fifths.

A change in the structure and chemical composition of bones also entails a change in their physical properties. In children, the bones are more elastic and less brittle than in adults. Cartilage in children is also more plastic.

Age-related differences in the structure and composition of bones are especially pronounced in the number, location, and structure of the Haversian canals. With age, their number decreases, and the location and structure change. The older the child, the more dense matter in his bones, in young children there is more spongy substance. By the age of 7, the structure of tubular bones is similar to that of an adult, however, between 10-12 years, the spongy substance of the bones changes even more intensively, its structure stabilizes by the age of 18-20.

The younger the child, the more the periosteum is fused to the bone. The final demarcation between bone and periosteum occurs by the age of 7. By the age of 12, the dense substance of the bone has an almost homogeneous structure; by the age of 15, single areas of resorption of the dense substance completely disappear, and by the age of 17, large osteocytes predominate in it.

From 7 to 10 years, the growth of the bone marrow cavity in the tubular bones sharply slows down, and it is finally formed from 11-12 to 18 years. The increase in the bone marrow canal occurs in parallel with the uniform growth of the dense substance.

Between the plates of the spongy substance and in the medullary canal is the bone marrow. Due to the large number of blood vessels in the tissues, newborns have only red bone marrow - hematopoiesis occurs in it. From six months, a gradual process of replacing the tubular bones in the diaphysis of the red bone marrow with yellow, consisting mostly of fat cells, begins. Replacement of the red brain is completed by 12-15 years. In adults, red bone marrow is stored in the epiphyses of tubular bones, in the sternum, ribs and spine and is approximately 1500 cubic meters. cm.

The union of fractures and the formation of callus in children occurs after 21-25 days, in infants this process occurs even faster. Dislocations in children under 10 years of age are rare due to the high extensibility of the ligamentous apparatus.

3.2. Types and functional features of the muscle tissue of children and adolescents

General information about muscles. There are about 600 skeletal muscles in the human body. The muscular system makes up a significant part of the total human body weight. So, at the age of 17-18 years it is 43-44%, and in people with good physical fitness it can even reach 50%. In newborns, total muscle mass accounts for only 23% of body weight.

The growth and development of individual muscle groups occur unevenly. First of all, the abdominal muscles develop in infants, and a little later, the masticatory muscles. The muscles of a child, unlike the muscles of an adult, are paler, softer and more elastic. By the end of the first year of life, the muscles of the back and limbs noticeably increase, at this time the child begins to walk.

During the period from birth to the end of the growth of the child, the mass of muscles increases by 35 times. At the age of 12-16 years (puberty), due to the lengthening of the tubular bones, the tendons of the muscles also intensively lengthen. At this time, the muscles become long and thin, which is why teenagers look long-legged and long-armed. At 15-18 years of age, transverse muscle growth occurs. Their development continues up to 25-30 years.

Muscle structure. The muscle is divided into a middle part - the belly, consisting of muscle tissue, and the end sections - tendons, formed by dense connective tissue. Tendons attach muscles to bones, but this is not necessary. Muscles can also attach to various organs (the eyeball), to the skin (muscles of the face and neck), etc. In the muscles of a newborn, the tendons are rather poorly developed, and only by the age of 12-14 are the muscle-tendon relationships that are characteristic of muscles established adult. The muscles of all higher animals are the most important working organs - effectors.

Muscles are smooth and striated. In the human body, smooth muscles are found in the internal organs, blood vessels and skin. They are almost not controlled by the central nervous system, so they (as well as the heart muscle) are sometimes called involuntary. These muscles have automatism and their own nervous network (intramural, or metasympathetic), which largely ensures their autonomy. The regulation of the tone and motor activity of smooth muscles is carried out by impulses coming through the autonomic nervous system and humorally (i.e., through tissue fluid). Smooth muscles are able to carry out rather slow movements and long tonic contractions. The motor activity of smooth muscles often has a rhythmic character, for example, pendulum and peristaltic bowel movements. Prolonged tonic contractions of smooth muscles are very clearly expressed in the sphincters of hollow organs, which prevents the release of contents. This ensures the accumulation of urine in the bladder and bile in the gallbladder, the formation of feces in the large intestine, etc.

The smooth muscles of the walls of blood vessels, especially arteries and arterioles, are in a state of constant tonic contraction. The tone of the muscle layer of the walls of the arteries regulates the size of their lumen and thus the level of blood pressure and blood supply to the organs.

Striated muscles consist of many individual muscle fibers, which are located in a common connective tissue sheath and are attached to tendons, which, in turn, are connected to the skeleton. Striated muscles are divided into two types:

a) parallel-fibrous (all fibers are parallel to the long axis of the muscle);

b) pinnate (the fibers are located obliquely, attached on one side to the central tendon cord, and on the other to the outer tendon sheath).

Muscle strength is proportional to the number of fibers, i.e., the area of ​​the so-called physiological cross-section of the muscle, the surface area that intersects all active muscle fibers. Each skeletal muscle fiber is a thin (10 to 100 microns in diameter), long (up to 2-3 cm) multinuclear formation - a symplast - arising in early ontogenesis from the fusion of myoblast cells.

The main feature of a muscle fiber is the presence in its protoplasm (sarcoplasm) of a mass of thin (about 1 micron in diameter) filaments - myofibrils, which are located along the longitudinal axis of the fiber. Myofibrils consist of alternating light and dark areas - discs. Moreover, in the mass of neighboring myofibrils in striated fibers, the same-name disks are located at the same level, which gives regular transverse striation (striation) to the entire muscle fiber.

A complex of one dark and two halves of light discs adjacent to it, limited by thin Z-lines, is called a sarcomere. Sarcomeres are the smallest element of the contractile apparatus of a muscle fiber.

The membrane of the muscle fiber - the plasmalemma - has a similar structure to the nerve membrane. Its distinguishing feature is that it produces regular T-shaped invaginations (50 nm diameter tubes) approximately at the sarcomere boundaries. Invaginations of the plasmalemma increase its area and, consequently, the total electric capacitance.

Inside the muscle fiber between the bundles of myofibrils, parallel to the longitudinal axis of the symplast, there are systems of tubules of the sarcoplasmic reticulum, which is a branched closed system that is closely adjacent to the myofibrils and its blind ends (terminal cisterns) to the T-shaped protrusions of the plasmalemma (T-system). The T-system and the sarcoplasmic reticulum are the apparatus for transmitting excitation signals from the plasmalemma to the contractile apparatus of the myofibrils.

Outside, the entire muscle is enclosed in a thin connective tissue sheath - fascia.

Contractility as the main property of muscles. Excitability, conductivity and contractility are the main physiological properties of muscles. Muscle contractility consists of shortening the muscle or developing tension. During the experiment, the muscle responds with a single contraction in response to a single stimulus. In humans and animals, muscles from the central nervous system receive not single impulses, but a series of impulses, to which they respond with a strong, prolonged contraction. This muscle contraction is called tetanic (or tetanus).

When muscles contract, they perform work that depends on their strength. The thicker the muscle, the more muscle fibers in it, the stronger it is. Muscle in terms of 1 square. cm cross-section can lift a load up to 10 kg. The strength of the muscles also depends on the features of their attachment to the bones. Bones and the muscles attached to them are a kind of leverage. The strength of a muscle depends on how far from the fulcrum of the lever and closer to the point of application of gravity it is attached.

A person is able to maintain the same posture for a long time. This is called static muscle tension. For example, when a person simply stands or holds his head upright (i.e., makes the so-called static efforts), his muscles are in a state of tension. Some exercises on rings, parallel bars, holding a raised bar require such static work, which requires the simultaneous contraction of almost all muscle fibers. Of course, such a state cannot be prolonged due to developing fatigue.

During dynamic work, various muscle groups contract. At the same time, the muscles that perform dynamic work contract quickly, work with great tension and therefore soon get tired. Usually, during dynamic work, different groups of muscle fibers contract in turn. This gives the muscle the ability to do work for a long time.

By controlling the work of the muscles, the nervous system adapts their work to the current needs of the body, in connection with this, the muscles work economically, with a high efficiency. Work will become maximum, and fatigue will develop gradually, if for each type of muscular activity an average (optimal) rhythm and load value is selected.

The work of muscles is a necessary condition for their existence. If the muscles are inactive for a long time, muscle atrophy develops, they lose their efficiency. Training, that is, constant, fairly intense work of the muscles, helps to increase their volume, increase strength and performance, and this is important for the physical development of the body as a whole.

Muscle tone. In humans, muscles are somewhat contracted even at rest. A condition in which tension is maintained for a long time is called muscle tone. Muscle tone may decrease slightly and the body may relax during sleep or anesthesia. Complete disappearance of muscle tone occurs only after death. Tonic muscle contraction does not cause fatigue. The internal organs are held in their normal position only due to muscle tone. The amount of muscle tone depends on the functional state of the central nervous system.

The tone of skeletal muscles is directly determined by the supply of nerve impulses from the motor neurons of the spinal cord to the muscle with a large interval. The activity of neurons is supported by impulses coming from the overlying sections of the central nervous system, from receptors (proprioceptors) that are located in the muscles themselves. The role of muscle tone in ensuring coordination of movements is great. In newborns, the tone of the flexors of the arm predominates; in children of 1-2 months - the tone of the extensor muscles, in children of 3-5 months - the balance of the tone of the antagonist muscles. This circumstance is associated with increased excitability of the red nuclei of the midbrain. As the functional maturation of the pyramidal system, as well as the cerebral cortex of the brain, muscle tone decreases.

The increased muscle tone of the legs of the newborn gradually decreases (this occurs in the second half of the child's life), which is a necessary prerequisite for the development of walking.

Fatigue. During prolonged or strenuous work, muscle performance decreases, which is restored after rest. This phenomenon is called physical fatigue. With pronounced fatigue, prolonged shortening of the muscles and their inability to completely relax (contracture) develop. This is primarily due to changes that occur in the nervous system, disruption of the conduction of nerve impulses at synapses. When tired, the reserves of chemical substances that serve as sources of contraction energy are depleted, and metabolic products (lactic acid, etc.) accumulate.

The rate of onset of fatigue depends on the state of the nervous system, the frequency of the rhythm in which the work is performed, and on the magnitude of the load. Fatigue can be associated with an unfavorable environment. Uninteresting work quickly causes fatigue.

The younger the child, the faster he gets tired. In infancy, fatigue occurs after 1,5-2 hours of wakefulness. Immobility, prolonged inhibition of movements tire children.

Physical fatigue is a normal physiological phenomenon. After rest, working capacity is not only restored, but may also exceed the initial level. In 1903 I.M. Sechenov found that the performance of tired muscles of the right hand is restored much faster if, during rest, work is done with the left hand. Such a rest, in contrast to the simple rest of I.M. Sechenov called active.

Thus, the alternation of mental and physical labor, outdoor games before classes, physical culture breaks during lessons and during breaks increase the efficiency of students.

3.3. Growth and muscle work

During fetal development, muscle fibers are formed heterochronously. Initially, the muscles of the tongue, lips, diaphragm, intercostal and dorsal are differentiated, in the limbs - first the muscles of the arms, then the legs, in each limb first - the proximal sections, and then the distal ones. Muscles of embryos contain less proteins and more (up to 80%) water. The development and growth of different muscles after birth also occur unevenly. Earlier and more muscles begin to develop, providing motor functions that are extremely important for life. These are the muscles that are involved in breathing, sucking, grasping objects, i.e., the diaphragm, muscles of the tongue, lips, hands, intercostal muscles. In addition, the muscles involved in the process of teaching and nurturing certain skills in children are trained and developed more.

A newborn has all the skeletal muscles, but they weigh 37 times less than an adult. Skeletal muscles grow and develop until about 20-25 years of age, influencing the growth and formation of the skeleton. The increase in muscle weight with age occurs unevenly, this process is especially fast during puberty.

Body weight increases with age, mainly due to an increase in skeletal muscle weight. The average weight of skeletal muscles as a percentage of body weight is distributed as follows: in newborns - 23,3; at 8 years old - 27,2; at 12 years old - 29,4; at the age of 15 - 32,6; at 18 years old - 44,2.

Age-related features of growth and development of skeletal muscles. The following pattern of growth and development of skeletal muscles is observed at different age periods.

Period up to 1 year: more than the muscles of the pelvis, hips and legs, the muscles of the shoulder girdle and arms are developed.

The period from 2 to 4 years: in the arm and shoulder girdle, the proximal muscles are much thicker than the distal ones, the superficial muscles are thicker than the deep ones, the functionally active muscles are thicker than the less active ones. The fibers grow especially fast in the longissimus dorsi muscle and in the gluteus maximus muscle.

The period from 4 to 5 years: the muscles of the shoulder and forearm are developed, the muscles of the hands are not sufficiently developed. In early childhood, the muscles of the trunk develop much faster than the muscles of the arms and legs.

The period from 6 to 7 years: there is an acceleration in the development of the muscles of the hand, when the child begins to do light work and learn to write. The development of the flexors is ahead of the development of the extensors.

In addition, the weight and physiological diameter of the flexors are greater than those of the extensors. The muscles of the fingers, especially the flexors that are involved in the capture of objects, have the greatest weight and physiological diameter. Compared with them, the flexors of the hand have a relatively smaller weight and physiological diameter.

Period up to 9 years: the physiological diameter of the muscles that cause finger movements increases, while the muscles of the wrist and elbow joints grow less intensively.

Period up to 10 years: the diameter of the long flexor of the thumb by the age of 10 reaches almost 65% of the length of the diameter of an adult.

Period from 12 to 16 years: the muscles that ensure the vertical position of the body grow, especially the iliopsoas, which plays an important role in walking. By the age of 15-16, the thickness of the fibers of the iliopsoas muscle becomes the largest.

The anatomical diameter of the shoulder in the period from 3 to 16 years increases in boys by 2,5-3 times, in girls - less.

The deep muscles of the back in the first years of life in children are still weak, their tendon-ligamentous apparatus is also underdeveloped, however, by the age of 12-14, these muscles are strengthened by the tendon-ligamentous apparatus, but less than in adults.

The abdominal muscles in newborns are not developed. From 1 year to 3 years, these muscles and their aponeuroses differ, and only by the age of 14-16 the anterior wall of the abdomen is strengthened almost in the same way as in an adult. Up to 9 years, the rectus abdominis muscle grows very intensively, its weight increases almost 90 times compared to the weight of a newborn, the internal oblique muscle - more than 70 times, the external oblique - 67 times, the transverse - 60 times. These muscles resist the gradually increasing pressure of the internal organs.

In the biceps muscle of the shoulder and the quadriceps muscle of the thigh, muscle fibers thicken: by 1 year - twice; by 6 years - five times; by the age of 17 - eight times; by the age of 20 - 17 times.

Muscle growth in length occurs at the junction of muscle fibers and tendons. This process continues until the age of 23-25. From 13 to 15 years, the contractile part of the muscle grows especially quickly. By the age of 14-15, muscle differentiation reaches a high level. The growth of fibers in thickness continues up to 30-35 years. The diameter of the muscle fibers thickens: by 1 year - twice; by 5 years - five times; by the age of 17 - eight times; by the age of 20 - 17 times.

Muscle mass especially intensively increases in girls at 11-12 years old, in boys - at 13-14 years old. In adolescents, in two to three years, the mass of skeletal muscles increases by 12%, while in the previous 7 years - only by 5%. The weight of skeletal muscles in adolescents is approximately 35% in relation to body weight, while muscle strength increases significantly. The muscles of the back, shoulder girdle, arms and legs develop significantly, which causes increased growth of tubular bones. The correct selection of physical exercises contributes to the harmonious development of skeletal muscles.

Age-related features of the structure of skeletal muscles. The chemical composition and structure of skeletal muscles also change with age. The muscles of children contain more water and less dense substances than those of adults. The biochemical activity of red muscle fibers is greater than white ones. This is explained by differences in the number of mitochondria or in the activity of their enzymes. The amount of myoglobin (an indicator of the intensity of oxidative processes) increases with age. In a newborn, skeletal muscle contains 0,6% myoglobin, in adults it is 2,7%. In addition, children contain relatively less contractile proteins - myosin and actin. With age, this difference decreases.

Muscle fibers in children contain relatively more nuclei, they are shorter and thinner, but with age, both their length and thickness increase. Muscle fibers in newborns are thin, tender, their transverse striation is relatively weak and surrounded by large layers of loose connective tissue. Relatively more space is occupied by tendons. Many nuclei within muscle fibers do not lie near the cell membrane. Myofibrils are surrounded by clear layers of sarcoplasm.

The following dynamics of changes in the structure of skeletal muscles depending on age is observed.

1. At 2-3 years old, muscle fibers are twice as thick as in newborns, they are denser, the number of myofibrils increases, and the number of sarcoplasms decreases, the nuclei are adjacent to the membrane.

2. At 7 years old, the thickness of muscle fibers is three times thicker than in newborns, and their transverse striation is clearly expressed.

3. By the age of 15-16, the structure of muscle tissue becomes the same as in adults. By this time, the formation of the sarcolemma is completed.

The maturation of muscle fibers can be traced by a change in the frequency and amplitude of biocurrents recorded from the biceps muscle of the shoulder when holding the load:

▪ in children 7-8 years old, as the time of holding the load increases, the frequency and amplitude of biocurrents decrease more and more. This proves the immaturity of some of their muscle fibers;

▪ in children 12-14 years old, the frequency and amplitude of biocurrents do not change during 6-9 seconds of holding the load at maximum height or decrease at a later date. This indicates the maturity of the muscle fibers.

In children, unlike adults, the muscles are attached to the bones further from the axes of rotation of the joints, therefore, their contraction is accompanied by less loss of strength than in adults. With age, the ratio between the muscle and its tendon, which grows more intensively, changes significantly. As a result, the nature of the attachment of the muscle to the bone changes, therefore, the efficiency increases. Approximately by the age of 12-14, the "muscle-tendon" relationship, which is typical for an adult, stabilizes. In the girdle of the upper extremities up to 15 years, the development of the muscular belly and tendons occurs equally intensively, after 15 and up to 23-25 ​​years the tendon grows more intensively.

The elasticity of children's muscles is about twice as high as that of adults. When contracted, they shorten more, and when stretched, they lengthen more.

Muscle spindles appear on the 10-14th week of uterine life. An increase in their length and diameter occurs in the first years of a child's life. In the period from 6 to 10 years, the transverse size of the spindles changes slightly. In the period of 12-15 years, muscle spindles complete their development and have the same structure as in adults at the age of 20-30.

The beginning of the formation of sensitive innervation occurs at 3,5-4 months of uterine life, and by 7-8 months the nerve fibers reach significant development. By the time of birth, afferent nerve fibers are actively myelinated.

The muscle spindles of a single muscle have the same structure, but their number and the level of development of individual structures in different muscles are not the same. The complexity of their structure depends on the amplitude of movement and the force of muscle contraction. This is due to the coordination work of the muscle: the higher it is, the more muscle spindles in it and the more difficult they are. In some muscles, there are no muscle spindles that are not subject to stretching. Such muscles, for example, are the short muscles of the palm and foot.

Motor nerve endings (myoneural apparatus) appear in a child in the uterine period of life (at the age of 3,5-5 months). In different muscles they develop in the same way. By the time of birth, the number of nerve endings in the muscles of the arm is greater than in the intercostal muscles and muscles of the lower leg. In a newborn, the motor nerve fibers are covered with a myelin sheath, which thickens greatly by the age of 7. By the age of 3-5, the nerve endings become much more complicated, by the age of 7-14 they are even more differentiated, and by the age of 19-20 they reach full maturity.

Age-related changes in muscle excitability and lability. For the functioning of the muscular system, not only the properties of the muscles themselves are important, but also age-related changes in the physiological properties of the motor nerves that innervate them. To assess the excitability of nerve fibers, a relative indicator expressed in time units is used - chronaxy. In newborns, a more elongated chronaxia is observed. During the first year of life, the level of chronaxy decreases by approximately 3-4 times. In subsequent years, the value of chronaxy gradually shortens, but in school-age children it still exceeds the chronaxy of an adult. Thus, a decrease in chronaxy from birth to the school period indicates that the excitability of nerves and muscles increases with age.

For children 8-11 years old, as well as for adults, the excess of flexor chronaxy over extensor chronaxy is characteristic. The difference in the chronaxy of the antagonist muscles is most pronounced on the arms than on the legs. The chronaxia of the distal muscles exceeds that of the proximal muscles. For example, the chronaxia of the muscles of the shoulder is approximately two times shorter than the chronaxia of the muscles of the forearm. Less toned muscles have a longer chronaxy than more toned ones. For example, the biceps femoris and tibialis anterior have longer chronaxies than their antagonists, the quadriceps femoris and gastrocnemius. The transition from light to darkness lengthens the chronaxy, and vice versa.

During the day, in children of primary school age, chronaxy changes. After 1-2 general education lessons, there is a decrease in motor chronaxy, and by the end of the school day it often recovers to its previous level or even increases. After easy general education lessons, motor chronaxia most often decreases, and after difficult lessons it increases.

As we grow older, fluctuations in motor chronaxy gradually decrease, while chronaxy of the vestibular apparatus increases.

Functional mobility, or lability, in contrast to chronaxy, determines not only the shortest time required for the onset of excitation, but also the time required for completion of excitation and restoration of the tissue's ability to give new subsequent excitation impulses. The faster the skeletal muscle reacts, the more excitation impulses pass through it per unit time, the greater its lability. Consequently, muscle lability increases with an increase in the mobility of the nervous process in motor neurons (acceleration of the transition of excitation into inhibition), and vice versa - with an increase in the speed of muscle contraction. The slower the muscles react, the less their lability. In children, lability increases with age, by the age of 14-15 it reaches the level of adult lability.

Change in muscle tone. In early childhood, there is significant tension in certain muscles, such as the hands and hip flexors, due to the involvement of skeletal muscles in generating heat at rest. This muscle tone is of reflex origin and decreases with age.

The tone of skeletal muscles is manifested in their resistance to active deformation during compression and stretching. At the age of 8-9 years, in boys, muscle tone, for example, the muscles of the back of the thigh, is higher than in girls. By the age of 10-11, muscle tone decreases, and then again increases significantly. The greatest increase in skeletal muscle tone is observed in adolescents aged 12-15, especially boys, in whom it reaches youthful values. With the transition from pre-preschool to preschool age, there is a gradual cessation of the participation of skeletal muscles in heat production at rest. At rest, the muscles become more and more relaxed.

In contrast to the voluntary tension of skeletal muscles, the process of their voluntary relaxation is more difficult to achieve. This ability increases with age, so the stiffness of movements decreases in boys up to 12-13 years old, in girls - up to 14-15 years old. Then the reverse process occurs: the stiffness of movements increases again from the age of 14-15, while in boys aged 16-18 it is significantly greater than in girls.

Sarcomere structure and mechanism of muscle fiber contraction. A sarcomere is a repeating segment of myofibril, consisting of two halves of a light (optically isotropic) disk (I-disc) and one dark (anisotropic) disk (A-disc). Electron microscopic and biochemical analysis revealed that the dark disk is formed by a parallel bundle of thick (diameter about 10 nm) myosin filaments, the length of which is about 1,6 μm. The molecular weight of the myosin protein is 500 D. The heads of myosin molecules (000 nm long) are located on the myosin filaments. The light discs contain thin filaments (20 nm in diameter and 5 µm in length), which are built from protein and actin (molecular weight - 1 D), as well as tropomyosin and troponin. In the region of the Z-line, delimiting adjacent sarcomeres, a bundle of thin filaments is held together by a Z-membrane.

The ratio of thin and thick filaments in the sarcomere is 2: 1. The myosin and actin filaments of the sarcomere are arranged so that the thin filaments can freely enter between the thick ones, i.e., “move” into the A-disk, this happens during muscle contraction. Therefore, the length of the light part of the sarcomere (I-disk) can be different: with passive stretching of the muscle, it increases to a maximum, with contraction, it can decrease to zero.

The mechanism of contraction is the movement (pulling) of thin filaments along the thick filaments to the center of the sarcomere due to the "rowing" movements of the myosin heads, which periodically attach to the thin filaments, forming transverse actomyosin bridges. Investigating the movements of the bridges using the X-ray diffraction method, it was determined that the amplitude of these movements is 20 nm, and the frequency is 5-50 oscillations per second. In this case, each bridge either attaches and pulls the thread, then detaches in anticipation of a new attachment. A huge number of bridges work randomly, so their total thrust is uniform in time. Numerous studies have established the following mechanism for the cyclic operation of the myosin bridge.

1. At rest, the bridge is charged with energy (myosin is phosphorylated), but it cannot connect to the actin filament, since a system of tropomyosin filament and troponin globule is wedged between them.

2. Upon activation of the muscle fiber and the appearance of Ca + 2 ions in the myoplasm (in the presence of ATP), troponin changes its conformation and moves the tropomyosin thread away, opening up the possibility for the myosin head to connect with actin.

3. The connection of the head of phosphorylated myosin with actin sharply changes the conformation of the bridge (its "bending" occurs) and moves the actin filaments by one step (20 nm), and then the bridge breaks. The energy required for this appears as a result of the breakdown of the macroergic phosphate bond included in phosphoryl lactomyosin.

4. Then, due to a drop in the local concentration of Ca + 2 and its detachment from troponin, tropomyosin again blocks actin, and myosin is again phosphorylated due to ATP. ATP not only charges the systems for further work, but also contributes to the temporary separation of the threads, that is, it plasticizes the muscle, making it capable of stretching under the influence of external forces. It is believed that one ATP molecule is consumed per working movement of one bridge, and actomyosin plays the role of ATPase (in the presence of Mg + 2 and Ca + 2). With a single contraction, a total of 0,3 μM ATP is spent per 1 g of muscle.

Thus, ATP plays a dual role in muscle work: on the one hand, by phosphorylation of myosin, it provides energy for contraction, on the other hand, being in a free state, it provides muscle relaxation (its plasticization). If ATP disappears from the myoplasm, a continuous contraction develops - contracture.

All these phenomena can be demonstrated on isolated actomyosin filament complexes: such filaments harden without ATP (rigor is observed), in the presence of ATP they relax, and when Ca+2 is added they produce a reversible contraction similar to normal.

Muscles are permeated with blood vessels, through which nutrients and oxygen come to them with blood, and metabolic products are carried out. In addition, the muscles are also rich in lymphatic vessels.

Muscles have nerve endings - receptors that perceive the degree of contraction and stretching of the muscle.

Major muscle groups of the human body. The shape and size of muscles depend on the work they perform. The muscles are distinguished between long, broad, short and circular. Long muscles are located on the limbs, short ones - where the range of movement is small (for example, between the vertebrae). The broad muscles are located mainly on the torso, in the walls of the body cavities (for example, the abdominal muscles, back, chest). Circular muscles - sphincters - lie around the openings of the body, narrowing them when contracting.

By function, the muscles are divided into flexors, extensors, adductors and abductors, as well as muscles that rotate inward and outward.

I. The muscles of the trunk include:

1) chest muscles;

2) abdominal muscles;

3) back muscles.

II. The muscles located between the ribs (intercostal), as well as other muscles of the chest, are involved in the function of breathing. They are called respiratory muscles. These include the diaphragm, which separates the chest cavity from the abdominal cavity.

III. Well-developed chest muscles move and strengthen the upper limbs on the body. These include:

1) pectoralis major muscle;

2) pectoralis minor muscle;

3) serratus anterior muscle.

IV. The abdominal muscles perform various functions. They form the wall of the abdominal cavity and, due to their tone, keep the internal organs from moving, lowering and falling out. By contracting, the abdominal muscles act on the internal organs as the abdominal press, contributing to the release of urine, feces and childbirth. The contraction of the abdominal muscles also helps the movement of blood in the venous system, the implementation of respiratory movements. The abdominal muscles are involved in forward flexion of the spinal column.

Due to the possible weakness of the abdominal muscles, not only the prolapse of the abdominal organs occurs, but also the formation of hernias. A hernia is the exit of internal organs (intestines, stomach, greater omentum) from the abdominal cavity under the skin of the abdomen.

V. The muscles of the abdominal wall include:

1) rectus abdominis muscle;

2) pyramidalis muscle;

3) quadratus lumborum muscle;

4) broad abdominal muscles (external and internal, oblique and transverse).

VI. A dense tendon cord runs along the midline of the abdomen - the so-called white line. On the sides of it is the rectus abdominis muscle, which has a longitudinal direction of the fibers.

VII. On the back are numerous muscles along the spinal column. These are deep back muscles. They are attached mainly to the processes of the vertebrae and are involved in the movements of the spinal column back and to the side.

VIII. The superficial back muscles include:

1) trapezius muscle of the back;

2) latissimus dorsi muscle. They provide movement of the upper limbs and chest.

IX. Among the muscles of the head, there are:

1) chewing muscles. These include: temporal muscle; chewing muscle; pterygoid muscles. Contractions of these muscles cause complex chewing movements of the lower jaw;

2) facial muscles. These muscles with one or sometimes two ends are attached to the skin of the face. When contracted, they displace the skin, creating a certain facial expression, that is, one or another facial expression. The facial muscles also include the circular muscles of the eye and mouth.

X. The muscles of the neck throw back the head, tilt and turn it.

XI. The scalene muscles raise the ribs, thus participating in inspiration.

XII. The muscles attached to the hyoid bone, during contraction, change the position of the tongue and larynx when swallowing and pronouncing various sounds.

XIII. The belt of the upper limbs is connected to the body only in the area of ​​the sternoclavicular joint. It is strengthened by the muscles of the torso:

1) trapezius muscle;

2) pectoralis minor muscle;

3) rhomboid muscle;

4) serratus anterior muscle;

5) the levator scapulae muscle.

XIV. The muscles of the limb girdle move the upper limb in the shoulder joint. The most important of these is the deltoid muscle. When contracted, this muscle flexes the arm at the shoulder joint and abducts the arms to a horizontal position.

XV. In the area of ​​​​the shoulder in front there is a group of flexor muscles, in the back - extensor muscles. Among the muscles of the anterior group, the biceps of the shoulder is distinguished, the back - the triceps of the shoulder.

XVI. The muscles of the forearm on the front surface are represented by flexors, on the back - by extensors.

XVII. Among the muscles of the hand are:

1) palmaris longus muscle;

2) flexors of the fingers.

XVIII. The muscles located in the lower extremity belt area move the leg at the hip joint, as well as the spinal column. The anterior muscle group is represented by one large muscle - the iliopsoas. The posterior external group of muscles of the pelvic girdle includes:

1) large muscle;

2) gluteus medius muscle;

3) gluteus minimus muscle.

XIX. The legs have a more massive skeleton than the arms. Their musculature has more strength, but less variety and limited range of motion.

On the thigh in front is the longest in the human body (up to 50 cm) tailor muscle. It flexes the leg at the hip and knee joints.

The quadriceps femoris muscle lies deeper than the sartorius muscle, while it fits the femur from almost all sides. The main function of this muscle is to extend the knee joint. When standing, the quadriceps muscle does not allow the knee joint to bend.

On the back of the lower leg is the gastrocnemius muscle, which flexes the lower leg, flexes and somewhat rotates the foot outward.

3.4. The role of muscle movements in the development of the body

Studies have shown that from the first years of life, the movements of the child play a significant role in the functioning of speech. It has been proven that the formation of speech in interaction with the motor analyzer is particularly successful.

Physical education, which consists in strengthening the health and physical improvement of children, significantly affects the development of thinking, attention and memory. This is not just a biological meaning: there is an expansion of human capabilities in the perception, processing and use of information, the assimilation of knowledge, a versatile study of the surrounding nature and oneself.

Physical exercises improve the muscular system and vegetative functions (respiration, blood circulation, etc.), without which it is impossible to perform muscular work. In addition, exercise stimulates the functions of the central nervous system.

However, physical exercises are the leading, but not the only factor influencing the body in the course of physical education. It is very important to remember the general rational mode, proper organization of nutrition and sleep. Of great importance is hardening, etc.

Age-related patterns of motor development. Age-related physiology has collected a huge amount of factual material about age-related patterns of development of motor skills in children and adolescents.

The most significant changes in motor function are observed in primary school age. In accordance with the morphological data, the nervous structures of the child's motor apparatus (spinal cord, pathways) mature at the earliest stages of ontogenesis. With regard to the central structures of the motor analyzer, it has been established that their morphological maturation occurs at the age of 7 to 12 years. In addition, by this time, the sensory and motor endings of the muscular apparatus reach full development. The development of the muscles themselves and their growth continue until the age of 25-30, which explains the gradual increase in the absolute strength of the muscles.

Thus, we can say that the main tasks of school physical education must be solved as fully as possible in the first eight years of schooling, otherwise the most productive age periods for the development of children's motor abilities will be missed.

Period 7-11 years. Studies show that schoolchildren during this period have relatively low levels of muscle strength. Strength and especially static exercises cause them to quickly fatigue. Children of primary school age are more adapted to short-term speed-strength exercises, but they should be gradually taught to maintain static postures, which has a positive effect on posture.

Period 14-17 years. This period is characterized by the most intensive growth of muscle strength in boys. In girls, the growth of muscle strength begins somewhat earlier. This difference in the dynamics of the development of muscle strength is most pronounced at 11-12 years of age. The maximum increase in relative strength, i.e. strength per kilogram of mass, is observed up to 13-14 years. Moreover, by this age, the indicators of the relative muscle strength of boys significantly exceed the corresponding indicators for girls.

Endurance. Observations show that children 7-11 years old have a low level of endurance for dynamic work, but from 11-12 years old boys and girls become more resilient. By age 14, muscular endurance is 50-70%, and by age 16, it is about 80% of adult endurance.

Interestingly enough, there is no relationship between endurance to static loads and muscle strength. However, the level of endurance depends, for example, on the degree of puberty. Experience shows that walking, slow running, skiing are good means of developing endurance.

The time when the level of motor qualities can be raised with the help of physical education means is adolescence. However, it should be remembered that this period coincides with the biological restructuring of the body associated with puberty. Therefore, the teacher requires exceptional attention to the correct planning of physical activity.

Physical activity planning. At the age of 7-11, there is an intensive development of speed of movements (frequency, speed of movements, reaction time, etc.), therefore, in adolescence, schoolchildren adapt very well to high-speed loads, which is expressed in high performance in running, swimming, i.e. Where speed and responsiveness are of paramount importance. Also during this period, there is greater mobility of the spinal column and high elasticity of the ligamentous apparatus. All these morphofunctional prerequisites are important for the development of such a quality as flexibility (note that by the age of 13-15 this indicator reaches its maximum).

At the age of 7-10 years, dexterity of movements develops at an accelerated pace. At this age, the mechanism of regulation of movements in children is still insufficiently perfect; nevertheless, they successfully master the basic elements of such complex actions as swimming, skating, cycling, etc. At the same time, preschool children and younger schoolchildren acquire skills related to with the accuracy of hand movements, reproduction of the given efforts. These parameters reach a relatively high level of development by adolescence.

By the age of 12-14, the accuracy of throws, throwing at a target, and the accuracy of jumps increase. At the same time, according to some data, there is a deterioration in the coordination of movements in adolescents associated with morphological and functional changes during puberty.

We can say that adolescence has great potential for improving the motor apparatus. This is confirmed by the achievements of adolescents in rhythmic and artistic gymnastics, figure skating, and other sports. However, when organizing physical education in high school, it should be taken into account that the process of body formation in 16-17-year-old schoolchildren has not yet been completed, therefore, for those who do not systematically go in for sports, it is necessary to dose the loads associated with the manifestation of maximum strength and endurance. These facts, which testify to the heterochronous development of motor qualities, should be taken into account and strive for the harmonious development of different aspects of the motor skills of children, adolescents and young people.

In addition, the development of motor skills varies over a fairly wide range in children of the same age. Therefore, physical education should take into account the functional capabilities of each child, while not forgetting about age characteristics. The child needs to be taught skills and abilities, for the achievement of which he already has morphological and functional prerequisites.

Normalization of physical activity. Normalizing the volume of physical activity at different stages of ontogenesis is another important problem of physical education at school. Of course, the more a child moves daily, the better for the development of his motor functions. The preschooler is on the move almost continuously, except for the periods allocated for sleep and eating. After entering school, children's physical activity is reduced by half. Due to the independent motor activity of students in grades I-III, only 50% of the optimal number of movements is realized. That’s why organized forms of physical exercise are so important at this age.

At the same time, even in healthy, properly developing schoolchildren, only spontaneous motor activity and physical education lessons cannot provide the required daily range of motion. A physical education lesson compensates on average 11% of the required daily number of movements. In total, morning exercises, gymnastics before classes at school, physical education breaks in classes, outdoor games during breaks, walks with games after classes make up to 60% of the required daily range of motion for children 7-11 years old.

Research Institute of Physiology of Children and Adolescents of the Academy of Medical Sciences (now - the Institute of Developmental Physiology of the Russian Academy of Education) proved that 5-6 hours of physical exercise per week (two physical education lessons, daily physical culture and health-improving forms of work, classes in the sports section) contribute to favorable physical development, improvement the general physiological and immune reactivity of the body and are the average optimal and necessary norm. It has been established that daily 15-20-minute outdoor games for children in grades I-II after the third lesson increase mental performance by 3-4 times.

Adolescents need active rest after the third or fourth lesson, as well as before preparing homework, while physical education or outdoor recreation after the fifth or sixth lesson leads to a deterioration in performance indicators and inhibition of the phagocytic activity of blood leukocytes.

The importance of physical culture for the development of the musculoskeletal system. Skeletal muscles influence the course of metabolic processes and the functioning of internal organs: respiratory movements are carried out by the chest muscles and diaphragm, and the abdominal muscles normalize the activity of the abdominal organs, blood circulation and breathing. The power and size of muscles directly depend on exercise and training. This is due to the fact that during work the blood supply to the muscles increases, the regulation of their activity by the nervous system improves, which leads to the growth of muscle fibers, i.e., an increase in muscle mass. The result of training the muscular system is the ability to perform physical work and endurance.

An increase in the physical activity of children and adolescents leads to changes in the skeletal system and a more intensive growth of their body. Exercise strengthens bones and makes them more resistant to stress and injury. No less important is the fact that sports, physical exercises, taking into account the age characteristics of children and adolescents, eliminate posture disorders.

Versatile muscular activity contributes to an increase in the body's working capacity, while reducing the energy costs of the body to perform work. Systematic physical activity forms a more perfect mechanism of respiratory movements. This is expressed in an increase in the depth of breathing, vital capacity of the lungs. During muscular work, pulmonary ventilation can reach up to 120 l / min. Deep breathing of trained people better saturates the blood with oxygen. Blood vessels become more elastic during training, which improves the conditions for the movement of blood.

If a person does not move enough according to the nature of his work, does not go in for sports, then in middle and old age, the elasticity and contractility of his muscles decrease. This leads to a number of unpleasant consequences: his muscles become flabby; as a result of weakness of the abdominal muscles, the internal organs prolapse and the function of the gastrointestinal tract is disturbed; weakness of the back muscles causes a change in posture, stoop gradually develops, coordination of movements is disturbed.

Thus, the favorable effect exerted by physical exercises on the formation of a healthy, strong, hardy person with a correct physique and harmoniously developed muscles is obvious.

3.5. Features of the growth of the bones of the skull

The skull is the skeleton of the head. In accordance with the features of development, structure and functions, two sections of the skull are distinguished: cerebral and facial (visceral). The brain part of the skull forms a cavity inside which the brain is located. The facial region forms the bone base of the respiratory apparatus and the alimentary canal.

The medulla of the skull consists of a roof (or vault of the skull) and a base. The parietal bone of the cranial vault is a quadrangular plate with four serrated edges. Two parietal bones connected by sutures form the parietal tubercle. In front of the parietal bones lies the frontal bone, most of which is represented by scales.

The convex part of the facial part of the skull is formed by the frontal tubercles, below which are the bones that form the walls of the orbits. Between the eye sockets is the nasal part, adjacent to the nasal bones, below which are the cells of the ethmoid bone.

Behind the parietal bones is the occipital bone, thanks to which the base of the skull is formed and the skull is connected to the spine. On the sides of the roof of the skull are two temporal bones, also involved in the formation of the base of the skull. Each of them contains the corresponding sections of the organ of hearing and the vestibular apparatus. At the base of the skull is the sphenoid bone.

The bones of the base of the skull, developed from cartilage, are connected by cartilage tissue, which is replaced by bone tissue with age. The bones of the roof, developed from the connective tissue, are connected by connective tissue sutures, which become bony in old age. This also applies to the facial region of the skull.

The facial section of the skull consists of the upper jaw, zygomatic, lacrimal, ethmoid, palatine, nasal bones, inferior nasal concha, vomer, mandible and hyoid bone.

Age features of the skull. The brain and facial parts of the skull are formed from mesenchyme. The bones of the skull develop in a primary and secondary way (see 3.1). The skull of children differs significantly from the skull of adults in its size compared to body size, structure and proportions of individual parts of the body. In a newborn, the cerebral part of the skull is six times larger than the facial part, in an adult - 2,5 times. In other words, in a newborn, the facial part of the skull is relatively smaller than the brain part. With age, these differences disappear. Moreover, not only the shape of the skull and its constituent bones changes, but also the number of skull bones.

From birth to 7 years of age, the skull grows unevenly. There are three waves of acceleration in the growth of the skull:

1) up to 3-4 years;

2) from 6 to 8 years;

3) from 11 to 15 years.

The fastest growth of the skull occurs in the first year of life. The occipital bone protrudes and, together with the parietal bones, grows especially rapidly. The ratio of the volume of the skull of a child and an adult is as follows: in a newborn, the volume of the skull is equal to one third of the volume of an adult; at 6 months - one second; at 2 years - two-thirds.

During the first year of life, the thickness of the walls of the skull increases three times. In the first or second year of life, fontanelles (areas of connective tissue) are closed and replaced with bone sutures: occipital - in the second month; wedge-shaped - in the second or third month; mastoid - at the end of the first or beginning of the second year; frontal - in the second year of life. By the age of 1,5 years, the fontanelles are completely overgrown, and by the age of four, cranial sutures are formed.

At the age of 3 to 7 years, the base of the skull, together with the occipital bone, grows faster than the vault. At the age of 6-7 years, the frontal bone is completely fused. By the age of 7, the base of the skull and the foramen magnum reach a relatively constant value, and there is a sharp slowdown in the development of the skull. From 7 to 13 years of age, the growth of the base of the skull slows down even more.

At 6-7 and at 11-13 years old, the growth of the bones of the cranial vault increases slightly, and by the age of 10 it basically ends. The capacity of the skull by 10 years is 1300 cubic meters. cm (for comparison: in an adult - 1500-1700 cc).

From 13 to 14 years of age, the frontal bone grows intensively, the development of the facial section of the skull in all directions predominates, and the characteristic features of the physiognomy develop.

At the age of 18-20, the formation of synostosis between the bodies of the occipital and sphenoid bones ends. As a result, the growth of the base of the skull in length stops. Full fusion of the bones of the skull occurs in adulthood, but the development of the skull continues. After 30 years, the sutures of the skull gradually become bony.

The development of the lower jaw is directly dependent on the work of the masticatory muscles and the condition of the teeth. In its growth, two waves of acceleration are observed:

1) up to 3 years;

2) from 8 to 11 years.

Head sizes in schoolchildren increase very slowly. At all ages, boys have a larger average head circumference than girls. The largest increase in the head is observed between the ages of 11 and 17, i.e., during puberty (for girls - by 13-14 years, and for boys - by 13-15).

The ratio of head circumference to height decreases with age. If at 9-10 years old the head circumference is on average 52 cm, then at 17-18 years old it is 55 cm. In men, the capacity of the cranial cavity is approximately 100 cubic meters. see more than women.

There are also individual features of the skull. These include two extreme forms of skull development: long-headed and short-headed.

3.6. Spinal growth. The spine of an adult and a child

The spine consists of 24 free vertebrae (7 cervical, 12 thoracic and 5 lumbar) and 9-10 non-free (5 sacral and 4-5 coccygeal). Free vertebrae, articulated among themselves, are connected by ligaments, between which there are elastic intervertebral discs made of fibrocartilage. The sacral and coccygeal vertebrae are fused to form the sacrum and coccyx. The vertebrae develop from cartilage tissue, the thickness of which decreases with age.

There are four stages in the development of the epiphyses of the vertebrae: up to 8 years - the cartilaginous epiphysis; from 9 to 13 years - calcification of the epiphysis; from 14 to 17 years old - bone epiphysis; after 17 years - the fusion of the epiphysis with the vertebral body.

From 3 to 15 years, the size of the lower lumbar vertebrae increases more than the upper thoracic. This is due to an increase in body weight, its pressure on the underlying vertebrae.

From the age of 3, the vertebrae grow equally in height and width; from 5-7 years old - more in height.

At the age of 6-8 years, ossification centers are formed in the upper and lower surfaces of the vertebral bodies and at the ends of the spinous and transverse processes. Up to 5 years, the spinal canal develops especially rapidly. Since the vertebral bodies grow faster than the arches, the capacity of the canal decreases relatively, which corresponds to a decrease in the relative size of the spinal cord.

By the age of 10, the development of the spinal canal is completed, but the structure of the vertebral body continues to develop in children of senior school age.

By the age of 25, ossification of the cervical, thoracic and lumbar vertebrae ends, by the age of 20 - the sacral, by the age of 30 - the coccygeal vertebrae.

The length of the spine increases especially sharply during the first and second years of life, then the growth of the spine slows down and accelerates again from 7 to 9 years (more in girls than in boys). From 9 to 14 years old, the increase in the length of the spine in boys and girls slows down several times, and from 14 to 20 years old even more.

In boys, the growth of the spine ends after 20 years, in girls it grows up to 18 years, i.e., the growth of the spine in women stops earlier than in men. The average length of the spine in men is 70-73 cm, in women - 66-69 cm. By the end of puberty, the growth of the length of the spine is almost completed (approximately equal to 40% of the body length).

The mobility of the spine depends on the height of the intervertebral cartilage discs and their elasticity, as well as on the frontal and sagittal size of the vertebral bodies. In an adult, the total height of the intervertebral discs is equal to one fourth of the height of the movable part of the spine. The higher the intervertebral discs, the greater the mobility of the spine. The height of the discs in the lumbar region is one third of the height of the body of the adjacent vertebra, in the upper and lower parts of the thoracic region - one fifth, in its middle part - one sixth, in the cervical region - one fourth, therefore, in the cervical and lumbar regions, the spine has the greatest mobility.

By the age of 17-25, as a result of the replacement of intervertebral discs with bone tissue, the spine becomes immobile in the sacral region.

The flexion of the spine is greater than its extension. The greatest flexion of the spine occurs in the cervical region (70°), less in the lumbar, and the least in the thoracic region. Tilts to the side are greatest between the thoracic and lumbar regions (100°). The greatest circular motion is observed in the cervical spine (75°), it is almost impossible in the lumbar spine (5°). Thus, the cervical spine is the most mobile, the lumbar is less mobile, and the thoracic is the least mobile, because its movements are inhibited by the ribs.

The mobility of the spine in children, especially 7-9 years old, is much greater than in adults. This depends on the relatively larger size of the intervertebral discs and their greater elasticity. The development of intervertebral discs takes a long time and ends by the age of 17-20.

Physiological curves of the spine. After birth, the spine acquires four physiological curves. At 6-7 weeks, with the raising of the child’s head, anterior bending (lordosis) occurs in the cervical region. At 6 months, as a result of sitting, posterior curves (kyphosis) are formed in the thoracic and sacral regions. At 1 year of age, with the onset of standing, lordosis forms in the lumbar region. Initially, these physiological curves of the spine are held by the muscles, and then by the ligaments, cartilage and bones of the vertebrae.

By the age of 3-4 years, the curves of the spine gradually increase as a result of standing, walking, gravity and muscle work. By the age of 7, cervical lordosis and thoracic kyphosis are finally formed; by the age of 12 - lumbar lordosis, which is finally formed by the period of puberty. Lifting excessive weights increases lumbar lordosis.

In adults, the physiological curves of the spine are distributed as follows.

1. Cervical bend: moderate lordosis, formed by all cervical and upper thoracic vertebrae; the greatest bulge falls on the fifth or sixth cervical vertebrae.

2. Strong thoracic kyphosis, the greatest bulge falls on the sixth-seventh thoracic vertebrae.

3. Strong lumbar lordosis, formed by the last thoracic and all lumbar vertebrae.

4. Strong sacrococcygeal kyphosis.

Due to the spring movement of the spine, the magnitude of its bends can change. As a result of changes in the curvature of the spine and the height of the intervertebral discs, the length of the spine also changes: with age and during the day. During the day, a person's height varies within 1 cm, and sometimes 2-2,5 cm and even 4-6 cm. In the prone position, the length of the human body is 2-3 cm longer than in the standing position.

3.7. Chest development

The chest is made up of 12 pairs of ribs. The true ribs (the first - the seventh pair) are connected to the sternum with the help of cartilages, of the remaining five false ribs, the cartilaginous ends of the eighth, ninth and tenth pairs are connected to the cartilage of the overlying rib, and the eleventh and twelfth pairs do not have costal cartilages and have the greatest mobility, since end freely. The second - seventh pairs of ribs are connected to the sternum by small joints.

The ribs are connected to the vertebrae by joints, which, when the chest is raised, determine the movement of the upper ribs mainly forward, and the lower ribs to the sides.

The sternum is an unpaired bone in which three parts are distinguished: the handle, the body and the xiphoid process. The handle of the sternum articulates with the clavicle with the help of a joint containing an intracartilaginous disk (by the nature of the movements, it approaches the spherical joints).

The shape of the chest depends on age and gender. In addition, the shape of the chest changes due to the redistribution of the force of gravity of the body when standing and walking, depending on the development of the muscles of the shoulder girdle.

Age-related changes in the formation of the chest. The ribs develop from mesenchyme, which transforms into cartilage in the second month of uterine life. Their ossification begins in the fifth to eighth week, and that of the sternum in the sixth month. Ossification nuclei in the head and tubercle appear in the upper ten ribs at 5-6 years, and in the last two ribs at 15 years. The fusion of parts of the rib ends by the age of 18-25.

Up to 1-2 years, the rib consists of a spongy substance. From 3-4 years of age, a compact layer develops in the middle of the rib. From the age of 7, the compact layer grows along the entire rib. From the age of 10, the compact layer continues to grow in the region of the corner. By the age of 20, ossification of the ribs is completed.

In the xiphoid process, the nucleus of ossification appears at the age of 6-12 years. At the age of 15-16, the lower segments of the body of the sternum fuse. At the age of 25, the xiphoid process fuses with the body of the sternum.

The sternum develops from many paired ossification points that merge extremely slowly. Ossification of the manubrium and body of the sternum ends by the age of 21-25, the xiphoid process - by the age of 30. The fusion of the three parts of the sternum into one bone occurs much later, and not in all people. Thus, the sternum is formed and develops later than all other bones of the skeleton.

Chest shape. In humans, there are two extreme shapes of the chest: long, narrow and short, wide. The shape of the sternum also corresponds to them. Among the main shapes of the chest, there are conical, cylindrical and flat shapes.

The shape of the chest changes significantly with age. After birth and for the first few years of life, the ribcage is cone-shaped with the base facing down. From the age of 2,5-3 years, the growth of the chest goes parallel to the growth of the body, in connection with this, its length corresponds to the thoracic spine. Then the growth of the body accelerates, and the chest becomes relatively shorter. In the first three years, there is an increase in the circumference of the chest, which leads to the predominance of the transverse diameter in the upper part of the chest.

Gradually, the chest changes its conical shape and approaches that of an adult, that is, it takes the form of a cone with the base turned upward. The chest acquires its final shape by the age of 12-13, but is smaller than in adults.

Sex differences in chest shape and circumference. Sex differences in the shape of the chest appear from about 15 years of age. From this age, an intensive increase in the sagittal size of the chest begins. In girls, during inhalation, the upper ribs rise sharply, in boys - the lower ones.

Gender differences are also observed in the growth of the circumference of the chest. In boys, the circumference of the chest from 8 to 10 years old increases by 1-2 cm per year, by puberty (from 11 years old) - by 2-5 cm. In girls up to 7-8 years old, the chest circumference exceeds half the size of their growth. In boys, this ratio is observed up to 9-10 years, from this age half of the height becomes larger than the size of the chest circumference. From the age of 11, in boys, its growth is less than in girls.

Exceeding half of the height above the circumference of the chest depends on the growth rate of the body, which is greater than the growth rate of the circumference of the chest. The growth of the circumference of the chest is inferior to the addition of body weight, so the ratio of body weight to the circumference of the chest gradually decreases with age. The chest circumference grows most rapidly during puberty and in the summer-autumn period. Normal nutrition, good hygienic conditions and physical exercise have a dominant influence on the growth of the chest circumference.

The parameters of the development of the chest depend on the development of skeletal muscles: the more developed the skeletal muscles, the more developed the chest. Under favorable conditions, the circumference of the chest in children 12-15 years old is 7-8 cm more than under unfavorable conditions. In the first case, the circumference of the chest will equal half the height on average by the age of 15, and not by the age of 20-21, as in children who were in unfavorable living conditions.

Improper seating of children at a desk can lead to chest deformity and, as a result, a violation of the development of the heart, large vessels and lungs.

3.8. Features of the development of the pelvis and lower extremities. Skeleton of the lower extremities

The pelvic girdle consists of the pubic, ilium, and ischium bones, which develop independently and merge with age to form a pelvis, posteriorly connected to the sacral spine. The pelvis serves as a support for the internal organs and legs. Due to the mobility of the lumbar spine, the pelvis increases the range of motion of the leg.

The leg skeleton consists of the femur (thigh skeleton), the tibia and fibula (tibia skeleton) and the bones of the foot.

The tarsus is made up of the talus, calcaneus, navicular, cuboid, and three cuneiform bones. The metatarsus is made up of five metatarsal bones. The toes consist of phalanges: two phalanges in the first toe and three phalanges in the remaining fingers. Sesamoid ossicles are located, as in the hand, but are much better expressed. The largest sesamoid bone of the leg skeleton is the patella, located inside the tendon of the quadriceps femoris. It increases the shoulder strength of this muscle and protects the knee joint from the front.

Development of the pelvic bones. The most intensive growth of the pelvic bones is observed in the first three years of life. In the process of fusion of the pelvic bones, several stages can be distinguished: 5-6 years (beginning of fusion); 7-8 years (pubic and ischial bones fuse); 14-16 years (pelvic bones are almost fused); 20-25 years (end of complete fusion).

These terms must be taken into account in labor movements and physical exercises (especially for girls). With sharp jumps from a great height and when wearing high-heeled shoes, the non-united pelvic bones are displaced, which leads to their improper fusion and narrowing of the exit from the pelvic cavity, leading to difficulty in childbirth. Cohesion disorders are also caused by excessive improper sitting or standing, carrying heavy loads, especially when the load is unevenly distributed.

The size of the pelvis in men is smaller than in women. Distinguish between the upper (large) pelvis and the lower (small) pelvis. The transverse size of the entrance to the small pelvis in girls changes abruptly in several stages: at 8-10 years old (it increases very quickly); at 10-12 years old (there is some slowdown in its growth); from 12 to 14-15 years (growth increases again). The anteroposterior size increases more gradually; from the age of 9 it is less than the transverse. In boys, both sizes of the pelvis increase evenly.

Development of lower limb bones. By the time of birth, the femur consists of cartilage, only the diaphysis is bone. Synostosis in long bones ends between the ages of 18 and 24 years. The kneecap takes on the shape characteristic of an adult by the age of 10.

The development of the bones of the tarsus occurs much earlier than the bones of the wrist, the ossification nuclei in them (in the calcaneus, talus and cuboid bones) appear even in the uterine period. In the sphenoid bones, they occur at 1-3-4 years, in the scaphoid - at 4,5 years. At the age of 12-16, the ossification of the calcaneus ends.

The bones of the metatarsus ossify later than the bones of the tarsus, at the age of 3-6 years. Ossification of the phalanges of the foot occurs in the third or fourth year of life. The final ossification of the bones of the legs occurs: femoral, tibial and fibular - by 20-24 years; metatarsal - to 17-21 in men and to 14-19 in women; phalanges - by 15-21 in men and by 13-17 years in women.

From the age of 7, the legs grow faster in boys. The greatest ratio of leg length to body is achieved in boys by the age of 15, in girls - by 13 years.

The human foot forms an arch that rests on the calcaneus and the anterior ends of the metatarsal bones. The general arch of the foot is made up of the longitudinal and transverse arches. The formation of the arch of the foot in humans occurred as a result of upright walking.

For the formation of the arch of the foot, the development of the muscles of the legs, in particular those that hold the longitudinal and transverse arches, is of great importance. The arch allows you to evenly distribute the weight of the body, acts like a spring, softening the shock and shock of the body while walking. It protects the muscles, vessels and nerves of the plantar surface from pressure. Flattening of the arch (flat feet) develops with prolonged standing, carrying heavy weights, and wearing narrow shoes. Flat feet leads to violations of posture, the mechanics of walking.

3.9. Upper limb bone development

The skeleton of the upper limbs includes the shoulder girdle and the skeleton of the hand. The shoulder girdle consists of the scapula and collarbone, the skeleton of the arm consists of the shoulder, forearm and hand. The hand is divided into the wrist, metacarpus and fingers.

The shoulder blade is a flat, triangular-shaped bone located on the back. The clavicle is a tubular bone, one end of which articulates with the sternum and ribs, and the other with the scapula. The costoclavicular joint appears in children from 11-12 years old; it reaches its greatest development in adults.

The arm skeleton consists of the humerus (shoulder skeleton), the ulna and radius (forearm skeleton), and the bones of the hand.

The wrist consists of eight small bones arranged in two rows, forming a groove on the palm and a bulge on its back surface.

The metacarpus consists of five small tubular bones, of which the shortest and thickest is the thumb bone, the longest is the second bone, and each of the following bones is smaller than the previous one. The exception is the thumb (first) finger, which consists of two phalanges. The other four fingers have three phalanges. The largest phalanx is proximal, the smaller is the middle, and the smallest is the distal.

On the palmar surface, there are permanent sesamoid bones - inside the tendons between the metacarpal bone of the thumb and its proximal phalanx, and non-permanent - between the metacarpal bone and the proximal phalanx of the second and fifth fingers. The pisiform bone of the wrist is also a sesamoid bone.

The joints of the wrist, metacarpus and fingers are reinforced with a powerful ligamentous apparatus.

Age-related features of the development of the upper limbs. In a newborn, the clavicle is almost completely bone, the formation of an ossification nucleus in its sternal region occurs at 16-18 years, fusion with its body - at 20-25 years. Fusion of the ossification nucleus of the coracoid process with the body of the scapula occurs at 16-17 years. Synestosis of the acromial process with its body ends at 18-25 years.

All long bones in a newborn, such as the humerus, radius, ulna, have cartilaginous epiphyses and bone diaphyses. There are no bones in the wrist, and cartilage ossification begins: in the first year of life - in the capitate and hamate bones; at 2-3 years old - in a trihedral bone; at 3-4 years - in the lunate bone; at 4-5 years old - in the navicular bone; at 4-6 years old - in a large polygonal bone; at 7-15 years old - in the pisiform bone.

Sesamoid bones in the first metacarpophalangeal joint appear at 12-15 years of age. At the age of 15-18, the lower epiphysis of the humerus merges with its body, and the upper epiphyses merge with the bodies of the bones of the forearm. In the third year of life, ossification of the proximal and distal epiphyses of the phalanges occurs. "Bone age" determines the centers of ossification of the hand.

Ossification of the bones of the upper limbs ends: at 20-25 years old - in the collarbone, scapula and humerus; at 21-25 years old - in the radius; at 21-24 years old - in the ulna; at 10-13 years old - in the bones of the wrist; at 12 years old - in the metacarpus; at 9-11 years old - in the phalanges of the fingers.

Ossification ends in men on average two years later than in women. The last centers of ossification can be found in the clavicle and scapula at 18-20 years old, in the humerus - at 12-14 years old, in the radius - at 5-7 years old, in the ulna - at 7-8 years old, in the metacarpal bones and phalanges fingers - in 2-3 years. Ossification of sesamoid bones usually begins during puberty: in boys - at 13-14 years old, in girls - at 12-13. The beginning of the fusion of parts of the first metacarpal bone indicates the beginning of puberty.

3.10. Effect of furniture on posture. Hygienic requirements for school equipment

School furniture should correspond to the age-related changes in the growth and proportions of the children's body, exclude the possibility of damage to the body and be easy to keep clean.

Desk. This is the main type of school furniture. Selecting a desk that matches the child’s height and proper seating are the prevention of posture and vision problems. The standards approve five table numbers according to student height (in cm): A - 115-130, B - 130-145, C - 145-160, D - 160-175, D - 175-190.

For normal reading and writing conditions, the slope of the desk top should be 14-15°. A book or notebook should be placed freely on the table top of the school desk at an angle of 25 ° to its edge.

Chair. The back of the chair provides an additional point of support for the body in the lumbosacral region. The curve of the chair back should be at the level of the lumbar curve of the spine and correspond to its height.

The chair back distance is the distance from the edge of the table top to the back of the chair. For the correct calculation of the distance, it is necessary to add 3-5 cm to the diameter of the student's torso.

The anteroposterior size of the seat of the chair should correspond to 2/3-3/4 of the thigh, the height of the chair above the floor should correspond to the length of the lower leg to the popliteal cavity with an addition of 2 cm and taking into account the height of the heel.

The seat distance is the distance from the edge of the table top to the front edge of the seat. A negative distance is recommended, at which the front edge of the seat extends 2-3 cm beyond the edge of the table top, as it eliminates spinal curvature and visual impairment.

The difference between the height of the edge of the table top and the height of the seat is called the desk differential. It should be equal to the distance from the seat to the elbow of the hand pressed to the body, with the addition of 2-2,5 cm.

The most rational ratios of the height of children and the workplace with a height of 110-119 cm are: table height - 51 cm, seat height - 30 cm, seat depth - 24-25 cm. For every 10 cm increase in height, the corresponding dimensions increase by 4, 3 and 2 cm, respectively, starting from a height of 150-159 cm, the seat depth increases by 4 cm.

Correct seating at the desk: a straight position of the torso with a slight tilt of the head forward, support on the back of the seat (without chest support on the edge of the desk cover), legs bent at a straight or slightly larger (100-110 °) angle resting on the floor or the footboard of the desk.

Note that the seating of students, taking into account their physiological characteristics, plays an equally important role. So, schoolchildren with hearing loss are recommended to be seated at the front desks, and short-sighted - at the windows.

Topic 4. DEVELOPMENT OF REGULATORY SYSTEMS OF THE ORGANISM

4.1. The meaning and functional activity of the elements of the nervous system

The coordination of physiological and biochemical processes in the body occurs through regulatory systems: nervous and humoral. Humoral regulation is carried out through the liquid media of the body - blood, lymph, tissue fluid, nervous regulation - through nerve impulses.

The main purpose of the nervous system is to ensure the functioning of the body as a whole through the relationship between individual organs and their systems. The nervous system perceives and analyzes various signals from the environment and internal organs.

The nervous mechanism of regulation of body functions is more perfect than the humoral one. This, firstly, is explained by the speed of propagation of excitation through the nervous system (up to 100-120 m / s), and secondly, by the fact that nerve impulses come directly to certain organs. However, it should be borne in mind that all the completeness and subtlety of the organism's adaptation to the environment are carried out through the interaction of both nervous and humoral mechanisms of regulation.

General plan of the structure of the nervous system. In the nervous system, according to functional and structural principles, the peripheral and central nervous systems are distinguished.

The central nervous system consists of the brain and spinal cord. The brain is located inside the brain region of the skull, and the spinal cord is located in the spinal canal. On a section of the brain and spinal cord, there are areas of dark color (gray matter) formed by the bodies of nerve cells (neurons), and white (white matter), consisting of clusters of nerve fibers covered with a myelin sheath.

The peripheral part of the nervous system is made up of nerves, such as bundles of nerve fibers, that extend beyond the brain and spinal cord and travel to various organs of the body. It also includes any collections of nerve cells outside the spinal cord and brain, such as ganglions or ganglia.

Neuron (from the Greek. neuron - nerve) - the main structural and functional unit of the nervous system. A neuron is a complex highly differentiated cell of the nervous system, the function of which is to perceive irritation, process irritation and transmit it to various organs of the body. A neuron consists of a cell body, one long branching process - an axon, and several short branching processes - dendrites.

Axons are of various lengths: from a few centimeters to 1-1,5 m. The end of the axon branches strongly, forming contacts with many cells.

Dendrites are short highly branching processes. From 1 to 1000 dendrites can depart from one cell.

In different parts of the nervous system, the body of a neuron can have a different size (diameter from 4 to 130 microns) and shape (stellate, round, polygonal). The body of a neuron is covered with a membrane and contains, like all cells, cytoplasm, a nucleus with one or more nucleoli, mitochondria, ribosomes, the Golgi apparatus, and the endoplasmic reticulum.

Excitation is transmitted along the dendrites from receptors or other neurons to the cell body, and along the axon, signals arrive at other neurons or working organs. It has been established that from 30 to 50% of nerve fibers transmit information to the central nervous system from receptors. On the dendrites there are microscopic outgrowths that significantly increase the surface of contact with other neurons.

Nerve fiber. Nerve fibers are responsible for conducting nerve impulses in the body. Nerve fibers are:

a) myelinated (pulp); sensory and motor fibers of this type are part of the nerves that supply the sense organs and skeletal muscles, and also participate in the activity of the autonomic nervous system;

b) unmyelinated (non-fleshy), belong mainly to the sympathetic nervous system.

Myelin has an insulating function and has a slightly yellowish color, so the fleshy fibers look light. The myelin sheath in the pulpy nerves is interrupted at intervals of equal length, leaving open sections of the axial cylinder - the so-called intercepts of Ranvier.

Amyelinated nerve fibers do not have a myelin sheath, they are isolated from each other only by Schwann cells (myelocytes).

4.2. Age-related changes in the morphofunctional organization of the neuron

In the early stages of embryonic development, the nerve cell has a large nucleus surrounded by a small amount of cytoplasm. In the process of development, the relative volume of the nucleus decreases. Axon growth begins in the third month of fetal development. Dendrites grow later than the axon. Synapses on dendrites develop after birth.

The growth of the myelin sheath leads to an increase in the speed of conduction of excitation along the nerve fiber, which leads to an increase in the excitability of the neuron.

The process of myelination first occurs in the peripheral nerves, then the fibers of the spinal cord, the brain stem, the cerebellum undergo myelination, and later all the fibers of the cerebral hemispheres. Motor nerve fibers are covered with a myelin sheath already at the time of birth. Completion of the myelination process occurs by the age of three, although the growth of the myelin sheath and axial cylinder continues after 3 years.

Nerves. A nerve is a collection of nerve fibers covered on top with a connective tissue sheath. The nerve that transmits excitation from the central nervous system to the innervated organ (effector) is called centrifugal, or efferent. The nerve that transmits excitation in the direction of the central nervous system is called centripetal, or afferent.

Most nerves are mixed, they include both centripetal and centrifugal fibers.

Irritability. Irritability is the ability of living systems, under the influence of stimuli, to move from a state of physiological rest to a state of activity, i.e., to the process of movement and the formation of various chemical compounds.

There are physical stimuli (temperature, pressure, light, sound), physicochemical (changes in osmotic pressure, active reaction of the environment, electrolyte composition, colloidal state) and chemical (food chemicals, chemical compounds formed in the body - hormones, metabolic products substances, etc.).

The natural stimuli of cells that cause their activity are nerve impulses.

Excitability. Cells of nervous tissue, like cells of muscle tissue, have the ability to quickly respond to stimulation, which is why such cells are called excitable. The ability of cells to respond to external and internal factors (stimulants) is called excitability. The measure of excitability is the threshold of irritation, i.e. the minimum strength of the stimulus that causes excitation.

Excitation is able to spread from one cell to another and move from one place in the cell to another.

Excitation is characterized by a complex of chemical, functional, physico-chemical, electrical phenomena. An obligatory sign of excitation is a change in the electrical state of the surface cell membrane.

4.3. Properties of excitatory impulses in the central nervous system. Bioelectric Phenomena

The main reason for the emergence and spread of excitation is a change in the electric charge on the surface of a living cell, i.e., the so-called bioelectric phenomena.

On both sides of the surface cell membrane at rest, a potential difference is created equal to about -60-(-90) mV, and the cell surface is charged electropositively with respect to the cytoplasm. This potential difference is called the resting potential, or membrane potential. The value of the membrane potential for cells of different tissues is different: the higher the functional specialization of the cell, the greater it is. For example, for cells of nervous and muscular tissues it is -80-(-90) mV, for epithelial tissue -18-(-20) mV.

The cause of the occurrence of bioelectric phenomena is the selective permeability of the cell membrane. Inside the cell in the cytoplasm, there are 30-50 times more potassium ions than outside the cell, 8-10 times less sodium ions, and 50 times less chloride ions. At rest, the cell membrane is more permeable to potassium ions than to sodium ions, and potassium ions exit through the pores in the membrane to the outside. The migration of positively charged potassium ions from the cell imparts a positive charge to the outer surface of the membrane. Thus, the cell surface at rest carries a positive charge, while the inner side of the membrane is negatively charged due to chloride ions, amino acids, and other organic ions, which practically do not penetrate the membrane.

When a section of a nerve or muscle fiber is exposed to an irritant, excitation occurs in this place, manifested in a rapid fluctuation of the membrane potential, called the action potential.

An action potential occurs due to a change in the ion permeability of the membrane. There is an increase in the permeability of the membrane for sodium cations. Sodium ions enter the cell under the action of electrostatic forces of osmosis, while at rest the cell membrane was poorly permeable for these ions. In this case, the influx of positively charged sodium ions from the external environment of the cell into the cytoplasm significantly exceeds the flow of potassium ions from the cell to the outside. As a result, there is a change in the membrane potential (a decrease in the membrane potential difference, as well as the appearance of a potential difference of the opposite sign - the depolarization phase). The inner surface of the membrane became positively charged, and the outer surface, due to the loss of positively charged sodium ions, negatively, at this moment the peak of the action potential is recorded. An action potential occurs when the membrane depolarization reaches a critical (threshold) level.

The increase in the permeability of the membrane for sodium ions lasts a short time. Then, recovery processes occur in the cell, leading to a decrease in the permeability of the membrane for sodium ions and an increase for potassium ions. Since potassium ions are also positively charged, their exit from the cell restores the original potential ratios outside and inside the cell (repolarization phase).

Changing the ionic composition inside and outside the cell is achieved in several ways: active and passive transmembrane ion transport. Passive transport is provided by the pores present in the membrane and selective (selective) channels for ions (sodium, potassium, chlorine, calcium). These channels have a gate system and can be closed or open. Active transport is carried out on the principle of the sodium-potassium pump, which works by consuming the energy of ATP. Its main component is the membrane NA, KATPase.

Conducting excitation. The conduction of excitation is due to the fact that the action potential that arises in one cell (or in one of its areas) becomes a stimulus that causes excitation of neighboring areas.

In the pulpy nerve fibers, the myelin sheath has resistance and prevents the flow of ions, i.e., it acts as an electrical insulator. In myelinated fibers, excitation occurs only in areas not covered by the myelin sheath, the so-called nodes of Ranvier. Excitation in the pulpy fibers spreads spasmodically from one interception of Ranvier to another. It seems to "jump" over the sections of the fiber covered with myelin, as a result of which such a mechanism for the spread of excitation is called saltatory (from the Italian salto - jump). This explains the high speed of conduction of excitation along the pulpy nerve fibers (up to 120 m/s).

The excitation spreads slowly along the non-fleshy nerve fibers (from 1 to 30 m/s). This is due to the fact that the bioelectrical processes of the cell membrane take place in each section of the fiber, along its entire length.

There is a certain relationship between the speed of the conduction of excitation and the diameter of the nerve fiber: the thicker the fiber, the greater the speed of conduction of the excitation.

Transmission of excitation at synapses. A synapse (from the Greek synapsis - connection) is the area of ​​​​contact of two cell membranes that ensure the transition of excitation from nerve endings to excited structures. Excitation from one nerve cell to another is a unidirectional process: the impulse is always transmitted from the axon of one neuron to the cell body and dendrites of another neuron.

The axons of most neurons strongly branch at the end and form numerous endings on the bodies of nerve cells and their dendrites, as well as on muscle fibers and gland cells. The number of synapses on the body of one neuron can reach 100 or more, and on the dendrites of one neuron - several thousand. One nerve fiber can form more than 10 synapses on many nerve cells.

The synapse is complex. It is formed by two membranes - presynaptic and postsynaptic, between which there is a synaptic gap. The presynaptic part of the synapse is located on the nerve ending, the postsynaptic membrane is on the body or dendrites of the neuron to which the nerve impulse is transmitted. Large accumulations of mitochondria are always observed in the presynaptic region.

Excitation through synapses is transmitted chemically with the help of a special substance - an intermediary, or mediator, located in synaptic vesicles located in the presynaptic terminal. Different synapses produce different neurotransmitters. Most often it is acetylcholine, adrenaline or norepinephrine.

There are also electrical synapses. They are distinguished by a narrow synaptic cleft and the presence of transverse channels crossing both membranes, that is, there is a direct connection between the cytoplasms of both cells. Channels are formed by protein molecules of each of the membranes connected complementary. The scheme of transmission of excitation in such a synapse is similar to the scheme of transmission of the action potential in a homogeneous nerve conductor.

In chemical synapses, the mechanism of impulse transmission is as follows. The arrival of a nerve impulse at the presynaptic ending is accompanied by a synchronous release of the neurotransmitter into the synaptic cleft from the synaptic vesicles located in its immediate vicinity. Usually, a series of impulses comes to the presynaptic ending, their frequency increases with an increase in the strength of the stimulus, leading to an increase in the release of the mediator into the synaptic cleft. The dimensions of the synaptic cleft are very small, and the neurotransmitter, quickly reaching the postsynaptic membrane, interacts with its substance. As a result of this interaction, the structure of the postsynaptic membrane temporarily changes, its permeability for sodium ions increases, which leads to the movement of ions and, as a result, the emergence of an excitatory postsynaptic potential. When this potential reaches a certain value, a propagating excitation occurs - an action potential. After a few milliseconds, the neurotransmitter is destroyed by special enzymes.

There are also special inhibitory synapses. It is believed that in specialized inhibitory neurons, in the nerve endings of axons, a special mediator is produced that has an inhibitory effect on the subsequent neuron. In the cerebral cortex, gamma-aminobutyric acid is considered such a mediator. The structure and mechanism of inhibitory synapses are similar to those of excitatory synapses, only the result of their action is hyperpolarization. This leads to the emergence of an inhibitory postsynaptic potential, resulting in inhibition.

Each nerve cell has many excitatory and inhibitory synapses, which creates conditions for different responses to past signals.

4.4. Processes of excitation and inhibition in the central nervous system

Excitation and inhibition are not independent processes, but two stages of a single nervous process, they always go one after another.

If excitation occurs in a certain group of neurons, then at first it spreads to neighboring neurons, i.e., irradiation of nervous excitation occurs. Then the excitation is concentrated in one point. After that, excitability decreases around the group of excited neurons, and they come into a state of inhibition, a process of simultaneous negative induction occurs.

In neurons that have been excited, after excitation, inhibition necessarily occurs, and vice versa, after inhibition, excitation appears in the same neurons. This is sequential induction. If excitability increases around groups of inhibited neurons and they enter a state of excitation, this is a simultaneous positive induction. Consequently, excitation turns into inhibition, and vice versa. This means that these two stages of the nervous process go hand in hand with each other.

4.5. The structure and functioning of the spinal cord

The spinal cord is a long cord (in an adult) about 45 cm long. At the top it passes into the medulla oblongata, at the bottom (in the region of I-II lumbar vertebrae) the spinal cord narrows and has the shape of a cone, passing into the final thread. At the place of origin of the nerves to the upper and lower extremities, the spinal cord has a cervical and lumbar thickening. In the center of the spinal cord runs a canal that goes to the brain. The spinal cord is divided by two grooves (anterior and posterior) into the right and left halves.

The central canal is surrounded by gray matter, which forms the anterior and posterior horns. In the thoracic region, between the anterior and posterior horns, there are lateral horns. Around the gray matter are bundles of white matter in the form of anterior, posterior and lateral funiculi. Gray matter is represented by a cluster of nerve cells, white matter consists of nerve fibers. In the gray matter of the anterior horns are the bodies of motor (centrifugal) neurons, the processes of which form the anterior root. In the posterior horns there are cells of intermediate neurons that communicate between centripetal and centrifugal neurons. The posterior root is formed by fibers of sensitive (centripetal) cells, the bodies of which are located in the spinal cord (intervertebral) nodes. Through the posterior sensory roots, excitation is transmitted from the periphery to the spinal cord. Through the anterior motor roots, excitation is transmitted from the spinal cord to the muscles and other organs.

The vegetative nuclei of the sympathetic nervous system are located in the gray matter of the lateral horns of the spinal cord.

The bulk of the white matter of the spinal cord is formed by the nerve fibers of the spinal cord pathway. These pathways provide communication between different parts of the central nervous system and form ascending and descending pathways for the transmission of impulses.

The spinal cord consists of 31-33 segments: 8 cervical, 12 thoracic, 5 lumbar and 1-3 coccygeal. Anterior and posterior roots emerge from each segment. Both roots merge as they exit the brain and form the spinal nerve. 31 pairs of spinal nerves leave the spinal cord. The spinal nerves are mixed, they are formed by centripetal and centrifugal fibers. The spinal cord is covered by three membranes: dura, arachnoid and vascular.

Spinal cord development. The development of the spinal cord begins earlier than the development of other parts of the nervous system. In the embryo, the spinal cord has already reached a significant size, while the brain is at the stage of the brain vesicles.

In the early stages of fetal development, the spinal cord fills the entire cavity of the spinal canal, but then the spinal column overtakes the growth of the spinal cord, and by the time of birth it ends at the level of the third lumbar vertebra.

The length of the spinal cord in newborns is 14-16 cm. Its length doubles by the age of 10. The spinal cord grows slowly in thickness. On the transverse section of the spinal cord of young children, the predominance of the anterior horns over the posterior ones is clearly distinguished. During school years, children experience an increase in the size of nerve cells in the spinal cord.

Functions of the spinal cord. The spinal cord is involved in the implementation of complex motor reactions of the body. This is the reflex function of the spinal cord.

In the gray matter of the spinal cord, the reflex pathways of many motor reactions are closed, for example, the knee reflex (when tapping the tendon of the quadriceps femoris muscle in the knee area, the lower leg is extended in the knee joint). The path of this reflex passes through the II-IV lumbar segments of the spinal cord. In children in the first days of life, the knee jerk is caused very easily, but it manifests itself not in extension of the lower leg, but in flexion. This is due to the predominance of the tone of the flexor muscles over the extensors. In healthy one-year-old children, the reflex always occurs, but it is less pronounced.

The spinal cord innervates all skeletal muscles, except for the muscles of the head, which are innervated by cranial nerves. In the spinal cord there are reflex centers of the muscles of the trunk, limbs and neck, as well as many centers of the autonomic nervous system: reflexes of urination and defecation, reflex swelling of the penis (erection) and ejaculation of the seed in men (ejaculation).

Conductive function of the spinal cord. Centripetal impulses entering the spinal cord through the dorsal roots are transmitted along the spinal cord pathways to the overlying parts of the brain. In turn, from the overlying parts of the central nervous system, impulses arrive through the spinal cord, changing the state of skeletal muscles and internal organs. The activity of the spinal cord in humans is largely subject to the coordinating influence of the overlying parts of the central nervous system.

4.6. The structure and functioning of the brain

In the structure of the brain, three large sections are distinguished: the trunk, the subcortical section, and the cerebral cortex. The brain stem is formed by the medulla oblongata, hindbrain, and midbrain. There are 12 pairs of cranial nerves at the base of the brain.

Medulla oblongata and pons (hindbrain). The medulla oblongata is a continuation of the spinal cord in the cranial cavity. Its length is about 28 mm, its width gradually increases and reaches 24 mm at its widest point. The central canal of the spinal cord directly passes into the canal of the medulla oblongata, significantly expanding in it and turning into the fourth ventricle. In the substance of the medulla oblongata there are separate accumulations of gray matter that form the nuclei of the cranial nerves. The white matter of the medulla oblongata is formed by fibers of the pathways. In front of the medulla oblongata, the pons is located in the form of a transverse shaft.

The roots of the cranial nerves depart from the medulla oblongata: XII - hypoglossal, XI - accessory nerve, X - vagus nerve, IX - glossopharyngeal nerve. Between the medulla oblongata and the bridge, the roots of the VII and VIII cranial nerves - facial and auditory - emerge. The roots of the VI and V nerves - the efferent and trigeminal - come out of the bridge.

In the hindbrain, the paths of many complexly coordinated motor reflexes are closed. Here are vital centers for the regulation of respiration, cardiovascular activity, the functions of the digestive organs, and metabolism. The nuclei of the medulla oblongata are involved in the implementation of such reflex acts as the separation of digestive juices, chewing, sucking, swallowing, vomiting, sneezing.

In a newborn, the medulla oblongata together with the bridge weighs about 8 g, which is 2% of the mass of the brain (in an adult - 1,6%). The nuclei of the medulla oblongata begin to form in the prenatal period of development and are already formed by the time of birth. The maturation of the nuclei of the medulla oblongata ends by 7 years.

Cerebellum. Behind the medulla oblongata and the pons is the cerebellum. It has two hemispheres connected by a worm. The gray matter of the cerebellum lies superficially, forming its cortex with a thickness of 1-2,5 mm. The surface of the cerebellum is covered with a large number of grooves.

Under the cerebellar cortex is white matter, inside which there are four nuclei of gray matter. White matter fibers carry out communication between different parts of the cerebellum, and also form the lower, middle and upper legs of the cerebellum. The peduncles provide connections between the cerebellum and other parts of the brain.

The cerebellum is involved in the coordination of complex motor acts, so it receives impulses from all receptors that are irritated during body movements. The presence of feedback from the cerebellum and the cerebral cortex makes it possible for it to influence voluntary movements, and for the large hemispheres through the cerebellum to regulate the tone of skeletal muscles, to coordinate their contractions. In a person with disorders or loss of cerebellar functions, the regulation of muscle tone is disturbed: the movements of the arms and legs become sharp, uncoordinated; staggering gait (reminiscent of a drunken gait); there is a tremor of the limbs and head.

In newborns, the cerebellar vermis is better developed than the hemispheres themselves. The most intensive growth of the cerebellum is observed in the first year of life. Then the rate of its development decreases, and by the age of 15 it reaches the same size as in an adult.

Midbrain. The midbrain consists of the cerebral peduncles and the quadrigeminum. The cavity of the midbrain is represented by a narrow canal - the cerebral aqueduct, which communicates from below with the fourth ventricle, and from above - with the third. In the wall of the cerebral aqueduct there are nuclei of the III and IV cranial nerves - oculomotor and trochlear. All ascending pathways to the cerebral cortex and cerebellum and descending pathways carrying impulses to the medulla oblongata and spinal cord pass through the midbrain.

In the midbrain there are accumulations of gray matter in the form of nuclei of the quadrigemina, the nuclei of the oculomotor and trochlear nerves, the red nucleus and the substantia nigra. The anterior tubercles of the quadrigemina are the primary visual centers, and the posterior tubercles are the primary auditory centers. With their help, orienting reflexes to light and sound are carried out (eye movement, head turn, ear alertness in animals). The substantia nigra provides coordination of complex acts of swallowing and chewing, regulates fine movements of the fingers (fine motor skills), etc. The red nucleus also regulates muscle tone.

Reticular formation. Throughout the entire brain stem (from the upper end of the spinal cord to the optic thalamus and the hypothalamus inclusive) there is a formation consisting of clusters of neurons of various shapes and types, which are densely intertwined with fibers running in different directions. Under magnification, this formation resembles a network, which is why it is called a reticular, or reticular, formation. In the reticular formation of the human brainstem, 48 separate nuclei and cell groups have been described.

When the structures of the reticular formation are irritated, no visible reaction is noted, however, the excitability of various parts of the central nervous system changes. Both ascending centripetal and descending centrifugal pathways pass through the reticular formation. Here they interact and regulate the excitability of all parts of the central nervous system.

Along the ascending pathways, the reticular formation has an activating effect on the cerebral cortex and maintains a waking state in it. The axons of the reticular neurons of the brainstem reach the cerebral cortex, thus forming an ascending reticular activating system. Moreover, some of these fibers on their way to the cortex are interrupted in the thalamus, while others go straight to the cortex. In turn, the reticular formation of the brain stem receives fibers and impulses coming from the cerebral cortex and regulating the activity of the reticular formation itself. It also has a high sensitivity to such physiologically active substances as adrenaline and acetylcholine.

Diencephalon. Together with the telencephalon, formed by the cortex and subcortical ganglia, the diencephalon (visual thalamus and subcutaneous region) is part of the forebrain. The diencephalon consists of four parts that surround the cavity of the third ventricle - the epithalamus, dorsal thalamus, ventral thalamus and hypothalamus.

The main part of the diencephalon is the thalamus (thalamus). This is a large paired formation of gray matter ovoid. The gray matter of the thalamus is divided into three regions by thin white layers: anterior, medial and lateral. Each region is a cluster of nuclei. Depending on the characteristics of their influence on the activity of the cells of the cerebral cortex, the nuclei are usually divided into two groups: specific and nonspecific (or diffuse).

Specific nuclei of the thalamus, thanks to their fibers, reach the cerebral cortex, where they form a limited number of synaptic connections. When they are irritated by single electric discharges, a response quickly occurs in the corresponding limited areas of the cortex, the latent period is only 1-6 ms.

Impulses from nonspecific thalamic nuclei arrive simultaneously in different parts of the cerebral cortex. When nonspecific nuclei are irritated, a response occurs after 10-50 ms from almost the entire surface of the cortex, diffusely; at the same time, the potentials in the cells of the cortex have a large latent period and fluctuate in waves. This is an engagement reaction.

Centripetal impulses from all receptors of the body (visual, auditory, impulses from receptors of the skin, face, trunk, limbs, from proprioreceptors, taste receptors, receptors of internal organs (visceroreceptors)), except for those that come from olfactory receptors, first enter the nuclei of the thalamus , and then to the cerebral cortex, where they are processed and receive an emotional coloring. Impulses from the cerebellum also come here, which then go to the motor zone of the cerebral cortex.

When the visual tubercles are affected, the manifestation of emotions is disturbed, the nature of sensations changes: often slight touches on the skin, sound or light cause attacks of severe pain in patients or, on the contrary, even severe pain irritation is not felt. Therefore, the thalamus is considered the highest center of pain sensitivity, however, the cerebral cortex also participates in the formation of pain sensations.

The hypothalamus adjoins the optic tubercle from below, separated from it by the corresponding furrow. Its anterior border is the optic chiasm. The hypothalamus consists of 32 pairs of nuclei, which are combined into three groups: anterior, middle and posterior. With the help of nerve fibers, the hypothalamus communicates with the reticular formation of the brain stem, with the pituitary gland and with the thalamus.

The hypothalamus is the main subcortical center for the regulation of the autonomic functions of the body; it influences both through the nervous system and through the endocrine glands. In the cells of the nuclei of the anterior group of the hypothalamus, a neurosecrete is produced, which is transported along the hypothalamic-pituitary pathway to the pituitary gland. The hypothalamus and pituitary gland are often combined into the hypothalamic-pituitary system.

There is a connection between the hypothalamus and the adrenal glands: the excitation of the hypothalamus causes the secretion of adrenaline and norepinephrine. Thus, the hypothalamus regulates the activity of the endocrine glands. The hypothalamus is also involved in the regulation of the cardiovascular and digestive systems.

The gray hillock (one of the large nuclei of the hypothalamus) is involved in the regulation of metabolic functions and many glands of the endocrine system. The destruction of the gray tubercle causes atrophy of the gonads, and its prolonged irritation can lead to early puberty, the appearance of skin ulcers, gastric and duodenal ulcers.

The hypothalamus is involved in the regulation of body temperature, water metabolism, carbohydrate metabolism. In patients with dysfunction of the hypothalamus, the menstrual cycle is very often disturbed, sexual weakness is observed, etc. The nuclei of the hypothalamus are involved in many complex behavioral reactions (sexual, nutritional, aggressive-defensive). The hypothalamus regulates sleep and wakefulness.

Most of the nuclei of the visual hillocks are well developed by the time of birth. After birth, there is only an increase in the visual tubercles in volume due to the growth of nerve cells and the development of nerve fibers. This process continues until the age of 13-15.

In newborns, the differentiation of the nuclei of the hypothalamic region is not completed, and it receives its final development during puberty.

Basal ganglia. Inside the cerebral hemispheres, between the diencephalon and the frontal lobes, there are accumulations of gray matter - the so-called basal, or subcortical, ganglia. These are three paired formations: the caudate nucleus, the putamen, and the globus pallidus.

The caudate nucleus and putamen have similar cellular structure and embryonic development. They are combined into a single structure - the striatum. Phylogenetically, this new formation first appears in reptiles.

The pale ball is a more ancient formation, it can be found already in bony fish. It regulates complex motor acts, such as hand movements when walking, contractions of mimic muscles. In a person with a violation of the functions of the pale ball, the face becomes mask-like, the gait is slowed down, devoid of friendly hand movements, all movements are difficult.

The basal ganglia are connected by centripetal pathways to the cerebral cortex, cerebellum, and thalamus. With lesions of the striatum, a person has continuous movements of the limbs and chorea (strong, without any order and sequence of movements, capturing almost the entire musculature). The subcortical nuclei are associated with the vegetative functions of the body: with their participation, the most complex food, sexual and other reflexes are carried out.

Greater hemispheres of the brain. The cerebral hemispheres consist of the subcortical ganglia and the medullary cloak surrounding the lateral ventricles. In an adult, the mass of the cerebral hemispheres accounts for about 80% of the mass of the brain. The right and left hemispheres are separated by a deep longitudinal sulcus. In the depths of this groove is the corpus callosum, formed by nerve fibers. The corpus callosum connects the left and right hemispheres.

The cerebral cloak is represented by the cerebral cortex, the gray matter of the cerebral hemispheres, which is formed by nerve cells with processes extending from them and neuroglia cells. Glial cells perform a supporting function for neurons, participate in the metabolism of neurons.

The cerebral cortex is the highest, phylogenetically youngest formation of the central nervous system. There are between 12 and 18 billion nerve cells in the cortex. The bark has a thickness of 1,5 to 3 mm. The total surface of the hemispheres of the cortex in an adult is 1700-2000 square meters. cm. A significant increase in the area of ​​the hemispheres is due to numerous grooves that divide its entire surface into convex convolutions and lobes.

There are three main furrows: central, lateral and parietal-occipital. They divide each hemisphere into four lobes: frontal, parietal, occipital, and temporal. The frontal lobe is in front of the central sulcus. The parietal lobe is bounded in front by the central sulcus, behind by the parietal-occipital sulcus, below by the lateral sulcus. Behind the parieto-occipital sulcus is the occipital lobe. The temporal lobe is limited at the top by a deep lateral groove. There is no sharp boundary between the temporal and occipital lobes. Each lobe of the brain, in turn, is divided by furrows into a series of convolutions.

Brain growth and development. The weight of a newborn's brain is 340-400 g, which corresponds to 1/8-1/9 of the weight of his body (in an adult, the weight of the brain is 1/40 of the body weight).

Until the fourth month of fetal development, the surface of the cerebral hemispheres is smooth - lisencephalic. However, by the age of five months, the formation of a lateral, then central, parietal-occipital sulcus occurs. By the time of birth, the cerebral cortex has the same type of structure as in an adult, but in children it is much thinner. The shape and size of the furrows and convolutions change significantly even after birth.

The nerve cells of the newborn have a simple fusiform shape with very few processes. Myelination of nerve fibers, the arrangement of layers of the cortex, the differentiation of nerve cells are mostly completed by 3 years. The subsequent development of the brain is associated with an increase in the number of associative fibers and the formation of new neural connections. The mass of the brain in these years increases slightly.

Structural and functional organization of the cerebral cortex. The nerve cells and fibers that form the cortex are arranged in seven layers. In different layers of the cortex, nerve cells differ in shape, size and location.

I layer - molecular. There are few nerve cells in this layer, they are very small. The layer is formed mainly by a plexus of nerve fibers.

II layer - outer granular. It consists of small nerve cells, similar to grains, and cells in the form of very small pyramids. This layer is poor in myelin fibers.

III layer - pyramidal. Formed by medium and large pyramidal cells. This layer is thicker than the first two.

IV layer - internal granular. It consists, like layer II, of small granular cells of various shapes. In some areas of the cortex (for example, in the motor area), this layer may be absent.

Layer V - ganglionic. Consists of large pyramidal cells. In the motor area of ​​the cortex, pyramidal cells reach their greatest size.

Layer VI is polymorphic. Here the cells are triangular and spindle-shaped. This layer is adjacent to the white matter of the brain.

Layer VII is distinguished only in some areas of the cortex. It consists of spindle-shaped neurons. This layer is much poorer in cells and richer in fibers.

In the process of activity, both permanent and temporary connections arise between the nerve cells of all layers of the cortex.

According to the peculiarities of the cellular composition and structure, the cerebral cortex is divided into a number of sections - the so-called fields.

White matter of the cerebral hemispheres. The white matter of the cerebral hemispheres is located under the cortex, above the corpus callosum. The white matter consists of associative, commissural and projection fibers.

Associative fibers connect separate parts of the same hemisphere. Short associative fibers connect separate convolutions and close fields, long ones - convolutions of various lobes within one hemisphere.

Commissural fibers connect the symmetrical parts of both hemispheres, and almost all of them pass through the corpus callosum.

The projection fibers go beyond the hemispheres as part of the descending and ascending pathways, along which the two-way connection of the cortex with the underlying parts of the central nervous system is carried out.

4.7. Functions of the autonomic nervous system

Two types of centrifugal nerve fibers emerge from the spinal cord and other parts of the central nervous system:

1) motor fibers of neurons of the anterior horns of the spinal cord, reaching along the peripheral nerves directly to the skeletal muscles;

2) vegetative fibers of neurons of the lateral horns of the spinal cord, reaching only the peripheral nodes, or ganglia, of the autonomic nervous system. Further, centrifugal impulses of the autonomic nervous system come to the organ from neurons located in the nodes. Nerve fibers located before the nodes are called pre-nodal, after the nodes - post-nodal. Unlike the motor centrifugal pathway, the autonomic centrifugal pathway can be interrupted in more than one of the nodes.

The autonomic nervous system is divided into sympathetic and parasympathetic. There are three main foci of localization of the parasympathetic nervous system:

1) in the spinal cord. Located in the lateral horns of the 2nd-4th sacral segments;

2) in the medulla oblongata. Parasympathetic fibers of the VII, IX, X and XII pairs of cranial nerves come out of it;

3) in the midbrain. Parasympathetic fibers of the III pair of cranial nerves emerge from it.

Parasympathetic fibers are interrupted in the nodes located on the organ or inside it, for example, in the nodes of the heart.

The sympathetic nervous system begins in the lateral horns from the 1st-2nd thoracic to the 3rd-4th lumbar segments. Sympathetic fibers are interrupted in the paravertebral nodes of the border sympathetic trunk and in the prevertebral nodes located at some distance from the spine, for example, in the nodes of the solar plexus, superior and inferior mesenteric.

There are three types of Dogel neurons in the nodes of the autonomic nervous system:

a) neurons with short, highly branched dendrites and a thin, non-fleshy neurite. On this main type of neurons, present in all large nodes, pre-nodal fibers terminate, and their neurites are post-nodal. These neurons perform a motor, effector function;

b) neurons with 2-4 or more long, slightly branching or non-branching processes extending beyond the node. Prenodal fibers do not terminate on these neurons. They are located in the heart, intestines and other internal organs and are sensitive. Through these neurons, local, peripheral reflexes are carried out;

c) neurons that have dendrites that do not extend beyond the node, and neurites that go to other nodes. They perform an associative function or are a type of neurons of the first type.

Functions of the autonomic nervous system. Autonomic fibers differ from the motor fibers of striated muscles by significantly lower excitability, a longer latent period of irritation and longer refractoriness, lower speed of excitation (10-15 m/s in prenodal and 1-2 m/s in postnodal fibers).

The main substances that excite the sympathetic nervous system are adrenaline and norepinephrine (sympathin), the parasympathetic nervous system is acetylcholine. Acetylcholine, epinephrine and norepinephrine can cause not only excitation, but also inhibition: the reaction depends on the dose and the initial metabolism in the innervated organ. These substances are synthesized in the bodies of neurons and in the synaptic endings of fibers in the innervated organs. Adrenaline and norepinephrine are formed in the bodies of neurons and in the inhibitory synapses of the prenodal sympathetic fibers, norepinephrine - in the endings of all postnodal sympathetic fibers, with the exception of the sweat glands. Acetylcholine is produced at the synapses of all excitatory prenodular sympathetic and parasympathetic fibers. The endings of autonomic fibers, where adrenaline and norepinephrine are formed, are called adrenergic, and those endings where acetylcholine is formed are called cholinergic.

Autonomic innervation of organs. There is an opinion that all organs are innervated by sympathetic and parasympathetic nerves, acting on the principle of antagonists, but this idea is incorrect. The sensory organs, nervous system, striated muscles, sweat glands, smooth muscles of the nictitating membranes, muscles that dilate the pupil, most of the blood vessels, ureters and spleen, adrenal glands, pituitary gland are innervated only by sympathetic nerve fibers. Some organs, such as the ciliary muscles of the eye and the muscles that constrict the pupil, are innervated only by parasympathetic fibers. The midgut has no parasympathetic fibers. Some organs are innervated primarily by sympathetic fibers (uterus), while others are innervated by parasympathetic fibers (vagina).

The autonomic nervous system performs two functions:

a) effector - causes the activity of a non-working organ or increases the activity of a working organ and slows down or reduces the function of a working organ;

b) trophic - increases or decreases the metabolism in the organ and throughout the body.

Sympathetic fibers differ from parasympathetic ones in less excitability, a large latent period of irritation and the duration of the consequences. In turn, parasympathetic fibers have a lower threshold of irritation; they begin to function immediately after irritation and stop their action even during irritation (which is explained by the rapid destruction of acetylcholine). Even in organs that receive dual innervation, there is no antagonism between sympathetic and parasympathetic fibers, but interaction.

4.8. Endocrine glands. Their relationship and functions

Endocrine glands (endocrine) do not have excretory ducts and secrete directly into the internal environment - blood, lymph, tissue and cerebrospinal fluid. This feature distinguishes them from the glands of external secretion (digestive) and excretory glands (kidneys and sweat), which secrete the products they form into the external environment.

Hormones. Endocrine glands produce various chemicals called hormones. Hormones act on metabolism in negligible quantities; they serve as catalysts, exerting their effects through the blood and nervous system. Hormones have a huge impact on mental and physical development, growth, changes in the structure of the body and its functions, and determine gender differences.

Hormones are characterized by specificity of action: they have a selective effect only on a certain function (or functions). The effect of hormones on metabolism is carried out mainly through changes in the activity of certain enzymes, and hormones affect either directly their synthesis or the synthesis of other substances involved in a particular enzymatic process. The action of the hormone depends on the dose and can be inhibited by various compounds (sometimes called antihormones).

It has been established that hormones actively influence the formation of the body already in the early stages of intrauterine development. For example, the thyroid, sex glands and gonadotropic hormones of the pituitary gland function in the embryo. There are age-related features of the functioning and structure of the endocrine glands. So, some endocrine glands function especially intensively in childhood, others - in adulthood.

Thyroid gland. The thyroid gland consists of an isthmus and two lateral lobes, located on the neck in front and on the sides of the trachea. The weight of the thyroid gland is: in a newborn - 1,5-2,0 g, by 3 years - 5,0 g, by 5 years - 5,5 g, by 5-8 years - 9,5 g, by 11-12 years (at the beginning of puberty) - 10,0-18,0 g, by 13-15 years - 22-35 g, in an adult - 25-40 g. By old age, the weight of the gland decreases, and in men it is more than in women .

The thyroid gland is richly supplied with blood: the volume of blood passing through it in an adult is 5-6 cubic meters. dm of blood per hour. The gland secretes two hormones - thyroxine, or tetraiodothyronine (T4), and triiodothyronine (T3). Thyroxine is synthesized from the amino acid tyrosine and iodine. In an adult, the body contains 25 mg of iodine, of which 15 mg is in the thyroid gland. Both hormones (T3 and T4) are formed in the thyroid gland simultaneously and continuously as a result of proteolytic cleavage of thyroglobulin. T3 is synthesized 5-7 times less than T4, it contains less iodine, but its activity is 10 times greater than the activity of thyroxine. In tissues, T4 is converted to T3. T3 is excreted from the body faster than thyroxine.

Both hormones enhance oxygen absorption and oxidative processes, increase heat generation, inhibit the formation of glycogen, increasing its breakdown in the liver. The effect of hormones on protein metabolism is associated with age. In adults and children, thyroid hormones have the opposite effect: in adults, with an excess of the hormone, the breakdown of proteins increases and emaciation occurs, in children, protein synthesis increases and the growth and formation of the body accelerate. Both hormones increase the synthesis and breakdown of cholesterol with a predominance of breakdown. An artificial increase in the content of thyroid hormones increases the basal metabolism and increases the activity of proteolytic enzymes. The cessation of their entry into the blood sharply reduces the basal metabolism. Thyroid hormones boost immunity.

Dysfunction of the thyroid gland leads to severe diseases and developmental pathologies. With hyperfunction of the thyroid gland, signs of Graves' disease appear. In 80% of cases, it develops after a mental trauma; occurs at all ages, but more often from 20 to 40 years, and in women 5-10 times more often than in men. With hypofunction of the thyroid gland, a disease such as myxedema is observed. In children, myxedema is the result of congenital absence of the thyroid gland (aplasia) or its atrophy with hypofunction or lack of secretion (hypoplasia). With myxedema, there are frequent cases of oligophrenia (caused by a violation of the formation of thyroxine due to a delay in the conversion of the amino acid phenylalanine to tyrosine). It is also possible to develop cretinism caused by the growth of the supporting connective tissue of the gland due to the cells that form the secret. This phenomenon often has a geographic location, therefore it is called endemic goiter. The cause of endemic goiter is a lack of iodine in food, mainly vegetable, as well as in drinking water.

The thyroid gland is innervated by sympathetic nerve fibers.

Parathyroid glands. Humans have four parathyroid glands. Their total weight is 0,13-0,25 g. They are located on the posterior surface of the thyroid gland, often even in its tissue. There are two types of cells in the parathyroid glands: principal and oxyphilic. Oxyphilic cells appear from 7-8 years of age, and by 10-12 years of age there are more of them. With age, there is an increase in the number of cells of adipose and supporting tissue, which by the age of 19-20 begins to displace glandular cells.

The parathyroid glands produce parathyroid hormone (parathyroidin, parathormone), which is a protein substance (albumose). The hormone is released continuously and regulates the development of the skeleton and the deposition of calcium in the bones. Its regulatory mechanism is based on the regulation of the function of osteoclasts that absorb bones. The active work of osteoclasts leads to the release of calcium from the bones, which ensures a constant content of calcium in the blood at the level of 5-11 mg%. Parathyroid hormone also maintains at a certain level the content of the enzyme phosphatase, which is involved in the deposition of calcium phosphate in the bones. The secretion of parathyroidin is regulated by the content of calcium in the blood: the less it is, the higher the secretion of the gland.

The parathyroid glands also produce another hormone, calcitonin, which reduces the amount of calcium in the blood; its secretion increases with an increase in the amount of calcium in the blood.

Atrophy of the parathyroid glands causes tetany (convulsive illness), which occurs as a result of a significant increase in the excitability of the central nervous system caused by a decrease in the calcium content in the blood. With tetany, convulsive contractions of the muscles of the larynx, paralysis of the respiratory muscles and cardiac arrest are observed. Chronic hypofunction of the parathyroid glands is accompanied by increased excitability of the nervous system, weak muscle cramps, digestive disorders, ossification of the teeth, hair loss. Overexcitation of the nervous system turns into inhibition. There are phenomena of poisoning by products of protein metabolism (guanidine). With chronic hyperfunction of the glands, the calcium content in the bones decreases, they are destroyed and become brittle; cardiac activity and digestion are disturbed, the strength of the muscular system decreases, apathy sets in, and in severe cases, death.

The parathyroid glands are innervated by branches of the recurrent and laryngeal nerves and by sympathetic nerve fibers.

Thymus gland. The thymus gland is located in the chest cavity behind the sternum, consists of right and left unequal lobes, united by connective tissue. Each lobule of the thymus gland consists of a cortical and medulla layer, the basis of which is reticular connective tissue. In the cortical layer there are many small lymphocytes, in the medulla there are relatively fewer lymphocytes.

With age, the size and structure of the gland change greatly: up to 1 year, its mass is 13 g; from 1 year to 5 years -23 g; from 6 to 10 years - 26 g; from 11 to 15 years old - 37,5 g; from 16 to 20 years old - 25,5 g; from 21 to 25 years old - 24,75 g; from 26 to 35 years - 20 g; from 36 to 45 years - 16 g; from 46 to 55 years - 12,85 g; from 66 to 75 years - 6 g. The greatest absolute weight of the gland in adolescents, then it begins to decline. The highest relative weight (per kg of body weight) in newborns is 4,2%, then it begins to decrease: at 6-10 years old - up to 1,2%, at 11-15 years old - up to 0,9%, at 16-20 years - up to 0,5%. With age, glandular tissue is gradually replaced by adipose tissue. The degeneration of the gland is detected from 9-15 years.

The thymus gland in terms of the content of ascorbic acid is in second place after the adrenal glands. In addition, it contains a lot of vitamins B2, D and zinc.

The hormone produced by the thymus gland is unknown, but it is believed that it regulates immunity (participates in the process of maturation of lymphocytes), takes part in the process of puberty (inhibits sexual development), enhances body growth and retains calcium salts in the bones. After its removal, the development of the sex glands sharply increases: the delay in the degeneration of the thymus slows down the development of the sex glands, and vice versa, after castration in early childhood, age-related changes in the gland do not occur. Thyroid hormones cause an increase in the thymus gland in a growing organism, and adrenal hormones, on the contrary, cause it to decrease. In the case of removal of the thymus gland, the adrenal glands and the thyroid gland hypertrophy, and an increase in the function of the thymus gland lowers the function of the thyroid gland.

The thymus gland is innervated by sympathetic and parasympathetic nerve fibers.

Adrenal glands (adrenal glands). These are paired glands, there are two of them. Both of them cover the upper ends of each bud. The average weight of both adrenal glands is 10-14 g, and in men they are relatively less than in women. Age-related changes in the relative weight of both adrenal glands are as follows: in newborns - 6-8 g, in children 1-5 years old - 5,6 g; 10 years - 6,5 g; 11-15 years - 8,5 g; 16-20 years old - 13 g; 21-30 years old - 13,7 g.

The adrenal gland consists of two layers: the cortical (consists of interrenal tissue, is of mesodermal origin, appears somewhat earlier in ontogeny than the brain) and the medulla (consists of chromaffin tissue, is of ectodermal origin).

The cortical layer of the adrenal glands of a newborn child significantly exceeds the medulla; in a one-year-old child, it is twice as thick as the medulla. At the age of 9-10 years, an increased growth of both layers is observed, but by the age of 11, the thickness of the medulla exceeds the thickness of the cortical layer. The end of the formation of the cortical layer falls on 10-12 years. The thickness of the medulla in the elderly is twice that of the cortex.

The cortical layer of the adrenal glands consists of four zones: the upper (glomerular); very narrow intermediate; medium (widest, beam); bottom mesh.

Major changes in the structure of the adrenal glands begin at age 20 and continue until age 50. During this period, the growth of the glomerular and reticular zones occurs. After 50 years, the reverse process is observed: the glomerular and reticular zones decrease until they disappear completely, due to this, the fascicular zone increases.

The functions of the layers of the adrenal glands are different. About 46 corticosteroids are formed in the cortical layer (similar in chemical structure to sex hormones), of which only 9 are biologically active. In addition, male and female sex hormones are formed in the cortical layer, which are involved in the development of the genital organs in children before puberty.

According to the nature of the action, corticosteroids are divided into two types.

I. Glucocorticoids (metabolocorticoids). These hormones enhance the breakdown of carbohydrates, proteins and fats, the conversion of proteins into carbohydrates and phosphorylation, increase the efficiency of skeletal muscles and reduce their fatigue. With a lack of glucocorticoids, muscle contractions stop (adynamia). Glucocorticoid hormones include (in descending order of biological activity) cortisol (hydrocortisone), corticosterone, cortisone, 11-deoxycortisol, 11-dehydrocorticosterone. Hydrocortisone and cortisone in all age groups increase the oxygen consumption of the heart muscle.

Hormones of the adrenal cortex, especially glucocorticoids, are involved in the body's protective reactions to stressful influences (pain irritations, cold, lack of oxygen, heavy physical exertion, etc.). Adrenocorticotropic hormone from the pituitary gland is also involved in the stress response.

The highest level of glucocorticoid secretion is observed during puberty, after its completion, their secretion stabilizes at a level close to that of adults.

II. Mineralocorticoids. They have little effect on carbohydrate metabolism and mainly affect the exchange of salts and water. These include (in descending order of biological activity) aldosterone, deoxycorticosterone, 18-hydroxy-deoxycorticosterone, 18-oxycorticosterone. Mineralocorticoids change carbohydrate metabolism, return fatigued muscles to working capacity by restoring the normal ratio of sodium and potassium ions and normal cellular permeability, increase water reabsorption in the kidneys, and increase arterial blood pressure. Mineralocorticoid deficiency reduces sodium reabsorption in the kidneys, which can lead to death.

The amount of mineralocorticoids is regulated by the amount of sodium and potassium in the body. The secretion of aldosterone increases with a lack of sodium ions and an excess of potassium ions, and, on the contrary, is inhibited with a lack of potassium ions and an excess of sodium ions in the blood. The daily secretion of aldosterone increases with age and reaches a maximum by 12-15 years. In children from 1,5-5 years old, aldosterone secretion is less, from 5 to 11 years old it reaches the level of adults. Deoxycorticosterone enhances body growth, while corticosterone suppresses it.

Different corticosteroids are secreted in different zones of the cortical layer: glucocorticoids - in the fascicular zone, mineralocorticoids - in the glomerular zone, sex hormones - in the reticular zone. During puberty, the secretion of hormones of the adrenal cortex is greatest.

Hypofunction of the adrenal cortex causes bronze, or Addison's disease. Hyperfunction of the cortical layer leads to premature formation of sex hormones, which is expressed in early puberty (boys 4-6 years old have a beard, sexual desire arises and genitals develop, like in adult men; girls 2 years old menstruation occurs). Changes can occur not only in children, but also in adults (in women, secondary male sexual characteristics appear, in men, the mammary glands grow and the genitals atrophy).

In the adrenal medulla, the hormone adrenaline and a little norepinephrine are continuously synthesized from tyrosine. Adrenaline affects the functions of all organs, except for the secretion of sweat glands. It inhibits the movements of the stomach and intestines, increases and speeds up the activity of the heart, narrows the blood vessels of the skin, internal organs and non-working skeletal muscles, dramatically increases metabolism, increases oxidative processes and heat generation, increases the breakdown of glycogen in the liver and muscles. Adrenaline enhances the secretion of adrenocorticotropic hormone from the pituitary gland, which increases the flow of glucocorticoids into the blood, which leads to an increase in the formation of glucose from proteins and an increase in blood sugar. There is an inverse relationship between sugar concentration and adrenaline secretion: a decrease in blood sugar leads to the secretion of adrenaline. In small doses, adrenaline excites mental activity, in large doses it inhibits. Adrenaline is destroyed by the enzyme monoamine oxidase.

The adrenal glands are innervated by sympathetic nerve fibers running in the celiac nerves. During muscular work and emotions, a reflex excitation of the sympathetic nervous system occurs, which leads to an increase in the flow of adrenaline into the blood. In turn, this increases skeletal muscle strength and endurance through trophic influence, increased blood pressure, and increased blood supply.

Pituitary gland (lower cerebral appendage). This is the main endocrine gland, affecting the functioning of all endocrine glands and many body functions. The pituitary gland is located in the sella turcica, directly below the brain. In adults, its weight is 0,55-0,65 g, in newborns - 0,1-0,15 g, at 10 years old - 0,33, at 20 years old - 0,54 g.

The pituitary gland has two lobes: the adenohypophysis (prehypophysis, the larger anterior glandular part) and the neurohypophysis (posthypophysis, posterior part). In addition, the middle lobe is distinguished, but in adults it is almost absent and more developed in children. In adults, the adenohypophysis makes up 75% of the pituitary gland, the intermediate share is 1-2%, and the neurohypophysis is 18-23%. During pregnancy, the pituitary gland enlarges.

Both lobes of the pituitary gland receive sympathetic nerve fibers that regulate its blood supply. The adenohypophysis consists of chromophobic and chromophilic cells, which, in turn, are divided into acidophilic and basophilic (the number of these cells increases at 14-18 years of age). The neurohypophysis is formed by neuroglial cells.

The pituitary gland produces more than 22 hormones. Almost all of them are synthesized in the adenohypophysis.

1. The most important hormones of the adenohypophysis include:

a) growth hormone (somatotropic hormone) - accelerates growth while maintaining relative proportions of the body. Has species specificity;

b) gonadotropic hormones - accelerate the development of the sex glands and increase the formation of sex hormones;

c) lactotropic hormone, or prolactin, - excites the separation of milk;

d) thyroid-stimulating hormone - potentiates the secretion of thyroid hormones;

e) parathyroid-stimulating hormone - causes an increase in the functions of the parathyroid glands and increases the calcium content in the blood;

f) adrenocorticotropic hormone (ACTH) - increases the secretion of glucocorticoids;

g) pancreotropic hormone - affects the development and function of the intrasecretory part of the pancreas;

h) hormones of protein, fat and carbohydrate metabolism, etc. - regulate the corresponding types of metabolism.

2. Hormones are formed in the neurohypophysis:

a) vasopressin (antidiuretic) - constricts blood vessels, especially the uterus, increases blood pressure, reduces urination;

b) oxytocin - causes uterine contraction and increases the tone of the intestinal muscles, but does not change the lumen of the blood vessels and the level of blood pressure.

Pituitary hormones affect the higher nervous activity, increasing it in small doses, and inhibiting it in large doses.

3. In the middle lobe of the pituitary gland, only one hormone is formed - intermedin (melanocyte-stimulating hormone), which causes the pseudopodium of the cells of the black pigment layer of the retina to move under strong illumination.

Hyperfunction of the anterior part of the adenohypophysis causes the following pathologies: if hyperfunction occurs before the end of ossification of long bones - gigantism (average growth increases up to one and a half times); if after the end of ossification - acromegaly (disproportionate growth of body parts). Hypofunction of the anterior pituitary gland in early childhood causes dwarf growth with normal mental development and maintaining relatively correct body proportions. Sex hormones reduce the action of growth hormone.

In girls, the formation of the "hypothalamic region - pituitary - adrenal cortex" system, which adapts the body to stress, as well as blood mediators, occurs later than in boys.

Epiphysis (superior cerebral appendage). The pineal gland is located at the posterior end of the visual hillocks and on the quadrigeminos, connected to the visual hillocks. In an adult, the pineal gland, or pineal gland, weighs about 0,1-0,2 g. It develops up to 4 years, and then begins to atrophy, especially intensively after 7-8 years.

The pineal gland has a depressing effect on sexual development in immature and inhibits the function of the gonads in sexually mature. It secretes a hormone that acts on the hypothalamic region and inhibits the formation of gonadotropic hormones in the pituitary gland, which causes inhibition of the internal secretion of the sex glands. The pineal hormone melatonin, unlike intermedin, reduces pigment cells. Melatonin is formed from serotonin.

The gland is innervated by sympathetic nerve fibers coming from the superior cervical ganglion.

The epiphysis has an inhibitory effect on the adrenal cortex. Hyperfunction of the pineal gland reduces the volume of the adrenal glands. Hypertrophy of the adrenal glands reduces the function of the pineal gland. The pineal gland affects carbohydrate metabolism, its hyperfunction causes hypoglycemia.

Pancreas. This gland, together with the gonads, belongs to the mixed glands, which are organs of both external and internal secretion. In the pancreas, hormones are produced in the so-called islets of Langerhans (208-1760 thousand). In newborns, the intrasecretory tissue of the gland is larger than the exocrine tissue. In children and young people, there is a gradual increase in the size of the islets.

The islets of Langerhans are round in shape, differ in structure from the tissue that synthesizes pancreatic juice, and consist of two types of cells: alpha and beta. Alpha cells are 3,5-4 times less than beta cells. In newborns, the number of beta cells is only twice as high, but their number increases with age. The islets also contain nerve cells and numerous parasympathetic and sympathetic nerve fibers. The relative number of islets in newborns is four times greater than in adults. Their number decreases rapidly in the first year of life, from the age of 4-5 the process of reduction slows down somewhat, and by the age of 12 the number of islets becomes the same as in adults, after 25 years the number of islets gradually decreases.

In alpha cells, the hormone glucagon is produced, in beta cells, the hormone insulin is continuously secreted (about 2 mg per day). Insulin has the following effects: reduces blood sugar by increasing the synthesis of glycogen from glucose in the liver and muscles; increases the permeability of cells to glucose and the absorption of sugar by muscles; retains water in tissues; activates the synthesis of proteins from amino acids and reduces the formation of carbohydrates from protein and fat. Under the action of insulin in the membranes of muscle cells and neurons, channels are opened for the free passage of sugar into the interior, which leads to a decrease in its content in the blood. An increase in blood sugar activates the synthesis of insulin and at the same time inhibits the secretion of glucagon. Glucagon increases blood sugar by increasing the conversion of glycogen to glucose. Decreased secretion of glucagon reduces blood sugar. Insulin has a stimulating effect on the secretion of gastric juice, rich in pepsin and hydrochloric acid, and enhances gastric motility.

After the introduction of a large dose of insulin, there is a sharp drop in blood sugar to 45-50 mg%, which leads to hypoglycemic shock (severe convulsions, impaired brain activity, loss of consciousness). The introduction of glucose immediately stops it. A persistent decrease in insulin secretion leads to diabetes mellitus.

Insulin is species specific. Adrenaline increases insulin secretion, and insulin secretion increases adrenaline secretion. The vagus nerves increase insulin secretion, while the sympathetic nerves inhibit it.

In the cells of the epithelium of the excretory ducts of the pancreas, the hormone lipocaine is formed, which increases the oxidation of higher fatty acids in the liver and inhibits its obesity.

The pancreatic hormone vagotonin increases the activity of the parasympathetic system, and the hormone centropnein excites the respiratory center and promotes the transport of oxygen by hemoglobin.

Sex glands. Like the pancreas, they are classified as mixed glands. Both male and female gonads are paired organs.

A. The male sex gland - the testicle (testicle) - has the shape of a somewhat compressed ellipsoid. In an adult, its weight averages 20-30 g. In children 8-10 years old, the weight of the testicle is 0,8 g; at 12-14 years old -1,5 g; at the age of 15 - 7 g. Intensive growth of the testicles goes up to 1 year and from 10 to 15 years. The period of puberty for boys: from 15-16 to 19-20 years, but individual fluctuations are possible.

Outside, the testicle is covered with a fibrous membrane, from the inner surface of which, along the posterior edge, a proliferation of connective tissue is wedged into it. Thin connective tissue crossbars diverge from this expansion, dividing the gland into 200-300 lobules. In the lobules, seminiferous tubules and intermediate connective tissue are distinguished. The wall of the convoluted tubules consists of two kinds of cells: the first form spermatozoa, the second are involved in the nutrition of developing spermatozoa. In addition, there are interstitial cells in the loose connective tissue that connects the tubules. Spermatozoa enter the epididymis through the direct and efferent tubules, and from it into the vas deferens. Above the prostate gland, both vas deferens pass into the vas deferens, which enter this gland, penetrate it and open into the urethra. The prostate gland (prostate) finally develops around the age of 17. The weight of the prostate in an adult is 17-28 g.

Spermatozoa are highly differentiated cells 50-60 microns long, which are formed at the beginning of puberty from primary germ cells - spermatogonia. The sperm has a head, neck and tail. In 1 cubic mm of seminal fluid contains about 60 thousand sperm. Sperm erupted at one time has a volume of up to 3 cubic meters. cm and contains about 200 million sperm.

Male sex hormones - androgens - are formed in interstitial cells, which are called the gland of puberty, or puberty. Androgens include: testosterone, androstandione, androsterone, etc. In the interstitial cells of the testis, female sex hormones, estrogens, are also formed. Estrogens and androgens are derivatives of steroids and are similar in chemical composition. Dehydroandrosterone has the properties of male and female sex hormones. Testosterone is six times more active than dehydroandrosterone.

B. Female sex glands - ovaries - have different sizes, shapes and weights. In a woman who has reached puberty, the ovary looks like a thickened ellipsoid weighing 5-8 g. The right ovary is slightly larger than the left. In a newborn girl, the weight of the ovary is 0,2 g. At 5 years old, the weight of each ovary is 1 g, at 8-10 years old - 1,5 g; at 16 years old - 2 years.

The ovary consists of two layers: cortical (egg cells are formed in it) and brain (consists of connective tissue containing blood vessels and nerves). Female egg cells are formed from primary egg cells - oogonia, which, together with the cells that feed them (follicular cells), form the primary egg follicles.

The egg follicle is a small egg cell surrounded by a row of flat follicular cells. In newborn girls, there are many egg follicles, and they are almost adjacent to each other; in older women, they disappear. In a 22-year-old healthy girl, the number of primary follicles in both ovaries can reach up to 400 or more. During life, only about 500 primary follicles mature and egg cells capable of fertilization are formed in them, the rest of the follicles atrophy. Follicles reach full development during puberty, from about 13-15 years old, when some mature follicles secrete the hormone estrone.

The period of puberty (pubertal) lasts in girls from 13-14 to 18 years. During maturation, an increase in the size of the egg cell occurs, follicular cells multiply intensively and form several layers. Then the growing follicle plunges deep into the cortical layer, is covered with a fibrous connective tissue membrane, filled with fluid and increases in size, turning into a Graafian vesicle. In this case, the egg cell with the follicular cells surrounding it is pushed to one side of the bubble. Approximately 12 days before Graafian menstruation, the vesicle bursts, and the egg cell, together with the follicular cells surrounding it, enters the abdominal cavity, from which it first enters the funnel of the oviduct, and then, thanks to the movements of the ciliated hairs, into the oviduct and uterus. Ovulation occurs. If the egg cell is fertilized, it attaches to the wall of the uterus and the embryo begins to develop from it.

After ovulation, the walls of the Graafian vesicle collapse. On the surface of the ovary, in place of the Graaffian vesicle, a temporary endocrine gland is formed - the corpus luteum. The corpus luteum secretes the hormone progesterone, which prepares the lining of the uterus to receive the fetus. If fertilization occurs, the corpus luteum persists and develops throughout the pregnancy or most of it. The corpus luteum during pregnancy reaches 2 cm or more and leaves a scar behind. If fertilization does not occur, then the corpus luteum atrophies and is absorbed by phagocytes (periodic corpus luteum), after which a new ovulation occurs.

The sexual cycle in women is manifested in menstruation. The first menstruation occurs after the maturation of the first egg cell, the bursting of the Graafian vesicle and the development of the corpus luteum. On average, the sexual cycle lasts 28 days and is divided into four periods:

1) the recovery period of the uterine mucosa for 7-8 days, or a period of rest;

2) the period of growth of the uterine mucosa and its increase within 7-8 days, or preovulation, caused by increased secretion of pituitary folliculotropic hormone and estrogen;

3) secretory period - secretion, rich in mucus and glycogen, in the uterine mucosa, corresponding to the maturation and rupture of the Graafian vesicle, or the ovulation period;

4) a period of rejection, or post-ovulation, lasting an average of 3-5 days, during which the uterus contracts tonically, its mucous membrane is torn off in small pieces and 50-150 cubic meters is released. see blood. The last period occurs only in the absence of fertilization.

Estrogens include: estrone (follicular hormone), estriol and estradiol. They are produced in the ovaries. A small amount of androgens is also secreted there. Progesterone is produced in the corpus luteum and placenta. During the period of rejection, progesterone inhibits the secretion of folliculotropic hormone and other gonadotropic hormones from the pituitary gland, which leads to a decrease in the amount of estrogen synthesized in the ovary.

Sex hormones have a significant impact on metabolism, which determines the quantitative and qualitative characteristics of the metabolism of male and female organisms. Androgens increase protein synthesis in the body and muscles, which increases their mass, promotes bone formation and therefore increases body weight, and reduces glycogen synthesis in the liver. Estrogens, on the contrary, increase the synthesis of glycogen in the liver and the deposition of fat in the body.

4.9. The development of the genital organs of the child. puberty

The human body reaches biological maturity during puberty. At this time, the awakening of the sexual instinct occurs, since children are not born with a developed sexual reflex. The timing of the onset of puberty and its intensity are different and depend on many factors: health status, diet, climate, living and socio-economic conditions. An important role is played by hereditary features. In urban areas, adolescent puberty usually occurs earlier than in rural areas.

During the transitional period, a profound restructuring of the whole organism takes place. The activity of the endocrine glands is activated. Under the influence of the hormones of the pituitary gland, the growth of the body in length is accelerated, the activity of the thyroid gland and adrenal glands is enhanced, and the active activity of the gonads begins. The excitability of the autonomic nervous system increases. Under the influence of sex hormones, the final formation of the genital organs and sex glands occurs, and secondary sexual characteristics begin to develop. In girls, the contours of the body are rounded, the deposition of fat in the subcutaneous tissue increases, the mammary glands increase and develop, the pelvic bones are distributed in width. In boys, hair grows on the face and body, the voice breaks, and seminal fluid accumulates.

Puberty of girls. Girls begin puberty earlier than boys. At the age of 7-8 years, the development of adipose tissue according to the female type occurs (fat is deposited in the mammary glands, on the hips, buttocks). At the age of 13-15 years, the body grows rapidly in length, vegetation appears on the pubis and in the armpits; changes also occur in the genital organs: the uterus increases in size, follicles mature in the ovaries, and menstruation begins. At the age of 16-17, the formation of the female-type skeleton ends. At the age of 19-20, menstrual function finally stabilizes, and anatomical and physiological maturity begins.

Puberty of boys. Puberty begins in boys at 10-11 years of age. At this time, the growth of the penis and testicles increases. At 12-13 years old, the shape of the larynx changes and the voice breaks. At the age of 13-14, a male-type skeleton is formed. At 15-16 years of age, hair under the arms and on the pubis grows rapidly, facial hair appears (mustache, beard), testicles enlarge, and involuntary ejaculation of semen begins. At the age of 16-19, muscle mass and physical strength increase, and the process of physical maturation ends.

Features of adolescent puberty. During puberty, the entire body is rebuilt, and the teenager’s psyche changes. At the same time, development occurs unevenly, some processes are ahead of others. For example, the growth of the limbs outstrips the growth of the torso, and the adolescent’s movements become angular due to a violation of coordination relationships in the central nervous system. In parallel with this, muscle strength increases (from 15 to 18 years, muscle mass increases by 12%, while from birth to 8 years it increases by only 4%).

Such a rapid growth of the bone skeleton and muscular system does not always keep pace with the internal organs - the heart, lungs, gastrointestinal tract. Thus, the heart outstrips blood vessels in growth, due to which blood pressure rises and makes it difficult for the heart to work. At the same time, the rapid restructuring of the whole organism places increased demands on the work of the cardiovascular system, and insufficient work of the heart ("youthful heart") leads to dizziness and cold extremities, headaches, fatigue, periodic bouts of lethargy, fainting due to for spasms of cerebral vessels. As a rule, these negative phenomena disappear with the end of puberty.

A sharp increase in the activity of the endocrine glands, intensive growth, structural and physiological changes in the body increase the excitability of the central nervous system, which is reflected on the emotional level: the emotions of adolescents are mobile, changeable, contradictory; increased sensitivity is combined in them with callousness, shyness - with swagger; excessive criticism and intolerance towards parental care are manifested.

During this period, there is sometimes a decrease in efficiency, neurotic reactions - irritability, tearfulness (especially in girls during menstruation).

There are new relationships between the sexes. Girls are more interested in their appearance. Boys tend to show their strength in front of girls. The first "love experiences" sometimes unsettle teenagers, they become withdrawn, they begin to study worse.

Topic 5. ANALYZERS. HYGIENE OF VISION AND HEARING

5.1. The concept of analyzers

An analyzer (sensory system) is a part of the nervous system, consisting of many specialized perceiving receptors, as well as intermediate and central nerve cells and nerve fibers connecting them. For sensation to occur, the following functional elements must be present:

1) sensory organ receptors that perform a perceiving function (for example, for a visual analyzer, these are retinal receptors);

2) a centripetal path from this sense organ to the cerebral hemispheres, providing a conductive function (for example, optic nerves and pathways through the diencephalon);

3) the perceiving zone in the cerebral hemispheres, which implements the analyzing function (the visual zone in the occipital region of the cerebral hemispheres).

Receptor specificity. Receptors are specialized formations adapted to perceive certain influences of the external and internal environment. Receptors have specificity, i.e., high excitability only to certain stimuli, called adequate. In particular, for the eye an adequate stimulus is light, and for the ear - sound waves, etc. When adequate stimuli act, sensations arise that are characteristic of a particular sense organ. Thus, irritation of the eye causes visual sensations, ear - auditory sensations, etc. In addition to adequate ones, there are also inadequate (inadequate) stimuli that cause only a small part of the sensations characteristic of a given sense organ, or act in an unusual way. For example, mechanical or electrical irritation of the eye is perceived as a bright flash of light ("phosphene"), but does not give an image of an object and the perception of colors. The specificity of the sense organs is the result of the body's adaptation to environmental conditions.

Each receptor is characterized by the following properties:

a) a certain value of the threshold of excitability, i.e., the smallest strength of the stimulus that can cause a sensation;

b) chronaxia;

c) time threshold - the smallest interval between two stimuli, at which two sensations differ;

d) discrimination threshold - the smallest increase in the strength of the stimulus, causing a barely noticeable difference in sensation (for example, in order to distinguish the difference in the pressure of the load on the skin with closed eyes, you need to add about 3,2-5,3% of the initial load);

e) adaptation - a sharp drop (increase) in the strength of sensation immediately after the onset of the stimulus. Adaptation is based on a decrease in the frequency of excitation waves that occurs in the receptor when it is stimulated.

Organs of taste. The epithelium of the oral mucosa contains taste buds that have a round or oval shape. They consist of oblong and flat cells located at the base of the bulb. Elongated cells are divided into supporting cells (located on the periphery) and taste cells (located in the center). Each taste bud contains from two to six taste cells, and their total number in an adult reaches 9 thousand. Taste buds are located in the papillae of the mucous membrane of the tongue. The apex of the taste bud does not reach the surface of the epithelium, but communicates with the surface using the taste canal. Individual taste buds are located on the surface of the soft palate, the posterior wall of the pharynx, and the epiglottis. Centripetal impulses from each taste bud are carried along two or three nerve fibers. These fibers are part of the chorda tympani and the lingual nerve, which innervate the anterior two-thirds of the tongue, and from the posterior third they form part of the glossopharyngeal nerve. Next, through the visual hillocks, centripetal impulses enter the taste zone of the cerebral hemispheres.

Olfactory organs. Olfactory receptors are located in the upper part of the nasal cavity. Olfactory cells are neurons surrounded by supporting columnar cells. Humans have 60 million olfactory cells, the surface of each of them is covered with cilia, which increase the olfactory surface, which in humans is approximately 5 square meters. see. From the olfactory cells, centripetal impulses along nerve fibers passing through the holes in the ethmoid bone enter the olfactory nerve, and then through the subcortical centers, where the second and third neurons are located, enter the olfactory zone of the cerebral hemispheres. Since the olfactory surface is located away from the respiratory tract, air with odorous substances penetrates to it only by diffusion.

Skin sensitivity organs. Skin receptors are divided into tactile (their irritation causes sensations of touch), thermoreceptors (cause sensations of heat and cold) and pain receptors.

The sensations of touch, or touch and pressure, differ in character, for example, one cannot feel the pulse with the tongue. There are approximately 500 tactile receptors in human skin. The threshold of excitability of tactile receptors in different parts of the body is not the same: the highest excitability in the receptors of the skin of the nose, fingertips and mucous membrane of the lips, the smallest - in the skin of the abdomen and inguinal region. For tactile receptors, the simultaneous spatial threshold (the smallest distance between receptors at which simultaneous skin irritation causes two sensations) is the smallest, for pain receptors it is the largest. Tactile receptors also have the smallest time threshold, that is, the time interval between two successive stimuli at which two separate sensations are evoked.

The total number of thermoreceptors is about 300 thousand, of which 250 thousand are thermal, and 30 thousand are cold. Cold receptors are located closer to the surface of the skin, and thermal receptors are deeper.

There are from 900 thousand to 1 million pain receptors. Pain is stimulated by defensive reflexes of the skeletal muscles and internal organs, but prolonged strong irritation of pain receptors causes a violation of many body functions. Pain sensations are more difficult to localize than other types of skin sensitivity, since the excitation that occurs when pain receptors are irritated widely radiates through the nervous system. Simultaneous irritation of the receptors of vision, hearing, smell and taste reduces the sensation of pain.

Vibration sensations (oscillations of objects with a frequency of 2-10 times per second) are well perceived by the skin of the fingers and the bones of the skull. Centripetal impulses from skin receptors enter the spinal cord through the posterior roots and reach the neurons of the posterior horns. Then, along the nerve fibers that make up the posterior columns (gentle and wedge-shaped bundles) and the lateral (spinal-thalamic bundle), the impulses reach the anterior nuclei of the visual tubercles. From here, the fibers of the third neuron begin, which, together with the fibers of proprioceptive sensitivity, reach the zone of musculoskeletal sensitivity in the posterior central gyrus of the cerebral hemispheres.

5.2. organs of vision. The structure of the eye

The eyeball consists of three shells: outer, middle and inner. The outer, or fibrous, membrane is formed from dense connective tissue - the cornea (in front) and the opaque sclera, or tunica (back). The middle (vascular) membrane contains blood vessels and consists of three sections:

1) anterior section (iris, or iris). The iris contains smooth muscle fibers that make up two muscles: a circular, constricting pupil, located almost in the center of the iris, and a radial, dilating the pupil. Closer to the anterior surface of the iris is a pigment that determines the color of the eye and the opacity of this shell. The iris adjoins with its back surface to the lens;

2) middle section (ciliary body). The ciliary body is located at the junction of the sclera with the cornea and has up to 70 ciliary radial processes. Inside the ciliary body is the ciliary, or ciliary, muscle, which consists of smooth muscle fibers. The ciliary muscle is attached by ciliary ligaments to the tendon ring and the lens bag;

3) the posterior section (the choroid itself).

The inner shell (retina) has the most complex structure. The main receptors in the retina are rods and cones. There are about 130 million rods and about 7 million cones in the human retina. Each rod and cone has two segments - an outer and an internal one; the cone has a shorter outer segment. The outer segments of the rods contain visual purple, or rhodopsin (purple-colored substance), and the outer segments of the cones contain iodopsin (purple color). The internal segments of the rods and cones are connected to neurons that have two processes (bipolar cells), which are in contact with ganglion neurons, which are part of the optic nerve with their fibers. Each optic nerve contains about 1 million nerve fibers.

The distribution of rods and cones in the retina has the following order: in the middle of the retina there is a central fovea (yellow spot) with a diameter of 1 mm, it contains only cones, closer to the central fovea are cones and rods, and on the periphery of the retina - only rods. In the fovea, each cone is connected to one neuron through a bipolar cell, and to the side of it, several cones are also connected to one neuron. Rods, unlike cones, are connected to one bipolar cell in several pieces (about 200). Due to this structure, the greatest visual acuity is provided in the fovea. At a distance of approximately 4 mm medially from the central fossa is the papilla of the optic nerve (blind spot), in the center of the nipple are the central artery and the central vein of the retina.

Between the posterior surface of the cornea and the anterior surface of the iris and part of the lens is the anterior chamber of the eye. Between the posterior surface of the iris, the anterior surface of the ciliary ligament and the anterior surface of the lens is the posterior chamber of the eye. Both chambers are filled with transparent aqueous humor. The entire space between the lens and the retina is occupied by a transparent vitreous body.

Light refraction in the eye. The light-refracting media of the eye include: the cornea, the aqueous humor of the anterior chamber of the eye, the lens and the vitreous body. Much of the clarity of vision depends on the transparency of these media, but the refractive power of the eye depends almost entirely on refraction in the cornea and lens. Refraction is measured in diopters. Diopter is the reciprocal of focal length. The refractive power of the cornea is constant and equal to 43 diopters. The refractive power of the lens is not constant and varies widely: when viewing at a close distance - 33 diopters, at a distance - 19 diopters. The refractive power of the entire optical system of the eye: when looking into the distance - 58 diopters, at a close distance - 70 diopters.

Parallel light rays, after refraction in the cornea and lens, converge to one point in the fovea. The line passing through the centers of the cornea and lens to the center of the macula is called the visual axis.

Accommodation. The ability of the eye to clearly distinguish objects located at different distances is called accommodation. The phenomenon of accommodation is based on the reflex contraction or relaxation of the ciliary, or ciliary, muscle innervated by the parasympathetic fibers of the oculomotor nerve. Contraction and relaxation of the ciliary muscle changes the curvature of the lens:

a) when the muscle contracts, the ciliary ligament relaxes, which causes an increase in light refraction, because the lens becomes more convex. Such a contraction of the ciliary muscle, or visual tension, occurs when an object approaches the eye, that is, when viewing an object that is as close as possible;

b) when the muscle relaxes, the ciliary ligaments stretch, the lens bag squeezes it, the curvature of the lens decreases and its refraction decreases. This occurs when the object is removed from the eye, i.e., when looking into the distance.

The contraction of the ciliary muscle begins when an object approaches a distance of about 65 m, then its contractions increase and become distinct when an object approaches a distance of 10 m. Further, as the object approaches, the contractions of the muscles increase more and more and finally reach the limit at which clear vision becomes impossible. The minimum distance from an object to the eye at which it is clearly visible is called the nearest point of clear vision. In a normal eye, the far point of clear vision is at infinity.

Farsightedness and myopia. A healthy eye, when looking into the distance, refracts a beam of parallel rays so that they are focused in the central fovea. With myopia, parallel rays gather in focus in front of the fovea, diverging rays enter it and therefore the image of the object blurs. The causes of myopia may be tension in the ciliary muscle when accommodating close distances or the longitudinal axis of the eye being too long.

In farsightedness (due to a short longitudinal axis), parallel rays are focused behind the retina, and converging rays enter the fovea, which also causes blurred images.

Both vision defects can be corrected. Myopia is corrected by biconcave lenses, which reduce refraction and shift the focus to the retina; farsightedness - biconvex lenses that increase the refraction and therefore move the focus to the retina.

5.3. Light and color sensitivity. Light-receiving function

Under the action of light rays, a photochemical cleavage reaction of rhodopsin and iodopsin occurs, and the reaction rate depends on the wavelength of the beam. The splitting of rhodopsin in the light gives a light sensation (colorless), iodopsin - color. Rhodopsin is cleaved much faster than iodopsin (about 1000 times), so the excitability of rods to light is greater than that of cones. This allows you to see at dusk and in low light.

Rhodopsin consists of the protein opsin and oxidized vitamin A (retinene). Iodopsin also consists of a combination of retinene with the protein opsin, but of a different chemical composition. In the dark, with sufficient intake of vitamin A, the restoration of rhodopsin and iodopsin increases, therefore, with an excess of vitamin A (hypovitaminosis), a sharp deterioration in night vision occurs - hemeralopia. The difference in the rate of splitting of rhodopsin and iodopsin leads to a difference in the signals entering the optic nerve.

As a result of a photochemical reaction, the resulting excitation from the ganglion cells is transmitted along the optic nerve to the external geniculate bodies, where the primary signal processing takes place. Then the impulses are transmitted to the visual areas of the cerebral hemispheres, where they are decoded into visual images.

Color perception. The human eye perceives light rays of different wavelengths from 390 to 760 nm: red - 620-760, orange - 585-620, yellow - 575-585, green-yellow - 550-575, green - 510-550, blue - 480- 510, blue - 450-480, purple - 390-450. Light rays having a wavelength less than 390 nm and more than 760 nm are not perceived by the eye. The most widespread theory of color perception, the main provisions of which were first expressed by M.V. Lomonosov in 1756, and further developed by the English scientist Thomas Young (1802) and G.L.F. Helmholtz (1866) and confirmed by data from modern morphophysiological and electrophysiological studies, is as follows.

There are three types of cones, each of which contains only one color-reactive substance that is excitable to one of the primary colors (red, green or blue), as well as three groups of fibers, each of which conducts impulses from one type of cone. The color stimulus acts on all three types of cones, but to varying degrees. Different combinations of the degree of excitation of cones create different color sensations. With equal irritation of all three types of cones, a sensation of white color occurs. This theory is called the three-component color theory.

Features of vision coordination in newborns. A child is born seeing, but his clear, clear vision has not yet developed. In the first days after birth, children's eye movements are not coordinated. Thus, one can observe that the child’s right and left eyes move in opposite directions, or when one eye is immobile, the other moves freely. During the same period, uncoordinated movements of the eyelids and eyeball are observed (one eyelid may be open and the other lowered). The development of visual coordination occurs by the second month of life.

The lacrimal glands in a newborn are developed normally, but he cries without tears - there is no protective lacrimal reflex due to the underdevelopment of the corresponding nerve centers. Tears when crying in children appear after 1,2-2 months.

5.4. Light regime in educational institutions

As a rule, the educational process is closely associated with significant visual strain. A normal or slightly increased level of illumination of school premises (classrooms, classrooms, laboratories, educational workshops, assembly halls, etc.) helps to reduce the tension of the nervous system, maintain working capacity and maintain an active state of students.

Sunlight, in particular ultraviolet rays, promote the growth and development of the child's body, reduce the risk of the spread of infectious diseases, and provide the formation of vitamin D in the body.

With insufficient lighting in the classrooms, schoolchildren tilt their heads too low when reading, writing, etc. This causes increased blood flow to the eyeball, which puts additional pressure on it, which leads to a change in its shape and contributes to the development of myopia. To avoid this, it is desirable to ensure the penetration of direct sunlight into the school premises and strictly observe the rules of artificial lighting.

Daylight. The illumination of the student's and teacher's workplace by direct or reflected rays of the sun depends on several parameters: the location of the school building on the site (orientation), the interval between tall buildings, compliance with the natural illumination coefficient, and the light coefficient.

The natural illuminance coefficient (LKR) is the ratio of the illuminance (in lux) indoors to the illuminance at the same level outdoors, expressed as a percentage. This coefficient is considered the main indicator of classroom illumination. It is determined using a luxmeter. The minimum allowable KEO for classrooms in areas of central Russia is 1,5%. In northern latitudes, this coefficient is higher, in southern latitudes it is lower.

Light coefficient is the ratio of glass area in windows to floor area. In the classrooms and workshops of the school, it should be at least 1: 4, in the corridors and the gym - 1: 5, 1: 6, respectively, in auxiliary rooms - 1: 8, on landings - 1: 12.

The illumination of classrooms with natural light depends on the shape and size of the windows, their height, as well as on the external environment of the building (neighboring houses, green spaces).

Rounding the upper part of the window opening with one-sided lighting violates the ratio of the height of the window edge to the depth (width) of the room, which should be 1:2, i.e. the depth of the room should exceed twice the height from the floor to the upper edge of the window. In practice, this means: the higher the upper edge of the window, the more direct sunlight enters the room and the better the desks in the third row from the windows are lit.

To prevent the blinding effect of direct sunlight and overheating of the rooms, special visors are hung above the windows from the outside, and from the inside the room is shaded with light curtains. To prevent the blinding effect of reflected rays, it is not recommended to paint ceilings and walls with oil paints.

The color of the furniture also affects the illumination of the school premises, so the desks are painted in light colors or covered with light plastic. Dirty window panes and flowers on window sills reduce light. It is allowed to put flowers on window sills with a height (together with a flowerpot) of no more than 25-30 cm. Tall flowers are placed at the windows on stands, and so that their crown does not protrude above the window sill above 25-30 cm, or in piers on ladder stands or pots.

Artificial lighting. As sources of artificial lighting for school premises, incandescent lamps with a power of 250-350 W and fluorescent lamps of “white” light (SB type) with a power of 40 and 80 W are used. Fluorescent lamps of diffused light are suspended in rooms where the ceiling height is 3,3 m; for lower heights, ceiling lamps are used. All luminaires must be equipped with silent ballasts. The total power of fluorescent lamps in the classroom should be 1040 W, incandescent lamps - 2400 W, which is achieved by installing at least eight lamps of 130 W each for fluorescent lighting and eight lamps of 300 W each for incandescent lamps. Illumination rate (in watts) per 1 sq. m of classroom area (the so-called specific power) with fluorescent lamps is 21-22, with incandescent lamps - 42-48. The first corresponds to illumination of 300 lux, the second - 150 lux at the student’s workplace.

Mixed lighting (natural and artificial) does not affect the organs of vision. What can not be said about the simultaneous use of incandescent lamps and fluorescent lamps in the room, which have a different nature of the glow and color of the light flux.

5.5. auditory analyzer

The main function of the hearing organs is the perception of fluctuations in the air environment. The organs of hearing are closely connected with the organs of balance. The receptors of the auditory and vestibular systems are located in the inner ear.

Phylogenetically they have a common origin. Both receptor apparatuses are innervated by the fibers of the third pair of cranial nerves, both respond to physical indicators: the vestibular apparatus perceives angular accelerations, the auditory apparatus perceives air vibrations.

Auditory perceptions are very closely related to speech - a child who has lost his hearing in early childhood loses his speech ability, although his speech apparatus is absolutely normal.

In the embryo, the hearing organs develop from the auditory vesicle, which initially communicates with the outer surface of the body, but as the embryo develops, it laces off from the skin and forms three semicircular canals located in three mutually perpendicular planes. The part of the primary auditory vesicle that connects these canals is called the vestibule. It consists of two chambers - oval (uterus) and round (pouch).

In the lower part of the vestibule, a hollow protrusion, or tongue, is formed from thin membranous chambers, which is extended in the embryos and then twisted in the form of a cochlea. The tongue forms the organ of Corti (the perceiving part of the organ of hearing). This process occurs at the 12th week of intrauterine development, and at the 20th week myelination of the fibers of the auditory nerve begins. In the last months of intrauterine development, cell differentiation begins in the cortical section of the auditory analyzer, proceeding especially intensively in the first two years of life. The formation of the auditory analyzer ends by the age of 12-13.

Hearing organ. The human hearing organ consists of the outer ear, middle ear and inner ear. The outer ear serves to capture sounds; it is formed by the auricle and the external auditory canal. The auricle is formed by elastic cartilage, covered on the outside with skin. At the bottom, the auricle is supplemented by a skin fold - the lobe, which is filled with fatty tissue. Determining the direction of sound in humans is associated with binaural hearing, i.e. hearing with two ears. Any lateral sound reaches one ear before the other. The difference in time (several fractions of a millisecond) of arrival of sound waves perceived by the left and right ears makes it possible to determine the direction of the sound. When one ear is affected, a person determines the direction of sound by rotating the head.

The external auditory canal in an adult has a length of 2,5 cm, a capacity of 1 cu. see The skin lining the ear canal has fine hairs and modified sweat glands that produce earwax. They play a protective role. Earwax is made up of fat cells that contain pigment.

The outer and middle ear are separated by the tympanic membrane, which is a thin connective tissue plate. The thickness of the tympanic membrane is about 0,1 mm, on the outside it is covered with epithelium, and on the inside - with a mucous membrane. The tympanic membrane is located obliquely and begins to oscillate when sound waves hit it. Since the eardrum does not have its own period of oscillation, it fluctuates with any sound according to its wavelength.

The middle ear is a tympanic cavity, which has the shape of a small flat drum with a tightly stretched oscillating membrane and an auditory tube. In the cavity of the middle ear are the auditory ossicles - the hammer, anvil and stirrup. The handle of the malleus is woven into the eardrum; the other end of the malleus is connected to the anvil, and the latter, with the help of a joint, is movably articulated with the stirrup. The stirrup muscle is attached to the stirrup, which holds it against the membrane of the oval window, which separates the inner ear from the middle ear. The function of the auditory ossicles is to provide an increase in the pressure of a sound wave during transmission from the tympanic membrane to the membrane of the oval window. This increase (about 30-40 times) helps weak sound waves incident on the eardrum overcome the resistance of the oval window membrane and transmit vibrations to the inner ear, transforming there into endolymph vibrations.

The tympanic cavity is connected to the nasopharynx by means of an auditory (Eustachian) tube 3,5 cm long, very narrow (2 mm), maintaining the same pressure from the outside and inside on the tympanic membrane, thereby providing the most favorable conditions for its oscillation. The opening of the tube in the pharynx is most often in a collapsed state, and air passes into the tympanic cavity during the act of swallowing and yawning.

The inner ear is located in the stony part of the temporal bone and is a bony labyrinth, inside which there is a membranous labyrinth of connective tissue, which, as it were, is inserted into the bony labyrinth and repeats its shape. Between the bony and membranous labyrinths there is a fluid - perilymph, and inside the membranous labyrinth - endolymph. In addition to the oval window, there is a round window in the wall separating the middle ear from the inner ear, which makes it possible for the fluid to oscillate.

The bony labyrinth consists of three parts: in the center is the vestibule, in front of it is the cochlea, and behind it are the semicircular canals. Bone cochlea - a spirally meandering canal, forming two and a half turns around a conical rod. The diameter of the bone canal at the base of the cochlea is 0,04 mm, at the top - 0,5 mm. A bone spiral plate departs from the rod, which divides the canal cavity into two parts - stairs.

Inside the middle canal of the cochlea is the spiral (corti) organ. It has a basilar (main) plate, consisting of about 24 thousand thin fibrous fibers of various lengths. These fibers are very resilient and weakly bonded to each other. On the main plate along it in five rows are the supporting and hair sensitive cells - these are the auditory receptors.

The inner hair cells are arranged in one row, there are 3,5 thousand of them along the entire length of the membranous canal. The outer hair cells are arranged in three to four rows, there are 12-20 thousand of them. Each receptor cell has an elongated shape, it has 60-70 the smallest hairs (4-5 microns long). The hairs of the receptor cells are washed by the endolymph and come into contact with the integumentary plate, which hangs over them. Hair cells are covered by nerve fibers of the cochlear branch of the auditory nerve. The second neuron of the auditory pathway is located in the medulla oblongata; then the path goes, crossing, to the posterior tubercles of the quadrigemina, and from them to the temporal region of the cortex, where the central part of the auditory analyzer is located.

There are several auditory centers in the cerebral cortex. Some of them (lower temporal gyrus) are designed to perceive simpler sounds - tones and noises. Others are associated with the most complex sound sensations that arise when a person speaks himself, listens to speech or music.

Mechanism of sound perception. For the auditory analyzer, sound is an adequate stimulus. Sound waves arise as alternating condensations and rarefactions of air and propagate in all directions from the sound source. All vibrations of air, water or other elastic medium break down into periodic (tones) and non-periodic (noise).

Tones are high and low. Low tones correspond to a smaller number of vibrations per second. Each sound tone is characterized by a sound wave length, which corresponds to a certain number of oscillations per second: the greater the number of oscillations, the shorter the wavelength. For high sounds, the wave is short, it is measured in millimeters. The wavelength of low sounds is measured in meters.

The upper sound threshold in an adult is 20 Hz; the lowest is 000-12 Hz. Children have a higher upper limit of hearing - 24 Hz; in older people it is lower - about 22 Hz. The ear has the greatest susceptibility to sounds with an oscillation frequency ranging from 000 to 15 Hz. Below 000 Hz and above 1000 Hz, the excitability of the ear is greatly reduced.

In newborns, the middle ear cavity is filled with amniotic fluid. This makes it difficult for the auditory ossicles to vibrate. Over time, the liquid resolves, and instead of it, air enters from the nasopharynx through the Eustachian tube. A newborn child shudders at loud sounds, his breathing changes, he stops crying. Children's hearing becomes clearer by the end of the second - the beginning of the third month. After two months, the child differentiates qualitatively different sounds, at 3-4 months he distinguishes the pitch of the sound, at 4-5 months the sounds become conditioned reflex stimuli for him. By the age of 1-2, children distinguish sounds with a difference of one or two, and by four or five years - even 3/4 and 1/2 musical tones.

Hearing acuity is determined by the smallest sound intensity that causes a sound sensation. This is the so-called threshold of hearing. In an adult, the hearing threshold is 10-12 dB, in children 6-9 years old it is 17-24 dB, in children 10-12 years old - 14-19 dB. The greatest hearing acuity is achieved by the age of 14-19.

5.6. vestibular apparatus

The vestibular apparatus is located in the inner ear and consists of semicircular canals located in three mutually perpendicular planes, and two sacs (oval and round) lying closer to the cochlea. On the inner surface of the sacs there are hair cells. They are located in a gelatinous mass, which contains a large number of calcareous crystals - otoliths.

In the extensions of the semicircular canals (ampullae) there is one crescent-shaped bone crest each. The membranous labyrinth and an accumulation of supporting and sensory receptors, which are equipped with hairs, adjoin the scallop. The semicircular canals are filled with endolymph.

The stimuli of the otolithic apparatus are accelerating or slowing down movement of the body, shaking, pitching and tilting the body or head to the side, causing pressure of the otoliths on the hairs of the receptor cells. The stimulus of the receptors of the semicircular canals is an accelerated or slow rotational movement in any plane. Impulses coming from the otolithic apparatus and semicircular canals make it possible to analyze the position of the head in space and changes in the speed and direction of movements. Increased irritation of the vestibular apparatus is accompanied by an increase or slowdown in contractions of the heart, respiration, vomiting, and increased sweating. With increased excitability of the vestibular apparatus in conditions of sea rolling, signs of "seasickness" occur, which are characterized by the above vegetative disorders. Similar changes are observed when flying, traveling by train and car.

Topic 6. ANATOMICAL AND PHYSIOLOGICAL FEATURES OF BRAIN MATURATION

6.1. Development of the cerebral hemispheres and localization of functions in the cerebral cortex

Age-related changes in the structure of the brain. The brain of newborns and preschoolers is shorter and wider than that of schoolchildren and adults. Up to 4 years of age, the brain grows almost uniformly in length, width, and height, and from 4 to 7 years of age, its height increases especially rapidly. Individual lobes of the brain grow unevenly: the frontal and parietal lobes grow faster than the temporal and especially the occipital lobes. The average absolute brain weight in boys and girls is respectively (in grams):

▪ in newborns - 391 and 388;

▪ at 2 years - 1011 and 896;

▪ at 3 years - 1080 and 1068;

▪ at 5 years - 1154 and 1168;

▪ at 9 - 1270 and 1236.

By age 7, the weight of the brain corresponds to 4/5 of the weight of the brain in adults. After 9 years, the weight of the brain is added slowly, by the age of 20 it reaches the level of adults, and the brain has the greatest weight in 20-30 years.

Individual fluctuations in brain weight are 40-60%. This is due to variations in body weight in adults. From birth to adulthood, brain weight increases by about four times and body weight by 20 times. The cerebral hemispheres account for 80% of the total weight of the brain. With age, the ratio between the number of neurons and the number of glial cells changes: the relative number of neurons decreases, and the relative number of glial cells increases. In addition, the chemical composition of the brain and its water content also change. So, in the brain of a newborn, water is 91,5%, an eight-year-old child - 86,0%. The brain of adults differs from the brain of children in metabolism: it is half the size. At the age of 15 to 20 years, the lumen of the blood vessels of the brain increases.

The amount of cerebrospinal fluid in newborns is less than in adults (40-60 g), and the protein content is higher. In the future, from 8-10 years old, the amount of cerebrospinal fluid in children is almost the same as in adults, and the amount of proteins already from 6-12 months of development of the cerebral hemispheres in children corresponds to the level of adults. The development of neurons in the cerebral hemispheres precedes the appearance of furrows and convolutions. In the first months of life, they are present in both gray and white matter. The structure of the neurons of a three-year-old child does not differ from the neurons of an adult, however, the complication of their structure occurs up to 40 years. The number of neurons at birth is approximately the same as in adults, after birth only a small number of new highly differentiated neurons appear, and poorly differentiated neurons continue to divide.

Already at the beginning of the fourth month of intrauterine life, the large hemispheres are covered with visual tubercles, during this period there is only one impression on their surface - the future Sylvian furrow. There are cases when a three-month-old fetus has parieto-occipital and spur grooves. A five-month-old embryo has a sylvian, parietal-occipital, corpus callosum, and central sulcus. A six-month-old fetus has all the main furrows. Secondary furrows appear after 6 months of intrauterine life, tertiary furrows - at the end of intrauterine life. By the end of the seventh month of intrauterine development, the cerebral hemispheres cover the entire cerebellum. Asymmetry in the structure of the sulci in both hemispheres is observed already at the beginning of their laying and persists throughout the entire period of brain development.

Newborns have all primary, secondary and tertiary sulci, but they continue to develop after birth, especially up to 1-2 years. By the age of 7-12, the furrows and convolutions have the same appearance as in an adult.

Even in the prenatal period of life, children develop motor and musculoskeletal sensitivity, and then almost simultaneously - visual and auditory. The first to mature is a part of the premotor zone, which regulates the motor and secretory functions of the internal organs.

Development of the brain stem, cerebellum and limbic lobe. The formations of the brain stem develop unevenly; before birth, gray matter predominates in them, after birth - white matter. In the first two years of life, due to the development of automatic movements, the sagittal size of the caudate body and the lenticular nucleus increases twofold, the frontal size of the thalamus opticus and the lenticular nucleus increases threefold, and the caudate nucleus doubles. In a newborn, the volume of subcortical formations of the mentor zone (this includes the caudate body, putamen, substantia innominate, globus pallidus, corpus lewis, red nucleus, substantia nigra) is 19-40% in relation to an adult, and in a 7-year-old child - 94-98%. .

The visual hillock grows rather slowly. The development of the sagittal size of the thalamus lags behind, and only by the age of 13 does the sagittal size double. The development of the nuclei of the visual hillock occurs at different times: in the newborn, the median nuclei reach greater development, after birth, the lateral nuclei involved in the sensitivity of the skin develop faster. Accelerated growth of the thalamus is observed at the age of 4, by the age of 7 its structure is close to that of an adult, and at the age of 13 it reaches the size of an adult.

The surface of the lateral geniculate body in a newborn is 46% of its size in an adult, by 2 years - 74%, by 7 years - 96%. By this age, the size of the neurons of the internal geniculate body increases. The gray tubercle matures by 6 years, the nuclei that perform vegetative functions - by 7 years, secreting pituitary hormones - by 13-14 years, the central gray matter of the hypothalamic region completes its development by 13-17 years.

The hypothalamic region is formed in fetal life, but the development of its nuclei is completed at different ages. The hypothalamic region develops faster than the cerebral cortex. By the age of 3, the nuclei of the mammillary bodies and the Lewis bodies mature. The development of the hypothalamic region ends during puberty.

The red nucleus of the midbrain is formed together with its pathways before the pyramidal pathways. The substantia nigra of the midbrain becomes sufficiently developed by the age of 16. By the age of 5, the Varoliev bridge reaches the level at which it is located in an adult. The formation of the tender and sphenoid nuclei of the medulla oblongata is basically completed by the age of 6.

The formations of the medulla oblongata do not develop simultaneously. With age, the volume of neurons increases, and their number per unit area decreases. The maturation of the nuclei of the vagus nerves ends mainly by the age of 7. This is due to the development of coordination of movements and lungs.

In a newborn, the cerebellar vermis is more developed than its hemispheres, and the entire cerebellum weighs on average 21–23 g. It grows especially intensively in the first years of life, reaching 84–94 g by one year, and 15 g at 150 years. with the development of motor coordination. With age, the relative amount of gray matter decreases and the amount of white increases, which prevails over gray in schoolchildren and adults. The dentate nucleus grows especially intensively in the first year of life. The neurons of the cerebellar cortex complete their development at different times: basket neurons of the outer molecular layer - by one year, Purkinje neurons - by 8 years. The thickness of the molecular layer increases with age more than the thickness of the granular layer.

The cerebellar peduncles develop non-simultaneously and unevenly. The lower legs grow intensively in the first year of life, then their growth slows down. From 1 to 7 years there is a significant increase in the connection of the lower legs with the cerebellar hemispheres. The middle legs (the most developed), passing into the pons, grow intensively up to 2 years. The upper legs, starting in the dentate nucleus and ending in the red nucleus of the midbrain, which include centripetal and centrifugal fibers that connect the cerebellum with the visual tubercles, striatum and cerebral cortex, are fully formed at school age.

Although the limbic lobe develops faster than other areas of the neocortex, its surface in relation to the entire cortex of the hemisphere decreases with age: in a newborn it is 5,4%, at 2 years old - 3,9%, at 7 years old and in an adult - 3,4%.

Development of pathways. Particularly rapid development of projection pathways occurs after birth and up to 1 year; from 2 to 7 years, it gradually slows down; after 7 years, growth is very slow. As projection paths develop, asymmetry increases: centripetal paths are formed earlier than centrifugal ones. Myelination of some centrifugal tracts sometimes ends 4-10 years after birth.

First of all, projection paths are formed, then adhesive ones, then association ones. As you grow older, the association paths become wider and begin to prevail over the projection ones - this is due to the development of perceiving zones. The development of the corpus callosum directly depends on the development of the perceiving zones. The cingulate bundle is formed earlier than other association pathways. The uncinate bundle develops earlier than the upper longitudinal bundle.

6.2. Conditioned and unconditioned reflexes. I.P. Pavlov

Reflexes are the body's responses to external and internal stimuli. Reflexes are unconditional and conditional.

Unconditioned reflexes are congenital, permanent, hereditarily transmitted reactions inherent in representatives of this type of organism. The unconditioned include pupillary, knee, Achilles and other reflexes. Some unconditioned reflexes are carried out only at a certain age, for example, during the breeding season, and with the normal development of the nervous system. Such reflexes include sucking and motor reflexes, which are already present in an 18-week-old fetus.

Unconditioned reflexes are the basis for the development of conditioned reflexes in animals and humans. In children, as they grow older, they turn into synthetic complexes of reflexes that increase the adaptability of the body to environmental conditions.

Conditioned reflexes are adaptive reactions of the body, which are temporary and strictly individual. They occur in one or more representatives of a species that have been subjected to training (training) or exposure to the environment. The development of conditioned reflexes occurs gradually, in the presence of certain environmental conditions, for example, the repetition of a conditioned stimulus. If the conditions for the development of reflexes are constant from generation to generation, then conditioned reflexes can become unconditioned and be inherited in a number of generations. An example of such a reflex is the opening of the beak by blind and fledgling chicks in response to the shaking of the nest by a bird that comes to feed them.

Conducted by I.P. Pavlov, numerous experiments have shown that the basis for the development of conditioned reflexes are impulses coming through afferent fibers from extero- or interoreceptors. For their formation, the following conditions are necessary:

a) the action of an indifferent (in the future conditioned) stimulus must be earlier than the action of an unconditioned stimulus (for a defensive motor reflex, the minimum time difference is 0,1 s). In a different sequence, the reflex is not developed or is very weak and quickly fades;

b) the action of the conditioned stimulus for some time must be combined with the action of the unconditioned stimulus, i.e., the conditioned stimulus is reinforced by the unconditioned one. This combination of stimuli should be repeated several times.

In addition, a prerequisite for the development of a conditioned reflex is the normal function of the cerebral cortex, the absence of disease processes in the body and extraneous stimuli. Otherwise, in addition to the developed reinforced reflex, there will also be an orienting reflex, or a reflex of the internal organs (intestines, bladder, etc.).

The mechanism of formation of a conditioned reflex. An active conditioned stimulus always causes a weak focus of excitation in the corresponding area of ​​the cerebral cortex. The added unconditioned stimulus creates a second, stronger focus of excitation in the corresponding subcortical nuclei and the area of ​​the cerebral cortex, which distracts the impulses of the first (conditioned), weaker stimulus. As a result, a temporary connection arises between the foci of excitation of the cerebral cortex; with each repetition (i.e., reinforcement), this connection becomes stronger. The conditioned stimulus turns into a conditioned reflex signal.

To develop a conditioned reflex in a person, secretory, blinking or motor techniques with verbal reinforcement are used; in animals - secretory and motor techniques with food reinforcement.

The studies of I.P. Pavlov on the development of a conditioned reflex in dogs. For example, the task is to develop a reflex in a dog according to the salivation method, that is, to cause salivation to a light stimulus, reinforced by food - an unconditioned stimulus. First, the light is turned on, to which the dog reacts with an orienting reaction (turns its head, ears, etc.). Pavlov called this reaction the “what is it?” reflex. Then the dog is given food - an unconditioned stimulus (reinforcement). This is done several times. As a result, the orienting reaction appears less and less frequently, and then disappears altogether. In response to impulses that enter the cortex from two foci of excitation (in the visual zone and in the food center), the temporal connection between them is strengthened, as a result, the dog's saliva is released to the light stimulus even without reinforcement. This happens because a trace of the movement of a weak impulse towards a strong one remains in the cerebral cortex. The newly formed reflex (its arc) retains the ability to reproduce the conduction of excitation, i.e., to carry out a conditioned reflex.

The signal for the conditioned reflex can also be the trace left by the impulses of the present stimulus. For example, if you act on a conditioned stimulus for 10 seconds, and then a minute after it stops giving food, then the light itself will not cause a conditioned reflex separation of saliva, but a few seconds after it stops, a conditioned reflex will appear. Such a conditioned reflex is called a follow-up reflex. Trace conditioned reflexes develop with great intensity in children from the second year of life, contributing to the development of speech and thinking.

To develop a conditioned reflex, you need a conditioned stimulus of sufficient strength and high excitability of the cells of the cerebral cortex. In addition, the strength of the unconditioned stimulus must be sufficient, otherwise the unconditioned reflex will go out under the influence of a stronger conditioned stimulus. In this case, the cells of the cerebral cortex should be free from third-party stimuli. Compliance with these conditions accelerates the development of a conditioned reflex.

Classification of conditioned reflexes. Depending on the method of development, conditioned reflexes are divided into: secretory, motor, vascular, reflexes-changes in internal organs, etc.

The reflex, which is developed by reinforcing the conditioned stimulus with an unconditioned one, is called the first-order conditioned reflex. Based on it, you can develop a new reflex. For example, by combining a light signal with feeding, a dog has developed a strong conditioned salivation reflex. If a bell (sound stimulus) is given before the light signal, then after several repetitions of this combination, the dog begins to salivate in response to the sound signal. This will be a second-order reflex, or a secondary reflex, reinforced not by an unconditioned stimulus, but by a first-order conditioned reflex.

In practice, it has been established that on the basis of a secondary conditioned food reflex, it is not possible to develop conditioned reflexes of other orders in dogs. In children, it was possible to develop a sixth-order conditioned reflex.

To develop conditioned reflexes of higher orders, you need to "turn on" a new indifferent stimulus 10-15 seconds before the start of the action of the conditioned stimulus of the previously developed reflex. If the intervals are shorter, then a new reflex will not appear, and the one developed before will fade away, because inhibition will develop in the cerebral cortex.

6.3. Inhibition of conditioned reflexes

I.P. Pavlov identified two types of inhibition of conditioned reflexes - unconditioned (external) and conditioned (internal) inhibition.

Unconditional inhibition. The complete stop of a reflex that has begun or a decrease in its activity under the influence of changes in the external environment is called unconditioned inhibition. Under the influence of a new stimulus (noise penetrating from outside, changes in lighting, etc.), another (special) focus of excitation is created in the cerebral cortex, delaying or interrupting the reflex act that has begun. It was found that the younger the conditioned reflex, the easier it is to inhibit. This is due to the development of the induction process in the central nervous system. Since inhibition is caused by an external stimulus, Pavlov called it external, or inductive, inhibition. Unconditioned inhibition occurs suddenly, it is characteristic of the body from birth and is characteristic of the entire central nervous system.

External inhibition can be observed in children working in a team, when any noise penetrating into the room disrupts the course of the reflex act. For example, during the lesson, the children heard a sharp screech of car brakes. Students turn towards a strong stimulus, lose attention, balance and rational posture. As a result, errors, etc., are possible.

Unconditional inhibition can also occur without the appearance of a second focus of excitation. This happens with a decrease or complete cessation of the efficiency of the cells of the cerebral cortex due to the great strength of the stimulus. To prevent destruction, cells fall into a state of inhibition. This type of inhibition is called transcendent, it plays a protective role in the body.

Conditioned (internal) inhibition. This type of inhibition is characteristic of the higher parts of the central nervous system and develops only in the absence of reinforcement of the conditioned signal by an unconditioned stimulus, i.e., when two foci of excitation do not coincide in time. It is developed gradually during the process of ontogenesis, sometimes with great difficulty. Extinction and differentiation conditioned inhibition are distinguished.

Fading inhibition develops if the repetition of a conditioned signal is not reinforced by an unconditioned one. For example, a predator appears less often in those places where the amount of prey has decreased, because the previously developed conditioned reflex fades due to the lack of food reinforcement, which was a conditioned stimulus. This contributes to the adaptation of animals to changing living conditions.

6.4. Analytical and synthetic activity of the cerebral cortex

Many stimuli of the external world and the internal environment of the body are perceived by receptors and become sources of impulses that enter the cerebral cortex. Here they are analyzed, distinguished and synthesized, combined, generalized. The ability of the cortex to separate, isolate and distinguish between individual stimuli, to differentiate them is a manifestation of the analytical activity of the cerebral cortex.

First, stimuli are analyzed in receptors that specialize in light, sound stimuli, etc. The highest forms of analysis are carried out in the cerebral cortex. The analytical activity of the cerebral cortex is inextricably linked with its synthetic activity, expressed in the association, generalization of excitation that occurs in its various parts under the influence of numerous stimuli. As an example of the synthetic activity of the cerebral cortex, one can cite the formation of a temporary connection, which underlies the development of a conditioned reflex. Complex synthetic activity is manifested in the formation of reflexes of the second, third and higher orders. The generalization is based on the process of irradiation of excitation.

Analysis and synthesis are interconnected, and a complex analytical-synthetic activity takes place in the cortex.

dynamic stereotype. The external world acts on the body not through single stimuli, but usually through a system of simultaneous and sequential stimuli. If a system of successive stimuli is often repeated, this leads to the formation of systematicity, or a dynamic stereotype in the activity of the cerebral cortex. Thus, a dynamic stereotype is a sequential chain of conditioned reflex acts, carried out in a strictly defined, time-fixed order and resulting from a complex systemic reaction of the body to a complex system of positive (reinforced) and negative (non-reinforced, or inhibitory) conditioned stimuli.

The development of a stereotype is an example of the complex synthesizing activity of the cerebral cortex. A stereotype is difficult to develop, but if it is formed, then maintaining it does not require much effort of cortical activity, and many actions become automatic. The dynamic stereotype is the basis for the formation of habits in a person, the formation of a certain sequence in labor operations, the acquisition of skills and abilities. Walking, running, jumping, skiing, playing musical instruments, using a spoon, fork, knife, writing, etc. can serve as examples of a dynamic stereotype.

Stereotypes persist for many years and form the basis of human behavior, while they are very difficult to reprogram.

6.5. First and second signal systems

I.P. Pavlov considered human behavior as a higher nervous activity, where the analysis and synthesis of direct environmental signals, which constitute the first signal system of reality, are common to animals and humans. On this occasion, Pavlov wrote: “For an animal, reality is signaled almost exclusively only by stimuli and their traces in the cerebral hemispheres, directly coming to special cells of the visual, auditory and other receptors of the body. This is what we also have in ourselves as impressions, sensations and ideas from the surrounding external environment, both general natural and our social, excluding the word, audible and visible. This is the first signal system of reality that we have in common with animals. "

As a result of labor activity, social and family relations, a person has developed a new form of information transfer. A person began to perceive verbal information through understanding the meaning of words spoken by himself or others, visible - written or printed. This led to the emergence of a second signaling system, unique to man. It significantly expanded and qualitatively changed the higher nervous activity of a person, as it introduced a new principle into the work of the cerebral hemispheres (the relationship of the cortex with subcortical formations). On this occasion, Pavlov wrote: “If our sensations and ideas related to the world around us are the first signals of reality, concrete signals, then speech, especially especially kinesthetic stimuli that go to the cortex from the speech organs, are the second signals, signals of signals. They represent a distraction from reality and allow for generalization, which is ... specifically human thinking, and science is a tool for the highest orientation of a person in the world around him and in himself.

The second signaling system is the result of human sociality as a species. However, it should be remembered that the second signaling system is dependent on the first signaling system. Children born deaf make the same sounds as normal ones, but without reinforcing the emitted signals through auditory analyzers and not being able to imitate the voice of others, they become dumb.

It is known that without communication with people, the second signaling system (especially speech) does not develop. So, children who were carried away by wild animals and lived in an animal den (Mowgli's syndrome) did not understand human speech, did not know how to speak, and lost the ability to learn to speak. In addition, it is known that young people who have been isolated for decades, without communicating with other people, forget colloquial speech.

The physiological mechanism of human behavior is the result of a complex interaction of both signaling systems with subcortical formations of the cerebral hemispheres. Pavlov considered the second signaling system "the highest regulator of human behavior", prevailing over the first signaling system. But the latter, to a certain extent, controls the activity of the second signaling system. This allows a person to control his unconditioned reflexes, to restrain a significant part of the instinctive manifestations of the body and emotions. A person can consciously suppress defensive (even in response to painful stimuli), food and sexual reflexes. At the same time, subcortical formations and nuclei of the brain stem, especially the reticular formation, are sources (generators) of impulses that maintain normal brain tone.

6.6. Types of higher nervous activity

Conditioned reflex activity depends on the individual properties of the nervous system. The individual properties of the nervous system are due to the hereditary characteristics of the individual and his life experience. The totality of these properties is called the type of higher nervous activity.

I.P. Pavlov, on the basis of many years of studying the features of the formation and course of conditioned reflexes in animals, identified four main types of higher nervous activity. He based the division into types on three main indicators:

a) the strength of the processes of excitation and inhibition;

b) mutual balance, i.e., the ratio of the strength of the processes of excitation and inhibition;

c) the mobility of the processes of excitation and inhibition, i.e., the speed with which excitation can be replaced by inhibition, and vice versa.

Based on the manifestation of these three properties, Pavlov distinguished the following types of nervous activity;

1) the type is strong, unbalanced, with a predominance of excitation over inhibition ("unrestrained" type);

2) the type is strong, balanced, with great mobility of nervous processes ("live", mobile type);

3) the type is strong, balanced, with low mobility of nervous processes ("calm", inactive, inert type);

4) weak type, characterized by rapid exhaustion of nerve cells, leading to loss of efficiency.

Pavlov believed that the main types of higher nervous activity found in animals coincide with the four temperaments established for people by the Greek physician Hippocrates (XNUMXth century BC). The weak type corresponds to the melancholic temperament; strong unbalanced type - choleric temperament; strong balanced, mobile type - sanguine temperament; strong balanced, with low mobility of nervous processes - phlegmatic temperament. However, it should be borne in mind that the nervous processes undergo changes as the human body develops, therefore, at different age periods, a person may change the types of nervous activity. Such short-term transitions are possible under the influence of strong stress factors.

Depending on the interaction, the balance of the signaling systems, Pavlov, along with four types common to humans and animals, singled out specifically human types of higher nervous activity.

1. Artistic type. It is characterized by the predominance of the first signal system over the second. This type includes people who directly perceive reality, widely using sensory images.

2. Thinking type. This type includes people with a predominance of the second signal system, "thinkers" with a pronounced ability for abstract thinking.

3. Most people are of the average type with a balanced activity of the two signal systems. They are characterized by both figurative impressions and speculative conclusions.

Topic 7. AGE FEATURES OF BLOOD AND CIRCULATION

7.1. General characteristics of blood

Blood, lymph and tissue fluid are the internal environment of the body in which the vital activity of cells, tissues and organs is carried out. The internal environment of a person retains the relative constancy of its composition, which ensures the stability of all body functions and is the result of reflex and neurohumoral self-regulation. Blood, circulating in the blood vessels, performs a number of vital functions: transport (transports oxygen, nutrients, hormones, enzymes, and also delivers residual metabolic products to the excretory organs), regulatory (maintains a relatively constant body temperature), protective (blood cells provide immune responses).

Amount of blood. Deposited and circulating blood. The amount of blood in an adult is on average 7% of body weight, in newborns - from 10 to 20% of body weight, in infants - from 9 to 13%, in children from 6 to 16 years old - 7%. The younger the child, the higher his metabolism and the greater the amount of blood per 1 kg of body weight. Newborns have 1 cubic meters per 150 kg of body weight. cm of blood, in infants - 110 cubic meters. cm, for children from 7 to 12 years old - 70 cubic meters. cm, from 15 years old - 65 cubic meters. cm. The amount of blood in boys and men is relatively greater than in girls and women. At rest, approximately 40-45% of the blood circulates in the blood vessels, and the rest is in the depot (capillaries of the liver, spleen and subcutaneous tissue). Blood from the depot enters the general bloodstream when body temperature rises, muscle work, rise to altitude, and blood loss. Rapid loss of circulating blood is life-threatening. For example, with arterial bleeding and loss of 1/3-1/2 of the total amount of blood, death occurs due to a sharp drop in blood pressure.

Blood plasma. Plasma is the liquid part of the blood after all the formed elements have been separated. In adults it accounts for 55-60% of the total blood volume, in newborns it is less than 50% due to the large volume of red blood cells. The blood plasma of an adult contains 90-91% water, 6,6-8,2% proteins, of which 4-4,5% albumin, 2,8-3,1% globulin and 0,1-0,4%. fibrinogen; the rest of the plasma consists of minerals, sugar, metabolic products, enzymes, and hormones. The protein content in the plasma of newborns is 5,5-6,5%, in children under 7 years old - 6-7%.

With age, the amount of albumin decreases, and globulins increase, the total protein content approaches the level of adults by 3-4 years. Gamma globulins reach the adult norm by 3 years, alpha and beta globulins - by 7 years. The content of proteolytic enzymes in the blood after birth increases and by the 30th day of life reaches the level of adults.

Mineral substances of the blood include table salt (NaCl), 0,85-0,9%, potassium chloride (KC1), calcium chloride (CaCl12) and bicarbonates (NaHCO3), 0,02% each, etc. In newborns, the amount of sodium less than in adults, and reaches the norm by 7-8 years. From 6 to 18 years, the sodium content ranges from 170 to 220 mg%. The amount of potassium, on the contrary, is the highest in newborns, the lowest - at 4-6 years old and reaches the norm of adults by 13-19 years old.

The content of calcium in plasma in newborns is higher than in adults; from 1 to 6 years old it fluctuates, and from 6 to 18 years old it stabilizes at the level of adults.

Boys 7-16 years old have more inorganic phosphorus than adults, 1,3 times; organic phosphorus is more than inorganic, 1,5 times, but less than in adults.

The amount of glucose in the blood of an adult on an empty stomach is 0,1-0,12%. The amount of sugar in the blood in children (mg%) on an empty stomach: in newborns - 45-70; in children 7-11 years old - 70-80; 12-14 years old - 90-120. The change in blood sugar in children 7-8 years old is much greater than in 17-18 years old. Significant fluctuations in blood sugar during puberty. With intensive muscular work, the level of sugar in the blood decreases.

In addition, the blood plasma contains various nitrogenous substances, amounting to 20-40 mg per 100 cubic meters. see blood; 0,5-1,0% fat and fat-like substances.

The viscosity of the blood of an adult is 4-5, a newborn - 10-11, a child of the first month of life - 6, then a gradual decrease in viscosity is observed. The active reaction of the blood, depending on the concentration of hydrogen and hydroxide ions, is slightly alkaline. The average blood pH is 7,35. When acids formed in the process of metabolism enter the blood, they are neutralized by a reserve of alkalis. Some acids are removed from the body, for example, carbon dioxide is converted into carbon dioxide and water vapor, exhaled during increased ventilation of the lungs. With excessive accumulation of alkaline ions in the body, for example, with a vegetarian diet, they are neutralized by carbonic acid, which is delayed by a decrease in lung ventilation.

7.2. Formed elements of blood

The formed elements of blood include erythrocytes, leukocytes and platelets. Erythrocytes are non-nucleated red blood cells. They have a biconcave shape, which increases their surface by approximately 1,5 times. The number of red blood cells in 1 cubic meter. mm of blood is equal to: in men - 5-5,5 million; in women - 4-5,5 million. In newborns on the first day of life, their number reaches 6 million, then a decrease occurs to the adult norm. At 7-9 years old, the number of red blood cells is 5-6 million. The greatest fluctuations in the number of red blood cells are observed during puberty.

In adult erythrocytes, hemoglobin makes up about 32% of the weight of formed elements and, on average, 14% of the weight of whole blood (14 g per 100 g of blood). This amount of hemoglobin is equal to 100%. The content of hemoglobin in the erythrocytes of newborns reaches 14,5% of the adult norm, which is 17-25 g of hemoglobin per 100 g of blood. In the first two years, the amount of hemoglobin drops to 80-90%, and then again increases to normal. The relative content of hemoglobin increases with age and by the age of 14-15 reaches the adult norm. It is equal (in grams per 1 kg of body weight):

▪ at 7-9 years old - 7,5;

▪ 10-11 years old - 7,4;

▪ 12-13 years old - 8,4;

▪ 14-15 years old - 10,4.

Hemoglobin is species specific. If in a newborn it absorbs more oxygen than in an adult (and from the age of 2 this ability of hemoglobin is maximum), then from the age of 3 hemoglobin absorbs oxygen in the same way as in adults. A significant content of erythrocytes and hemoglobin, as well as a greater ability of hemoglobin to absorb oxygen in children under 1 year old, provide them with a more intensive metabolism.

With age, the amount of oxygen in arterial and venous blood increases. 0no equals (in cubic cm per minute): in children 5-6 years old in arterial blood - 400, in venous - 260; in adolescents 14-15 years old - 660 and 435, respectively; in adults - 800 and 540, respectively. The oxygen content in arterial blood (in cubic cm per 1 kg of weight per minute) is: in children 5-6 years old - 20; in adolescents 14-15 years old - 13; in adults - 11. This phenomenon in preschoolers is explained by the relatively large amount of blood and blood flow, significantly exceeding the blood flow of adults.

In addition to carrying oxygen, erythrocytes are involved in enzymatic processes, in maintaining an active blood reaction, and in the exchange of water and salts. During the day, from 300 to 2000 cubic meters pass through the erythrocytes. dm of water.

In the process of settling whole blood, to which substances that prevent blood clotting are added, erythrocytes gradually settle. The rate of erythrocyte sedimentation reaction (ESR) in men is 3-9 mm, in women - 7-12 mm per hour. S0E depends on the amount of proteins in the blood plasma and on the ratio of globulins to albumins. Since a newborn has about 6% of proteins in plasma and the ratio of globulins to albumins is also less than in adults, their ESR is about 2 mm, in infants it is 4-8 mm, and in older children it is 4-8 mm in hour. After a training load, in most children 7-11 years old, normal (up to 12 mm per hour) and slow ESR accelerate, and accelerated ESR slows down.

Hemolysis. Red blood cells are able to survive only in physiological solutions, in which the concentration of minerals, especially table salt, is the same as in blood plasma. In solutions where the sodium content is less or more than in the blood plasma, as well as under the influence of other factors, red blood cells are destroyed. The destruction of red blood cells is called hemolysis.

The ability of red blood cells to resist hemolysis is called resistance. With age, the resistance of erythrocytes decreases significantly: the erythrocytes of newborns have the greatest resistance, by the age of 10 it decreases by about 1,5 times.

In a healthy body, there is a constant process of destruction of red blood cells, which is carried out under the influence of special substances - hemolysins produced in the liver. Red blood cells live in a newborn for 14, and in an adult - no more than 100-150 days. Hemolysis occurs in the spleen and liver. Simultaneously with hemolysis, new erythrocytes are formed, so the number of erythrocytes is maintained at a relatively constant level.

Blood groups. Depending on the content of two types of adhesive substances (agglutinogens A and B) in erythrocytes, and two types of agglutinins (alpha and beta) in plasma, four blood groups are distinguished. When transfusing blood, it is necessary to avoid matching A with alpha and B with beta, because agglutination occurs, leading to blockage of blood vessels and preceding hemolysis in the recipient, and therefore leading to his death.

The erythrocytes of the first group (0) do not stick together with the plasma of other groups, which allows them to be administered to all people. People who have the first blood type are called universal donors. The plasma of the fourth group (AB) does not stick together red blood cells of other groups, therefore people with this blood type are universal recipients. Blood of the second group (A) can be transfused only to groups A and AB, blood of group B - only to B and AB. The blood group is genetically determined.

In addition, the agglutinogen Rh factor (Rh) is of particular importance in the practice of blood transfusion. The red blood cells of 85% of people contain the Rh factor (Rh-positive), while the red blood cells of 15% of people do not contain it (Rh-negative).

leukocytes. These are colorless nucleated blood cells. In an adult, 1 cu. mm of blood contains 6-8 thousand leukocytes. Based on the shape of the cell and nucleus, leukocytes are divided into: neutrophils; basophils; eosinophils; lymphocytes; monocytes.

Unlike adults, newborns in 1 cu. mm of blood contains 10-30 thousand leukocytes. The largest number of leukocytes is observed in children aged 2-3 months, and then it gradually decreases in waves and reaches the level of adults by the age of 10-11.

In children under 9-10 years of age, the relative content of neutrophils is significantly lower than in adults, and the number of lymphocytes is sharply increased up to 14-15 years. Up to 4 years, the absolute number of lymphocytes exceeds the number of neutrophils by about 1,5-2 times, from 4 to 6 years, the number of neutrophils and lymphocytes is first compared, and then neutrophils begin to predominate over lymphocytes, and from the age of 15 their ratio approaches the norms of adults. Leukocytes live up to 12-15 days.

Unlike erythrocytes, the content of leukocytes varies greatly. There is an increase in the total number of leukocytes (leukocytosis) and their decrease (leukopenia). Leukocytosis is observed in healthy people during muscular work, in the first 2-3 hours after eating and in pregnant women. In a lying person, leukocytosis is twice as high as in a standing person. Leukopenia occurs under the action of ionizing radiation. Some diseases change the relative content of different forms of leukocytes.

Platelets. These are the smallest nuclear-free plates of protoplasm. In adults, 1 cu. mm of blood contains 200-100 thousand platelets, in children under 1 year - 160-330 thousand; from 3 to 4 years - 350-370 thousand. Platelets live 4-5 and no more than 8-9 days. Platelet solids contain 16-19% lipids (mainly phosphatides), proteolytic enzymes, serotonin, coagulation factors and retractin. An increase in the number of platelets is called thrombocytosis, a decrease is called thrombopenia.

7.3. Circulation

Blood is able to perform vital functions only while in constant motion. The movement of blood in the body, its circulation constitute the essence of blood circulation.

The circulatory system maintains the constancy of the internal environment of the body. Thanks to blood circulation, oxygen, nutrients, salts, hormones, water are supplied to all organs and tissues and metabolic products are excreted from the body. Due to the low thermal conductivity of tissues, heat transfer from the organs of the human body (liver, muscles, etc.) to the skin and to the environment is carried out mainly due to blood circulation. The activity of all organs and the body as a whole is closely related to the function of the circulatory organs.

Systemic and pulmonary circulation. Blood circulation is ensured by the activity of the heart and blood vessels. The vascular system consists of two circles of blood circulation: large and small.

The systemic circulation begins from the left ventricle of the heart, from where blood enters the aorta. From the aorta, the path of arterial blood continues through the arteries, which, as they move away from the heart, branch, and the smallest of them break up into capillaries, penetrating the entire body in a dense network. Through the thin walls of the capillaries, the blood gives off nutrients and oxygen to the tissue fluid. In this case, the waste products of cells from the tissue fluid enter the blood. From the capillaries, blood flows into small veins, which, merging, form larger veins and flow into the superior and inferior vena cava. The superior and inferior vena cava bring venous blood to the right atrium, where the systemic circulation ends.

The pulmonary circulation begins from the right ventricle of the heart with the pulmonary artery. Venous blood is carried through the pulmonary artery to the capillaries of the lungs. In the lungs, there is an exchange of gases between the venous blood of the capillaries and the air in the alveoli of the lungs. From the lungs through the four pulmonary veins, arterial blood already returns to the left atrium, where the pulmonary circulation ends. From the left atrium, blood enters the left ventricle, from where the systemic circulation begins.

7.4. Heart: structure and age-related changes

The heart is a hollow muscular organ divided into four chambers: two atria and two ventricles. The left and right sides of the heart are separated by a solid septum. Blood from the atria enters the ventricles through openings in the septum between the atria and ventricles. The holes are equipped with valves that open only towards the ventricles. Valves are formed by interlocking flaps and therefore are called flap valves. The left side of the heart has a bicuspid valve, while the right side has a tricuspid valve.

Semilunar valves are located at the site of exit of the aorta from the left ventricle and the pulmonary artery from the right ventricle. The semilunar valves allow blood to pass from the ventricles to the aorta and pulmonary artery and prevent the back flow of blood from the vessels to the ventricles.

The valves of the heart ensure the movement of blood in only one direction: from the atria to the ventricles and from the ventricles to the arteries.

The mass of the human heart is from 250 to 360 g.

The expanded upper part of the heart is called the base, the narrowed lower part is called the apex. The heart lies obliquely behind the sternum. Its base is directed back, up and to the right, and the top is directed down, forward and to the left. The apex of the heart is adjacent to the anterior chest wall in the area near the left intercostal space; here, at the moment of contraction of the ventricles, a cardiac impulse is felt.

The bulk of the wall of the heart is a powerful muscle - the myocardium, consisting of a special kind of striated muscle tissue. The thickness of the myocardium is different in different parts of the heart. It is thinnest in the atria (2-3 mm). The left ventricle has the most powerful muscular wall: it is 2,5 times thicker than in the right ventricle.

Typical and atypical musculature of the heart. The bulk of the cardiac muscle is represented by fibers typical of the heart, which ensure contraction of the heart’s parts. Their main function is contractility. This is the typical working muscle of the heart. In addition to it, the cardiac muscle contains atypical fibers, the activity of which is associated with the occurrence of excitation in the heart and the conduction of excitation from the atria to the ventricles.

Atypical muscle fibers differ from contractile fibers both in structure and in physiological properties. They have less pronounced transverse striation, but they have the ability to be easily excited and more resistant to harmful influences. For the ability of the fibers of atypical muscles to conduct the resulting excitation through the heart, it is called the conduction system of the heart.

Atypical musculature occupies a very small part of the heart in terms of volume. The accumulation of atypical muscle cells is called nodes. One of these nodes is located in the right atrium, near the confluence (sinus) of the superior vena cava. This is the sinoatrial node. Here, in the heart of a healthy person, excitation impulses arise that determine the rhythm of heart contractions. The second node is located on the border between the right atrium and the ventricles in the septum of the heart, it is called the atrioventricular, or atrioventricular, node. In this region of the heart, excitation spreads from the atria to the ventricles.

From the atrioventricular node, excitation is directed along the atrioventricular bundle (Hiss bundle) of the fibers of the conduction system, which is located in the septum between the ventricles. The trunk of the atrioventricular bundle is divided into two legs, one of them goes to the right ventricle, the other to the left.

Excitation from atypical muscles is transmitted to the fibers of the contractile muscles of the heart with the help of fibers related to atypical muscles.

Age-related changes in the heart. After birth, a child’s heart not only grows, but also undergoes morphological processes (shape and proportions change). The newborn's heart occupies a transverse position and has an almost spherical shape. The relatively large liver makes the vault of the diaphragm high, so the position of the heart in a newborn is higher (it is located at the level of the fourth left intercostal space). By the end of the first year of life, under the influence of sitting and standing and due to the lowering of the diaphragm, the heart takes an oblique position. By 2-3 years, the apex of the heart reaches the fifth rib. In ten-year-old children, the boundaries of the heart become almost the same as in adults.

During the first year of life, the growth of the atria outstrips the growth of the ventricles, then they grow almost equally, and after 10 years, the growth of the ventricles begins to overtake the growth of the atria.

Children's hearts are relatively larger than those of adults. Its mass is approximately 0,63-0,80% of body weight, in an adult - 0,48-0,52%. The heart grows most intensively in the first year of life: by 8 months, the mass of the heart doubles, triples by 3 years, quadruples by 5 years, and 16 times by 11 years.

The mass of the heart in boys in the first years of life is greater than in girls. At the age of 12-13, a period of increased heart growth begins in girls, and its mass becomes larger than in boys. By the age of 16, the heart of girls again begins to lag behind the heart of boys in mass.

Cardiac cycle. The heart contracts rhythmically: contractions of the heart parts (systole) alternate with their relaxation (diastole). The period covering one contraction and one relaxation of the heart is called the cardiac cycle. In a state of relative rest, the adult heart beats approximately 75 times per minute. This means that the entire cycle lasts about 0,8 s.

Each cardiac cycle consists of three phases:

1) atrial systole (lasts 0,1 s);

2) ventricular systole (lasts 0,3 s);

3) total pause (0,4 s).

With great physical exertion, the heart contracts more often than 75 times per minute, while the duration of the total pause decreases.

Topic 8. AGE CHARACTERISTICS OF THE RESPIRATORY ORGANS

8.1. The structure of the respiratory and vocal apparatus

nasal cavity. When you breathe with your mouth closed, air enters the nasal cavity, and when you breathe open, it enters the oral cavity. The formation of the nasal cavity involves bones and cartilage, which also make up the nasal skeleton. Most of the mucous membrane of the nasal cavity is covered with multirow ciliated columnar epithelium, which contains mucous glands, and its smaller part contains olfactory cells. Thanks to the movement of the cilia of the ciliated epithelium, dust that enters with inhaled air is expelled out.

The nasal cavity is divided in half by the nasal septum. Each half has three turbinates - upper, middle and lower. They form three nasal passages: the upper one is under the upper concha, the middle one is under the middle concha, and the lower one is between the lower concha and the bottom of the nasal cavity. The inhaled air enters through the nostrils and, after passing through the nasal passages of each half of the nasal cavity, exits it into the nasopharynx through two posterior openings - the choanae.

The nasolacrimal canal opens into the nasal cavity, through which excess tears are excreted.

Adjacent to the nasal cavity are adnexal cavities, or sinuses connected to it by openings: maxillary, or maxillary (located in the body of the upper jaw), sphenoid (in the sphenoid bone), frontal (in the frontal bone) and ethmoid labyrinth (in the ethmoid bone). The inhaled air, in contact with the mucous membrane of the nasal cavity and adnexal cavities, in which there are numerous capillaries, is warmed and moistened.

Larynx. The nasopharynx is the upper part of the pharynx that conducts air from the nasal cavity to the larynx, which is attached to the hyoid bone. The larynx forms the initial part of the respiratory tube itself, which continues into the trachea, and at the same time functions as a voice apparatus. It consists of three unpaired and three paired cartilages, connected by ligaments. The unpaired cartilages include the thyroid, cricoid and epiglottis cartilages, and the paired cartilages include the arytenoid, corniculate and sphenoid. The main cartilage is the cricoid. Its narrow part is facing anteriorly, and its wide part is facing the esophagus. At the back of the cricoid cartilage, two triangular arytenoid cartilages are located symmetrically on the right and left sides, movably articulated with its posterior part. When the muscles contracting, pulling back the outer ends of the arytenoid cartilages, and the intercartilaginous muscles relax, these cartilages rotate around their axis and the glottis opens wide, necessary for inhalation. With contraction of the muscles between the arytenoid cartilages and tension of the ligaments, the glottis looks like two tightly stretched parallel muscle ridges, preventing the flow of air from the lungs.

Vocal cords. The true vocal cords are located in the sagittal direction from the internal angle of the junction of the plates of the thyroid cartilage to the vocal processes of the arytenoid cartilages. The true vocal cords include the internal thyroarytenoid muscles. A certain relationship is established between the degree of tension of the vocal cords and the pressure of air from the lungs: the stronger the ligaments are closed, the more pressure the air escaping from the lungs puts on them. This regulation is carried out by the muscles of the larynx and is important for the formation of sounds.

When swallowing, the entrance to the larynx is closed by the epiglottis. The mucous membrane of the larynx is covered with multi-row ciliated epithelium, and the vocal cords - with stratified squamous epithelium.

In the mucous membrane of the larynx there are various receptors that perceive tactile, temperature, chemical and pain stimuli; they form two reflex zones. Part of the laryngeal receptors is located superficially, where the mucous membrane covers the cartilage, and the other part is deep in the perichondrium, at the points of muscle attachment, in the pointed parts of the vocal processes. Both groups of receptors are located on the path of the inhaled air and are involved in the reflex regulation of breathing and in the protective reflex of closing the glottis. These receptors, signaling changes in the position of the cartilage and contractions of the muscles involved in voice formation, reflexively regulate it.

Trachea. The larynx passes into the windpipe, or trachea, which in an adult is 11-13 cm long and consists of 15-20 half-rings of hyaline cartilage connected by membranes of connective tissue. The cartilages are not closed at the back, so the esophagus, located behind the trachea, can enter its lumen when swallowing. The mucous membrane of the trachea is covered with multirow ciliated epithelium, the cilia of which create a flow of fluid secreted by the glands towards the pharynx; it removes dust particles settled from the air. The powerful development of elastic fibers prevents the formation of folds of the mucous membrane, which reduce the access of air. In the fibrous membrane, located outward from the cartilaginous half-rings, there are blood vessels and nerves.

Bronchi. The trachea branches into two main bronchi; each of them enters the gate of one of the lungs and divides into three branches in the right lung, consisting of three lobes, and two branches in the left lung, consisting of two lobes. These branches split into smaller ones. The wall of the large bronchi has the same structure as the trachea, but it contains closed cartilaginous rings; There are smooth muscle fibers in the wall of the small bronchi. The inner lining of the bronchi consists of ciliated epithelium.

The smallest bronchi - up to 1 mm in diameter - are called bronchioles. Each bronchiole is part of a lung lobule (lung lobes are made up of hundreds of lobules). The bronchiole in the lobule is divided into 12-18 terminal bronchioles, which, in turn, are divided into alveolar bronchioles.

Finally, the alveolar bronchioles branch into alveolar ducts, which are made up of alveoli. The thickness of the epithelial layer of the alveoli is 0,004 mm. The capillaries are attached to the alveoli. Gas exchange occurs through the walls of the alveoli and capillaries. The number of alveoli is approximately 700 million. The total surface of all alveoli in a man is up to 130 square meters. m, for a woman - up to 103,5 sq. m.

Outside, the lungs are covered with an airtight serous membrane, or visceral pleura, which passes into the pleura that covers the inside of the chest cavity - the parietal, or parietal, pleura.

8.2. Breathing movements. Acts of inhalation and exhalation

Due to the rhythmically performed acts of inhalation and exhalation, an exchange of gases takes place between atmospheric and alveolar air located in the pulmonary vesicles. There is no muscle tissue in the lungs, so they cannot actively contract. An active role in the act of inhalation and exhalation belongs to the respiratory muscles. With paralysis of the respiratory muscles, breathing becomes impossible, although the respiratory organs are not affected.

When inhaling, the external intercostal muscles and the diaphragm contract. The intercostal muscles lift the ribs and take them somewhat to the side, while the volume of the chest increases. When the diaphragm contracts, its dome flattens, which also leads to an increase in the volume of the chest. Other muscles of the chest and neck also take part in deep breathing. The lungs, being in a hermetically sealed chest, are passive and follow its moving walls during inhalation and exhalation, since they are attached to the chest with the help of the pleura. This is also facilitated by negative pressure in the chest cavity: negative pressure is called pressure below atmospheric. During inspiration, the pressure in the chest cavity is lower than atmospheric by 9-12 mm Hg. Art., and during exhalation - by 2-6 mm Hg. Art.

During development, the chest grows faster than the lungs, so the lungs are constantly (even when exhaling) stretched. The stretched elastic lung tissue tends to shrink. The force with which lung tissue is compressed counteracts atmospheric pressure. Around the lungs, in the pleural cavity, pressure is created equal to atmospheric pressure minus the elastic recoil of the lungs. This creates negative pressure around the lungs. Due to it, in the pleural cavity, the lungs follow the expanded chest; the lungs are stretched. In a distended lung, the pressure becomes lower than atmospheric pressure, due to which atmospheric air rushes into the lungs through the respiratory tract. The more the volume of the chest increases during inhalation, the more the lungs are stretched and the deeper the inhalation.

When the respiratory muscles relax, the ribs descend to their original position, the dome of the diaphragm rises, the volume of the chest and lungs decreases, and air is exhaled outward. In a deep exhalation, the abdominal muscles, internal intercostal and other muscles take part.

Types of breathing. In young children, the ribs have a slight bend and occupy an almost horizontal position. The upper ribs and the entire shoulder girdle are located high, the intercostal muscles are weak. Therefore, in newborns, diaphragmatic breathing predominates with little participation of the intercostal muscles. This type of breathing persists until the second half of the first year of life. As the intercostal muscles develop and the child grows, the chest moves down and the ribs take on an oblique position. The breathing of infants now becomes thoraco-abdominal with a predominance of diaphragmatic breathing.

At the age of 3 to 7 years, due to the development of the shoulder girdle, the chest type of breathing begins to predominate, and by the age of 7 it becomes pronounced.

At the age of 7-8, gender differences in the type of breathing begin: in boys, the abdominal type of breathing becomes predominant, in girls - chest. The sexual differentiation of respiration ends by the age of 14-17.

Respiration depth and frequency. The unique structure of the chest and the low endurance of the respiratory muscles make breathing movements in children less deep and frequent. An adult makes an average of 15-17 breathing movements per minute; in one breath during quiet breathing, he inhales 500 ml of air. During muscular work, breathing increases 2-3 times. In trained people, during the same work, the volume of pulmonary ventilation gradually increases, as breathing becomes rarer and deeper. During deep breathing, 80-90% of the alveolar air is ventilated. This ensures greater diffusion of gases through the alveoli. With shallow and frequent breathing, ventilation of the alveolar air is much less and a relatively large part of the inhaled air remains in the so-called dead space - in the nasopharynx, oral cavity, trachea, and bronchi. Thus, in trained people, the blood is more saturated with oxygen than in untrained people.

The depth of breathing is characterized by the volume of air entering the lungs in one breath - respiratory air. The breathing of a newborn is frequent and shallow, while its frequency is subject to significant fluctuations: 48-63 respiratory cycles per minute during sleep. The frequency of respiratory movements per minute during wakefulness is: 50-60 - in children of the first year of life; 35-40 - in children 1-2 years old; 25-35 - in children 2-4 years old; 23-26 - in children 4-6 years old. In school-age children, there is a further decrease in breathing - up to 18-20 times per minute.

The high frequency of respiratory movements in the child provides high pulmonary ventilation. The volume of respiratory air in a child is: 30 ml - in 1 month; 70 ml - in 1 year; 156 ml - at 6 years old; 230 ml - at 10 years old; 300 ml - at 14 years old.

Due to the high respiratory rate in children, the minute volume of breathing (in terms of 1 kg of weight) is much higher than in adults. The minute volume of breathing is the amount of air that a person inhales in 1 minute. It is determined by the product of the value of respiratory air by the number of respiratory movements in 1 minute. The minute volume of breathing is:

▪ 650-700 ml of air - in a newborn;

▪ 2600-2700 ml - by the end of the first year of life;

▪ 3500 ml - by 6 years;

▪ 4300 ml - by 10 years;

▪ 4900 ml - at 14 years old;

▪ 5000-6000 ml - in an adult.

Vital capacity of the lungs. At rest, an adult can inhale and exhale about 500 ml of air, and with vigorous breathing - about another 1500 ml of air. The largest amount of air that a person can exhale after a deep breath is called the vital capacity of the lungs.

The vital capacity of the lungs changes with age, depending on gender, the degree of development of the chest, respiratory muscles. As a rule, it is more in men than in women; athletes have more than untrained people. For example, for weightlifters, the vital capacity of the lungs is about 4000 ml, for football players - 4200 ml, for gymnasts - 4300, for swimmers - 4900, for rowers - 5500 ml or more.

Since the measurement of lung capacity requires the active and conscious participation of the subject, it can be determined in a child only after 4-5 years.

By the age of 16-17, the vital capacity of the lungs reaches values ​​characteristic of an adult.

8.3. Gas exchange in the lungs

Composition of inhaled, exhaled and alveolar air. Ventilation of the lungs occurs through inhalation and exhalation. Thus, a relatively constant gas composition is maintained in the alveoli. A person breathes atmospheric air containing oxygen (20,9%) and carbon dioxide (0,03%), and exhales air containing 16,3% oxygen and 4% carbon dioxide. In alveolar air, oxygen is 14,2%, carbon dioxide is 5,2%. The increased content of carbon dioxide in the alveolar air is explained by the fact that when exhaling, air that is in the respiratory organs and airways is mixed with the alveolar air.

In children, the lower efficiency of pulmonary ventilation is expressed in a different gas composition of both exhaled and alveolar air. The younger the child, the greater the percentage of oxygen and the lower the percentage of carbon dioxide in the exhaled and alveolar air, i.e. oxygen is used by the child's body less efficiently. Therefore, in order to consume the same volume of oxygen and release the same volume of carbon dioxide, children need to perform respiratory acts much more often.

Gas exchange in the lungs. In the lungs, oxygen from the alveolar air passes into the blood, and carbon dioxide from the blood enters the lungs.

The movement of gases is provided by diffusion. According to the laws of diffusion, a gas propagates from an environment with a high partial pressure to an environment with a lower pressure. Partial pressure is the part of the total pressure that is accounted for by the proportion of a given gas in a gas mixture. The higher the percentage of gas in the mixture, the higher its partial pressure. For gases dissolved in a liquid, the term "voltage" is used, corresponding to the term "partial pressure" used for free gases.

In the lungs, gas exchange takes place between the air contained in the alveoli and the blood. The alveoli are surrounded by a dense network of capillaries. The walls of the alveoli and the walls of the capillaries are very thin. For the implementation of gas exchange, the determining conditions are the surface area through which the diffusion of gases is carried out, and the difference in the partial pressure (voltage) of the diffusing gases. The lungs ideally meet these requirements: with a deep breath, the alveoli stretch and their surface reaches 100-150 square meters. m (the surface of the capillaries in the lungs is no less large), there is a sufficient difference in the partial pressure of the gases of the alveolar air and the tension of these gases in the venous blood.

Oxygen binding in blood. In the blood, oxygen combines with hemoglobin, forming an unstable compound - oxyhemoglobin, 1 g of which can bind 1,34 cubic meters. see oxygen. The amount of oxyhemoglobin formed is directly proportional to the partial pressure of oxygen. In alveolar air, the partial pressure of oxygen is 100-110 mm Hg. Art. Under these conditions, 97% of the hemoglobin in the blood is bound to oxygen.

In the form of oxyhemoglobin, oxygen is carried from the lungs to the tissues in the blood. Here, the partial pressure of oxygen is low, and oxyhemoglobin dissociates, releasing oxygen, which ensures the supply of oxygen to the tissues.

The presence of carbon dioxide in the air or tissues reduces the ability of hemoglobin to bind oxygen.

Carbon dioxide fixation in the blood. Carbon dioxide is carried in the blood in the chemical compounds sodium bicarbonate and potassium bicarbonate. Part of it is transported by hemoglobin.

In the capillaries of tissues, where the tension of carbon dioxide is high, the formation of carbonic acid and carboxyhemoglobin occurs. In the lungs, carbonic anhydrase, contained in red blood cells, promotes dehydration, which leads to the displacement of carbon dioxide from the blood.

Gas exchange in the lungs in children is closely related to the regulation of acid-base balance. In children, the respiratory center is very sensitive to the slightest changes in the pH reaction of the blood. Therefore, even with minor shifts in balance towards acidification, shortness of breath occurs in children. With development, the diffusion capacity of the lungs increases due to an increase in the total surface of the alveoli.

The body's need for oxygen and the release of carbon dioxide depends on the level of oxidative processes occurring in the body. With age, this level decreases, which means that the amount of gas exchange per 1 kg of weight decreases as the child grows.

8.4. Hygienic requirements for the air environment of educational institutions

The hygienic properties of the air environment are determined not only by its chemical composition, but also by its physical state: temperature, humidity, pressure, mobility, atmospheric electric field voltage, solar radiation, etc. For normal human life, the constancy of body temperature and the environment is of great importance, which has influence on the equilibrium of the processes of heat generation and heat transfer.

The high temperature of the surrounding air makes it difficult to release heat, which leads to an increase in body temperature. At the same time, the pulse and breathing become more frequent, fatigue increases, and working capacity decreases. It also hinders heat transfer and enhances sweating when a person stays in conditions of high relative humidity. At low temperatures, there is a large heat loss, which can lead to hypothermia of the body. With high humidity and low temperatures, the risk of hypothermia and colds increases significantly. In addition, the loss of heat by the body depends on the speed of air movement and the body itself (riding an open car, bicycle, etc.).

The electric and magnetic fields of the atmosphere also affect humans. For example, negative air particles have a positive effect on the body (relieve fatigue, increase efficiency), and positive ions, on the contrary, depress breathing, etc. Negative air ions are more mobile, and they are called light, positive ones are less mobile, therefore they are called heavy . In clean air, light ions predominate, and as it becomes polluted, they settle on dust particles, water droplets, turning into heavy ones. Therefore, the air becomes warm, stale and stuffy.

The air contains impurities of various origins: dust, smoke, various gases. All this adversely affects the health of people, animals and plant life.

In addition to dust, the air also contains microorganisms - bacteria, spores, mold fungi, etc. They are especially numerous in enclosed spaces.

Microclimate of school premises. Microclimate is the totality of physicochemical and biological properties of the air environment. For a school, this environment consists of its premises, for a city - its territory, etc. Hygienically normal air in a school is an important condition for the progress and performance of students. When 35-40 students stay in a classroom or office for a long time, the air ceases to meet hygienic requirements. Its chemical composition, physical properties and bacterial contamination change. All these indicators increase sharply towards the end of the lessons.

An indirect indicator of indoor air pollution is carbon dioxide content. The maximum allowable concentration (MPC) of carbon dioxide in school buildings is 0,1%, but even at a lower concentration (0,08%), a decrease in the level of attention and concentration is observed in young children.

The most favorable conditions in the classroom are a temperature of 16-18 °C and a relative humidity of 30-60%. With these standards, the working capacity and good health of students are preserved for the longest time. At the same time, the difference in air temperature along the vertical and horizontal of the class should not exceed 2-3 ° C, and the air speed should not exceed 0,1-0,2 m / s.

In the sports hall, recreational facilities, workshops, the air temperature should be maintained at 14-15 °C. Estimated norms of air volume per student in a class (the so-called air cube) usually do not exceed 4,5-6 cubic meters. m. But in order for the concentration of carbon dioxide in the air of the class during the lesson not to exceed 0,1%, a child of 10-12 years old needs about 16 cubic meters. m of air. At the age of 14-16 years, the need for it increases to 25-26 cubic meters. m. This value is called the volume of ventilation: the older the student, the greater it is. To ensure the specified volume, a three-fold change of air is necessary, which is achieved by ventilation (airing) of the room.

Natural ventilation. The flow of outside air into the room due to the difference in temperature and pressure through pores and cracks in the building material or through specially made openings is called natural ventilation. To ventilate classrooms of this type, windows and transoms are used. The latter have an advantage over vents, since the outside air first flows upward through the open transom, to the ceiling, where it warms up and descends warmly. At the same time, people in the room do not become overcooled and feel an influx of fresh air. Transoms can be left open during classes, even in winter.

The area of ​​open windows or transoms should not be less than 1/50 of the class floor area - this is the so-called ventilation coefficient. Airing classrooms should be carried out regularly, after each lesson. The most effective is through ventilation, when during the break the vents (or windows) and the doors of the classroom are opened at the same time. Through ventilation allows for 5 minutes to reduce the concentration of CO2 to normal, reduce humidity, the number of microorganisms and improve the ionic composition of the air. However, with such ventilation, there should be no children in the room.

Particular attention is paid to the ventilation of cabinets, chemical, physical and biological laboratories, where toxic gases and vapors may remain after experiments.

Artificial ventilation. This is supply, exhaust and supply and exhaust (mixed) ventilation with natural or mechanical impulse. Such ventilation is most often installed where it is necessary to remove exhaust air and gases generated during experiments. It is called forced ventilation, since the air is exhausted outside using special exhaust ducts that have several holes under the ceiling of the room. Air from the premises is directed to the attic and through pipes removed outside, where to enhance the air flow in the exhaust ducts, thermal stimulators of air movement - deflectors or electric fans - are installed. The installation of this type of ventilation is provided during the construction of buildings.

Exhaust ventilation should work especially well in latrines, cloakrooms, and a canteen so that the air and smells of these rooms do not penetrate into classrooms and other main and service rooms.

Topic 9. AGE DIGESTION

9.1. The structure of the alimentary canal

The alimentary canal consists of a system of organs that produce mechanical and chemical processing of food and its absorption. In humans, the alimentary canal looks like a tube 8-10 m long. The wall of the alimentary tube consists of three layers: the inner (mucous membrane), the middle (muscular membrane) and the outer (connective tissue, or serous, membrane). The smooth muscle tissue of the middle shell has two layers: inner - circular and outer - longitudinal. The following sections are distinguished in the alimentary canal:

a) oral cavity;

b) pharynx;

c) esophagus;

d) stomach;

e) small intestine; it includes three departments passing into each other: duodenum, jejunum and ileum;

f) large intestine - formed by the caecum, parts of the colon (ascending, transverse, descending and sigmoid colons) and the rectum.

The digestive juices produced by the glands enter the cavity of the alimentary canal. Part of the glands is located in the alimentary canal itself; large glands are located outside it, and the digestive juices produced by them enter its cavity through the excretory ducts.

Digestion of food begins in the oral cavity, where mechanical fragmentation and grinding of food occurs when it is chewed. The tongue and teeth are placed in the oral cavity. The tongue is a mobile muscular organ, covered with a mucous membrane, richly supplied with vessels and nerves.

The tongue moves food in the process of chewing, serves as an organ of taste and speech.

Teeth grind food; in addition, they take part in the formation of speech sounds. By function and shape, incisors, canines, small and large molars are distinguished. An adult has 32 teeth: 2 incisors, 1 canine, 2 small molars and 3 large molars develop in each half of the upper and lower jaws.

Teeth are laid in the uterine period and develop in the thickness of the jaw. In a child at 6-8 months of life, milk, or temporary, teeth begin to erupt. Teeth may appear earlier or later, depending on individual developmental characteristics. Most often, the middle incisors of the lower jaw erupt first, then the upper middle and upper lateral ones appear; at the end of the first year, usually 8 milk teeth erupt. During the second year of life, and sometimes at the beginning of the third, the eruption of all 20 milk teeth ends.

At the age of 6-7, milk teeth begin to fall out, and permanent teeth gradually grow to replace them. Before the change, the roots of the milk teeth dissolve, after which the teeth fall out. Small molars and third large molars, or wisdom teeth, grow without milk predecessors. The eruption of a permanent change of teeth ends by 14-15 years. The exception is wisdom teeth, the appearance of which is sometimes delayed up to 25-30 years; in 15% of cases they are absent on the upper jaw at all. The reason for the change of teeth is the growth of the jaws.

Mechanically crushed food in the mouth is mixed with saliva. The ducts of three pairs of large salivary glands open into the oral cavity: parotid, submandibular and sublingual. In addition, small salivary glands are located almost throughout the entire mucous membrane of the oral cavity and tongue. Intensive salivation begins with the appearance of milk teeth.

Saliva contains the enzyme amylase, which breaks down polysaccharides to dextrins and then to maltase and glucose. Mucin, a protein in saliva, makes saliva sticky. Thanks to mucin, food soaked in saliva is easier to swallow. Saliva contains a substance of a protein nature - lysozyme, which has a bactericidal effect.

With age, the amount of saliva secreted increases; the most significant jumps are observed in children from 9 to 12 months and from 9 to 11 years. In total, up to 800 cubic meters are separated from children per day. see saliva.

Esophagus. Food, crushed in the oral cavity and soaked in saliva, formed into food boluss, enters the pharynx through the pharynx, and from it into the esophagus. The esophagus is a muscular tube about 25 cm long in an adult. The inner lining of the esophagus is mucous, covered with stratified squamous epithelium with signs of keratinization in the upper layers. The epithelium protects the esophagus when a rough bolus of food moves through it. The mucous membrane forms deep longitudinal folds, which allows the esophagus to expand greatly as the bolus passes through.

In children, the mucous membrane of the esophagus is delicate, easily injured by coarse food, and rich in blood vessels. The length of the esophagus in newborns is about 10 cm, at the age of 5 years - 16 cm, at 15 years - 19 cm.

9.2. Digestion process

Features of digestion in the stomach. The stomach is the most expanded part of the digestive system. It looks like a curved bag that can hold up to 2 liters of food.

The stomach is located in the abdominal cavity asymmetrically: most of it is on the left, and the smaller part is on the right of the median plane of the body. The convex lower edge of the stomach is the greater curvature, the short concave edge is the lesser curvature. In the stomach, there is an entrance (cardiac part), a bottom (fundal part) and an exit (pyloric, or pyloric, part). The pylorus opens into the duodenum.

From the inside, the stomach is lined with a mucous membrane that forms many folds. In the thickness of the mucous membrane there are glands that produce gastric juice. There are three types of cells of the gastric glands: main (produce enzymes of gastric juice), parietal (produce hydrochloric acid), additional (produce mucus).

Human gastric juice is a colorless acidic liquid, which includes hydrochloric acid (0,5%), enzymes, minerals and mucus. The latter protect the gastric mucosa from mechanical and chemical damage. Hydrochloric acid kills bacteria in the stomach, softens fibrous foods, causes proteins to swell, and activates the digestive enzyme pepsin. During the day, an adult separates 1,2-2 liters of gastric juice.

Gastric juice contains two enzymes - pepsin and chymosin. Pepsin is produced by the gastric glands in an inactive form and is activated only in the acidic environment of the stomach. Pepsin breaks down proteins into albumose and peptones. Chymosin, or rennet, causes milk to curdle in the stomach. Finding chymosin in the gastric juice of children is especially easy during lactation. In older children, curdling occurs under the influence of pepsin and hydrochloric acid of gastric juice. Also in the gastric juice contains the enzyme lipase, which breaks down fats to glycerol and fatty acids. Gastric lipase acts on emulsified fats (milk fats).

In the stomach, food lingers from 4 to 11 hours and is subjected not only to chemical processing with the help of gastric juice, but also to mechanical action. In the thickness of the walls of the stomach there is a powerful muscle layer, consisting of smooth muscles, the muscle fibers of which run in the longitudinal, oblique and circular directions. Contractions of the muscles of the stomach contribute to better mixing of food with digestive juice, as well as the movement of food from the stomach to the intestines.

The stomach of infants has a rather horizontal position and is located almost entirely in the left hypochondrium. Only when the child begins to stand and walk does his stomach take a more upright position.

With age, the shape of the stomach also changes. In children under 1,5 years old, it is round, up to 2-3 years old it is pear-shaped, by the age of 7 the stomach has the shape of an adult.

The capacity of the stomach increases with age. If in a newborn it is 30-35 ml, then by the end of the first year of life it increases 10 times. At 10-12 years old, the capacity of the stomach reaches 1,5 liters.

The muscular layer of the stomach in children is poorly developed, especially in the bottom area. In newborns, the glandular epithelium of the stomach is poorly differentiated, the main cells are not yet mature enough. The differentiation of the cells of the glands of the stomach in children is completed by the age of seven, but they reach full development only at the end of the pubertal period.

The general acidity of gastric juice in children after birth is associated with the presence of lactic acid in its composition.

The function of hydrochloric acid synthesis develops in the period from 2,5 to 4 years. At the age of 4 to 7 years, the total acidity of gastric juice averages 35,4 units, in children from 7 to 12 years old it is 63. The relatively low content of hydrochloric acid in the gastric juice of children 4-6 years old leads to a decrease in its antimicrobial properties, which is manifested in the tendency of children to gastrointestinal diseases.

In a newborn child, the following enzymes and substances can be distinguished in the composition of gastric juice: pepsin, chymosin, lipase, lactic acid and associated hydrochloric acid. Pepsin, due to the low acidity of gastric juice, is able to break down only the proteins that make up milk. By the end of the first year of life, the activity of the enzyme chymosin rises to 256-512 units, although in the first month of a child's life it was only 16-32 units. The enzyme lipase, which is part of the gastric juice of infants, breaks down up to 25% of milk fat. However, one should take into account the fact that the fat of mother's milk is broken down not only by gastric lipase, but also by the lipase of mother's milk itself. This affects the rate of breakdown of fats in the stomach of artificially fed children. Their milk fats are always broken down more slowly than when breastfeeding. There is little lipase in cow's milk. As the child grows older, lipase activity increases from 10-12 to 35-40 units.

The amount of gastric juice, its acidity and digestive power, as well as in an adult, depend on food. For example, when feeding on women's milk, gastric juice is secreted with low acidity and digestive power; as gastric secretion develops, the most acidic juice is separated into meat, then into bread, and the juice into milk differs in the least acidity.

The secretory activity of the glands of the stomach is regulated by the vagus nerve. Gastric juice is released not only when the receptors of the oral cavity are irritated, but also by the smell, the type of food. It is also released at the time of the meal.

In an infant, the stomach is freed from food when breastfeeding after 2,5-3 hours, when fed with cow's milk - after 3-4 hours, food containing significant amounts of proteins and fats lingers in the stomach for 4,5-6,5 hours.

Digestion in the intestines. The contents of the stomach in the form of food gruel, soaked in acidic gastric juice, partially digested by muscle contractions of its walls, moves to its outlet (pyloric section) and passes from the stomach in doses to the initial section of the small intestine - the duodenum. The common bile duct of the liver and the pancreatic duct open into the duodenum.

In the duodenum, the most intensive and complete digestion of food slurry occurs. Under the influence of pancreatic juice, bile and intestinal juice, proteins, fats and carbohydrates are digested so that they become easily available for absorption and assimilation by the body.

Pure pancreatic juice is a colorless, transparent alkaline liquid. Intestinal juice contains the enzyme trypsin, which breaks down proteins into amino acids. Trypsin is produced by gland cells in an inactive form and is activated by intestinal juice. The lipase enzyme contained in the intestinal juice is activated by bile and, acting on fats, converts them into glycerol and fatty acids. The enzymes amylase and maltase convert complex carbohydrates into monosaccharides such as glucose. The separation of pancreatic juice lasts 6-14 hours and depends on the composition and properties of the food taken.

The bile produced by the liver cells enters the duodenum. And, although bile does not contain enzymes in its composition, its role in digestion is enormous. Bile activates the lipase produced by the cells of the pancreas; emulsifies fats, turning them into a suspension of small droplets (emulsified fats are easier to digest). In addition, bile actively influences the processes of absorption in the small intestine and enhances the secretion of pancreatic juice.

The duodenum continues into the jejunum of the small intestine, and the latter into the ileum. The length of the small intestine in an adult is 5-6 m. The inner lining of the small intestine is mucous and has many projections, or villi (about 4 million in an adult). Villi significantly increase the absorption surface of the small intestine. In addition to trypsin and lipases, intestinal juice contains over 20 enzymes that have a catalytic effect on the breakdown of nutrients.

In the walls of the small intestine there are longitudinal and circular muscles, the contractions of which cause pendulum-like and peristaltic movements, which improves the contact of food gruel with digestive juices and promotes the movement of the contents of the small intestine into the large intestine.

The length of the large intestine is 1,5-2 m. This is the widest section of the intestine. The large intestine is divided into the caecum with appendix (appendix), colon and rectum.

There is very little enzymatic processing of food in the large intestine. Here, the process of intensive absorption of water takes place, as a result of which feces are formed in its final sections, which is excreted from the body. Numerous symbiotic bacteria live in the large intestine. Some of them break down plant fiber, since human digestive juices do not contain enzymes for its digestion. Other bacteria synthesize vitamin K and some B vitamins, which are then absorbed by the human body.

In adults, the intestines are relatively shorter than in children: the length of the intestine in an adult exceeds the length of his body by 4-5 times, in an infant - 6 times. Especially intensively the intestine grows in length from 1 to 3 years due to the transition from dairy to mixed food and from 10 to 15 years.

The muscular layer of the intestine and its elastic fibers are less developed in children than in adults. In this regard, peristaltic movements in children are weaker. The digestive juices of the intestine already in the first days of a child's life contain all the main enzymes that ensure the process of digestion.

The growth and development of the pancreas continues up to 11 years, it grows most intensively at the age of 6 months to 2 years.

The liver in children is relatively larger than in adults. At 8-10 months, its mass doubles. The liver grows especially intensively at the age of 14-15, reaching a mass of 1300-1400 g. Bile secretion is already noted in a three-month-old fetus. With age, bile secretion increases.

Topic 10. AGE CHARACTERISTICS OF METABOLISM AND ENERGY

10.1. Characteristics of metabolic processes

The metabolism and energy is the basis of the life processes of the body. In the human body, in its organs, tissues, cells, there is a continuous process of synthesis, i.e., the formation of complex substances from simpler ones. At the same time, decomposition and oxidation of complex organic substances that make up the cells of the body occur.

The work of the body is accompanied by its continuous renewal: some cells die, others replace them. In an adult, 1/20 of the cells of the skin epithelium, half of all epithelial cells of the digestive tract, about 25 g of blood, etc. die and are replaced during the day. Growth and renewal of body cells are possible only if oxygen and nutrients are continuously supplied to the body. Nutrients are precisely the building and plastic material from which the body is built.

For continuous renewal, building new cells of the body, the work of its organs and systems - the heart, gastrointestinal tract, respiratory apparatus, kidneys and others, energy is needed for a person to do work. A person receives this energy during decay and oxidation in the process of metabolism. Consequently, the nutrients entering the body serve not only as a plastic building material, but also as a source of energy necessary for the normal functioning of the body.

Thus, metabolism is understood as a set of changes that substances undergo from the moment they enter the digestive tract and until the formation of final decay products excreted from the body.

Anabolism and catabolism. Metabolism, or metabolism, is a finely coordinated process of interaction between two mutually opposite processes occurring in a certain sequence. Anabolism is a set of biological synthesis reactions that require energy. Anabolic processes include the biological synthesis of proteins, fats, lipoids, and nucleic acids. Due to these reactions, simple substances entering cells, with the participation of enzymes, enter into metabolic reactions and become substances of the body itself. Anabolism creates the basis for the continuous renewal of worn-out structures.

Energy for anabolic processes is supplied by catabolism reactions, in which molecules of complex organic substances are broken down with the release of energy. The end products of catabolism are water, carbon dioxide, ammonia, urea, uric acid, etc. These substances are not available for further biological oxidation in the cell and are removed from the body.

The processes of anabolism and catabolism are inextricably linked. Catabolic processes supply energy and precursors for anabolism. Anabolic processes ensure the construction of structures that go to the restoration of dying cells, the formation of new tissues in connection with the growth processes of the body; provide the synthesis of hormones, enzymes and other compounds necessary for the life of the cell; supply macromolecules to be cleaved for catabolism reactions.

All metabolic processes are catalyzed and regulated by enzymes. Enzymes are biological catalysts that "start" reactions in the body's cells.

Transformation of substances. Chemical transformations of food substances begin in the digestive tract, where complex food substances are broken down into simpler ones (most often monomers), which can be absorbed into the blood or lymph. Substances received as a result of absorption into the blood or lymph are brought into the cells, where they undergo major changes. Complex organic compounds formed from the incoming simple substances are part of the cells and take part in the implementation of their functions. The transformations of substances that occur inside cells constitute the essence of intracellular metabolism. A decisive role in intracellular metabolism belongs to numerous cell enzymes that break intramolecular chemical bonds with the release of energy.

Oxidation and reduction reactions are of primary importance in energy metabolism. With the participation of special enzymes, other types of chemical reactions are also carried out, for example, reactions of transferring a phosphoric acid residue (phosphorylation), an NH2 amino group (transamination), a CH3 methyl group (transmethylation), etc. The energy released during these reactions is used to build new substances in the cell, to keep the body alive.

The end products of intracellular metabolism are partly used to build new cell substances; substances not used by the cell are removed from the body as a result of the activity of the excretory organs.

ATP. The main accumulating and energy-transferring substance used in the synthetic processes of both the cell and the whole organism is adenosine triphosphate, or adenosine triphosphate (ATP). The ATP molecule consists of a nitrogenous base (adenine), a sugar (ribose) and phosphoric acid (three phosphoric acid residues). Under the influence of the enzyme ATPase, the bonds between phosphorus and oxygen in the ATP molecule are broken and a water molecule is added. This is accompanied by the elimination of a phosphoric acid molecule. The cleavage of each of the two terminal phosphate groups in the ATP molecule occurs with the release of large amounts of energy. As a result, the two terminal phosphate bonds in the ATP molecule are called energy-rich bonds, or high-energy bonds.

10.2. The main forms of metabolism in the body

Protein metabolism. The role of proteins in metabolism. Proteins occupy a special place in metabolism. They are part of the cytoplasm, hemoglobin, blood plasma, many hormones, immune bodies, maintain the constancy of the body’s water-salt environment, and ensure its growth. Enzymes that are necessarily involved in all stages of metabolism are proteins.

Biological value of food proteins. The amino acids used to build the body's proteins are unequal. Some amino acids (leucine, methionine, phenylalanine, etc.) are essential for the body. If an essential amino acid is missing from food, protein synthesis in the body is severely disrupted. Amino acids that can be replaced by others or synthesized in the body itself during metabolism are called non-essential.

Food proteins containing all the necessary set of amino acids for normal protein synthesis of the body are called complete. These include mainly animal proteins. Food proteins that do not contain all the amino acids necessary for protein synthesis of the body are called defective (for example, gelatin, corn protein, wheat protein). The proteins of eggs, meat, milk, and fish have the highest biological value. With a mixed diet, when food contains products of animal and vegetable origin, a set of amino acids necessary for protein synthesis is usually delivered to the body.

The intake of all essential amino acids for a growing organism is especially important. For example, the absence of the amino acid lysine in food leads to a delay in the growth of the child, to the depletion of his muscular system. A lack of valine causes a disorder of the vestibular apparatus in children.

Of the nutrients, only nitrogen is included in the composition of proteins, therefore, the quantitative side of protein nutrition can be judged by the nitrogen balance. Nitrogen balance - this is the ratio of the amount of nitrogen received during the day with food, and the nitrogen excreted per day from the body with urine, feces. On average, the protein contains 16% nitrogen, i.e. 1 g of nitrogen is contained in 6,25 g of protein. Multiplying the amount of absorbed nitrogen by 6,25, you can determine the amount of protein received by the body.

In an adult, nitrogen balance is usually observed - the amounts of nitrogen introduced with food and excreted with excretion products coincide. When more nitrogen enters the body with food than it is excreted from the body, they speak of a positive nitrogen balance. Such a balance is observed in children due to an increase in body weight with growth, during pregnancy, and with great physical exertion. A negative balance is characterized by the fact that the amount of nitrogen introduced is less than that excreted. It can be with protein starvation, serious illnesses.

Breakdown of proteins in the body. Those amino acids that did not go into the synthesis of specific proteins undergo transformations, during which nitrogenous compounds are released. Nitrogen is split off from the amino acid as ammonia (NH3) or as the amino group NH2. An amino group, having split off from one amino acid, can be transferred to another, due to which the missing amino acids are built. These processes occur mainly in the liver, muscles, and kidneys. The nitrogen-free residue of the amino acid undergoes further transformations with the formation of carbon dioxide and water.

Ammonia, formed during the breakdown of proteins in the body (a poisonous substance), is neutralized in the liver, where it turns into urea; the latter in the urine is excreted from the body.

The end products of protein breakdown in the body are not only urea, but also uric acid and other nitrogenous substances. They are excreted from the body with urine and sweat.

Features of protein metabolism in children. In the child’s body, intensive processes of growth and formation of new cells and tissues occur. The protein requirement of a child's body is greater than that of an adult. The more intense the growth processes, the greater the need for protein.

In children, a positive nitrogen balance is observed, when the amount of nitrogen introduced with protein foods exceeds the amount of nitrogen excreted in the urine, which provides the growing body's need for protein. The daily requirement for protein per 1 kg of body weight in a child in the first year of life is 4-5 g, from 1 to 3 years - 4-4,5 g, from 6 to 10 years - 2,5-3 g, over 12 years old - 2-2,5 g, in adults - 1,5-1,8 g. It follows that, depending on age and body weight, children from 1 to 4 years old should receive 30-50 g of protein per day, from 4 to 7 years old - about 70 g, from 7 years old - 75-80 g. With these indicators, nitrogen is retained in the body as much as possible. Proteins are not stored in the body in reserve, so if you give them with food more than the body needs, then an increase in nitrogen retention and an increase in protein synthesis will not occur. Too low amount of protein in food causes the child to lose appetite, disturbs the acid-base balance, increases the excretion of nitrogen in the urine and feces. The child needs to be given the optimal amount of protein with a set of all the necessary amino acids, while it is important that the ratio of the amount of proteins, fats and carbohydrates in the child's food is 1:1:3; under these conditions, nitrogen is maximally retained in the body.

In the first days after birth, nitrogen makes up 6-7% of the daily amount of urine. With age, its relative content in the urine decreases.

Fat metabolism. The importance of fats in the body. Fat received from food in the digestive tract is broken down into glycerol and fatty acids, which are absorbed mainly into the lymph and only partially into the blood. Through the lymphatic and circulatory systems, fats enter adipose tissue. There is a lot of fat in the subcutaneous tissue, around some internal organs (for example, kidneys), as well as in the liver and muscles. Fats are part of cells (cytoplasm, nucleus, cell membranes), where their quantity is constant. Accumulations of fat can serve other functions. For example, subcutaneous fat prevents increased heat transfer, perinephric fat protects the kidney from bruises, etc.

Fat is used by the body as a rich source of energy. With the breakdown of 1 g of fat in the body, more than two times more energy is released than with the breakdown of the same amount of proteins or carbohydrates. The lack of fat in food disrupts the activity of the central nervous system and reproductive organs, reduces endurance to various diseases.

Fat is synthesized in the body not only from glycerol and fatty acids, but also from the metabolic products of proteins and carbohydrates. Some unsaturated fatty acids necessary for the body (linoleic, linolenic and arachidonic) must be supplied to the body in finished form, since it is not able to synthesize them on its own. Vegetable oils are the main source of unsaturated fatty acids. Most of them are in linseed and hemp oil, but there is a lot of linoleic acid in sunflower oil.

Vitamins soluble in them (A, D, E, etc.), which are of vital importance for humans, enter the body with fats.

For 1 kg of adult weight per day, 1,25 g of fat should be supplied with food (80-100 g per day).

The end products of fat metabolism are carbon dioxide and water.

Features of fat metabolism in children. In a child’s body, from the first six months of life, fats cover approximately 50% of the energy requirement. Without fats, it is impossible to develop general and specific immunity. Fat metabolism in children is unstable; if there is a lack of carbohydrates in food or with increased consumption, the fat depot is quickly depleted.

Absorption of fats in children is intensive. With breastfeeding, up to 90% of milk fats are absorbed, with artificial feeding - 85-90%. In older children, fats are absorbed by 95-97%.

For a more complete use of fat in the diet of children, carbohydrates must be present, since with their lack in nutrition, incomplete oxidation of fats occurs and acidic metabolic products accumulate in the blood.

The body's need for fat per 1 kg of body weight is higher, the younger the child. With age, the absolute amount of fat necessary for the normal development of children increases. From 1 to 3 years, the daily requirement for fat is 32,7 g, from 4 to 7 years - 39,2 g, from 8 to 13 years - 38,4 g.

Carbohydrate metabolism. The role of carbohydrates in the body. Over the course of a lifetime, a person eats about 10 tons of carbohydrates. They enter the body mainly in the form of starch. Having broken down into glucose in the digestive tract, carbohydrates are absorbed into the blood and absorbed by cells. Plant foods are especially rich in carbohydrates: bread, cereals, vegetables, fruits. Animal products (with the exception of milk) are low in carbohydrates.

Carbohydrates are the main source of energy, especially with increased muscle work. In adults, more than half of the energy the body receives from carbohydrates. The breakdown of carbohydrates with the release of energy can proceed both in anoxic conditions and in the presence of oxygen. The end products of carbohydrate metabolism are carbon dioxide and water. Carbohydrates have the ability to quickly break down and oxidize. With severe fatigue, with great physical exertion, taking a few grams of sugar improves the condition of the body.

In the blood, the amount of glucose is maintained at a relatively constant level (about 110 mg%). A decrease in glucose content causes a decrease in body temperature, a disorder in the activity of the nervous system, and fatigue. The liver plays a large role in maintaining a constant blood sugar level. An increase in the amount of glucose causes its deposition in the liver in the form of a reserve animal starch - glycogen, which is mobilized by the liver with a decrease in blood sugar. Glycogen is formed not only in the liver, but also in the muscles, where it can accumulate up to 1-2%. Glycogen reserves in the liver reach 150 g. During starvation and muscular work, these reserves are depleted.

If the content of glucose in the blood increases to 0,17%, then it begins to be excreted from the body with urine; as a rule, this occurs when eating a large amount of carbohydrates in food. This is another mechanism for regulating blood sugar levels.

However, there may be a persistent increase in blood sugar. This occurs when the function of the endocrine glands is impaired. Violation of the functioning of the pancreas leads to the development of diabetes mellitus. With this disease, the ability of body tissues to absorb sugar is lost, as well as to convert it into glycogen and store it in the liver. Therefore, the level of sugar in the blood is constantly elevated, which leads to increased excretion of it in the urine.

The value of glucose for the body is not limited to its role as an energy source. It is part of the cytoplasm and therefore necessary for the formation of new cells, especially during the growth period. Carbohydrates are also included in the composition of nucleic acids.

Carbohydrates are also important in the metabolism in the central nervous system. With a sharp decrease in the amount of sugar in the blood, there are sharp disorders in the activity of the nervous system. There are convulsions, delirium, loss of consciousness, changes in the activity of the heart. If such a person is injected with glucose into the blood or given to eat ordinary sugar, then after a while these severe symptoms disappear.

Completely sugar from the blood does not disappear even in the absence of it in food, since in the body carbohydrates can be formed from proteins and fats.

The need for glucose in different organs is not the same. The brain retains up to 12% of glucose brought in, intestines - 9%, muscles - 7%, kidneys - 5%. The spleen and lungs almost do not detain it at all.

Carbohydrate metabolism in children. In children, carbohydrate metabolism occurs with great intensity, which is explained by the high level of metabolism in the children's body. Carbohydrates in a child’s body not only serve as the main source of energy, but also play an important plastic role in the formation of cell membranes and connective tissue substances. Carbohydrates also participate in the oxidation of acidic products of protein and fat metabolism, which helps maintain acid-base balance in the body.

The intensive growth of the child's body requires significant amounts of plastic material - proteins and fats, so the formation of carbohydrates in children from proteins and fats is limited. The daily requirement for carbohydrates in children is high and amounts to 10-12 g per 1 kg of body weight in infancy. In subsequent years, the required amount of carbohydrates ranges from 8-9 to 12-15 g per 1 kg of weight. A child aged 1 to 3 years should be given an average of 193 g of carbohydrates per day with food, from 4 to 7 years - 287 g, from 9 to 13 years - 370 g, from 14 to 17 years - 470 g, for an adult - 500 G.

Carbohydrates are absorbed by the child's body better than adults (in infants - by 98-99%). In general, children are relatively more tolerant of high blood sugar than adults. In adults, glucose appears in the urine if it enters 2,5-3 g per 1 kg of body weight, and in children this occurs only when 8-12 g of glucose per 1 kg of body weight enters. Taking small amounts of carbohydrates with food can cause a two-fold increase in blood sugar in children, but after 1 hour the blood sugar begins to decrease and after 2 hours it is completely normal.

Water and mineral metabolism. Vitamins. The importance of water and mineral salts. All transformations of substances in the body take place in an aquatic environment. Water dissolves nutrients that enter the body and transports dissolved substances. Together with minerals, it takes part in the construction of cells and in many metabolic reactions. Water is involved in the regulation of body temperature: by evaporating, it cools the body, protecting it from overheating.

Water and mineral salts create mainly the internal environment of the body, being the main component of blood plasma, lymph and tissue fluid. Some salts dissolved in the liquid part of the blood are involved in the transport of gases by the blood.

Water and mineral salts are part of the digestive juices, which determines their importance for the digestive process. And although neither water nor mineral salts are sources of energy in the body, their normal intake and removal from the body is a condition for its normal activity. Water in an adult is approximately 65% ​​of body weight, in children - about 80%.

Loss of water by the body leads to very severe disorders. For example, in case of indigestion in infants, dehydration of the body is a great danger, this entails convulsions, loss of consciousness. Depriving a person of water for several days is fatal.

Water exchange. The body is constantly replenished with water by absorbing it from the digestive tract. A person needs 2-2,5 liters of water per day with a normal diet and normal ambient temperature. This amount of water comes from the following sources: water consumed when drinking (about 1 l); water contained in food (about 1 l); water, which is formed in the body during the metabolism of proteins, fats and carbohydrates (300-350 cubic cm).

The main organs that remove water from the body are the kidneys, sweat glands, lungs and intestines. The kidneys remove 1,2-1,5 liters of water from the body per day as part of the urine. Sweat glands remove 500-700 cubic meters of water through the skin in the form of sweat. cm of water per day. At normal temperature and humidity per 1 sq. cm of the skin, about 10 mg of water is released every 1 minutes. Light in the form of water vapor displays 350 cubic meters. see water; this amount increases sharply with deepening and quickening of breathing, and then 700-800 cubic meters can stand out per day. see water. Through the intestines with feces, 100-150 cubic meters are excreted per day. see water; with a disorder of the intestines, more water can be excreted, which leads to depletion of the body with water.

For the normal functioning of the body, it is important that the flow of water into the body completely covers its consumption. If more water is excreted from the body than it enters, there is a feeling of thirst. The ratio of the amount of water consumed to the amount allocated is the water balance.

In the body of a child, extracellular water predominates, which leads to a greater hydrolability of children, that is, the ability to quickly lose and quickly accumulate water. The need for water per 1 kg of body weight decreases with age, and its absolute amount increases. A three-month-old child needs 150-170 g of water per 1 kg of body weight, at 2 years old - 95 g, at 12-13 years old - 45 g. The daily water requirement for a one-year-old child is 800 ml, at 4 years old - 950-1000 ml, -5 years old - 6 ml, at 1200-7 years old - 10 ml, at 1350-11 years old - 14 ml.

The importance of mineral salts in the process of child growth and development. The presence of minerals is associated with the phenomenon of excitability and conductivity in the nervous system. Mineral salts provide a number of vital functions of the body, such as the growth and development of bones, nerve elements, muscles; determine the blood reaction (pH), contribute to the normal functioning of the heart and nervous system; used for the formation of hemoglobin (iron), hydrochloric acid of gastric juice (chlorine); maintain a certain osmotic pressure.

In a newborn, minerals make up 2,55% of body weight, in an adult - 5%. With a mixed diet, an adult receives all the minerals he needs in sufficient quantities with food, and only table salt is added to human food during its culinary processing. A growing child's body especially needs an additional intake of many minerals.

Minerals have an important influence on the development of the child. Bone growth, the timing of cartilage ossification, and the state of oxidative processes in the body are associated with calcium and phosphorus metabolism. Calcium affects the excitability of the nervous system, muscle contractility, blood clotting, protein and fat metabolism in the body. Phosphorus is needed not only for the growth of bone tissue, but also for the normal functioning of the nervous system, most glandular and other organs. Iron is part of the hemoglobin in the blood.

The greatest need for calcium is noted in the first year of a child's life; at this age it is eight times greater than in the second year of life, and 13 times greater than in the third year; then the need for calcium decreases, increasing slightly during puberty. Schoolchildren have a daily requirement for calcium - 0,68-2,36 g, for phosphorus - 1,5-4,0 g. The optimal ratio between the concentration of calcium and phosphorus salts for preschool children is 1: 1, at the age of 8-10 years - 1: 1,5, in adolescents and older students - 1: 2. With such relationships, the development of the skeleton proceeds normally. Milk has an ideal ratio of calcium and phosphorus salts, so the inclusion of milk in the diet of children is mandatory.

The need for iron in children is higher than in adults: 1-1,2 mg per 1 kg of weight per day (in adults - 0,9 mg). Sodium children should receive 25-40 mg per day, potassium - 12-30 mg, chlorine - 12-15 mg.

Vitamins. These are organic compounds that are absolutely necessary for the normal functioning of the body. Vitamins are part of many enzymes, which explains the important role of vitamins in metabolism. Vitamins contribute to the action of hormones, increasing the body's resistance to adverse environmental influences (infections, high and low temperatures, etc.). They are necessary to stimulate growth, tissue and cell restoration after injury and surgery.

Unlike enzymes and hormones, most vitamins are not formed in the human body. Their main source is vegetables, fruits and berries. Vitamins are also found in milk, meat, and fish. Vitamins are required in very small amounts, but their deficiency or absence in food disrupts the formation of the corresponding enzymes, which leads to diseases - beriberi.

All vitamins are divided into two large groups:

a) soluble in water;

b) soluble in fats. Water-soluble vitamins include the group of vitamins B, vitamins C and P. Fat-soluble vitamins include vitamins A1 and A2, D, E, K.

Vitamin B1 (thiamine, aneurin) is found in hazelnuts, brown rice, wholemeal bread, barley and oatmeal, especially in brewer's yeast and liver. The daily requirement for a vitamin is 7 mg for children under 1 years old, 7 mg from 14 to 1,5 years old, 14 mg from 2 years old, and 2-3 mg for adults.

In the absence of vitamin B1 in food, beriberi develops. The patient loses his appetite, quickly gets tired, gradually there is weakness in the muscles of the legs. Then there is a loss of sensitivity in the muscles of the legs, damage to the auditory and optic nerves, cells of the medulla oblongata and spinal cord die, paralysis of the limbs occurs, and without timely treatment - death.

Vitamin B2 (riboflavin). In humans, the first sign of a lack of this vitamin is a skin lesion (most often in the lip area). Cracks appear, which become wet and covered with a dark crust. Later, damage to the eyes and skin develops, accompanied by the falling off of keratinized scales. In the future, malignant anemia, damage to the nervous system, a sudden drop in blood pressure, convulsions, and loss of consciousness may develop.

Vitamin B2 is contained in bread, buckwheat, milk, eggs, liver, meat, tomatoes. The daily requirement for it is 2-4 mg.

Vitamin PP (nicotinamide) is found in green vegetables, carrots, potatoes, peas, yeast, buckwheat, rye and wheat bread, milk, meat, and liver. The daily requirement for it in children is 15 mg, in adults - 15-25 mg.

With beriberi PP, there is a burning sensation in the mouth, profuse salivation and diarrhea. The tongue becomes crimson red. Red spots appear on the arms, neck, face. The skin becomes rough and rough, which is why the disease is called pellagra (from the Italian pelle agra - rough skin). With a severe course of the disease, memory weakens, psychoses and hallucinations develop.

Vitamin B12 (cyanocobalamin) in humans is synthesized in the intestines. Contained in the kidneys, liver of mammals and fish. With its deficiency in the body, malignant anemia develops, associated with a violation of the formation of red blood cells.

Vitamin C (ascorbic acid) is widely distributed in nature in vegetables, fruits, needles, and in the liver. Ascorbic acid is well preserved in sauerkraut. 100 g of needles contain 250 mg of vitamin C, 100 g of rose hips - 150 mg. The need for vitamin C is 50-100 mg per day.

Vitamin C deficiency causes scurvy. Usually the disease begins with general malaise, depression. The skin acquires a dirty gray tint, the gums bleed, the teeth fall out. Dark spots of hemorrhages appear on the body, some of them ulcerate and cause sharp pain.

Vitamin A (retinol, axerophthol) in the human body is formed from the widespread natural pigment carotene, which is found in large quantities in fresh carrots, tomatoes, lettuce, apricots, fish oil, butter, liver, kidneys, egg yolk. The daily requirement for vitamin A in children is 1 mg, adults - 2 mg.

With a lack of vitamin A, the growth of children slows down, "night blindness" develops, that is, a sharp drop in visual acuity in dim lighting, leading in severe cases to complete but reversible blindness.

Vitamin D (ergocalciferol) is especially necessary for children to prevent one of the most common childhood diseases - rickets. With rickets, the process of bone formation is disrupted, the bones of the skull become soft and pliable, the limbs are bent. On the softened parts of the skull, hypertrophied parietal and frontal tubercles are formed. Sluggish, pale, with an unnaturally large head and a short bow-legged body, a large belly, such children lag behind in development.

All these serious violations are associated with the absence or deficiency of vitamin D in the body, which is found in yolks, cow's milk, and fish oil.

Vitamin D can be formed in human skin from provitamin ergosterol under the influence of ultraviolet rays. Fish oil, sun exposure or artificial ultraviolet irradiation are the means of preventing and treating rickets.

10.3. Age features of energy metabolism

Even in conditions of complete rest, a person consumes a certain amount of energy: energy is continuously spent in the body on physiological processes that do not stop for a minute. The minimum level of metabolism and energy expenditure for the body is called the basic metabolism. The main metabolism is determined in a person in a state of muscle rest - lying down, on an empty stomach, i.e. 12-16 hours after eating, at an ambient temperature of 18-20 ° C (comfort temperature). In a middle-aged person, the basal metabolism is 4187 J per 1 kg of mass per hour. On average, this is 7-140 J per day. For each individual, the basal metabolic rate is relatively constant.

Features of basal metabolism in children. Since children have a relatively larger body surface per unit mass than an adult, their basal metabolism is more intense than that of adults. In children there is also a significant predominance of assimilation processes over dissimilation processes. The younger the child, the higher the energy costs for growth. Thus, energy expenditure associated with growth at the age of 3 months is 36%, at the age of 6 months - 26%, and at 9 months - 21% of the total energy value of food.

The basal metabolism per 1 kg of mass in an adult is 96 J. Thus, in children 600-8 years old, the basal metabolism is two or two and a half times higher than in adults.

The basal metabolic rate in girls is somewhat lower than in boys. This difference begins to appear already in the second half of the first year of life. The work performed in boys entails a higher energy expenditure than in girls.

Determining the basal metabolic rate often has diagnostic value. The basal metabolism increases with excessive thyroid function and some other diseases. With insufficiency of the function of the thyroid gland, pituitary gland, gonads, the basal metabolism decreases.

Energy expenditure during muscle activity. The harder the muscular work, the more energy a person spends. For schoolchildren, preparing for a lesson and a lesson at school require energy 20-50% higher than the basal metabolic energy.

When walking, energy costs are 150-170% higher than the main metabolism. When running, climbing stairs, energy costs exceed the basic metabolism by 3-4 times.

Training the body significantly reduces the energy consumption for the work performed. This is due to a decrease in the number of muscles involved in the work, as well as a change in breathing and blood circulation.

People of different professions have different energy expenditures. With mental labor, energy costs are lower than with physical labor. Boys have a higher total daily energy expenditure than girls.

Topic 11. HYGIENE OF LABOR TRAINING AND PRODUCTIVE LABOR OF STUDENTS

Hygiene of labor lessons in primary school. During labor lessons, children design using children's construction sets, make models of ships, airplanes and others from wood, cardboard and paper, sculpt, and embroider. To ensure that these activities do not harm children's health, it is first necessary to maintain the correct working posture. This means that the body should be straight or slightly forward, with the head slightly tilted. It is advisable to change body position frequently to avoid tiring static efforts. Compression of the chest and abdominal cavity and visual strain should not be allowed.

The material used in labor lessons must be clean, free from infection, not causing skin damage (splinters, abrasions, cuts, etc.), and must not contain chemically harmful substances. To this end, the building wooden material is well planed, cleaned, and sharp corners are leveled. Do not use paints containing lead, arsenic or other toxic substances. Children's designers and handles of metal tools are wiped with a 0,2-1% clarified solution of bleach before the lesson. The weight of all constituent elements of the building material should not exceed 1-2 kg. Cardboard is taken no thicker than 0,5 mm, so that it can be easily cut. For modeling, in addition to clay, you can use plasticine, because it stains your hands less.

In the first stage of learning to sew, in order to avoid stress, it is better to use large needles with a large eye, dark threads and light-colored fabric. Scissors should be 118-120 mm long, with rounded ends, easy to move, the length of their cutting edges is 70 mm. The weight of the knife should not exceed 75 g; the blade of the knife should be made of high quality steel, well sharpened, but without a sharp end; length - 70 mm, width - 15 mm. The handle of the knife should be 85 mm long, made of hard, polished wood. The awl is taken steel, spindle-shaped, 40 mm long; its handle is made of hard, smooth wood, 85 mm long, the diameter of the wide part is 30 mm.

The duration of labor lessons depends on age, health status and type of work, and labor operations and the material used should be varied. In this case, it is absolutely necessary to observe the rules of personal hygiene.

Hygiene of agricultural lessons. Starting from grade V, agricultural lessons are taught. Agricultural implements used in flower beds, vegetable gardens, and educational and experimental sites must correspond in shape, size, and weight to the age of children. Iron rakes should have a distance between teeth of 27-30 mm, and wooden ones - up to 50-55 mm.

For children of primary school age, an iron rake with 8 teeth and a wooden one with 7 teeth are recommended; for teenagers and high school age - iron rakes with 10 and wooden rakes with 9 teeth. Toddler hoes measure 100 x 90mm, handle length 100cm; for older people - 125-100 mm, handle length - 140 cm. The handles of shovels and rakes should be wooden, oval. The capacity of watering cans and buckets (in cubic dm) should be: for young children - 4-5, for teenagers - 4-6, for older children - 6-8.

The weight of the transported goods at 11-12 years old should not exceed 4 kg, at 13-14 years old - 6 kg. When carrying cargo on a stretcher together, its weight, including the weight of the stretcher, should not exceed: at 7-8 years old - 4 kg, at 9-10 years old - 6 kg, at 10-12 years old - 10 kg, at 13-15 years old - 14 kg, at 16-17 years old - 24 kg.

The duration of agricultural labor lessons for schoolchildren aged 8-9 years is up to 1 hour per day, at 10-12 years old - 1,5 hours, at 13-14 years old - 3 hours, at 14-17 years old - 5-6 hours in the absence of other physical work. Every 20-25 minutes for younger students and 30-40 minutes for older students, a five-minute rest is required. With a 5-6-hour working day, two shifts are recommended: from 7-8 in the morning to 10-11 in the afternoon and from 17-18 in the evening.

Hygienic requirements for labor lessons in carpentry and metalworking workshops. Labor lessons in carpentry and metalworking workshops also begin in grade V. The shape, dimensions, weight and ratio of parts of carpentry and plumbing tools must also be age appropriate. The weight of a carpenter's hammer should be less than that of a mechanic's hammer. For children 11-12 years old, a carpenter's hammer should weigh 200 g, 13-14 years old - 300 g, a plumber's hammer - 300 and 400 g, respectively.

When working, the tool and manufactured products must not be pressed against the chest. With the correct working posture, an even distribution of the load for the right and left halves of the body, a straightened position of the body and a slight tilt of the head forward are assumed. While sawing, the legs should be spread apart to the distance of the length of the foot, the knees are straightened, the body is slightly tilted forward. When planing, you need to stand half-turned to the workbench, push your left leg forward at a distance of twice the length of the foot, and turn the right foot in relation to the left by 70-80 ° and tilt the body slightly forward. To reduce the duration of static efforts, students should not stand for a long time, it is recommended to sit while the teacher explains.

Work in the workshops as a form of active recreation is put on the third or fourth lessons. At the very beginning of classes, students must be familiarized with safety and injury prevention.

The training workshop is designed for 20 workplaces, which are equipped with workbenches and machines. The height of carpentry workbenches should be 75,5; 78 and 80,5 cm for three groups of students with a height of 140-150 cm, the surface of the workbench is 125 x 45 cm. To determine the height of the workbench suitable for him, the student stands sideways to the end of the workbench and places his palm on it. If the height of the workbench corresponds to height, then the arm at the elbow joint does not bend, the forearm and shoulder remain in a straight line.

In carpentry workshops, workbenches should be arranged in three rows, perpendicular or at a 45° angle to the windows. The distance between them is at least 80 cm.

In metalwork workshops, the dimensions of the workplace should be 60 x 100 cm, the distance between the axes of adjacent vices should be 100 cm. The height of the metalwork bench from the floor to the jaws of the vice comes in two sizes - 85 and 95 cm. If the student’s height does not correspond to the height of the table, stands are used for legs with a height of 5, 10 and 15 cm. The machines are placed perpendicular to the windows so that the light falls from the left. In this case, multi-seat machines are arranged in four rows, and double-seat machines are doubled. It is advisable to arrange single machines in a checkerboard pattern. The minimum distance between machines should be 80 cm, between rows - 120 cm, distance from the inner wall - 80 cm.

Lighting and ventilation in workshops must comply with hygienic standards. During the labor lesson, it is recommended to take breaks for rest for 2-3 minutes: for younger students - every 10-15 minutes, for teenagers - every 15-20 minutes.

Hygiene in physics, chemistry and biology lessons. When conducting experiments related to the study of electricity in physics lessons, it is necessary to observe safety measures, since electric current with a voltage of over 100 V and 50 mA can be fatal. It is forbidden to check the presence of current with your fingers. Protective measures should be used to prevent burns when working with molten metals, glass, etc. During chemistry lessons, in order to avoid poisoning, burns with acids and alkalis, and accidents due to explosions during chemical experiments, safety precautions should be strictly followed. The burned part of the body should be immediately washed under a strong stream of cold running water. Exhaust ventilation is required in a chemical laboratory.

In biology lessons, when working on an experimental site, it is necessary to avoid sunstroke, as well as skin damage in order to prevent the penetration of the causative agent of tetanus, etc. In addition, the student's agricultural work must be varied.

Hygienic requirements for the layout of a school building. As a rule, schools are built according to standard designs, developed taking into account student places in primary, junior high and secondary schools. The land plot allocated for the construction of the school should be 0,3-4 hectares, of which 40-50% should be green space. On the school grounds there is a ground for ball games, gymnastics, and athletics (sports area); training and experimental zone for organizing and conducting agricultural work; areas for outdoor games and quiet relaxation; economic zone with independent entry. Optimally, a three-story building with several exits and wardrobes to ensure the organization of anti-epidemic measures. Hygienic requirements for a school building provide for sufficient isolation of individual groups of premises, convenient connection with the functional areas of the school site, and the allocation of a special educational section for six-year-old children.

The number of students in a class should not exceed 30 people. The elementary school provides a universal room (60 sq. m.) for extended-day groups. This makes it possible to organize children's leisure time. In addition, a room of 80 square meters must be provided. m for manual labor. For labor training of students in grades V-X, there is a room for career guidance and the basics of production, a universal workshop for technical types of labor, and a fabric processing room. Laboratory assistants are provided for all classrooms. In modern schools, classrooms for computer science and electronic computer technology have been organized, and the sports complex has been significantly improved. For schools with a capacity of 30-35 classes, there are two sports halls measuring 12 x 24 and 18 x 30 m. In addition, a group of schools is provided with a training shooting range, an indoor pool for teaching swimming and carrying out sports work. The composition of the premises for clubs (technical modeling, creativity, young naturalists), studios (painting, drawing and sculpture, choreography and drama), and a film and photo laboratory has been significantly expanded.

The area of ​​the dining room is determined at the rate of 0,65-0,75 square meters. m per seat, at the same time it must accommodate at least 25% of students. The composition of the premises for medical purposes includes a doctor's office, combined with a room of 12-15 square meters. In addition to the doctor's office, a number of schools have a dentist's office (with an area of ​​14 sq. m). Class size must be at least 64 sq. m, laboratory rooms - at least 66 sq. m. The distance from the blackboard to the last row of tables or desks should not exceed 8 m. ; 3 sq. m and more - 162 m).

List of used literature

1. Galperin S.I. Anatomy and physiology of man. Moscow: Higher school, 1974.

2. Kositsky G.I. Human physiology. M.: Medicine, 1985.

3. Matyushonok M.T., Turin G.G., Kryukova A.A. Physiology and hygiene of children and adolescents. Moscow: Higher school, 1974.

4. Nozdrachev A. D. General course of human and animal physiology: In 2 vols. T. 2. M .: Higher school, 1991.

5. Khripkova A.A. age physiology. Moscow: Education, 1978.

6. Small medical encyclopedia: In 6 volumes. T. 6. M .: Medicine, 1991-1996.

Author: Antonova O.A.

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