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.

Author: Antonova O.A.

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