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.

Author: Antonova O.A.

<< Back: 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)

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