Cardiovascular system - a set of hollow organs and vessels that provide the process of blood circulation, constant, rhythmic transportation of oxygen and nutrients in the blood and excretion of metabolic products. The system includes the heart, aorta, arterial and venous vessels.

The heart is the central organ of the cardiovascular system that performs a pumping function. The heart provides us with the energy to move, to speak, to express emotions. The heart beats rhythmically with a frequency of 65-75 beats per minute, on average - 72. At rest for 1 minute. the heart pumps about 6 liters of blood, and during hard physical work this volume reaches 40 liters or more.

The heart is surrounded by a connective tissue membrane - the pericardium. There are two types of valves in the heart: atrioventricular (separating the atria from the ventricles) and semilunar (between the ventricles and large vessels - the aorta and pulmonary artery). The main role of the valvular apparatus is to prevent the backflow of blood into the atrium (see Figure 1).

In the chambers of the heart, two circles of blood circulation originate and end.

The large circle begins with the aorta, which departs from the left ventricle. The aorta passes into arteries, arteries into arterioles, arterioles into capillaries, capillaries into venules, venules into veins. All veins of the large circle collect their blood in the vena cava: the upper one - from the upper part of the body, the lower one - from the lower one. Both veins drain into the right.

From the right atrium, blood enters the right ventricle, where the pulmonary circulation begins. Blood from the right ventricle enters the pulmonary trunk, which carries blood to the lungs. The pulmonary arteries branch to the capillaries, then the blood is collected in venules, veins and enters the left atrium, where the pulmonary circulation ends. The main role of the large circle is to ensure the metabolism of the body, the main role of the small circle is to saturate the blood with oxygen.

The main physiological functions of the heart are: excitability, the ability to conduct excitation, contractility, automatism.

Cardiac automatism is understood as the ability of the heart to contract under the influence of impulses arising in itself. This function is performed by atypical cardiac tissue which consists of: sinoauricular node, atrioventricular node, Hiss bundle. A feature of the automatism of the heart is that the overlying area of ​​automatism suppresses the automatism of the underlying one. The leading pacemaker is the sinoauricular node.

A cardiac cycle is understood as one complete contraction of the heart. The cardiac cycle consists of systole (contraction period) and diastole (relaxation period). Atrial systole supplies blood to the ventricles. Then the atria enter the diastole phase, which continues throughout the entire ventricular systole. During diastole, the ventricles fill with blood.

Heart rate is the number of heartbeats in one minute.

Arrhythmia is a violation of the heart rate, tachycardia is an increase in the heart rate (HR), often occurs with an increase in the influence of the sympathetic nervous system, bradycardia is a decrease in heart rate, often occurs with an increase in the influence of the parasympathetic nervous system.

The indicators of cardiac activity include: stroke volume - the amount of blood that is ejected into the vessels with each contraction of the heart.

Minute volume is the amount of blood that the heart pumps into the pulmonary trunk and aorta in a minute. The minute volume of the heart increases with physical activity. With a moderate load, the minute volume of the heart increases both due to an increase in the strength of heart contractions and due to the frequency. With loads of high power only due to an increase in heart rate.

The regulation of cardiac activity is carried out due to neurohumoral influences that change the intensity of heart contractions and adapt its activity to the needs of the body and the conditions of existence. The influence of the nervous system on the activity of the heart is carried out due to the vagus nerve (parasympathetic division of the central nervous system) and due to the sympathetic nerves (sympathetic division of the central nervous system). The endings of these nerves change the automatism of the sinoauricular node, the speed of the conduction of excitation through the conduction system of the heart, and the intensity of heart contractions. The vagus nerve, when excited, reduces the heart rate and the strength of heart contractions, reduces the excitability and tone of the heart muscle, and the speed of excitation. Sympathetic nerves, on the contrary, increase heart rate, increase the strength of heart contractions, increase the excitability and tone of the heart muscle, as well as the speed of excitation.

In the vascular system, there are: main (large elastic arteries), resistive (small arteries, arterioles, precapillary sphincters and postcapillary sphincters, venules), capillaries (exchange vessels), capacitive vessels (veins and venules), shunting vessels.

Blood pressure (BP) refers to the pressure in the walls of blood vessels. The pressure in the arteries fluctuates rhythmically, reaching its highest level during systole and decreasing during diastole. This is explained by the fact that the blood ejected during systole meets the resistance of the walls of the arteries and the mass of blood filling the arterial system, the pressure in the arteries rises and some stretching of their walls occurs. During diastole, blood pressure decreases and is maintained at a certain level due to the elastic contraction of the walls of the arteries and the resistance of the arterioles, due to which the blood continues to move into the arterioles, capillaries and veins. Therefore, the value of blood pressure is proportional to the amount of blood ejected by the heart into the aorta (i.e. stroke volume) and peripheral resistance. There are systolic (SBP), diastolic (DBP), pulse and mean blood pressure.

Systolic blood pressure is the pressure caused by the systole of the left ventricle (100 - 120 mm Hg). Diastolic pressure - is determined by the tone of the resistive vessels during the diastole of the heart (60-80 mm Hg). The difference between SBP and DBP is called pulse pressure. Mean BP equals the sum of DBP and 1/3 of pulse pressure. Average blood pressure expresses the energy of the continuous movement of blood and is constant for a given organism. An increase in blood pressure is called hypertension. A decrease in blood pressure is called hypotension. Normal systolic pressure ranges from 100-140 mm Hg, diastolic pressure 60-90 mm Hg. .

Blood pressure in healthy people is subject to significant physiological fluctuations depending on physical activity, emotional stress, body position, meal times, and other factors. The lowest pressure is in the morning, on an empty stomach, at rest, that is, in those conditions in which the main metabolism is determined, therefore this pressure is called the main or basal. A short-term increase in blood pressure can be observed with great physical exertion, especially in untrained individuals, with mental arousal, drinking alcohol, strong tea, coffee, excessive smoking and severe pain.

The pulse is called the rhythmic oscillations of the wall of the arteries, due to the contraction of the heart, the release of blood into the arterial system and the change in pressure in it during systole and diastole.

The following properties of the pulse are determined: rhythm, frequency, tension, filling, size and shape. In a healthy person, heart contractions and pulse waves follow each other at regular intervals, i.e. the pulse is rhythmic. Under normal conditions, the pulse rate corresponds to the heart rate and is equal to 60-80 beats per minute. The pulse rate is counted for 1 min. In the supine position, the pulse is on average 10 beats less than standing. In physically developed people, the pulse rate is below 60 beats / min, and in trained athletes up to 40-50 beats / min, which indicates an economical work of the heart.

The pulse of a healthy person at rest is rhythmic, without interruptions, good filling and tension. Such a pulse is considered rhythmic when the number of beats in 10 seconds is noted from the previous count for the same period of time by no more than one beat. For counting, use a stopwatch or an ordinary watch with a second hand. To obtain comparable data, you must always measure the pulse in the same position (lying, sitting or standing). For example, in the morning, measure the pulse immediately after sleeping while lying down. Before and after classes - sitting. When determining the value of the pulse, it should be remembered that the cardiovascular system is very sensitive to various influences (emotional, physical stress, etc.). That is why the most calm pulse is recorded in the morning, immediately after waking up, in a horizontal position.

In the formation of the heart, a number of stages can be distinguished:

lowering the heart tube into the chest cavity,

formation of cavities of the heart due to the formation of partitions,

separation of the common arterial trunk by the aorto-pulmonary septum, the formation of valves, the development of the conduction system.

Violation of any stage of the formation of the heart leads to the development of one or another congenital defect.

From 4 weeks, the heart tube grows intensively in length, twists in an S-shape, the caudal part moves to the left and up, the ventricles to the atria occupy a typical position. Violation of the movement of the heart tube leads to ectopia or dextrocardia of the heart.

The formation of cavities, heart valves is carried out from 4 to 7 weeks. The formation of the interatrial septum occurs in 2 stages. Initially, the primary interatrial septum is formed, in which the oval window and its cusp are then formed due to the germination of the secondary interatrial septum. The pathology of the formation of cardiac septa is accompanied by the occurrence of such congenital heart defects as defects of the interatrial, interventricular septum, common arterial trunk, common atrioventricular canal, three- or two-chamber heart, etc.

The conduction system of the heart is formed from 4 to 12 weeks. An adverse effect on the development of the conduction system of the heart can be caused by intrauterine infection, hypoxia, dysmicroelementoses, leading to congenital heart rhythm disturbances, which are the main cause of sudden death syndrome.

placental circulation

From 10-12 weeks until the birth of a child, placental circulation is carried out, which has distinctive features from blood circulation in postnatal life. Oxygen-enriched blood flows through the umbilical vein as part of the umbilical cord from the placenta through the venous (Arantia) duct to the fetal liver, from where it goes through the inferior vena cava to the right atrium. Through the open foramen ovale, blood from the right enters the left atrium, where it mixes with a small amount of venous blood from the lungs. Further arterial blood goes to the ascending aorta, vessels of the brain and heart. Collecting in the superior vena cava, the blood of the upper half of the body enters the right atrium, right ventricle, pulmonary artery, where it is divided into 2 streams. A small part of the venous blood (no more than 10% of the total circulating blood), due to the high resistance in the vessels of the pulmonary circulation, supplies the lungs with blood, while a larger volume of blood enters the descending aorta through the open arterial (Batalov) duct. The umbilical arteries carry blood from the tissues of the fetus to the placenta. Thus, most organs and tissues of the fetus receive mixed blood. Relatively oxygenated blood is received by the liver, brain and heart

Adaptation factors include:

- high rate of placental blood flow and low resistance of the vascular bed of the placenta, due to which intensive gas exchange is carried out;

- features of erythropoiesis, manifested by erythrocytosis with the presence of fetal hemoglobin;

- the predominance of anaerobic processes in the fetus;

- respiratory movements of the fetus with a closed glottis, increasing blood flow to the heart.

The heart rate by the end of gestation is 130-140 beats per minute. The heart rate is affected by the level of adrenaline, acetylcholine, blood oxygenation. Fetal hypoxia is accompanied by bradycardia, an increase in the stroke volume of the heart, and peripheral vascular spasm. That is why in some newborns, especially premature babies in the first months of life, with a lack of oxygen, bradycardia is determined, and apnea is possible.

In the first days of a child’s life, an anatomical and physiological restructuring of the circulatory organs occurs, which consists in the termination of placental circulation, functional closure of fetal shunts (oval window, arterial and venous ducts), inclusion of the pulmonary circulation into the bloodstream with its high resistance and tendency to vasoconstriction, an increase in cardiac ejection and pressure in the systemic circulation. The first breath of the child is accompanied by a stretching of the chest, an increase in the partial pressure of oxygen in the blood, a decrease in resistance in the arteries and arterioles of the pulmonary circulation, and an increase in blood flow in the lungs. At the same time, the exclusion of the placenta from the blood circulation leads to a decrease in the capacity of the large circle and an increase in pressure in it, accompanied by transient blood flow from the aorta to the pulmonary artery through the patent ductus arteriosus. Within 10-15 minutes after birth, a spasm of the smooth muscles of the arterial duct occurs, in the mechanism of which an increase in the partial pressure of oxygen, a decrease in prostaglandins E, and an increase in vasoconstrictors are important. Closure of the ductus arteriosus under physiological conditions can occur up to 48 hours after birth. An increase in pulmonary blood flow leads to an increase in blood flow to the left atrium, an increase in pressure in it and the closure of the oval window, which is carried out within 3-5 hours after birth. Thus, the large and small circles are separated.

The syndrome of disadaptation of the cardiovascular system of the early neonatal period includes pulmonary hypertension and persistence of fetal communications.

In the first year of life, three stages of the formation of hemodynamics are conditionally distinguished.

1. The period of early postnatal adaptation - the closure of fetal communications and the rapid redistribution of blood flow between the systemic and pulmonary circulation.

2. The period of late adaptation of hemodynamics (the first 2-3 months of life). Complete obliteration of fetal jesters (anatomical closure) occurs in the first six months of life: the venous duct is obliterated by 8 weeks, the arterial duct is obliterated by 6-8, the foramen ovale is completely closed by 6 months of postnatal life. Therefore, under certain conditions (increased pressure in the pulmonary circulation), fetal communications can function, which is accompanied by a decrease in blood flow in the lungs and hypoxemia.

3. The period of stabilization of hemodynamics.

AFO of the cardiovascular system of children

1. The volume of the child's heart relative to the volume of the chest is much larger, the position of the heart is more horizontal, which is reflected in the position of the apex beat and borders (Tables 21, 22). After two years, the diaphragm descends and the apical impulse shifts downward and inward. With age, the growth of the heart lags behind the overall growth of the body. The intensity of heart growth is noted at the age of the first two years, 12-14 years, 17-20 years. By the time of birth, the wall thickness of the left and right ventricles is equal, the size of the atria and great vessels relative to the ventricles is greater than in adults. In the postnatal period, resistance in the systemic circulation increases, the load on the left ventricle increases, its size and wall thickness increase to a greater extent than the right one, and by the age of 15 the ratio of the cavities of the left and right ventricles and the thickness of their walls is 3:1

The myocardium retains its embryonic structure by the time of birth. Cardiac muscle is characterized by low inotropic activity, which predisposes to rapid dilatation of the heart cavities with the development of heart failure under adverse conditions (hypoxia, increased stress). In the first 2 years of life, the thickness of muscle fibers increases, the number of nuclei decreases, and striation appears. From 3 to 8 years there is an intensive development of the connective tissue of the heart, muscle fibers thicken. By the age of 10, the morphological development of the heart muscle is almost completed.

The peculiarity of the coronary blood supply explains the rarity of heart attacks in young children. Up to two years of life, the loose type of blood supply with many anastomoses predominates. From 2 to 7 years, the diameter of the main coronary trunks increases, the peripheral branches undergo reverse development. By the age of 11, the main type of blood supply is formed.

Up to three years, the vagal inhibitory effect of the autonomic nervous system on the heart rhythm is poorly developed. The predominant effect of the sympathetic nervous system is manifested by the physiological tachycardia of the child (Table 23). Vagal regulation in a child begins to form after three years and is determined by a tendency to slow down the heart rate. The final formation of the vegetative regulation of the heart rate occurs by 5-6 years. That is why sinus respiratory arrhythmia is heard and recorded on the ECG in many preschool children. So, with 24-hour monitoring, episodes of moderate sinus arrhythmia are detected in more than 70% of newborns, and approximately 50% have significant arrhythmia. In healthy newborns, monitoring may reveal extrasystole, the frequency of which increases with age and is detected in 25% of the adolescents examined.

With ontogenetic development, the stroke volume of the heart increases in proportion to body weight. At the same time, the minute volume of the heart increases, but due to a decrease in the heart rate, this process proceeds more slowly. Due to this, the average intensity of blood flow per unit of body surface decreases, which corresponds to a decrease in the intensity of metabolic processes (Table 24).

In the antenatal period in the vessels of the pulmonary circulation and the pulmonary artery, high pressure is determined, by 10 mm Hg. Art. overpressure in the aorta. Therefore, by the time of birth, the arteries of the pulmonary circulation of a newborn child have a powerful muscle layer, endothelial hyperplasia, the aortic lumen is smaller than the lumen of the pulmonary artery. By the age of 10, the lumens of the aorta and pulmonary artery are aligned, and in subsequent years, the diameter of the aorta prevails. In the first months of life, there is an involution of the vessels of the pulmonary circulation with thinning of their walls and an increase in the lumen. Until the age of 10, a physiological accent of the II tone over the pulmonary artery is heard in children, which subsequently disappears in most schoolchildren (Table 25). The underdevelopment of arteriovenous anastomoses in the pulmonary circulation explains the rarity of hemoptysis up to 7 years with pulmonary congestion.

At the same time, the thickness of the walls of the arteries of the systemic circulation of the newborn is small, the muscle and elastic fibers in it are poorly developed, and the vascular resistance is low. Blood pressure in children is lower than in adults (Table 26). With age, the muscular and elastic tissue of the vessels develops, the resistance in them increases, the cardiac output increases, the pressure rises.

At the same time, the level of blood pressure in children differs in individuality, which is largely determined by the genotype. In addition, BP varies by gender, but the most important determinants of BP in children and adolescents are length and weight.

Already in the first months of life, systolic pressure in girls increases faster than in boys. In girls at an earlier age, a physiological decrease in diastolic pressure is observed, but the degree of its decrease is less pronounced in them than in boys. So, in girls, for the first 3 years, systolic pressure practically does not increase, while in boys it increases evenly. In the first 3-4 years of life, diastolic pressure changes in boys and girls: it does not change in boys, but increases in girls.

It should be noted that in girls, in connection with the appearance of the menstrual cycle, there is a premenstrual rise in blood pressure. Its value approaches the level of an adult earlier than in boys - approximately 3 - 3.5 years after the appearance of the first menstruation.

In the prepubertal and pubertal period, due to neuroendocrine restructuring, some schoolchildren are diagnosed with vegetative dystonia syndrome, which is manifested by emotional lability, blood pressure instability, excessive sweating, etc. Some children complain of heart, headache, and abdominal pain. Only after a thorough examination of such patients and the exclusion of organic pathology in them, the diagnosis of vegetative-vascular dystonia is made.

Table 21

Palpation of the heart (determination of apical and cardiac impulses)

Table 22

Determining the boundaries of cardiac dullness

Age group (according to Molchanov)	Limits of relative stupidity			Limits of absolute dullness (right ventricle)
	Right (right atrium)	Superior (left atrium)	Left (left ventricle)
	Right parasternal line		1-2 cm outwards from the left nipple line	Left sternal line		Left teat line
	Inward from the right parasternal line	2 intercostal space	1 cm outwards from the left nipple line		3 intercostal space
	Right sternal line		Left teat line			Left parasternal line

Table 23

Heart rate (HR) in children

Table 25

Auscultation of the heart

listening points	Valve operation	Tone ratio
1. Apex of the heart	Mitral	I tone louder II tone
2. 2nd intercostal space on the right along the parasternal line		II tone louder
3. 2nd intercostal space on the left along the parasternal line	pulmonary artery	II tone is louder than I, in children under 10 years of age, physiological accent of II tone over the pulmonary artery
4. Base of the xiphoid process	tricuspid	Itone louderII
5. 3-4 intercostal space to the left of the sternum - Botkin's point	Aorta (valve projection point)

Table 26

Approximate formulas for assessing blood pressure (BP) indicators

Note: on the legs, blood pressure is 20-30 mm Hg. Art. higher than hands

The cardiovascular system with its multilevel regulation is a functional system, the end result of which is to provide a given level of functioning of the whole organism. Possessing complex neuro-reflex and neurohumoral mechanisms, the circulatory system provides timely adequate blood supply to the relevant structures. Other things being equal, we can assume that any given level of functioning of the whole organism corresponds to an equivalent level of functioning of the circulatory apparatus (Baevsky R.M., 1979). The human heart is a four-chamber muscular hollow organ. In an adult, it has a mass of 250-300 grams, a length of 12-15 cm. The size of a person's heart approximately corresponds to the size of his clenched fist. The heart consists of the left atrium and left ventricle, the right atrium and the right ventricle.

There are age-related features of the location, condition, weight and function of the heart. The heart of a newborn differs from the heart of an adult in shape, mass and location. It has an almost spherical shape, its width is somewhat greater than its length. In the process of growth and development of the child, the mass of the heart increases. The growth rate of the heart is especially high in the first years of life and during puberty. At the age of 14-15, there is a particularly sharp increase in the size of the heart. Slower heart grows from 7 to 12 years. So, for example, in boys 9-19 years old, the heart mass is 111.1 grams, which is 2 times less than in adults (244.4 grams). Along with this, the ratio of the growth of the heart departments changes. The growth of the atria during the first year of life outstrips the growth of the ventricles, then they grow almost equally, and only after 10 years the growth of the ventricles begins to overtake the growth of the atria. The histological structure of the heart is rebuilt, so, to the greatest extent, the increase in the mass of the heart departments occurs due to the left ventricle.

The main mass of the wall of the heart is a powerful myocardial muscle. The heart muscle of children is characterized by a high level of energy consumption, which determines the significant stress of oxidative processes in the myocardium. This is reflected in the large consumption of oxygen by the muscle. The heart muscle continues to develop and differentiate up to 18-20 years (Farber D.A., 1990).

The bulk of the heart muscle is represented by fibers typical of the heart, which provide contraction of the heart. Their main function is contractility. The heart contracts rhythmically: the contraction of the heart alternates with their relaxation. Contraction of the heart is called systole, and relaxation is called diastole. Each of these periods, in turn, is divided into a number of phases and intervals that characterize various aspects of the activity of the heart. During the total systole of the ventricles, there are two periods that are different in their physiological essence: the period of tension and the period of exile. During a period of tension, the heart prepares for the expulsion of blood into the great vessels. At the beginning of the tension period, depolarization of the fibers of the heart muscle occurs and the contraction of the ventricular myocardium begins. This part of the voltage period is referred to as the asynchronous contraction phase. As soon as the optimal number of myocardial fibers is in a tense state, the atrioventricular valves close and the second part of the tension period begins - the isometric contraction phase. During this phase, the intraventricular pressure rises to the pressure in the aorta. As soon as the pressure in the ventricle exceeds the pressure in the aorta, its valves open and the second period of systole begins - the period of exile.

The duration of diastole is determined by subtracting the duration of the total systole from the total duration of the cardiac cycle. The cardiac cycle is the period of one contraction and relaxation of the heart. The total duration of the cardiac cycle increases with age, the duration of the period of exile increases accordingly. Some researchers believe that the duration of the exile period is due to a number of factors. In particular, Kositsky G.I. (1985), examining age-related changes in the structure of the cardiac cycle, came to the conclusion that in addition to slowing the heart rate, the duration of systole is influenced by age-related changes in hemodynamics: the lengthening of the period of exile in children with age is associated with an increase in cardiac output. The duration of the stress period, according to most authors, increases with age. Some researchers assign the main role in the age dynamics of the stress period to an increase in the duration of the cardiac cycle, others believe that the change in the duration of the stress period is also due to shifts in hemodynamic parameters, such as the volume of the ventricles of the heart and the maximum pressure in the aorta.

The total duration of the cardiac cycle in schoolchildren begins to gradually increase from 7 to 8-9 years, after which it increases sharply at 10 years. In the future, a significant lengthening of cardio intervals occurs at the age of 14-16, when the heart rate is set at a level close to its values ​​in adults (IO Tupitsin, 1985).

Functional differences in the cardiovascular system of children and adolescents persist up to 12 years. The heart rate in children is higher than in adults, which is associated with the predominance of sympathetic nerve tone in children. During the postnatal period, the tonic effect on the heart of the vagus nerve gradually increases (N.P. Gundobin, 1906). the vagus nerve begins to exert a noticeable influence from 2-4 years old, and at a younger age its influence approaches the level of an adult. A delay in the formation of the tonic influence of the vagus nerve on cardiac activity may indicate a delay in the physical development of the child (Ferber D.A. et al., 1990). a low functional reserve of adrenergic effects on the heart rhythm with a corresponding restructuring of metabolism and an increase in its contractile capacity; at the age of 14, a significant weakening of adrenergic effects and an increase in the tone of the parasympathetic system.

A.S. Golenko (1988) presented the results of a pedagogical experiment conducted to control changes in the static parameters of the heart rate in a state of relative rest before and after exercise. These results indicated that the change in sympathetic and parasympathetic influences on the sinus node and the weakening of centralization in the control of the heart rate by the end of the experiment in girls were less pronounced than in boys. According to Golenko A.S. (1988), at the age of 10-13 years, girls have a clear centralization of heart rate control.

Heart rate in children is more influenced by external influences: physical exercise, emotional stress. Emotional influences lead, as a rule, to an increase in the frequency of cardiac activity. It increases significantly during physical work and decreases with a decrease in the ambient temperature.

The normal heart rate for an adult is 75 times per minute. In a newborn, it is much higher - 140 times per minute. Intensively decreasing during the first years of life, by the age of 8-10 it is 85-90 beats per minute, and by the age of 15 it approaches the value of an adult. With the contraction of the heart in an adult at rest, each ventricle pushes out 60-80 cubic meters. see blood. Blood pressure in children is lower than in adults, and the blood circulation speed is higher (in a newborn, the linear blood flow velocity is 12 s, in 3-year-olds - 15 s, in 14-year-olds - 18.5 s). The stroke volume (the amount of blood ejected by the ventricles in one contraction) in children is much less than in an adult. In a newborn, it is only 2.5 cubic meters. see, during the first year of postnatal development it increases by 4 times, then the rate of its increase decreases, but it continues to grow until the age of 15-16, only at this stage the stroke volume approaches the level of an adult. With age, the minute and reserve volume of blood increase, which provides the heart with increasing adaptive capabilities to stress (Yu.A. Ermalaev, 1985). Children and adolescents respond to dynamic physical activity with an increase in heart rate, maximum blood pressure (stroke volume), than younger children, the more, even to less physical activity, they respond with an increase in heart rate, a smaller increase in stroke volume, providing approximately the same increase minute volume. The increase in minute volume in trained people occurs mainly due to an increase in systolic volume. At the same time, heart rate increases slightly. In untrained people, the minute volume of blood increases mainly due to increased heart rate. It is known that with an increase in heart rate, the duration of the general pause of the heart is shortened. It follows from this that the heart of untrained people works less economically and wears out faster. It is no coincidence that cardiovascular diseases are much less common in athletes than in people who are not involved in physical education. In well-trained athletes with great physical exertion, the stroke volume of blood can increase up to 200-300 cc.

Static load (and full tension also belongs to it) is accompanied by other resections of the cardiovascular system. Static load, unlike dynamic load, increases both maximum and minimum blood pressure. This is how schoolchildren of all ages react even to a light static load equal to 30% of the maximum compression force of the dynamometer. At the same time, at the beginning of the academic year, the change in hemodynamic parameters is less sharp than at the end of the year. At the beginning of the year, for example, in boys 8-9 years old, the minimum pressure increases by 5.5% and the maximum by 10%, and at the end of the year, by 11 and 21%, respectively, for the specified static load. Such a reaction is recorded for more than 5 minutes after the cessation of exposure to static force. Prolonged postural tension is accompanied by a spasm of arterioles in schoolchildren, which leads to a general increase in blood pressure. An increase in motor activity during training sessions is one of the measures to prevent cardiovascular disorders in students, in particular, the development of hypertension (A.G. Khripkova, 1990).

The state of the cardiovascular system is influenced by a dosed mental load, and the degree of change in hemodynamic parameters depends on the nature of the duration and intensity of the load. Analysis of studies conducted by Gorbunov N.P. together with Batenkova I.V. (2001) testified that the heart and blood vessels of junior schoolchildren subtly respond to mental stress. The most significant changes in the course of mental load are the indicators of cardiac output, the increase of which was noted in all the children studied. The degree of increase in cardiac output during the performance of the task depended on the age of the children and on the period of the school year. It has been established that during the academic year, students of the 1st grade undergo changes in the indicators of central hemodynamics, while the heart rate decreases, the maximum arterial pressure decreases, and the cardiac output increases.

In the second year of study, the maximum arterial pressure decreases, and the heart rate does not change significantly. In students of grades 3-4, the maximum blood pressure decreased, the heart rate decreased, and there was a decrease in cardiac output. Adaptive changes in the indicators of central hemodynamics in younger schoolchildren consist in slowing down the heart rate, lowering the maximum blood pressure, and increasing cardiac output. If we trace the age-related shifts in central hemodynamics according to the results obtained at the beginning of each academic year, we can see that adaptive shifts are not accompanied by a violation of the general age-related trend of increasing blood pressure and cardiac output with age while slowing down the heart rate.

The change in the functional state of the cardiovascular system in children and adolescents in the process of their adaptation to mental and physical stress is influenced in certain years of study by gender. According to the work of P.K. Prusova (1987), the dependence of the state of the cardiovascular system on the degree of puberty of adolescents training for endurance, the improvement of the functioning of the cardiorespiratory system does not always occur in parallel with the increase in the degree of puberty. So, at the time of the appearance of secondary signs of puberty, the sympathetic tone of the autonomic nervous system increases and is most pronounced during puberty. The intensity of the functioning of the cardiorespiratory system increases with an increase in the degree of puberty, and in the subsequent period it begins to decrease, a tendency towards more economical functioning appears. The study of regional blood circulation showed a decrease in the volumetric blood flow velocity with age at rest, which also indicates the economization of the functions of the blood circulation, which occurs as the child develops. The study of cerebral blood flow confirmed its qualitative changes that occur during the growth of the child, as well as the interhemispheric asymmetry of the brain blood supply characteristic of children.

The important role that the heart plays in the body dictates the need for preventive measures that contribute to its normal function, strengthen it, and protect against diseases that cause organic changes in the valvular apparatus and the heart muscle itself. Physical training and labor within the age limits of permissible physical activity is the most important measure to strengthen the heart.

All systems of the human body can exist and function normally only under certain conditions, which in a living organism are supported by the activity of many systems designed to ensure the constancy of the internal environment, that is, its homeostasis.

Homeostasis is maintained by the respiratory, circulatory, digestive and excretory systems, and the internal environment of the body is directly blood, lymph and interstitial fluid.

Blood performs a number of functions, including respiratory (carrying gases) transport (carrying water, food, energy and decay products); protective (destruction of pathogens, removal of toxic substances, prevention of blood loss), regulatory (transferred hormones and enzymes) and thermoregulatory. In terms of maintaining homeostasis, blood provides water-salt, acid-base, energy, plastic, mineral and temperature balance in the body.

With age, the specific amount of blood per 1 kilogram of body weight in the body of children decreases. In children under 1 year of age, the amount of blood relative to the entire body weight is up to 14.7%, at the age of 1-6 years - 10.9%, and only at 6-11 years old is it set at the level of adults (7%). This phenomenon is due to the needs of more intensive metabolic processes in the child's body. The total blood volume in adults weighing 70 kg is 5-6 liters.

When a person is at rest, a certain part of the blood (up to 40-50%) is in the blood depots (spleen, liver, in the tissue under the skin and lungs) and does not take an active part in the processes of blood circulation. With increased muscle work, or with bleeding, the deposited blood enters the bloodstream, increasing the intensity of metabolic processes or equalizing the amount of circulating blood.

Blood consists of two main parts: plasma (55% of the mass) and formed elements of 45% of the mass). Plasma, in turn, contains 90-92% water; 7-9% organic substances (proteins, carbohydrates, urea, fats, hormones, etc.) and up to 1% inorganic substances (iron, copper, potassium, calcium, phosphorus, sodium, chlorine, etc.).

The composition of the formed elements includes: erythrocytes, leukocytes and platelets (Table 11) and almost all of them are formed in the red bone marrow as a result of differentiation of the stem cells of this brain. The mass of the red brain in a newborn child is 90-95%, and in adults up to 50% of the entire marrow substance of the bones (in adults this is up to 1400 g, which corresponds to the mass of the liver). In adults, part of the red brain turns into adipose tissue (yellow marrow). In addition to red bone marrow, some formed elements (leukocytes, monocytes) are formed in the lymph nodes, and in newborns also in the liver.

To maintain the cellular composition of the blood at the desired level in the body of an adult weighing 70 kg, 2 * 10m (two trillion, trillion) erythrocytes, 45-10 * (450 billion, billion) neutrophils are formed daily; 100 billion Monocytes, 175-109 (1 trillion 750 billion) Platelets. On average, a person of 70 years of age with a body weight of 70 kg produces up to 460 kg of erythrocytes, 5400 kg of granulocytes (neutrophils), 40 kg of platelets, and 275 kg of lymphocytes. The constancy of the content of formed elements in the blood is supported by the fact that these cells have a limited lifespan.

Erythrocytes are red blood cells. In 1 mm 3 (or micro liters, μl) of the blood of men, there are normally from 4.5-6.35 million erythrocytes, and in women up to 4.0-5.6 million (an average of 5,400,000, respectively. And 4.8 million .). Each human erythrocyte cell is 7.5 microns (µm) in diameter, 2 µm thick, and contains approximately 29 pg (pt, 10 12 g) of hemoglobin; has a biconcave shape and does not have a nucleus when mature. Thus, in the blood of an adult, on average, there are 3-1013 erythrocytes and up to 900 g of hemoglobin. Due to the content of hemoglobin, erythrocytes perform the function of gas exchange at the level of all body tissues. Hemoglobin of erythrocytes including globin protein and 4 heme molecules (a protein connected to 2-valent iron). It is the latter compound that is not able to stably attach 2 oxygen molecules to itself at the level of the alveoli of the lungs (turning into oxyhemoglobin) and transport oxygen to the cells of the body, thereby ensuring the vital activity of the latter (oxidative metabolic processes). In the exchange of oxygen, cells give up excess products of their activity, including carbon dioxide, which is partially combined with renewed (giving up oxygen) hemoglobin, forming carbohemoglobin (up to 20%), or dissolves in plasma water to form carbonic acid (up to 80% of all carbon dioxide). gas). At the level of the lungs, carbon dioxide is removed from the outside, and oxygen again oxidizes hemoglobin and everything repeats. The exchange of gases (oxygen and carbon dioxide) between the blood, the intercellular fluid and the alveoli of the lungs is carried out due to the different partial pressures of the corresponding gases in the intercellular fluid and in the cavity of the alveoli, and this occurs by diffusion of gases.

The number of red blood cells can vary significantly depending on external conditions. For example, it can grow up to 6-8 million per 1 mm 3 in people living high in the mountains (in conditions of rarefied air, where the partial pressure of oxygen is reduced). A decrease in the number of erythrocytes by 3 million in 1 mm 3, or hemoglobin by 60% or more leads to an anemic state (anemia). In newborns, the number of erythrocytes in the first days of life can reach 7 million in I mm3, and at the age of 1 to 6 years it ranges from 4.0-5.2 million in 1 mm3. At the level of adults, the content of erythrocytes in the blood of children, according to A. G. Khripkov (1982), it is established at 10-16 years.

An important indicator of the state of erythrocytes is the erythrocyte sedimentation rate (ESR). In the presence of inflammatory processes, or chronic diseases, this rate increases. In children under 3 years of age, ESR is normally from 2 to 17 mm per hour; at 7-12 years old - up to 12 mm per hour; in adult men 7-9, and in women - 7-12 mm per hour. Erythrocytes are formed in the red bone marrow, live for about 120 days and, dying, are split in the liver.

Leukocytes are called white blood cells. Their most important function is to protect the body from toxic substances and pathogens through their absorption and digestion (splitting). This phenomenon is called phagocytosis. Leukocytes are formed in the bone marrow, as well as in the lymph nodes, and live only 5-7 days (much less if there is an infection). These are nuclear cells. According to the ability of the cytoplasm to have granules and stain, leukocytes are divided into: granulocytes and agranulocytes. Granulocytes include: basophils, eosinophils and neutrophils. Agranulocytes include monocytes and lymphocytes. Eosinophils make up from 1 to 4% of all leukocytes and mainly remove toxic substances and fragments of body proteins from the body. Basophils (up to 0.5%) contain heparin and promote wound healing processes by breaking down blood clots, including those with internal hemorrhages (for example, injuries). Schytrophils make up the largest number of leukocytes (up to 70%) and perform the main phagocytic function. They are young, stab and segmented. Activated by invasion (microbes that infect the body with an infection), the neutrophil covers one or more (up to 30) microbes with its plasma proteins (mainly immunoglobulins), attaches these microbes to the receptors of its membrane and quickly digests them by phagocytosis (release into the vacuole, around microbes, enzymes from the granules of its cytoplasm: defensins, proteases, myelopyroxidases, and others). If a neutrophil captures more than 15-20 microbes at a time, then it habitually dies, but creates a substrate from the absorbed microbes suitable for digestion by other macrophages. Neutrophils are most active in an alkaline environment, which occurs in the first moments of fighting infection, or inflammation. When the environment becomes acidic, then neutrophils are replaced by other forms of leukocytes, namely, monocytes, the number of which can increase significantly (up to 7%) during the period of an infectious disease. Monocytes are mainly formed in the spleen and liver. Up to 20-30% of leukocytes are lymphocytes, which are mainly formed in the bone marrow and lymph nodes, and are the most important factors of immune protection, that is, protection from microorganisms (antigens) that cause diseases, as well as protection from particles that are unnecessary for the body and molecules of endogenous origin. It is believed that three immune systems work in parallel in the human body (M. M. Bezrukikh, 2002): specific, non-specific and artificially created.

Specific immune protection is mainly provided by lymphocytes, which do this in two ways: cellular or humoral. Cellular immunity is provided by immunocompetent T-lymphocytes, which are formed from stem cells migrating from the red bone marrow in the thymus (see Section 4.5.) Once in the blood, T-lymphocytes create most of the lymphocytes of the blood itself (up to 80%), as well as settle in the peripheral organs of immunogenesis (primarily in the lymph nodes and spleen), forming in them thymus-dependent zones become active points of proliferation (multiplication) of T-lymphocytes outside the thymus. Differentiation of T-lymphocytes occurs in three directions. The first group of daughter cells is capable of reacting with it and destroying it when it encounters a "foreign" protein-antigen (the causative agent of the disease, or its own mutant). Such lymphocytes are called T-killerash ("killers") and are characterized by the fact that they are capable of lysis (destruction by dissolving cell membranes and protein binding) target cells (carriers of antigens). Thus, T-killers are a separate branch of stem cell differentiation (although their development, as will be described below, is regulated by G-helpers) and are designed to create, as it were, a primary barrier in the body's antiviral and antitumor immunity.

The other two populations of T-lymphocytes are called T-helpers and T-suppressors and carry out cellular immune protection through the regulation of the level of functioning of T-lymphocytes in the humoral immunity system. T-helpers ("helpers") in the event of the appearance of antigens in the body contribute to the rapid reproduction of effector cells (executors of immune defense). There are two subtypes of helper cells: T-helper-1, secrete specific interleukins of type 1L2 (hormone-like molecules) and β-interferon and are associated with cellular immunity (promote the development of T-helpers) T-helper-2 secrete interleukins of the type IL 4-1L 5 and interact predominantly with T-lymphocytes of humoral immunity. T-suppressors are able to regulate the activity of B and T-lymphocytes in response to antigens.

Humoral immunity is provided by lymphocytes that differentiate from brain stem cells not in the thymus, but in other places (in the small intestine, lymph nodes, pharyngeal tonsils, etc.) and are called B-lymphocytes. Such cells make up to 15% of all leukocytes. At the first contact with the antigen, T-lymphocytes that are sensitive to it multiply intensively. Some of the daughter cells differentiate into immunological memory cells and, at the level of lymph nodes in the £ zone, turn into plasma cells, which are then able to create humoral antibodies. T-helpers contribute to these processes. Antibodies are large protein molecules that have a specific affinity for a particular antigen (based on the chemical structure of the corresponding antigen) and are called immunoglobulins. Each immunoglobulin molecule is composed of two heavy and two light chains linked to each other by disulfide bonds and capable of activating cell membranes of antigens and attaching a blood plasma complement to them (contains 11 proteins capable of providing lysis or dissolution of cell membranes and binding protein binding of antigen cells) . Blood plasma complement has two ways of activation: classical (from immunoglobulins) and alternative (from endotoxins or toxic substances and from counting). There are 5 classes of immunoglobulins (lg): G, A, M, D, E, differing in functional features. So, for example, lg M is usually the first to be included in the immune response to an antigen, activates complement and promotes the uptake of this antigen by macrophages or cell lysis; lg A is located in the places of the most probable penetration of antigens (lymph nodes of the gastrointestinal tract, in the lacrimal, salivary and sweat glands, in the adenoids, in mother's milk, etc.) which creates a strong protective barrier, contributing to the phagocytosis of antigens; lg D promotes the proliferation (reproduction) of lymphocytes during infections, T-lymphocytes "recognize" antigens with the help of globulins included in the membrane, which form an antibody by binding links, the configuration of which corresponds to the three-dimensional structure of antigenic deterministic groups (haptens or low molecular weight substances that can bind to proteins of an antibody, transferring the properties of antigen proteins to them), as a key corresponds to a lock (G. William, 2002; G. Ulmer et al., 1986). Antigen-activated B- and T-lymphocytes multiply rapidly, are included in the body's defense processes and die en masse. At the same time, a large number of activated lymphocytes turn into B- and T-cells of the memory of your computer, which have a long lifespan and when the body is re-infected (sensitization), B- and T-memory cells "remember" and recognize the structure of antigens and quickly turn into effector (active) cells and stimulate lymph node plasma cells to produce appropriate antibodies.

Repeated contact with certain antigens can sometimes give hyperergic reactions, accompanied by increased capillary permeability, increased blood circulation, itching, bronchospasm, and the like. Such phenomena are called allergic reactions.

Nonspecific immunity due to the presence of "natural" antibodies in the blood, which most often occur when the body comes into contact with the intestinal flora. There are 9 substances that together form a protective complement. Some of these substances are able to neutralize viruses (lysozyme), the second (C-reactive protein) suppress the vital activity of microbes, the third (interferon) destroy viruses and suppress the reproduction of their own cells in tumors, etc. Nonspecific immunity is also caused by special cells, neutrophils and macrophages, which capable of phagocytosis, that is, the destruction (digestion) of foreign cells.

Specific and non-specific immunity is divided into innate (transmitted from the mother), and acquired, which is formed after a disease in the process of life.

In addition, there is the possibility of artificial immunization of the body, which is carried out either in the form of vaccination (when a weakened pathogen is introduced into the body and this causes the activation of protective forces that lead to the formation of appropriate antibodies), or in the form of passive immunization, when the so-called vaccination against a specific disease is done by the introduction of serum (blood plasma that does not contain fibrinogen or its coagulation factor, but has ready-made antibodies against a specific antigen). Such vaccinations are given, for example, against rabies, after being bitten by poisonous animals, and so on.

As V. I. Bobritskaya (2004) testifies, in a newborn child in the blood there are up to 20 thousand of all forms of leukocytes in 1 mm 3 of blood and in the first days of life their number grows even up to 30 thousand in 1 mm 3, which is associated with resorption decay products of hemorrhages in the baby's tissues, which usually occur at the time of birth. After 7-12 first days of life, the number of leukocytes decreases to 10-12 thousand in I mm3, which persists during the first year of a child's life. Further, the number of leukocytes gradually decreases and at the age of 13-15 it is set at the level of adults (4-8 thousand per 1 mm 3 of blood). In children of the first years of life (up to 7 years), lymphocytes are exaggerated among leukocytes, and only at 5-6 years their ratio levels off. In addition, children under 6-7 years old have a large number of immature neutrophils (young, rods - nuclear), which determines the relatively low defenses of the body of young children against infectious diseases. The ratio of different forms of leukocytes in the blood is called the leukocyte formula. With age in children, the leukocyte formula (Table 9) changes significantly: the number of neutrophils increases, while the percentage of lymphocytes and monocytes decreases. At 16-17 years old, the leukocyte formula takes on a composition characteristic of adults.

Invasion of the body always leads to inflammation. Acute inflammation is usually generated by antigen-antibody reactions in which plasma complement activation begins a few hours after immunological damage, reaches its peak after 24 hours, and fades after 42-48 hours. Chronic inflammation is associated with the influence of antibodies on the T-lymphocyte system, usually manifests itself through

1-2 days and peaks in 48-72 hours. At the site of inflammation, the temperature always rises (due to vasodilation), swelling occurs (in acute inflammation due to the release of proteins and phagocytes into the intercellular space, in chronic inflammation, infiltration of lymphocytes and macrophages is added) pain occurs (due to increased pressure in the tissues).

Diseases of the immune system are very dangerous for the body and often lead to fatal consequences, as the body actually becomes unprotected. There are 4 main groups of such diseases: primary or secondary immune deficiency dysfunction; malignant diseases; immune system infections. Among the latter, the herpes virus is known and threateningly spreading in the world, including in Ukraine, the anti-HIV virus or anmiHTLV-lll / LAV, which causes acquired immunodeficiency syndrome (AIDS or AIDS). The AIDS clinic is based on viral damage to the T-helper (Th) chain of the lymphocytic system, leading to a significant increase in the number of T-suppressors (Ts) and a violation of the Th / Ts ratio, which becomes 2: 1 instead of 1: 2, resulting in a complete cessation production of antibodies and the body dies from any infection.

Platelets, or platelets, are the smallest formed elements of the blood. These are non-nucleated cells, their number ranges from 200 to 400 thousand per 1 mm 3 and can increase significantly (3-5 times) after physical exertion, trauma and stress. Platelets are formed in the red bone marrow and live up to 5 days. The main function of platelets is to participate in the processes of blood clotting in wounds, which ensures the prevention of blood loss. When wounded, platelets are destroyed and release thromboplastin and serotonin into the blood. Serotonin contributes to the narrowing of blood vessels at the site of injury, and thromboplastin, through a series of intermediate reactions, reacts with plasma prothrombin and forms thrombin, which in turn reacts with plasma protein fibrinogen, forming fibrin. Fibrin in the form of thin threads forms a strong retina, which becomes the basis of a thrombus. The retina is filled with blood cells, and actually becomes a clot (thrombus), which closes the opening of the wound. All blood coagulation processes occur with the participation of many blood factors, the most important of which are calcium ions (Ca 2 *) and antihemophilia factors, the absence of which prevents blood coagulation and leads to hemophilia.

In newborns, relatively slow blood clotting is observed, due to the immaturity of many factors in this process. In children of preschool and primary school age, the period of blood clotting is from 4 to 6 minutes (in adults 3-5 minutes).

The composition of the blood by the presence of individual plasma proteins and formed elements (hemograms) in healthy children acquires the level inherent in adults at about 6-8 years of age. The dynamics of the protein fraction of blood in people of different ages is shown in Table. 1O.

In table. C C shows the average standards for the content of the main formed elements in the blood of healthy people.

Human blood is also distinguished by groups, depending on the ratio of natural protein factors that can "glue" erythrocytes and cause their agglutination (destruction and precipitation). Such factors in blood plasma and they are called antibodies Anti-A (a) and Anti-B (c) agglutinins, while in the membranes of erythrocytes there are antigens of blood groups - agglutinogen A and B. When agglutinin meets the corresponding agglutinogen, erythrocyte agglutination occurs.

Based on various combinations of blood composition with the presence of agglutinins and agglutinogens, four groups of people are distinguished according to the ABO system:

Group 0 or group 1 - contains only plasma agglutinins a and p. People with such blood up to 40%;

f group A, or group II - contains agglutinin and agglutinogen A. Approximately 39% of people with such blood; among this group, subgroups of agglutinogens A IA "

Group B, or group III - contains agglutinins a and erythrocyte agglutinogen B. People with such blood up to 15%;

Group AB, or group IV - contains only the agglutinogen of erythrocytes A and B. There are no agglutinins in their blood plasma at all. Up to 6% of people with such blood (V. Ganong, 2002).

The blood group plays an important role in blood transfusion, the need for which may arise in case of significant blood loss, poisoning, etc. The person who donates his blood is called a donor, and the one who receives the blood is called a recipient. In recent years, it has been proven (G. I. Kozinets et al., 1997) that in addition to combinations of agglutinogens and agglutinins according to the ABO system, there can be combinations of other agglutinogens and agglutinins in human blood, for example, Uk. Gg and others are less active and specific (they are in a lower titer), but can significantly affect the results of blood transfusion. Certain variants of agglutinogens A GA2 and others have also been found, which determine the presence of subgroups in the composition of the main blood groups according to the ABO system. This leads to the fact that in practice there are cases of blood incompatibility even in people with the same blood type according to the ABO system and, as a result, this requires in most cases an individual selection of a donor for each recipient and, best of all, that these are people with the same blood type.

For the success of a blood transfusion, the so-called Rh factor (Rh) is also of some importance. The Rh factor is a system of antigens, among which agglutinogen D is considered the most important. 85% of all people need it and therefore they are called Rh-positive. The rest, approximately 15% of people do not have this factor and are Rh negative. During the first transfusion of Rh-positive blood (with antigen D) to people with Rh-negative blood, anti-D agglutinins (d) are formed in the latter, which, when re-transfused with Rh-positive blood to people with Rh-negative blood, causes its agglutination with all the negative consequences .

The Rh factor is also important during pregnancy. If the father is Rh-positive and the mother is Rh-negative, then the child will have dominant, Rh-positive blood, and since the fetus's blood mixes with the mother's, this can lead to the formation of agglutinins d in the mother's blood, which can be deadly for the fetus , especially with repeated pregnancies, or with infusions of Rh-negative blood to the mother. Rh belonging is determined using anti-D serum.

Blood can perform all its functions only under the condition of its continuous movement, which is the essence of blood circulation. The circulatory system includes: the heart, which acts as a pump and blood vessels (arteries -> arterioles -> capillaries -> venules -> veins). The circulatory system also includes hematopoietic organs: red bone marrow, spleen, and in children in the first months after birth, and the liver. In adults, the liver functions as a graveyard for many dying blood cells, especially red blood cells.

There are two circles of blood circulation: large and small. The systemic circulation begins from the left ventricle of the heart, then through the aorta and arteries and arterioles of various orders, blood is carried throughout the body and reaches the cells at the level of capillaries (microcirculation), giving nutrients and oxygen to the intercellular fluid and taking carbon dioxide and waste products in return . From the capillaries, the blood is collected in the venules, then in the veins and is sent to the right atrium of the heart by the upper and lower empty veins, thus closing the systemic circulation.

The pulmonary circulation begins from the right ventricle with pulmonary arteries. Further, the blood is sent to the lungs and after them through the pulmonary veins returns to the left atrium.

Thus, the "left heart" performs a pumping function in providing blood circulation in a large circle, and the "right heart" - in a small circle of blood circulation. The structure of the heart is shown in fig. 31.

The atria have a relatively thin muscular wall of the myocardium, since they function as a temporary reservoir of blood entering the heart and push it only to the ventricles. ventricles (especially

left) have a thick muscular wall (myocardium), the muscles of which contract powerfully, pushing blood a considerable distance through the vessels of the whole body. There are valves between the atria and ventricles that direct blood flow in only one direction (from fury to ventricles).

The valves of the ventricles are also located at the beginning of all large vessels extending from the heart. The tricuspid valve is located between the atrium and the ventricle on the right side of the heart, and the bicuspid (mitral) valve on the left side. At the mouth of the vessels extending from the ventricles, semilunar valves are located. All heart valves not only direct the flow of blood, but also counteract ITS reverse flow.

The pumping function of the heart is that there is a consistent relaxation (diastole) and contraction (systolic) of the muscles of the atria and ventricles.

The blood that moves from the heart through the arteries of the great circle is called arterial (oxygenated). Venous blood (enriched with carbon dioxide) moves through the veins of the systemic circulation. On the arteries of the small circle, on the contrary; venous blood moves, and arterial blood moves through the veins.

The heart in children (relative to total body weight) is larger than in adults and accounts for 0.63-0.8% of body weight, while in adults it is 0.5-0.52%. The heart grows most intensively during the first year of life and in 8 months its mass doubles; up to 3 years, the heart increases three times; at 5 years old - increases 4 times, and at 16 years old - eight times and reaches a mass in young men (men) of 220-300 g, and in girls (women) 180-220 g. In physically trained people and athletes, the mass of the heart may be more than the specified parameters by 10-30%.

Normally, the human heart contracts rhythmically: systolic alternates with diastole, forming a cardiac cycle, the duration of which in a calm state is 0.8-1.0 seconds. Normally, at rest in an adult, 60-75 cardiac cycles, or heartbeats, occur per minute. This indicator is called the heart rate (HR). Since each systolic leads to the release of a portion of blood into the arterial bed (at rest for an adult, this is 65-70 cm3 of blood), there is an increase in the blood filling of the arteries and a corresponding stretching of the vascular wall. As a result, you can feel the stretching (push) of the artery wall in those places where this vessel passes close to the surface of the skin (for example, the carotid artery in the neck, the ulnar or radial artery on the wrist, etc.). During diastole of the heart, the walls of the arteries come and go back to their ascending position.

The oscillations of the walls of the arteries in time with the heartbeat is called the pulse, and the measured number of such oscillations for a certain time (for example, 1 minute) is called the pulse rate. The pulse adequately reflects the heart rate and is convenient for express monitoring of the work of the heart, for example, when determining the body's response to physical activity in sports, in the study of physical performance, emotional stress, etc. Coaches of sports sections, including children's, and physical education teachers also need to know the norms for heart rate for children of different ages, as well as be able to use these indicators to assess the body's physiological responses to physical activity. Age standards for pulse rate (477), as well as systolic blood volume (that is, the volume of blood that is pushed into the bloodstream by the left or right ventricle in one heartbeat), are given in Table. 12. With the normal development of children, the systolic blood volume gradually increases with age, and the heart rate decreases. The systolic volume of the heart (SD, ml) is calculated using the Starr formula:

Moderate physical activity helps to increase the strength of the heart muscles, increase its systolic volume and optimize (reduce) the frequency indicators of cardiac activity. The most important thing for training the heart is the uniformity and gradual increase in loads, the inadmissibility of overload and medical monitoring of the state of heart performance and blood pressure, especially in adolescence.

An important indicator of the work of the heart and the state of its functionality is the minute volume of blood (Table 12), which is calculated by multiplying the systolic blood volume by the PR for 1 minute. It is known that in physically trained people, an increase in minute blood volume (MBV) occurs due to an increase in systolic volume (that is, due to an increase in the power of the heart), while the pulse rate (PR) practically does not change. In poorly trained people during exercise, on the contrary, an increase in the IOC occurs mainly due to an increase in heart rate.

In table. 13 shows the criteria by which it is possible to predict the level of physical activity for children (including athletes) based on determining the increase in heart rate relative to its indicators at rest.

The movement of blood through the blood vessels is characterized by hemodynamic indicators, of which the three most important are distinguished: blood pressure, vascular resistance, and blood velocity.

Blood pressure is the pressure of the blood on the walls of blood vessels. The level of blood pressure depends on:

Indicators of the work of the heart;

The amount of blood in the bloodstream;

The intensity of the outflow of blood to the periphery;

The resistance of the walls of blood vessels and the elasticity of blood vessels;

Blood viscosity.

Blood pressure in the arteries changes along with the change in the work of the heart: during the period of the systole of the heart, it reaches a maximum (AT, or ATC) and is called maximum, or systolic pressure. In the diastolic phase of the heart, the pressure decreases to a certain initial level and is called diastolic, or minimum (AT, or ATX). Both systolic and diastolic blood pressure gradually decrease depending on the distance of the vessels from the heart (due to vascular resistance). Blood pressure is measured in millimeters mercury column (mm Hg) and is recorded by recording digital pressure values ​​in the form of a fraction: in the numerator AT, at the denominator AT, for example, 120/80 mm Hg.

The difference between systolic and diastolic pressure is called pulse pressure (PT) which is also measured in mmHg. Art. In our example above, the pulse pressure is 120 - 80 = 40 mm Hg. Art.

It is customary to measure blood pressure according to the Korotkov method (using a sphygmomanometer and a stethophonendoscope on the human brachial artery. Modern equipment allows you to measure blood pressure on the arteries of the wrist and other arteries. Blood pressure can vary significantly depending on the state of health of a person, as well as on the level of load and the excess of actual blood pressure over the corresponding age standards by 20% or more is called hypertension, and an insufficient level of pressure (80% or less of the age norm) is called hypotension.

In children under 10 years of age, normal blood pressure at rest is approximately: BP 90-105 mm Hg. in.; AT 50-65 mmHg Art. In children from 11 to 14 years old, functional juvenile hypertension can be observed, associated with hormonal changes during the pubertal period of development of the body with an increase in blood pressure on average: AT - 130-145 mm Hg. in.; AO "- 75-90 mm Hg. In adults, normal blood pressure can vary within: - 110-J 5ATD- 60-85 mm Hg. The value of blood pressure standards does not have significant differentiation depending on the sex of a person , and the age dynamics of these indicators is given in Table 14.

Vascular resistance is determined by the friction of blood against the walls of blood vessels and depends on the viscosity of the blood, the diameter and length of the vessels. Normal resistance to blood flow in the systemic circulation ranges from 1400 to 2800 dynes. With. / cm2, and in the pulmonary circulation from 140 to 280 dyn. With. / cm2.

Table 14

Age-related changes in mean blood pressure, mm Hg. Art. (S I. Galperin, 1965; A. G. Khripkova, ¡962)

Age, years	Boys (men)			Girls (women)
	BPs	ADD	ON	BPs	ADD	ON
baby	70	34	36	70	34	36
1	90	39	51	90	40	50
3-5	96	58	38	98	61	37
6	90	48	42	91	50	41
7	98	53	45	94	51	43
8	102	60	42	100	55	45
9	104	61	43	103	60	43
10	106	62	44	108	61	47
11	104	61	43	110	61	49
12	108	66	42	113	66	47
13	112	65	47	112	66	46
14	116	66	50	114	67	47
15	120	69	51	115	67	48
16	125	73	52	120	70	50
17	126	73	53	121	70	51
18 and over	110-135	60-85	50-60	110-135	60-85	55-60

The speed of blood movement is determined by the work of the heart and the condition of the vessels. The maximum speed of blood movement in the aorta (up to 500 mm / sec.), And the smallest - in the capillaries (0.5 mm / sec.), which is due to the fact that the total diameter of all capillaries is 800-1000 times larger than the diameter of the aorta. With the age of children, the speed of blood movement decreases, which is associated with an increase in the length of the vessels along with an increase in the length of the body. In newborns, the blood makes a complete circulation (i.e., passes through the large and small circles of blood circulation) in about 12 seconds; in 3-year-old children - in 15 seconds; at 14 per annum - in 18.5 seconds; in adults - in 22-25 seconds.

Blood circulation is regulated at two levels: at the level of the heart and at the level of blood vessels. The central regulation of the work of the heart is carried out from the centers of the parasympathetic (inhibitory action) and sympathetic (acceleration action) sections of the autonomic nervous system. In children under 6-7 years of age, the tonic influence of sympathetic innervations predominates, as evidenced by the increased pulse rate in children.

Reflex regulation of the work of the heart is possible from baroreceptors and chemoreceptors located mainly in the walls of blood vessels. Baroreceptors perceive blood pressure, and chemoreceptors perceive changes in the presence of oxygen (A.) and carbon dioxide (CO2) in the blood. Impulses from the receptors are sent to the diencephalon and from it they go to the center of regulation of the heart (medulla oblongata) and cause corresponding changes in its work (for example, an increased content of CO1 in the blood indicates circulatory failure and, thus, the heart begins to work more intensively). Reflex regulation is also possible along the path of conditioned reflexes, that is, from the cerebral cortex (for example, the pre-start excitement of athletes can significantly speed up the work of the heart, etc.).

Hormones can also affect the performance of the heart, especially adrenaline, whose action is similar to the action of the sympathetic innervations of the autonomic nervous system, that is, it accelerates the frequency and increases the strength of heart contractions.

The state of the vessels is also regulated by the central nervous system (from the vasomotor center), reflexively and humorally. Only vessels containing muscles in their walls, and these are, first of all, arteries of different levels, can influence hemodynamics. Parasympathetic impulses cause vasodilatation (vasodelation), while sympathetic impulses cause vasoconstriction (vasoconstriction). When the vessels dilate, the speed of blood movement decreases, the blood supply drops and vice versa.

Reflex changes in blood supply are also provided by pressure receptors and chemoreceptors on O2 and Cs72. In addition, there are chemoreceptors for the content of food digestion products in the blood (amino acids, monosugars, etc.): with the growth of digestion products in the blood, the vessels around the digestive tract expand (parasympathetic influence) and redistribution of blood occurs. There are also mechanoreceptors in the muscles that cause the redistribution of blood in the working muscles.

Humoral regulation of blood circulation is provided by the hormones adrenaline and vasopressin (cause narrowing of the lumen of blood vessels around the internal organs and their expansion in the muscles) and, sometimes, in the face (the effect of redness from stress). The hormones acetylcholine and histamine cause blood vessels to dilate.

During the development of a child, significant morphological and functional changes occur in his cardiovascular system. The formation of the heart in the embryo begins from the second week of embryogenesis and a four-chambered heart is formed by the end of the third week. The blood circulation of the fetus has its own characteristics, primarily related to the fact that before birth, oxygen enters the body through the placenta and the so-called umbilical vein.

The umbilical vein branches into two vessels, one feeding the liver, the other connected to the inferior vena cava. As a result, oxygen-rich blood (from the umbilical vein) and blood flowing from the organs and tissues of the fetus mix in the inferior vena cava. Thus, mixed blood enters the right atrium. As after birth, the atrial systole of the fetal heart directs blood into the ventricles, from there it enters the aorta from the left ventricle, and from the right ventricle into the pulmonary artery. However, the atria of the fetus are not isolated, but are connected using an oval hole, so the left ventricle sends blood to the aorta partially from the right atrium. A very small amount of blood enters the lungs through the pulmonary artery, since the lungs in the fetus do not function. Most of the blood ejected from the right ventricle into the pulmonary trunk, through a temporarily functioning vessel - the ductus botulinum - enters the aorta.

The most important role in the blood supply to the fetus is played by the umbilical arteries, which branch off from the iliac arteries. Through the umbilical opening, they leave the body of the fetus and, branching, form a dense network of capillaries in the placenta, from which the umbilical vein originates. The fetal circulatory system is closed. The mother's blood never enters the fetal blood vessels and vice versa. The supply of oxygen to the blood of the fetus is carried out by diffusion, since its partial pressure in the maternal vessels of the placenta is always higher than in the blood of the fetus.

After birth, the umbilical arteries and vein become empty and become ligaments. With the first breath of a newborn, the pulmonary circulation begins to function. Therefore, usually the botallian duct and the foramen ovale quickly overgrow. In children, the relative mass of the heart and the total lumen of the vessels are greater than in adults, which greatly facilitates the processes of blood circulation. The growth of the heart is closely related to the overall growth of the body. The heart grows most intensively in the first years of life and at the end of adolescence. The position and shape of the heart also change with age. In a newborn, the heart is spherical in shape and is located much higher than in an adult. Differences in these indicators are eliminated only by the age of ten. By the age of 12, the main functional differences in the cardiovascular system also disappear.

The heart rate (Table 5) in children under 12 - 14 years of age is higher than in adults, which is associated with the predominance of the tone of sympathetic centers in children.

In the process of postnatal development, the tonic influence of the vagus nerve is constantly increasing, and in adolescence, the degree of its influence in most children approaches the level of adults. A delay in the maturation of the tonic influence of the vagus nerve on cardiac activity could indicate a retardation of the child's development.

Table 5

Resting heart rate and respiration rate in children of different ages.

	Heart rate (bpm)	Respiratory rate (Vd/min)
newborns
boys

Table 6

The value of blood pressure at rest in children of different ages.

	Systolic blood pressure (mm Hg)	Diastolic BP (mm Hg)
adults

Blood pressure in children is lower than in adults (Table 6), and the rate of circulation is higher. The stroke volume of blood in a newborn is only 2.5 cm3, in the first year after birth it increases four times, then the growth rate decreases. To the level of an adult (70 - 75 cm3), stroke volume approaches only 15 - 16 years. With age, the minute volume of blood also increases, which provides the heart with increasing opportunities for adaptation to physical exertion.

Bioelectrical processes in the heart also have age-related features, so the electrocardiogram approaches the form of an adult by the age of 13-16.

Sometimes in the pubertal period there are reversible disturbances in the activity of the cardiovascular system associated with the restructuring of the endocrine system. At the age of 13-16, there may be an increase in heart rate, shortness of breath, vasospasm, violations of the electrocardiogram, etc. In the presence of circulatory dysfunctions, it is necessary to strictly dose and prevent excessive physical and emotional stress in a teenager.