Drawing of human blood circulation circles. Circulation circles

1. The importance of the circulatory system, the general plan of the structure. Large and small circles of blood circulation.

The circulatory system is the continuous movement of blood through a closed system of heart cavities and a network of blood vessels that provide all the vital functions of the body.

The heart is the primary pump that gives energy to the blood. This is a complex intersection of different blood streams. In a normal heart, mixing of these flows does not occur. The heart begins to contract about a month after conception, and from that moment its work does not stop until the last moment of life.

During a time equal to the average life expectancy, the heart performs 2.5 billion contractions, and at the same time it pumps 200 million liters of blood. This is a unique pump that is the size of a man's fist, and the average weight for a man is 300g, and for a woman - 220g. The heart has the shape of a blunt cone. Its length is 12-13 cm, width 9-10.5 cm, and the anterior-posterior size is 6-7 cm.

The system of blood vessels makes up 2 circles of blood circulation.

Systemic circulation begins in the left ventricle with the aorta. The aorta ensures the delivery of arterial blood to various organs and tissues. In this case, parallel vessels depart from the aorta, which bring blood to different organs: arteries turn into arterioles, and arterioles into capillaries. Capillaries provide the entire amount of metabolic processes in tissues. There the blood becomes venous, it flows away from the organs. It flows to the right atrium through the inferior and superior vena cava.

Pulmonary circulation begins in the right ventricle by the pulmonary trunk, which divides into the right and left pulmonary arteries. Arteries carry venous blood to the lungs, where gas exchange will occur. The outflow of blood from the lungs is carried out through the pulmonary veins (2 from each lung), which carry arterial blood to the left atrium. The main function of the small circle is transport; blood delivers oxygen, nutrients, water, salt to cells, and removes carbon dioxide and metabolic end products from tissues.

Circulation- this is the most important link in gas exchange processes. Thermal energy is transported with blood - this is heat exchange with the environment. Due to the circulatory function, hormones and other physiologically active substances are transferred. This ensures humoral regulation of the activity of tissues and organs. Modern ideas about the circulatory system were outlined by Harvey, who in 1628 published a treatise on the movement of blood in animals. He came to the conclusion that the circulatory system was closed. Using the method of clamping blood vessels, he established direction of blood movement. From the heart, blood moves through arterial vessels, through veins, blood moves towards the heart. The division is based on the direction of flow, and not on the content of blood. The main phases of the cardiac cycle were also described. The technical level did not allow the detection of capillaries at that time. The discovery of capillaries was made later (Malpighé), who confirmed Harvey's assumptions about the closed circulatory system. The gastrovascular system is a system of canals associated with the main cavity in animals.

2. Placental circulation. Features of blood circulation in a newborn.

The fetal circulatory system differs in many ways from that of the newborn. This is determined by both anatomical and functional characteristics of the fetal body, reflecting its adaptation processes during intrauterine life.

The anatomical features of the fetal cardiovascular system primarily consist in the existence of the foramen ovale between the right and left atria and the ductus arteriosus connecting the pulmonary artery to the aorta. This allows a significant amount of blood to bypass the non-functioning lungs. In addition, there is communication between the right and left ventricles of the heart. The blood circulation of the fetus begins in the vessels of the placenta, from where blood, enriched with oxygen and containing all the necessary nutrients, enters the umbilical cord vein. The arterial blood then enters the liver through the ductus venosus (Arantius). The fetal liver is a kind of blood depot. The left lobe plays the largest role in blood deposition. From the liver, through the same venous duct, blood flows into the inferior vena cava, and from there into the right atrium. The right atrium also receives blood from the superior vena cava. Between the confluence of the inferior and superior vena cava there is a valve of the inferior vena cava, which separates both blood flows. This valve directs the blood flow of the inferior vena cava from the right atrium to the left through the functioning foramen ovale. From the left atrium, blood flows into the left ventricle, and from there into the aorta. From the ascending aortic arch, blood enters the vessels of the head and upper body. Venous blood entering the right atrium from the superior vena cava flows into the right ventricle, and from it into the pulmonary arteries. From the pulmonary arteries, only a small part of the blood enters the non-functioning lungs. The bulk of blood from the pulmonary artery is directed through the arterial (botal) duct to the descending aortic arch. Blood from the descending aortic arch supplies the lower half of the body and lower extremities. After this, oxygen-poor blood flows through the branches of the iliac arteries into the paired arteries of the umbilical cord and through them into the placenta. The volumetric distribution of blood in the fetal circulation is as follows: approximately half of the total blood volume from the right side of the heart enters through the foramen ovale into the left side of the heart, 30% is discharged through the ductus arteriosus into the aorta, 12% enters the lungs. This distribution of blood is of very great physiological importance from the point of view of the individual organs of the fetus receiving blood rich in oxygen, namely, purely arterial blood is contained only in the umbilical cord vein, in the venous duct and liver vessels; mixed venous blood containing sufficient oxygen is found in the inferior vena cava and the ascending aortic arch, so the liver and upper body of the fetus are better supplied with arterial blood than the lower half of the body. Subsequently, as pregnancy progresses, a slight narrowing of the foramen ovale and a decrease in the size of the inferior vena cava occur. As a result, in the second half of pregnancy, the imbalance in the distribution of arterial blood decreases somewhat.

The physiological characteristics of the fetal blood circulation are important not only from the point of view of supplying it with oxygen. Fetal blood circulation is no less important for the implementation of the most important process of removing CO2 and other metabolic products from the fetal body. The anatomical features of the fetal circulation described above create the prerequisites for the implementation of a very short route of elimination of CO2 and metabolic products: aorta - umbilical cord arteries - placenta. The fetal cardiovascular system has pronounced adaptive reactions to acute and chronic stressful situations, thereby ensuring an uninterrupted supply of oxygen and essential nutrients to the blood, as well as the removal of CO2 and metabolic end products from the body. This is ensured by the presence of various neurogenic and humoral mechanisms that regulate heart rate, stroke volume, peripheral constriction and dilatation of the ductus arteriosus and other arteries. In addition, the fetal circulatory system is in close relationship with the hemodynamics of the placenta and mother. This relationship is clearly visible, for example, when compression syndrome of the inferior vena cava occurs. The essence of this syndrome is that in some women at the end of pregnancy, compression of the inferior vena cava and, apparently, partly of the aorta, occurs by the uterus. As a result, when a woman lies on her back, a redistribution of blood occurs, with a large amount of blood retained in the inferior vena cava, and blood pressure in the upper body decreases. Clinically, this is expressed in the occurrence of dizziness and fainting. Compression of the inferior vena cava by the pregnant uterus leads to circulatory disorders in the uterus, which in turn immediately affects the condition of the fetus (tachycardia, increased motor activity). Thus, consideration of the pathogenesis of inferior vena cava compression syndrome clearly demonstrates the presence of a close relationship between the maternal vascular system, the hemodynamics of the placenta and the fetus.

3. Heart, its hemodynamic functions. The cycle of heart activity, its phases. Pressure in the cavities of the heart, in different phases of the cardiac cycle. Heart rate and duration in different age periods.

The cardiac cycle is a period of time during which complete contraction and relaxation of all parts of the heart occurs. Contraction is systole, relaxation is diastole. The length of the cycle will depend on your heart rate. Normal contraction frequency ranges from 60 to 100 beats per minute, but the average frequency is 75 beats per minute. To determine the cycle duration, divide 60 s by frequency (60 s / 75 s = 0.8 s).

The cardiac cycle consists of 3 phases:

Atrial systole - 0.1 s

Ventricular systole - 0.3 s

Total pause 0.4 s

Heart condition in end of the general pause: The leaflet valves are open, the semilunar valves are closed and blood flows from the atria to the ventricles. By the end of the general pause, the ventricles are 70-80% filled with blood. The cardiac cycle begins with

atrial systole. At this time, the atria contract, which is necessary to complete the filling of the ventricles with blood. It is the contraction of the atrial myocardium and the increase in blood pressure in the atria - in the right up to 4-6 mm Hg, and in the left up to 8-12 mm Hg. ensures the pumping of additional blood into the ventricles and atrial systole completes the filling of the ventricles with blood. Blood cannot flow back because the circular muscles contract. The ventricles will contain end diastolic blood volume. On average, it is 120-130 ml, but in people engaged in physical activity up to 150-180 ml, which ensures more efficient work, this department goes into a state of diastole. Next comes ventricular systole.

Ventricular systole- the most complex phase of the cardiac cycle, lasting 0.3 s. In systole they secrete tension period, it lasts 0.08 s and period of exile. Each period is divided into 2 phases -

tension period

1. phase of asynchronous contraction - 0.05 s

2. isometric contraction phases - 0.03 s. This is the phase of isovalumic contraction.

period of exile

1. rapid expulsion phase 0.12s

2. slow phase 0.13 s.

The expulsion phase begins end systolic volume protodiastolic period

4. Valvular apparatus of the heart, its significance. Valve operation mechanism. Changes in pressure in different parts of the heart in different phases of the cardiac cycle.

In the heart, it is customary to distinguish atrioventricular valves located between the atria and ventricles - in the left half of the heart it is a bicuspid valve, in the right - a tricuspid valve, consisting of three leaflets. The valves open into the lumen of the ventricles and allow blood to pass from the atria into the ventricle. But during contraction, the valve closes and the ability of blood to flow back into the atrium is lost. On the left, the pressure is much greater. Structures with fewer elements are more reliable.

At the exit point of large vessels - the aorta and pulmonary trunk - there are semilunar valves, represented by three pockets. When the blood in the pockets is filled, the valves close, so the reverse movement of blood does not occur.

The purpose of the heart valve apparatus is to ensure one-way blood flow. Damage to the valve leaflets leads to valve insufficiency. In this case, reverse blood flow is observed as a result of loose valve connections, which disrupts hemodynamics. The boundaries of the heart change. Signs of development of insufficiency are obtained. The second problem associated with the valve area is valve stenosis - (for example, the venous ring is stenotic) - the lumen decreases. When they talk about stenosis, they mean either the atrioventricular valves or the place of origin of the vessels. Above the semilunar valves of the aorta, from its bulb, the coronary vessels depart. In 50% of people, the blood flow in the right is greater than in the left, in 20% the blood flow is greater in the left than in the right, 30% have the same outflow in both the right and left coronary arteries. Development of anastomoses between the coronary artery basins. Disruption of the blood flow of the coronary vessels is accompanied by myocardial ischemia, angina pectoris, and complete blockage leads to death - a heart attack. Venous outflow of blood occurs through the superficial venous system, the so-called coronary sinus. There are also veins that directly open into the lumen of the ventricle and right atrium.

Ventricular systole begins with a phase of asynchronous contraction. Some cardiomyocytes become excited and are involved in the excitation process. But the resulting tension in the ventricular myocardium ensures an increase in pressure in it. This phase ends with the closure of the leaflet valves and the ventricular cavity is closed. The ventricles are filled with blood and their cavity is closed, and the cardiomyocytes continue to develop a state of tension. The length of the cardiomyocyte cannot change. This is due to the properties of the liquid. Liquids do not compress. In a confined space, when cardiomyocytes are tense, it is impossible to compress the liquid. The length of cardiomyocytes does not change. Isometric contraction phase. Shortening at low length. This phase is called the isovalumic phase. During this phase, blood volume does not change. The ventricular space is closed, pressure increases, in the right one up to 5-12 mm Hg. in the left 65-75 mmHg, while the ventricular pressure will become greater than the diastolic pressure in the aorta and pulmonary trunk, and the excess of the pressure in the ventricles over the blood pressure in the vessels leads to the opening of the semilunar valves. The semilunar valves open and blood begins to flow into the aorta and pulmonary trunk.

The expulsion phase begins, when the ventricles contract, blood is pushed into the aorta, into the pulmonary trunk, the length of cardiomyocytes changes, the pressure increases and at the height of systole in the left ventricle 115-125 mm, in the right ventricle 25-30 mm. There is a rapid expulsion phase at first, and then the expulsion becomes slower. During ventricular systole, 60 - 70 ml of blood is pushed out and this amount of blood is the systolic volume. Systolic blood volume = 120-130 ml, i.e. There is still a sufficient volume of blood in the ventricles at the end of systole - end systolic volume and this is a kind of reserve so that, if necessary, the systolic output can be increased. The ventricles complete systole and relaxation begins in them. The pressure in the ventricles begins to fall and the blood that is thrown into the aorta, the pulmonary trunk rushes back into the ventricle, but on its way it encounters the pockets of the semilunar valve, which close the valve when filled. This period was called protodiastolic period- 0.04s. When the semilunar valves are closed, the leaflet valves are also closed, the period of isometric relaxation ventricles. It lasts 0.08s. Here the voltage drops without changing the length. This causes a decrease in pressure. Blood has accumulated in the ventricles. Blood begins to put pressure on the atrioventricular valves. They open at the beginning of ventricular diastole. The period of filling the blood with blood begins - 0.25 s, while a rapid filling phase is distinguished - 0.08 and a slow filling phase - 0.17 s. Blood flows freely from the atria into the ventricle. This is a passive process. The ventricles will be 70-80% filled with blood and the filling of the ventricles will be completed by the next systole.

5. Systolic and minute blood volume, methods of determination. Age-related changes in these volumes.

Cardiac output is the amount of blood ejected by the heart per unit time. There are:

Systolic (during 1st systole);

Minute blood volume (or MOC) is determined by two parameters, namely systolic volume and heart rate.

The systolic volume at rest is 65-70 ml, and is the same for the right and left ventricles. At rest, the ventricles eject 70% of the end-diastolic volume, and by the end of systole, 60-70 ml of blood remains in the ventricles.

V syst avg.=70ml, ν avg=70 beats/min,

V min=V syst * ν= 4900 ml per min ~ 5 l/min.

It is difficult to directly determine V min; an invasive method is used for this.

An indirect method based on gas exchange was proposed.

Fick method (method for determining IOC).

IOC = O2 ml/min / A - V(O2) ml/l of blood.

1. O2 consumption per minute is 300 ml;
2. O2 content in arterial blood = 20 vol%;
3. O2 content in venous blood = 14 vol%;
4. Arteriovenous difference in oxygen = 6 vol% or 60 ml of blood.

MOQ = 300 ml/60ml/l = 5l.

The value of systolic volume can be defined as V min/ν. Systolic volume depends on the strength of contractions of the ventricular myocardium and on the amount of blood filling the ventricles in diastole.

The Frank-Starling law states that systole is a function of diastole.

The value of minute volume is determined by the change in ν and systolic volume.

During physical activity, the value of minute volume can increase to 25-30 l, systolic volume increases to 150 ml, ν reaches 180-200 beats per minute.

The reactions of physically trained people relate primarily to changes in systolic volume, of untrained people - frequency, in children only due to frequency.

IOC distribution.

	Aorta and major arteries
	Small arteries
	Arterioles
	Capillaries
Total - 20%
	Small veins
	Large veins
Total - 64%
		Small circle

6. Modern ideas about the cellular structure of the myocardium. Types of cells in the myocardium. Nexuses, their role in conducting excitation.

The heart muscle has a cellular structure and the cellular structure of the myocardium was established back in 1850 by Kölliker, but for a long time it was believed that the myocardium is a network - sencidium. And only electron microscopy confirmed that each cardiomyocyte has its own membrane and is separated from other cardiomyocytes. The area of ​​contact of cardiomyocytes is the intercalary discs. Currently, cardiac muscle cells are divided into cells of the working myocardium - cardiomyocytes of the working myocardium of the atria and ventricles and into cells of the conduction system of the heart. Highlight:

-Ppacemaker cells

-transitional cells

-Purkinje cells

The cells of the working myocardium belong to striated muscle cells and cardiomyocytes have an elongated shape, their length reaches 50 µm, and their diameter is 10-15 µm. Fibers consist of myofibrils, the smallest working structure of which is the sarcomere. The latter has thick myosin and thin actin branches. The thin filaments contain regulatory proteins - tropanin and tropomyosin. Cardiomyocytes also have a longitudinal system of L tubules and transverse T tubules. However, T tubules, unlike the T-tubules of skeletal muscles, originate at the level of membranes Z (in skeletal ones - at the border of disk A and I). Neighboring cardiomyocytes are connected using an intercalary disc—the membrane contact area. In this case, the structure of the intercalary disk is heterogeneous. IN the insert disk, you can select the gap area (10-15 Nm). The second zone of tight contact is desmosomes. In the region of desmosomes, a thickening of the membrane is observed, and tonofibrils (threads connecting adjacent membranes) pass here. Desmosomes are 400 nm long. There are tight junctions, they are called nexuses, in which the outer layers of adjacent membranes merge, now discovered - conexons - bonding due to special proteins - conexins. Nexuses - 10-13%, this area has a very low electrical resistance of 1.4 ohms per kV.cm. This makes it possible to transmit an electrical signal from one cell to another and therefore cardiomyocytes are simultaneously included in the excitation process. Myocardium is a functional sensorium. Cardiomyocytes are isolated from each other and contact in the area of ​​intercalated discs, where the membranes of neighboring cardiomyocytes come into contact.

7. Automaticity of the heart. Conduction system of the heart. Automatic gradient. The Stannius Experience. 8. Physiological properties of the heart muscle. Refractory phase. The relationship between the phases of action potential, contraction and excitability in different phases of the cardiac cycle.

Cardiomyocytes are isolated from each other and contact in the area of ​​intercalated discs, where the membranes of neighboring cardiomyocytes come into contact.

Connesxons are connections in the membrane of neighboring cells. These structures are formed due to connexin proteins. The connexon is surrounded by 6 such proteins, a channel is formed inside the connexon that allows ions to pass, thus the electric current spreads from one cell to another. “f area has a resistance of 1.4 ohms per cm2 (low). Excitation covers cardiomyocytes simultaneously. They function as functional sensors. Nexuses are very sensitive to a lack of oxygen, to the action of catecholamines, to stressful situations, and to physical activity. This can cause disruption of the conduction of excitation in the myocardium. Under experimental conditions, disruption of tight junctions can be achieved by placing pieces of myocardium in a hypertonic sucrose solution. Important for the rhythmic activity of the heart conduction system of the heart- this system consists of a complex of muscle cells that form bundles and nodes, and the cells of the conduction system differ from the cells of the working myocardium - they are poor in myofibrils, rich in sarcoplasm and contain a high glycogen content. These features on light microscopy make them appear lighter in color with little cross-striation and have been termed atypical cells.

The conduction system includes:

1. Sinoatrial node (or Keith-Flyaka node), located in the right atrium at the confluence of the superior vena cava

2. Atrioventricular node (or Aschoff-Tavara node), which lies in the right atrium on the border with the ventricle - this is the posterior wall of the right atrium

These two nodes are connected by intraatrial tracts.

3. Atrial tracts

Anterior - with Bachman's branch (to the left atrium)

Middle tract (Wenckebach)

Posterior tract (Torel)

4. Bundle of Hiss (departs from the atrioventricular node. Passes through fibrous tissue and provides communication between the atrium myocardium and the ventricular myocardium. Passes into the interventricular septum, where it divides into the right and left bundle branches of Hiss)

5. Right and left legs of the Hiss bundle (they run along the interventricular septum. The left leg has two branches - anterior and posterior. The final branches will be Purkinje fibers).

6. Purkinje fibers

In the conduction system of the heart, which is formed by modified types of muscle cells, there are three types of cells: pacemaker (P), transition cells and Purkinje cells.

1. P cells. They are located in the sino-arterial node, less so in the atrioventricular nucleus. These are the smallest cells, they have few t-fibrils and mitochondria, there is no t-system, l. the system is poorly developed. The main function of these cells is to generate action potentials due to the innate property of slow diastolic depolarization. They undergo a periodic decrease in membrane potential, which leads them to self-excitation.

2. Transitional cells carry out the transmission of excitation in the region of the atriventricular nucleus. They are found between P cells and Purkinje cells. These cells are elongated and lack sarcoplasmic reticulum. These cells exhibit a slow conduction speed.

3. Purkinje cells wide and short, they have more myofibrils, the sarcoplasmic reticulum is better developed, the T-system is absent.

9. Ionic mechanisms of action potential occurrence in cells of the conduction system. The role of slow Ca channels. Features of the development of slow diastolic depolarization in true and latent pacemakers. Differences in the action potential in the cells of the cardiac conduction system and working cardiomyocytes.

The cells of the conducting system have distinctive features of the potential.

1. Reduced membrane potential during the diastolic period (50-70mV)

2. The fourth phase is not stable and there is a gradual decrease in the membrane potential to a threshold critical level of depolarization and in diastole gradually slowly continues to decrease reaching a critical level of depolarization at which self-excitation of P-cells occurs. In P-cells, there is an increase in the penetration of sodium ions and a decrease in the output of potassium ions. The permeability of calcium ions increases. These shifts in ionic composition cause the membrane potential in the P-cell to decrease to a threshold level and the P-cell to self-excite, producing an action potential. The Plateau phase is poorly defined. Phase zero smoothly transitions through the TV process of repolarization, which restores the diastolic membrane potential, and then the cycle repeats again and the P-cells enter a state of excitation. The cells of the sinoatrial node have the greatest excitability. The potential in it is particularly low and the rate of diastolic depolarization is the highest. This will affect the frequency of excitation. P-cells of the sinus node generate a frequency of up to 100 beats per minute. The nervous system (sympathetic system) suppresses the action of the node (70 beats). The sympathetic system can increase automaticity. Humoral factors - adrenaline, norepinephrine. Physical factors - mechanical factor - stretching, stimulate automaticity, warming also increases automaticity. All this is used in medicine. This is the basis for direct and indirect cardiac massage. The area of ​​the atrioventricular node also has automaticity. The degree of automaticity of the atrioventricular node is much less pronounced and, as a rule, it is 2 times less than in the sinus node - 35-40. In the conduction system of the ventricles, impulses can also occur (20-30 per minute). As the conduction system progresses, a gradual decrease in the level of automaticity occurs, which is called the automaticity gradient. The sinus node is the center of first-order automation.

10. Morphological and physiological characteristics of the working muscle of the heart. The mechanism of excitation in working cardiomyocytes. Analysis of action potential phases. Duration of PD, its relationship with refractory periods.

The action potential of the ventricular myocardium lasts about 0.3 s (more than 100 times longer than the action potential of skeletal muscle). During PD, the cell membrane becomes immune to the action of other stimuli, i.e., refractory. The relationships between the phases of myocardial action potential and the magnitude of its excitability are shown in Fig. 7.4. Distinguish between periods absolute refractoriness(lasts 0.27 s, i.e. slightly shorter than the duration of the AP; period relative refractoriness, during which the heart muscle can respond with contraction only to very strong stimulation (lasts 0.03 s), and a short period supernormal excitability, when the heart muscle can respond with contraction to subthreshold stimulation.

Myocardial contraction (systole) lasts about 0.3 s, which approximately coincides in time with the refractory phase. Consequently, during the period of contraction, the heart is unable to respond to other stimuli. The presence of a long refractory phase prevents the development of continuous shortening (tetanus) of the heart muscle, which would lead to the inability of the heart to perform its pumping function.

11. Heart reaction to additional stimulation. Extrasystoles, their types. Compensatory pause, its origin.

The refractory period of the heart muscle lasts and coincides in time as long as the contraction lasts. Following relative refractoriness, there is a short period of increased excitability - excitability becomes higher than the initial level - super normal excitability. During this phase, the heart is especially sensitive to the effects of other irritants (other irritants or extrasystoles may occur - extraordinary systoles). The presence of a long refractory period should protect the heart from repeated excitations. The heart performs a pumping function. The interval between normal and extraordinary contraction shortens. The pause can be normal or extended. An extended pause is called compensatory. The cause of extrasystoles is the occurrence of other foci of excitation - the atrioventricular node, elements of the ventricular part of the conduction system, cells of the working myocardium. This may be due to impaired blood supply, impaired conduction in the heart muscle, but all additional foci are ectopic foci of excitation. Depending on the location, there are different extrasystoles - sinus, premiddle, atrioventricular. Ventricular extrasystoles are accompanied by an extended compensatory phase. 3 additional irritation is the cause of extraordinary contraction. During extrasystole, the heart loses excitability. Another impulse comes to them from the sinus node. A pause is needed to restore normal rhythm. When a malfunction occurs in the heart, the heart skips one normal contraction and then returns to a normal rhythm.

12. Conduction of excitation in the heart. Atrioventricular delay. Blockade of the conduction system of the heart.

Conductivity- ability to carry out stimulation. The speed of excitation in different departments is not the same. In the atrium myocardium - 1 m/s and the excitation time takes 0.035 s

Excitation speed

Myocardium - 1 m/s 0.035

Atrioventricular node 0.02 - 0-05 m/s. 0.04 s

Conduction of the ventricular system - 2-4.2 m/s. 0.32

In total, from the sinus node to the ventricular myocardium - 0.107 s

Ventricular myocardium - 0.8-0.9 m/s

Impaired conduction of the heart leads to the development of blockades - sinus, atrioventricular, Hiss bundle and its legs. The sinus node may turn off. Will the atrioventricular node turn on as a pacemaker? Sinus blocks are rare. More in the atrioventricular nodes. As the delay increases (more than 0.21 s), the excitation reaches the ventricle, albeit slowly. Loss of individual excitations that arise in the sinus node (For example, out of three, only two reach - this is the second degree of blockade. The third degree of blockade, when the atria and ventricles work uncoordinated. Blockade of the legs and bundle is a blockade of the ventricles. Blockades of the legs of the Hiss bundle and accordingly, one ventricle lags behind the other).

13. Electromechanical coupling in the cardiac muscle. The role of Ca ions in the mechanisms of contraction of working cardiomyocytes. Sources of Ca ions. Laws of “All or nothing”, “Frank-Starling”. The phenomenon of potentiation (the “ladder” phenomenon), its mechanism.

Cardiomyocytes include fibrils and sarcomeres. There are longitudinal tubules and T tubules of the outer membrane, which enter inside at the level of the membrane. They are wide. The contractile function of cardiomyocytes is associated with the proteins myosin and actin. On thin actin proteins there is a system of troponin and tropomyosin. This prevents the myosin heads from engaging with the myosin heads. Removing the blockage - with calcium ions. Calcium channels open along the tubules. An increase in calcium in the sarcoplasm removes the inhibitory effect of actin and myosin. Myosin bridges move the tonic filament toward the center. The myocardium obeys 2 laws in its contractile function - all or nothing. The strength of contraction depends on the initial length of cardiomyocytes - Frank and Staraling. If myocytes are pre-stretched, they respond with greater contraction force. Stretching depends on blood filling. The more, the stronger. This law is formulated as - systole is a function of diastole. This is an important adaptive mechanism. This synchronizes the work of the right and left ventricles.

14. Physical phenomena associated with the work of the heart. Apical impulse.

erhushechny push represents a rhythmic pulsation in the fifth intercostal space 1 cm inward from the midclavicular line, caused by beats of the apex of the heart.

In diastole, the ventricles have the shape of an irregular oblique cone. In systole, they take on the shape of a more regular cone, while the anatomical region of the heart lengthens, the apex rises and the heart rotates from left to right. The base of the heart descends slightly. These changes in the shape of the heart make it possible for the heart to touch the chest wall. This is also facilitated by the hydrodynamic effect during blood release.

The apical impulse is better determined in a horizontal position with a slight turn to the left side. The apical impulse is examined by palpation, placing the palm of the right hand parallel to the intercostal space. In this case, the following are determined propulsion properties: localization, area (1.5-2 cm2), height or amplitude of vibration and force of the push.

With an increase in the mass of the right ventricle, pulsation is sometimes observed over the entire area of ​​​​the projection of the heart, then they speak of a cardiac impulse.

When the heart works, there are sound manifestations in the form of heart sounds. To study heart sounds, the method of auscultation and graphic recording of sounds using a microphone and a phonocardiograph amplifier is used.

15. Heart sounds, their origin, components, features of heart sounds in children. Methods for studying heart sounds (auscultation, phonocardiography).

First tone appears in ventricular systole and is therefore called systolic. In its properties it is dull, drawn-out, low. Its duration ranges from 0.1 to 0.17 s. The main reason for the appearance of the first background is the process of closing and vibration of the cusps of the atrioventricular valves, as well as contraction of the ventricular myocardium and the occurrence of turbulent blood movement in the pulmonary trunk and aorta.

On the phonocardiogram. 9-13 vibrations. A low-amplitude signal is identified, then high-amplitude vibrations of the valve leaflets and a low-amplitude vascular segment. In children, this tone is shorter than 0.07-0.12 s

Second tone occurs 0.2 s after the first one. He is short and tall. Lasts 0.06 - 0.1 s. Associated with the closure of the semilunar valves of the aorta and pulmonary trunk at the beginning of diastole. Therefore, it received the name diastolic tone. When the ventricles relax, the blood rushes back into the ventricles, but on its way it encounters the semilunar valves, which creates a second sound.

On the phonocardiogram it corresponds to 2-4 vibrations. Normally, during the inhalation phase, you can sometimes hear a splitting of the second tone. During the inhalation phase, blood flow to the right ventricle becomes lower due to a decrease in intrathoracic pressure and the systole of the right ventricle lasts slightly longer than the left, so the pulmonary valve closes a little more slowly. As you exhale, they close simultaneously.

In pathology, splitting is present both in the inhalation and exhalation phases.

Third tone occurs 0.13 s after the second. It is associated with vibrations of the walls of the ventricle during the phase of rapid filling with blood. The phonocardiogram shows 1-3 vibrations. 0.04s.

Fourth tone. Associated with atrial systole. It is recorded in the form of low-frequency oscillations, which can merge with the systole of the heart.

When listening to the tone, determine their strength, clarity, timbre, frequency, rhythm, presence or absence of noise.

It is proposed to listen to heart sounds at five points.

The first sound is better heard in the area of ​​​​the projection of the apex of the heart in the 5th right intercostal space 1 cm deep. The tricuspid valve is heard in the lower third of the sternum in the middle.

The second sound is better heard in the second intercostal space on the right for the aortic valve and the second intercostal space on the left for the pulmonary valve.

Gotken's fifth point - place of attachment of 3-4 ribs to the sternum on the left. This point corresponds to the projection of the aortic and ventral valves onto the chest wall.

When auscultating, you can also hear noises. The appearance of noise is associated either with a narrowing of the valve openings, which is referred to as stenosis, or with damage to the valve leaflets and their loose closure, then valve insufficiency occurs. Depending on the time of appearance of noises, they can be systolic or diastolic.

16. Electrocardiogram, the origin of its waves. ECG intervals and segments. Clinical significance of the ECG. Age-related features of ECG.

Excitation of a huge number of cells of the working myocardium causes the appearance of a negative charge on the surface of these cells. The heart becomes a powerful electric generator. Body tissues, having a relatively high electrical conductivity, make it possible to record the electrical potentials of the heart from the surface of the body. This method of studying the electrical activity of the heart, introduced into practice by V. Einthoven, A. F. Samoilov, T. Lewis, V. F. Zelenin, etc., was called electrocardiography, and the curve recorded with its help is called electrocardiogram (ECG). Electrocardiography is widely used in medicine as a diagnostic method that allows one to assess the dynamics of the spread of excitation in the heart and judge cardiac dysfunction due to ECG changes.

Currently, they use special devices - electrocardiographs with electronic amplifiers and oscilloscopes. The curves are recorded on a moving paper tape. Instruments have also been developed that record ECGs during active muscular activity and at a distance from the subject. These devices - teleelectrocardiographs - are based on the principle of transmitting an ECG over a distance using radio communication. In this way, ECG is recorded in athletes during competitions, in astronauts during space flight, etc. Devices have been created for transmitting electrical potentials arising during heart activity via telephone wires and recording ECG in a specialized center located at a great distance from the patient .

Due to the specific position of the heart in the chest and the peculiar shape of the human body, the electrical lines of force that arise between the excited (-) and unexcited (+) parts of the heart are distributed unevenly over the surface of the body. For this reason, depending on the location of application of the electrodes, the shape of the ECG and the voltage of its teeth will be different. To record an ECG, potentials are drawn from the limbs and the surface of the chest. Usually three so-called standard limb leads: Lead I: right hand - left hand; Lead II: right arm - left leg; III lead: left arm - left leg (Fig. 7.5). In addition, three are registered unipolar enhanced leads according to Goldberger: aVR; aVL; aVF. When recording enhanced leads, two electrodes used to record standard leads are combined into one and the potential difference between the combined and active electrodes is recorded. So, with aVR, the electrode placed on the right hand is active, with aVL - on the left hand, with aVF - on the left leg. Wilson proposed registration of six chest leads.

Formation of various ECG components:

1) Wave P - reflects depolarization of the atria. Duration 0.08-0.10 sec, amplitude 0.5-2 mm.

2) PQ interval - conduction of AP along the conduction system of the heart from the SA to the AV node and further to the ventricular myocardium, including atrioventricular delay. Duration 0.12-0.20 sec.

3) Q wave - excitation of the apex of the heart and the right papillary muscle. Duration 0-0.03 sec, amplitude 0-3 mm.

4) Wave R - excitation of the bulk of the ventricles. Duration 0.03-0.09, amplitude 10-20 mm.

5) Wave S - the end of ventricular excitation. Duration 0-0.03 sec, amplitude 0-6 mm.

6) QRS complex - coverage of ventricular excitation. Duration 0.06-0.10 sec

7) ST segment - reflects the process of complete coverage of the ventricles by excitation. The duration is highly dependent on heart rate. Displacement of this segment up or down by more than 1 mm may indicate myocardial ischemia.

8) Wave T - repolarization of the ventricles. Duration 0.05-0.25 sec, amplitude 2-5 mm.

9) Q-T interval - the duration of the ventricular depolarization-repolarization cycle. Duration 0.30-0.40 sec.

17. Methods for recording ECG in humans. Dependence of the size of ECG waves in various leads on the position of the electrical axis of the heart (Einthoven’s triangle rule).

In general, the heart can also be considered as electric dipole(negatively charged base, positively charged top). The line that connects the areas of the heart with the maximum potential difference - electrical line of the heart . When projected, it coincides with the anatomical axis. When the heart works, an electric field arises. The power lines of this electric field propagate in the human body as in a volumetric conductor. Different areas of the body will receive different charges.

The orientation of the heart's electrical field causes the upper torso, right arm, head and neck to have a negative charge. The lower half of the torso, both legs and left arm have a positive charge.

If you place electrodes on the surface of the body, it will be registered potential difference. To register potential differences, there are various lead systems.

Leadis an electrical circuit that has a potential difference and is connected to an electrocardiograph. The electrocardiogram is recorded using 12 leads. These are 3 standard bipolar leads. Then 3 reinforced unipolar leads and 6 chest leads.

Standard leads.

1 lead. Right and left forearms

2 lead. Right hand - left shin.

3 lead. Left hand - left foot.

Unipolar leads. The magnitude of potentials at one point relative to others is measured.

1 lead. Right hand - left hand + left leg (AVR)

2 lead. AVL Left hand - right hand right leg

3. AVF abduction left leg - right arm + left arm.

Chest leads. They are single-pole.

1 lead. 4th intercostal space to the right of the sternum.

2 lead. 4th intercostal space to the left of the sternum.

4 lead. Projection of the apex of the heart

3 lead. Midway between second and fourth.

4 lead. 5th intercostal space along the anterior axillary line.

6 lead. 5th intercostal space in the midaxillary line.

The change in the electromotive force of the heart during the cycle, recorded on the curve is called electrocardiogram . The electrocardiogram reflects a certain sequence of occurrence of excitation in different parts of the heart and is a complex of teeth and segments horizontally located between them.

18. Nervous regulation of the heart. Characteristics of the influences of the sympathetic nervous system on the heart. Strengthening nerve of I.P. Pavlov.

Nervous extracardiac regulation. This regulation is carried out by impulses coming to the heart from the central nervous system along the vagus and sympathetic nerves.

Like all autonomic nerves, cardiac nerves are formed by two neurons. The bodies of the first neurons, the processes of which make up the vagus nerves (parasympathetic division of the autonomic nervous system), are located in the medulla oblongata (Fig. 7.11). The processes of these neurons end in the intramural ganglia of the heart. Here are the second neurons, the processes of which go to the conduction system, the myocardium and coronary vessels.

The first neurons of the sympathetic part of the autonomic nervous system, transmitting impulses to the heart, are located in the lateral horns of the five upper segments of the thoracic spinal cord. The processes of these neurons end in the cervical and upper thoracic sympathetic ganglia. These nodes contain second neurons, the processes of which go to the heart. Most of the sympathetic nerve fibers innervating the heart arise from the stellate ganglion.

With prolonged irritation of the vagus nerve, the heart contractions that initially stopped are restored, despite the ongoing irritation. This phenomenon is called

I. P. Pavlov (1887) discovered nerve fibers (strengthening nerve) that enhance heart contractions without a noticeable increase in rhythm (positive inotropic effect).

The inotropic effect of the “amplifying” nerve is clearly visible when intraventricular pressure is recorded with an electromanometer. The pronounced influence of the “reinforcing” nerve on myocardial contractility is manifested especially in cases of contractility disorders. One of these extreme forms of contractility disorders is alternation of heart contractions, when one “normal” myocardial contraction (a pressure develops in the ventricle that exceeds the pressure in the aorta and blood is ejected from the ventricle into the aorta) alternates with a “weak” myocardial contraction, in which the pressure in the ventricle during systole does not reach the pressure in the aorta and blood ejection does not occur. The “enhancing” nerve not only enhances normal contractions of the ventricles, but also eliminates alternation, restoring ineffective contractions to normal ones (Fig. 7.13). According to I.P. Pavlov, these fibers are specifically trophic, that is, they stimulate metabolic processes.

The totality of the data presented makes it possible to imagine the influence of the nervous system on the heart rhythm as corrective, i.e. the heart rhythm originates in its pacemaker, and nervous influences accelerate or slow down the rate of spontaneous depolarization of pacemaker cells, thus accelerating or slowing down the heart rate .

In recent years, facts have become known indicating the possibility of not only corrective, but also triggering influences of the nervous system on the heart rhythm, when signals arriving along the nerves initiate heart contractions. This can be observed in experiments with irritation of the vagus nerve in a mode close to natural impulses in it, i.e., in “volleys” (“packs”) of impulses, and not in a continuous stream, as was traditionally done. When the vagus nerve is irritated by “volleys” of impulses, the heart contracts in the rhythm of these “volleys” (each “volley” corresponds to one heart contraction). By changing the frequency and characteristics of the “volleys,” you can control the heart rhythm over a wide range.

19. Characteristics of the influence of the vagus nerves on the heart. Tone of the vagus nerve centers. Proof of its presence is age-related changes in the tone of the vagus nerves. Factors that support the tone of the vagus nerves. The phenomenon of the heart “escaping” from the influence of the vagus. Features of the influence of the right and left vagus nerves on the heart.

The influence of the vagus nerves on the heart was first studied by the Weber brothers (1845). They found that irritation of these nerves slows down the heart until it stops completely in diastole. This was the first case of discovery of the inhibitory influence of nerves in the body.

With electrical stimulation of the peripheral segment of the cut vagus nerve, a decrease in heart contractions occurs. This phenomenon is called negative chronotropic effect. At the same time, there is a decrease in the amplitude of contractions - negative inotropic effect.

With severe irritation of the vagus nerves, the heart stops working for a while. During this period, the excitability of the heart muscle is reduced. A decrease in the excitability of the heart muscle is called negative bathmotropic effect. Slowing down the conduction of excitation in the heart is called negative dromotropic effect. Often there is a complete blockade of excitation conduction in the atrioventricular node.

With prolonged irritation of the vagus nerve, the heart contractions that initially stopped are restored, despite the ongoing irritation. This phenomenon is called the heart escaping from the influence of the vagus nerve.

The influence of sympathetic nerves on the heart was first studied by the Tsion brothers (1867), and then by I. P. Pavlov. Zions described an increase in cardiac activity when the sympathetic nerves of the heart are irritated (positive chronotropic effect); They named the corresponding fibers nn. accelerantes cordis (heart accelerators).

When sympathetic nerves are irritated, the spontaneous depolarization of pacemaker cells in diastole accelerates, which leads to increased heart rate.

Irritation of the cardiac branches of the sympathetic nerve improves the conduction of excitation in the heart (positive dromotropic effect) and increases the excitability of the heart (positive bathmotropic effect). The effect of sympathetic nerve irritation is observed after a long latent period (10 s or more) and continues long after the cessation of nerve irritation.

20. Molecular-cellular mechanisms of excitation transmission from autonomic (autonomic) nerves to the heart.

The chemical mechanism of transmission of nerve impulses in the heart. When the peripheral segments of the vagus nerves are irritated, ACh is released at their endings in the heart, and when the sympathetic nerves are irritated, norepinephrine is released. These substances are direct agents that inhibit or enhance the activity of the heart, and therefore are called mediators (transmitters) of nervous influences. The existence of mediators was shown by Levy (1921). He irritated the vagus or sympathetic nerve of an isolated frog heart, and then transferred fluid from this heart to another, also isolated, but not subject to nervous influence - the second heart gave the same reaction (Fig. 7.14, 7.15). Consequently, when the nerves of the first heart are irritated, the corresponding mediator passes into the fluid that feeds it. In the lower curves you can see the effects caused by the transferred Ringer's solution, which was in the heart during irritation.

ACh, formed in the endings of the vagus nerve, is quickly destroyed by the enzyme cholinesterase, present in the blood and cells, so ACh has only a local effect. Norepinephrine is destroyed much more slowly than ACh, and therefore acts longer. This explains the fact that after the cessation of irritation of the sympathetic nerve, increased frequency and intensification of heart contractions persist for some time.

Data have been obtained indicating that upon excitation, along with the main transmitter substance, other biologically active substances, in particular peptides, also enter the synaptic cleft. The latter have a modulating effect, changing the magnitude and direction of the heart's reaction to the main mediator. Thus, opioid peptides inhibit the effects of vagus nerve irritation, and delta sleep peptide enhances vagal bradycardia.

21. Humoral regulation of cardiac activity. The mechanism of action of true, tissue hormones and metabolic factors on cardiomyocytes. The importance of electrolytes in the work of the heart. Endocrine function of the heart.

Changes in the functioning of the heart are observed under the influence of a number of biologically active substances circulating in the blood.

Catecholamines (adrenaline, norepinephrine) increase strength and increase heart rate, which has important biological significance. During physical activity or emotional stress, the adrenal medulla releases a large amount of adrenaline into the blood, which leads to increased cardiac activity, which is extremely necessary in these conditions.

This effect occurs as a result of stimulation of myocardial receptors by catecholamines, causing activation of the intracellular enzyme adenylate cyclase, which accelerates the formation of 3,5"-cyclic adenosine monophosphate (cAMP). It activates phosphorylase, which causes the breakdown of intramuscular glycogen and the formation of glucose (a source of energy for the contracting myocardium). In addition, phosphorylase is necessary for the activation of Ca 2+ ions, an agent that couples excitation and contraction in the myocardium (this also enhances the positive inotropic effect of catecholamines). In addition, catecholamines increase the permeability of cell membranes for Ca 2+ ions, promoting, on the one hand, an increase in their entry from the intercellular space into the cell, and on the other, the mobilization of Ca 2+ ions from intracellular stores.

Activation of adenylate cyclase is noted in the myocardium and under the action of glucagon, a hormone secreted α -cells of pancreatic islets, which also causes a positive inotropic effect.

Hormones of the adrenal cortex, angiotensin and serotonin also increase the strength of myocardial contractions, and thyroxine increases heart rate. Hypoxemia, hypercapnia and acidosis inhibit myocardial contractile activity.

Atrial myocytes form atriopeptide, or natriuretic hormone. The secretion of this hormone is stimulated by stretching of the atria by the inflowing volume of blood, changes in the level of sodium in the blood, the content of vasopressin in the blood, as well as the influence of extracardiac nerves. Natriuretic hormone has a wide spectrum of physiological activity. It greatly increases the excretion of Na + and Cl - ions by the kidneys, suppressing their reabsorption in the nephron tubules. The effect on diuresis is also due to an increase in glomerular filtration and suppression of water reabsorption in the tubules. Natriuretic hormone suppresses renin secretion and inhibits the effects of angiotensin II and aldosterone. Natriuretic hormone relaxes the smooth muscle cells of small vessels, thereby helping to lower blood pressure, as well as the smooth muscles of the intestine.

22. The importance of the centers of the medulla oblongata and hypothalamus in the regulation of heart function. The role of the limbic system and the cerebral cortex in the mechanisms of adaptation of the heart to external and internal stimuli.

The centers of the vagus and sympathetic nerves are the second level of the hierarchy of nerve centers that regulate the functioning of the heart. By integrating reflex and descending influences from the higher parts of the brain, they form signals that control the activity of the heart, including determining the rhythm of its contractions. A higher level of this hierarchy is the centers of the hypothalamic region. With electrical stimulation of various zones of the hypothalamus, reactions of the cardiovascular system are observed that are much stronger and more pronounced than the reactions that occur under natural conditions. With local point stimulation of some points of the hypothalamus, it was possible to observe isolated reactions: a change in the heart rhythm, or the strength of contractions of the left ventricle, or the degree of relaxation of the left ventricle, etc. Thus, it was possible to reveal that the hypothalamus contains structures that can regulate individual functions of the heart. Under natural conditions, these structures do not work in isolation. The hypothalamus is an integrative center that can change any parameters of cardiac activity and the state of any parts of the cardiovascular system in order to meet the body's needs for behavioral reactions that arise in response to changing environmental (and internal) environmental conditions.

The hypothalamus is only one of the levels of the hierarchy of centers that regulate the activity of the heart. It is an executive organ that ensures integrative restructuring of the functions of the cardiovascular system (and other systems) of the body according to signals coming from the higher parts of the brain - the limbic system or the neocortex. Irritation of certain structures of the limbic system or neocortex, along with motor reactions, changes the functions of the cardiovascular system: blood pressure, heart rate, etc.

The anatomical proximity of the centers responsible for the occurrence of motor and cardiovascular reactions in the cerebral cortex contributes to optimal autonomic support of the body's behavioral reactions.

23. Movement of blood through vessels. Factors that determine the continuous movement of blood through the vessels. Biophysical features of different parts of the vascular bed. Resistive, capacitive and exchange vessels.

Features of the circulatory system:

1) closure of the vascular bed, which includes the pumping organ the heart;

2) elasticity of the vascular wall (the elasticity of the arteries is greater than the elasticity of the veins, but the capacity of the veins exceeds the capacity of the arteries);

3) branching of blood vessels (difference from other hydrodynamic systems);

4) variety of vessel diameters (the diameter of the aorta is 1.5 cm, and the diameter of the capillaries is 8-10 microns);

5) blood circulates in the vascular system, the viscosity of which is 5 times higher than the viscosity of water.

Types of blood vessels:

1) great vessels of the elastic type: the aorta, large arteries branching from it; there are many elastic and few muscle elements in the wall, as a result of which these vessels have elasticity and extensibility; the task of these vessels is to transform pulsating blood flow into a smooth and continuous one;

2) resistance vessels or resistive vessels - vessels of the muscular type, in the wall there is a high content of smooth muscle elements, the resistance of which changes the lumen of the vessels, and therefore the resistance to blood flow;

3) exchange vessels or “exchange heroes” are represented by capillaries, which ensure the metabolic process and the respiratory function between blood and cells; the number of functioning capillaries depends on the functional and metabolic activity in tissues;

4) shunt vessels or arteriovenular anastomoses directly connect arterioles and venules; if these shunts are open, then blood is discharged from the arterioles into the venules, bypassing the capillaries; if they are closed, then the blood flows from the arterioles into the venules through the capillaries;

5) capacitive vessels are represented by veins, which are characterized by high extensibility but low elasticity; these vessels contain up to 70% of all blood and significantly influence the amount of venous return of blood to the heart.

24. Basic hemodynamic parameters. Poiseuille's formula. The nature of blood movement through the vessels, its features. The possibility of using the laws of hydrodynamics to explain the movement of blood through vessels.

The movement of blood obeys the laws of hydrodynamics, namely, it occurs from an area of ​​​​higher pressure to an area of ​​lower pressure.

The amount of blood flowing through a vessel is directly proportional to the pressure difference and inversely proportional to the resistance:

Q=(p1—p2) /R= ∆p/R,

where Q is blood flow, p is pressure, R is resistance;

An analogue of Ohm's law for a section of an electrical circuit:

where I is current, E is voltage, R is resistance.

Resistance is associated with the friction of blood particles against the walls of blood vessels, which is referred to as external friction, and there is also friction between particles - internal friction or viscosity.

Hagen Poiselle's Law:

where η is viscosity, l is the length of the vessel, r is the radius of the vessel.

Q=∆pπr 4 /8ηl.

These parameters determine the amount of blood flowing through the cross-section of the vascular bed.

For the movement of blood, it is not the absolute pressure values ​​that matter, but the pressure difference:

p1=100 mm Hg, p2=10 mm Hg, Q =10 ml/s;

p1=500 mm Hg, p2=410 mm Hg, Q=10 ml/s.

The physical value of blood flow resistance is expressed in [Dyn*s/cm 5 ]. Relative resistance units were introduced:

If p = 90 mm Hg, Q = 90 ml/s, then R = 1 is a unit of resistance.

The amount of resistance in the vascular bed depends on the location of the vascular elements.

If we consider the values ​​of resistance that arise in series-connected vessels, then the total resistance will be equal to the sum of the vessels in individual vessels:

In the vascular system, blood supply is carried out through branches extending from the aorta and running in parallel:

R=1/R1 + 1/R2+…+ 1/Rn,

that is, the total resistance is equal to the sum of the reciprocal values ​​of the resistance in each element.

Physiological processes obey general physical laws.

25. The speed of blood movement in various parts of the vascular system. The concept of volumetric and linear speed of blood movement. Blood circulation time, methods for determining it. Age-related changes in blood circulation time.

Blood movement is assessed by determining the volumetric and linear velocity of blood flow.

Volume velocity- the amount of blood passing through the cross section of the vascular bed per unit time: Q = ∆p / R, Q = Vπr 4. At rest, IOC = 5 l/min, the volumetric blood flow rate at each section of the vascular bed will be constant (5 l pass through all vessels per minute), however, each organ receives a different amount of blood, as a result, Q is distributed in %, for an individual organ it is necessary know the pressure in the arteries and veins through which the blood supply is carried out, as well as the pressure inside the organ itself.

Linear speed- speed of movement of particles along the wall of the vessel: V = Q / πr 4

In the direction from the aorta, the total cross-sectional area increases, reaching a maximum at the level of capillaries, the total lumen of which is 800 times larger than the lumen of the aorta; the total lumen of the veins is 2 times greater than the total lumen of the arteries, since each artery is accompanied by two veins, so the linear speed is greater.

The blood flow in the vascular system is laminar, each layer moves parallel to the other layer without mixing. The wall layers experience great friction, as a result the speed tends to 0; towards the center of the vessel the speed increases, reaching a maximum value in the axial part. Laminar blood flow is silent. Sound phenomena occur when laminar blood flow becomes turbulent (vortices occur): Vc = R * η / ρ * r, where R is the Reynolds number, R = V * ρ * r / η. If R > 2000, then the flow becomes turbulent, which is observed when the vessels narrow, when the speed increases in places where the vessels branch, or when obstacles appear along the way. Turbulent blood flow has noise.

Blood circulation time- the time during which the blood passes a full circle (both small and large). It is 25 s, which falls on 27 systoles (1/5 for a small circle - 5 s, 4/5 for a large one - 20 s). Normally, 2.5 liters of blood circulates, circulation 25s, which is enough to ensure IOC.

26. Blood pressure in various parts of the vascular system. Factors that determine blood pressure. Invasive (bloody) and non-invasive (bloodless) methods of recording blood pressure.

Blood pressure - the pressure of blood on the walls of blood vessels and chambers of the heart, is an important energy parameter, because it is a factor that ensures the movement of blood.

The source of energy is the contraction of the heart muscles, which performs the pumping function.

There are:

Blood pressure;

Venous pressure;

Intracardiac pressure;

Capillary pressure.

The amount of blood pressure reflects the amount of energy that reflects the energy of the moving flow. This energy consists of potential, kinetic energy and gravitational potential energy:

E = P+ ρV 2 /2 + ρgh,

where P is potential energy, ρV 2 /2 is kinetic energy, ρgh is the energy of a blood column or gravitational potential energy.

The most important indicator is blood pressure, which reflects the interaction of many factors, thereby being an integrated indicator reflecting the interaction of the following factors:

Systolic blood volume;

Heart rate and rhythm;

Elasticity of artery walls;

Resistance of resistive vessels;

Blood velocity in capacitance vessels;

Circulating blood speed;

Blood viscosity;

Hydrostatic pressure of the blood column: P = Q * R.

27. Blood pressure (maximum, minimum, pulse, average). The influence of various factors on blood pressure. Age-related changes in blood pressure in humans.

In blood pressure, a distinction is made between lateral and end pressure. Lateral pressure- blood pressure on the walls of blood vessels reflects the potential energy of blood movement. Final pressure- pressure, reflecting the sum of potential and kinetic energy of blood movement.

As the blood moves, both types of pressure decrease, since the energy of the flow is spent on overcoming resistance, with the maximum decrease occurring where the vascular bed narrows, where it is necessary to overcome the greatest resistance.

The final pressure is 10-20 mm Hg higher than the lateral pressure. The difference is called percussion or pulse pressure.

Blood pressure is not a stable indicator; in natural conditions it changes during the cardiac cycle; blood pressure is divided into:

Systolic or maximum pressure (pressure established during ventricular systole);

Diastolic or minimum pressure that occurs at the end of diastole;

The difference between the systolic and diastolic pressures is the pulse pressure;

Mean arterial pressure, which reflects the movement of blood if there were no pulse fluctuations.

In different departments the pressure will take different values. In the left atrium, systolic pressure is 8-12 mmHg, diastolic is 0, in the left ventricle syst = 130, diast = 4, in the aorta syst = 110-125 mmHg, diast = 80-85, in the brachial artery syst = 110-120, diast = 70-80, at the arterial end of the capillaries sist 30-50, but there are no fluctuations, at the venous end of the capillaries sist = 15-25, small veins sist = 78-10 (average 7.1), in vena cava syst = 2-4, in the right atrium syst = 3-6 (average 4.6), diast = 0 or “-”, in the right ventricle syst = 25-30, diast = 0-2, in the pulmonary trunk syst = 16-30, diast = 5-14, in the pulmonary veins syst = 4-8.

In the large and small circles, there is a gradual decrease in pressure, which reflects the consumption of energy used to overcome resistance. The average pressure is not an arithmetic mean, for example, 120 over 80, an average of 100 is an incorrect data, since the duration of ventricular systole and diastole is different in time. To calculate the average pressure, two mathematical formulas have been proposed:

Average p = (p syst + 2*p disat)/3, (for example, (120 + 2*80)/3 = 250/3 = 93 mm Hg), shifted towards diastolic or minimum.

Wed p = p diast + 1/3 * p pulse, (for example, 80 + 13 = 93 mmHg)

28. Rhythmic fluctuations in blood pressure (waves of three orders) associated with the work of the heart, breathing, changes in the tone of the vasomotor center and, in pathology, changes in the tone of the liver arteries.

Blood pressure in the arteries is not constant: it continuously fluctuates within a certain average level. On the blood pressure curve, these fluctuations have different appearances.

First order waves (pulse) the most frequent. They are synchronized with heart contractions. During each systole, a portion of blood enters the arteries and increases their elastic stretch, while the pressure in the arteries increases. During diastole, the flow of blood from the ventricles into the arterial system stops and only the outflow of blood from the large arteries occurs: the stretching of their walls decreases and the pressure decreases. Pressure fluctuations, gradually fading, spread from the aorta and pulmonary artery to all their branches. The highest pressure in the arteries (systolic, or maximum, pressure) is observed during the passage of the top of the pulse wave, and the smallest (diastolic, or minimum, pressure) — during the passage of the base of the pulse wave. The difference between systolic and diastolic pressure, i.e. the amplitude of pressure fluctuations, is called pulse pressure. It creates a wave of the first order. Pulse pressure, other things being equal, is proportional to the amount of blood ejected by the heart at each systole.

In small arteries, pulse pressure decreases and, consequently, the difference between systolic and diastolic pressure decreases. There are no pulse waves of arterial pressure in arterioles and capillaries.

In addition to systolic, diastolic and pulse arterial pressure, the so-called mean arterial pressure. It represents the average pressure value at which, in the absence of pulse fluctuations, the same hemodynamic effect is observed as with natural pulsating blood pressure, i.e., average arterial pressure is the resultant of all changes in pressure in the vessels.

The duration of the decrease in diastolic pressure is longer than the increase in systolic pressure, so the average pressure is closer to the value of diastolic pressure. The average pressure in the same artery is a more constant value, while systolic and diastolic are variable.

In addition to pulse fluctuations, the blood pressure curve shows second order waves, coinciding with respiratory movements: that’s why they are called respiratory waves: In humans, inhalation is accompanied by a decrease in blood pressure, and exhalation is accompanied by an increase.

In some cases, the blood pressure curve shows third order waves. These are even slower increases and decreases in pressure, each of which covers several second-order respiratory waves. These waves are caused by periodic changes in the tone of the vasomotor centers. They are most often observed when there is insufficient oxygen supply to the brain, for example, when rising to a height, after blood loss, or poisoning with certain poisons.

In addition to direct, indirect, or bloodless, methods of determining pressure are used. They are based on measuring the pressure that must be applied to the wall of a given vessel from the outside in order to stop the flow of blood through it. For such a study, use Riva-Rocci sphygmomanometer. The person being examined is placed on the shoulder with a hollow rubber cuff, which is connected to a rubber bulb used for pumping air, and to a pressure gauge. When inflated, the cuff compresses the shoulder, and the pressure gauge shows the amount of this pressure. To measure blood pressure using this device, according to the proposal of N. S. Korotkov, listen to vascular sounds arising in the artery to the periphery of the cuff placed on the shoulder.

There are no sounds when blood moves in an uncompressed artery. If the pressure in the cuff is raised above the level of systolic blood pressure, the cuff completely compresses the lumen of the artery and blood flow in it stops. There are also no sounds. If you now gradually release air from the cuff (i.e., carry out decompression), then at the moment when the pressure in it becomes slightly below the level of systolic blood pressure, the blood during systole overcomes the compressed area and breaks through the cuff. The impact of a portion of blood on the wall of the artery, moving through the compressed area with high speed and kinetic energy, generates a sound heard below the cuff. The pressure in the cuff, at which the first sounds appear in the artery, occurs at the moment of passage of the top of the pulse wave and corresponds to the maximum, i.e., systolic, pressure. With a further decrease in pressure in the cuff, a moment comes when it becomes below diastolic, blood begins to flow through the artery both during the top and bottom of the pulse wave. At this point, sounds in the artery below the cuff disappear. The pressure in the cuff at the moment of disappearance of sounds in the artery corresponds to the minimum value, i.e., diastolic pressure. The pressure values ​​in the artery, determined by the Korotkov method and recorded in the same person by inserting a catheter connected to an electromanometer into the artery, do not differ significantly from each other.

In a middle-aged adult, systolic pressure in the aorta with direct measurements is 110-125 mmHg. A significant decrease in pressure occurs in small arteries, in arterioles. Here the pressure decreases sharply, becoming equal to 20-30 mm Hg at the arterial end of the capillary.

In clinical practice, blood pressure is usually determined in the brachial artery. In healthy people aged 15-50 years, the maximum pressure measured by the Korotkoff method is 110-125 mmHg. Over the age of 50, it usually increases. In 60-year-olds, the maximum pressure is on average 135-140 mm Hg. In newborns, the maximum blood pressure is 50 mm Hg, but after a few days it becomes 70 mm Hg. and by the end of the 1st month of life - 80 mm Hg.

The minimum blood pressure in middle-aged adults in the brachial artery is on average 60-80 mm Hg, pulse pressure is 35-50 mm Hg, and the average is 90-95 mm Hg.

29. Blood pressure in capillaries and veins. Factors influencing venous pressure. The concept of microcirculation. Transcapillary exchange.

Capillaries are the thinnest vessels, with a diameter of 5-7 microns, a length of 0.5-1.1 mm. These vessels lie in the intercellular spaces, in close contact with the cells of the organs and tissues of the body. The total length of all the capillaries of the human body is about 100,000 km, i.e. a thread that could encircle the globe along the equator 3 times. The physiological significance of capillaries is that the exchange of substances between blood and tissues occurs through their walls. The walls of the capillaries are formed by only one layer of endothelial cells, outside of which there is a thin connective tissue basement membrane.

The speed of blood flow in the capillaries is low and amounts to 0.5-1 mm/s. Thus, each blood particle remains in the capillary for approximately 1 s. The small thickness of the blood layer (7-8 microns) and its close contact with the cells of organs and tissues, as well as the continuous change of blood in the capillaries, provide the possibility of exchange of substances between blood and tissue (intercellular) fluid.

In tissues characterized by intense metabolism, the number of capillaries per 1 mm 2 of cross section is greater than in tissues in which metabolism is less intense. Thus, in the heart there are 2 times more capillaries per 1 mm2 section than in skeletal muscle. In the gray matter of the brain, where there are many cellular elements, the capillary network is much denser than in the white matter.

There are two types of functioning capillaries. Some of them form the shortest path between arterioles and venules (main capillaries). Others are lateral branches from the first: they extend from the arterial end of the main capillaries and flow into their venous end. These side branches form capillary networks. The volumetric and linear velocity of blood flow in the main capillaries is greater than in the side branches. Trunk capillaries play an important role in the distribution of blood in capillary networks and in other microcirculation phenomena.

Blood pressure in the capillaries is measured directly: under the control of a binocular microscope, a thin cannula connected to an electromanometer is inserted into the capillary. In humans, the pressure at the arterial end of the capillary is 32 mmHg, and at the venous end it is 15 mmHg, and at the top of the nail bed capillary loop it is 24 mmHg. In the capillaries of the renal glomeruli, the pressure reaches 65-70 mm Hg, and in the capillaries intertwining the renal tubules - only 14-18 mm Hg. The pressure in the capillaries of the lungs is very low - on average 6 mm Hg. Capillary pressure is measured in a body position in which the capillaries of the area under study are at the same level as the heart. When arterioles dilate, the pressure in the capillaries increases, and when they narrow, it decreases.

Blood flows only in the “standby” capillaries. Some capillaries are excluded from the blood circulation. During periods of intense activity of organs (for example, during muscle contraction or secretory activity of glands), when the metabolism in them increases, the number of functioning capillaries increases significantly.

The regulation of capillary blood circulation by the nervous system and the influence of physiologically active substances on it - hormones and metabolites - are carried out when they act on the arteries and arterioles. The narrowing or expansion of arteries and arterioles changes both the number of functioning capillaries, the distribution of blood in the branching capillary network, and the composition of the blood flowing through the capillaries, i.e., the ratio of red blood cells and plasma. In this case, the total blood flow through the metarterioles and capillaries is determined by the contraction of the smooth muscle cells of the arterioles, and the degree of contraction of the precapillary sphincters (smooth muscle cells located at the mouth of the capillary as it departs from the metaarterioles) determines how much of the blood will pass through true capillaries.

In some areas of the body, such as the skin, lungs and kidneys, there are direct connections between arterioles and venules - arteriovenous anastomoses. This is the shortest path between arterioles and venules. Under normal conditions, the anastomoses are closed and blood flows through the capillary network. If the anastomoses are opened, then some of the blood can flow into the veins, bypassing the capillaries.

Arteriovenous anastomoses play the role of shunts that regulate capillary blood circulation. An example of this is a change in capillary blood circulation in the skin with an increase (over 35°C) or decrease (below 15°C) in ambient temperature. Anastomoses in the skin open and blood flow is established from the arterioles directly into the veins, which plays an important role in the processes of thermoregulation.

The structural and functional unit of blood flow in small vessels is vascular module - a relatively hemodynamically isolated complex of microvessels that supplies blood to a certain cell population of the organ. At the same time, there is a specificity of vascularization of the tissues of various organs, which is manifested in the peculiarities of the branching of microvessels, the density of capillarization of tissues, etc. The presence of modules makes it possible to regulate local blood flow in individual microsections of tissues.

Microcirculation is a collective concept. It combines the mechanisms of blood flow in small vessels and the exchange of liquid and gases and substances dissolved in it between the vessels and tissue fluid, which is closely related to the blood flow.

The movement of blood in the veins ensures the filling of the cavities of the heart during diastole. Due to the small thickness of the muscle layer, the walls of the veins are much more stretchable than the walls of the arteries, so a large amount of blood can accumulate in the veins. Even if the pressure in the venous system increases by only a few millimeters, the volume of blood in the veins will increase 2-3 times, and with an increase in pressure in the veins by 10 mm Hg. The capacity of the venous system will increase 6 times. The capacity of the veins may also change as the smooth muscle of the vein wall contracts or relaxes. Thus, the veins (as well as the vessels of the pulmonary circulation) are a reservoir of blood of variable capacity.

Venous pressure. Venous pressure in humans can be measured by inserting a hollow needle into a superficial (usually ulnar) vein and connecting it to a sensitive electromanometer. In the veins located outside the thoracic cavity, the pressure is 5-9 mm Hg.

To determine venous pressure, it is necessary that this vein is located at the level of the heart. This is important because the hydrostatic pressure of the blood column filling the veins is added to the value of blood pressure, for example in the veins of the legs in a standing position.

In the veins of the thoracic cavity, as well as in the jugular veins, the pressure is close to atmospheric and fluctuates depending on the phase of breathing. When you inhale, when the chest expands, the pressure decreases and becomes negative, i.e. below atmospheric. When exhaling, the opposite changes occur and the pressure rises (during normal exhalation it does not rise above 2-5 mm Hg). Injury to veins located near the chest cavity (for example, the jugular veins) is dangerous, since the pressure in them is negative at the moment of inspiration. When inhaling, atmospheric air may enter the venous cavity and develop air embolism, i.e., transfer of air bubbles by blood and subsequent blockage of arterioles and capillaries, which can lead to death.

30. Arterial pulse, its origin, characteristics. Venous pulse, its origin.

Arterial pulse is the rhythmic oscillation of the artery wall caused by an increase in pressure during systole. The pulsation of the arteries can be easily detected by touching any accessible artery: radial (a. radialis), temporal (a. temporalis), external artery of the foot (a. dorsalis pedis), etc.

A pulse wave, or an oscillatory change in the diameter or volume of arterial vessels, is caused by a wave of increased pressure that occurs in the aorta at the moment of expulsion of blood from the ventricles. At this time, the pressure in the aorta rises sharply and its wall stretches. The wave of increased pressure and the vibrations of the vascular wall caused by this stretching propagate at a certain speed from the aorta to the arterioles and capillaries, where the pulse wave dies out.

The speed of propagation of the pulse wave does not depend on the speed of blood movement. The maximum linear speed of blood flow through the arteries does not exceed 0.3-0.5 m/s, and the speed of pulse wave propagation in young and middle-aged people with normal blood pressure and normal vascular elasticity is equal in the aorta 5,5 -8.0 m/s, and in peripheral arteries - 6.0-9.5 m/s. With age, as the elasticity of blood vessels decreases, the speed of propagation of the pulse wave, especially in the aorta, increases.

For a detailed analysis of an individual pulse oscillation, it is graphically recorded using special devices - sphygmographs. Currently, to study the pulse, sensors are used that convert mechanical vibrations of the vascular wall into electrical changes, which are recorded.

In the pulse curve (sphygmogram) of the aorta and large arteries, two main parts are distinguished - rise and fall. Rising curve - anacrotic - occurs as a result of an increase in blood pressure and the resulting stretching to which the walls of the arteries are exposed under the influence of blood ejected from the heart at the beginning of the expulsion phase. At the end of ventricular systole, when the pressure in it begins to fall, the pulse curve declines - catacrota. At the moment when the ventricle begins to relax and the pressure in its cavity becomes lower than in the aorta, the blood thrown into the arterial system rushes back to the ventricle; the pressure in the arteries drops sharply and a deep notch appears on the pulse curve of large arteries - Incisura. The movement of blood back to the heart encounters an obstacle, since the semilunar valves, under the influence of the reverse flow of blood, close and prevent it from flowing into the heart. The wave of blood is reflected from the valves and creates a secondary wave of increased pressure, again causing stretching of the arterial walls. As a result, a secondary or dicrotic, rise. The shapes of the pulse curve of the aorta and the large vessels extending directly from it, the so-called central pulse, and the pulse curve of the peripheral arteries are somewhat different (Fig. 7.19).

Pulse examination, both palpatory and instrumental, through registration of a sphygmogram provides valuable information about the functioning of the cardiovascular system. This study allows you to evaluate both the fact of the presence of heartbeats and the frequency of its contractions, rhythm (rhythmic or arrhythmic pulse). Rhythm fluctuations can also be physiological in nature. Thus, “respiratory arrhythmia,” manifested in an increase in pulse rate during inhalation and a decrease during exhalation, is usually expressed in young people. Tension (hard or soft pulse) is determined by the amount of force that must be applied to make the pulse in the distal part of the artery disappear. Pulse voltage to a certain extent reflects the value of average blood pressure.

Venous pulse. In small and medium veins there are no pulse fluctuations in blood pressure. In large veins near the heart, pulse fluctuations are noted - the venous pulse, which has a different origin than the arterial pulse. It is caused by obstruction of blood flow from the veins to the heart during systole of the atria and ventricles. During systole of these parts of the heart, the pressure inside the veins increases and vibrations of their walls occur. It is most convenient to record the venous pulse of the jugular vein.

On the venous pulse curve - venogram — three teeth are distinguished: a, s, v (Fig. 7.21). Prong A coincides with the systole of the right atrium and is due to the fact that at the moment of atrial systole, the mouths of the hollow veins are clamped by a ring of muscle fibers, as a result of which the flow of blood from the veins into the atria is temporarily suspended. During atrial diastole, blood access into them becomes free again, and at this time the venous pulse curve drops sharply. Soon a small spike appears on the venous pulse curve c. It is caused by a push from the pulsating carotid artery lying near the jugular vein. After the prong c the curve begins to fall, which is replaced by a new rise - a tooth v. The latter is due to the fact that by the end of ventricular systole the atria are filled with blood, further blood flow into them is impossible, blood stagnates in the veins and their walls stretch. After the prong v there is a drop in the curve, coinciding with ventricular diastole and the flow of blood into them from the atria.

31. Local mechanisms of blood circulation regulation. Characteristics of processes occurring in a separate section of the vascular bed or organ (reaction of blood vessels to changes in blood flow speed, blood pressure, influence of metabolic products). Myogenic autoregulation. The role of vascular endothelium in the regulation of local blood circulation.

With enhanced function of any organ or tissue, the intensity of metabolic processes increases and the concentration of metabolic products (metabolites) increases - carbon monoxide (IV) CO 2 and carbonic acid, adenosine diphosphate, phosphoric and lactic acids and other substances. Osmotic pressure increases (due to the appearance of a significant amount of low molecular weight products), the pH value decreases as a result of the accumulation of hydrogen ions. All this and a number of other factors lead to the dilation of blood vessels in the working organ. The smooth muscles of the vascular wall are very sensitive to the action of these metabolic products.

Entering the general bloodstream and reaching the vasomotor center with the blood flow, many of these substances increase its tone. The generalized increase in vascular tone in the body that occurs during the central action of these substances leads to an increase in systemic blood pressure with a significant increase in blood flow through working organs.

In skeletal muscle at rest, there are about 30 open, i.e., functioning, capillaries per 1 mm 2 of cross-section, and with maximum muscle work, the number of open capillaries per 1 mm 2 increases 100 times.

The minute volume of blood pumped by the heart during intense physical work can increase no more than 5-6 times, so an increase in blood supply to working muscles by 100 times is possible only due to blood redistribution. Thus, during the period of digestion, there is an increased blood flow to the digestive organs and a decrease in blood supply to the skin and skeletal muscles. During mental stress, blood supply to the brain increases.

Intense muscular work leads to a narrowing of the blood vessels of the digestive organs and increased blood flow to the working skeletal muscles. Blood flow to these muscles increases as a result of the local vasodilatory effect of metabolic products formed in working muscles, as well as due to reflex vasodilation. So, when working with one hand, the vessels dilate not only in this, but also in the other hand, as well as in the lower extremities.

It has been suggested that in the vessels of a working organ, muscle tone decreases not only due to the accumulation of metabolic products, but also as a result of the influence of mechanical factors: contraction of skeletal muscles is accompanied by stretching of the vascular walls, a decrease in vascular tone in this area and, consequently, Indeed, a significant increase in local blood circulation.

In addition to metabolic products that accumulate in working organs and tissues, the muscles of the vascular wall are also influenced by other humoral factors: hormones, ions, etc. Thus, the adrenal medulla hormone adrenaline causes a sharp contraction of the smooth muscles of the arterioles of the internal organs and, as a result, This is a significant increase in systemic blood pressure. Adrenaline also enhances cardiac activity, but the vessels of working skeletal muscles and the vessels of the brain do not narrow under the influence of adrenaline. Thus, the release of a large amount of adrenaline into the blood, formed during emotional stress, significantly increases the level of systemic blood pressure and at the same time improves blood supply to the brain and muscles and thereby leads to the mobilization of the body’s energy and plastic resources, necessary in emergency conditions, when -of which emotional tension arises.

The vessels of a number of internal organs and tissues have individual regulatory features, which are explained by the structure and function of each of these organs or tissues, as well as the degree of their participation in certain general reactions of the body. For example, skin vessels play an important role in thermoregulation. Their expansion with increasing body temperature contributes to the transfer of heat to the environment, and their narrowing reduces heat transfer.

Redistribution of blood also occurs when moving from a horizontal to a vertical position. In this case, the venous outflow of blood from the legs is hampered and the amount of blood entering the heart through the inferior vena cava decreases (fluoroscopy clearly shows a decrease in the size of the heart). As a result, venous blood flow to the heart can be significantly reduced.

In recent years, the important role of the endothelium of the vascular wall in the regulation of blood flow has been established. The vascular endothelium synthesizes and secretes factors that actively influence the tone of vascular smooth muscles. Endothelial cells - endothelial cells, under the influence of chemical stimuli brought by the blood, or under the influence of mechanical irritation (stretching), are capable of releasing substances that directly act on the smooth muscle cells of blood vessels, causing them to contract or relax. The lifespan of these substances is short, so their effect is limited to the vascular wall and usually does not extend to other smooth muscle organs. One of the factors causing relaxation of blood vessels is, apparently, nitrates and nitrites. A possible vasoconstrictor factor is vasoconstrictor peptide endothelium, consisting of 21 amino acid residues.

32. Vascular tone, its regulation. The meaning of the sympathetic nervous system. The concept of alpha and beta adrenergic receptors.

Narrowing of arteries and arterioles supplied predominantly by sympathetic nerves (vasoconstriction) was first discovered by Walter (1842) in experiments on frogs, and then by Bernard (1852) in experiments on rabbit ears. Bernard's classic experience is that cutting the sympathetic nerve on one side of the neck in a rabbit causes vasodilation, manifested by redness and warming of the ear of the operated side. If the sympathetic nerve in the neck is irritated, the ear on the side of the irritated nerve turns pale due to the narrowing of its arteries and arterioles, and the temperature drops.

The main vasoconstrictor nerves of the abdominal organs are sympathetic fibers passing through the splanchnic nerve (p. splanchnicus). After transection of these nerves, blood flow through the vessels of the abdominal cavity, deprived of vasoconstrictor sympathetic innervation, increases sharply due to dilation of the arteries and arterioles. When p. splanchnicus is irritated, the vessels of the stomach and small intestine narrow.

Sympathetic vasoconstrictor nerves to the extremities go as part of the spinal mixed nerves, as well as along the walls of the arteries (in their adventitia). Since transection of the sympathetic nerves causes dilation of the vessels of the area innervated by these nerves, it is believed that the arteries and arterioles are under the continuous vasoconstrictor influence of the sympathetic nerves.

To restore the normal level of arterial tone after transection of the sympathetic nerves, it is enough to irritate their peripheral segments with electrical stimuli at a frequency of 1-2 per second. Increasing the frequency of stimulation can cause constriction of arterial vessels.

Vasodilator effects (vasodilation) was first discovered during irritation of several nerve branches belonging to the parasympathetic division of the nervous system. For example, irritation of the chorda tympani (chorda timpani) causes dilation of the vessels of the submandibular gland and tongue, p. cavernosi penis - dilation of the vessels of the cavernous bodies of the penis.

In some organs, for example in skeletal muscles, dilatation of arteries and arterioles occurs when the sympathetic nerves are irritated, which contain, in addition to vasoconstrictors, vasodilators. In this case, activation α -adrenergic receptors leads to compression (constriction) of blood vessels. Activation β -adrenergic receptors, on the contrary, causes vasodilation. It should be noted that β -adrenergic receptors are not found in all organs.

33. The mechanism of vasodilatory reactions. Vasodilator nerves, their importance in the regulation of regional blood circulation.

Vasodilation (mainly of the skin) can also be caused by irritation of the peripheral segments of the dorsal roots of the spinal cord, which contain afferent (sensitive) fibers.

These facts, discovered in the 70s of the last century, caused a lot of controversy among physiologists. According to the theory of Beilis and L.A. Orbeli, the same dorsal root fibers transmit impulses in both directions: one branch of each fiber goes to the receptor, and the other to the blood vessel. Receptor neurons, the bodies of which are located in the spinal ganglia, have a dual function: they transmit afferent impulses to the spinal cord and efferent impulses to the vessels. Transmission of impulses in two directions is possible because afferent fibers, like all other nerve fibers, have bilateral conductivity.

According to another point of view, the dilation of skin vessels when the dorsal roots are irritated occurs due to the fact that acetylcholine and histamine are formed in the receptor nerve endings, which diffuse through the tissues and dilate nearby vessels.

34. Central mechanisms of blood circulation regulation. Vasomotor center, its localization. Pressor and depressor sections, their physiological characteristics. The importance of the vasomotor center in maintaining vascular tone and regulating systemic blood pressure.

V.F. Ovsyannikov (1871) established that the nerve center that provides a certain degree of narrowing of the arterial bed - the vasomotor center - is located in the medulla oblongata. The localization of this center was determined by cutting the brain stem at different levels. If the transection is performed in a dog or cat above the quadrigeminal area, then blood pressure does not change. If you cut the brain between the medulla oblongata and the spinal cord, the maximum blood pressure in the carotid artery decreases to 60-70 mm Hg. From here it follows that the vasomotor center is localized in the medulla oblongata and is in a state of tonic activity, i.e., long-term constant excitation. Elimination of its influence causes vasodilatation and a drop in blood pressure.

A more detailed analysis showed that the vasomotor center of the medulla oblongata is located at the bottom of the IV ventricle and consists of two sections - pressor and depressor. Irritation of the pressor part of the vasomotor center causes a narrowing of the arteries and a rise, and irritation of the second part causes the dilation of the arteries and a drop in blood pressure.

They believe that depressor section of the vasomotor center causes vasodilation, lowering the tone of the pressor region and thus reducing the effect of vasoconstrictor nerves.

Influences coming from the vasoconstrictor center of the medulla oblongata come to the nerve centers of the sympathetic part of the autonomic nervous system, located in the lateral horns of the thoracic segments of the spinal cord, which regulate vascular tone in individual parts of the body. The spinal centers are capable, some time after turning off the vasoconstrictor center of the medulla oblongata, to slightly increase blood pressure, which has decreased due to the expansion of arteries and arterioles.

In addition to the vasomotor centers of the medulla oblongata and spinal cord, the state of blood vessels is influenced by the nerve centers of the diencephalon and cerebral hemispheres.

35. Reflex regulation of blood circulation. Reflexogenic zones of the cardiovascular system. Classification of interoreceptors.

As noted, arteries and arterioles are constantly in a state of narrowing, largely determined by the tonic activity of the vasomotor center. The tone of the vasomotor center depends on afferent signals coming from peripheral receptors located in some vascular areas and on the surface of the body, as well as on the influence of humoral stimuli acting directly on the nerve center. Consequently, the tone of the vasomotor center has both reflex and humoral origin.

According to the classification of V.N. Chernigovsky, reflex changes in arterial tone - vascular reflexes - can be divided into two groups: intrinsic and associated reflexes.

Own vascular reflexes. They are caused by signals from the receptors of the vessels themselves. Receptors concentrated in the aortic arch and in the area where the carotid artery branches into internal and external are of particular physiological importance. These areas of the vascular system are called vascular reflexogenic zones.

depressor.

Receptors of vascular reflexogenic zones are excited when blood pressure in the vessels increases, which is why they are called pressoreceptors, or baroreceptors. If the sinocarotid and aortic nerves are cut on both sides, hypertension occurs, i.e., a steady increase in blood pressure, reaching 200-250 mm Hg in the dog’s carotid artery. instead of 100-120 mm Hg. normal.

36. The role of the aortic and sinocarotid reflexogenic zones in the regulation of blood circulation. Depressor reflex, its mechanism, vascular and cardiac components.

The receptors located in the aortic arch are the ends of centripetal fibers passing through the aortic nerve. Zion and Ludwig functionally designated this nerve as depressor. Electrical stimulation of the central end of the nerve causes a drop in blood pressure due to a reflex increase in the tone of the vagus nerve nuclei and a reflex decrease in the tone of the vasoconstrictor center. As a result, cardiac activity is inhibited, and the blood vessels of the internal organs dilate. If the vagus nerves of an experimental animal, for example a rabbit, are cut, then irritation of the aortic nerve causes only a reflex vasodilation without slowing the heart rate.

In the reflexogenic zone of the carotid sinus (carotid sinus, sinus caroticus) there are receptors from which centripetal nerve fibers come, forming the sinocarotid nerve, or Hering’s nerve. This nerve enters the brain as part of the glossopharyngeal nerve. When blood is injected into an isolated carotid sinus through a cannula under pressure, a drop in blood pressure in the vessels of the body can be observed (Fig. 7.22). The decrease in systemic blood pressure is due to the fact that stretching the wall of the carotid artery excites the receptors of the carotid sinus, reflexively lowers the tone of the vasoconstrictor center and increases the tone of the vagus nerve nuclei.

37. Pressor reflex from chemoreceptors, its components and significance.

Reflexes are divided into depressor - lowering blood pressure, pressor - increasing e, accelerating, decelerating, interoceptive, exteroceptive, unconditional, conditional, proper, conjugate.

The main reflex is the reflex of maintaining the pressure level. Those. reflexes aimed at maintaining the level of pressure from baroreceptors. Baroreceptors of the aorta and carotid sinus sense pressure levels. Perceive the magnitude of pressure fluctuations during systole and diastole + average pressure.

In response to increased pressure, baroreceptors stimulate the activity of the vasodilator zone. At the same time, they increase the tone of the vagus nerve nuclei. In response, reflex reactions develop and reflex changes occur. The vasodilator zone suppresses the tone of the vasoconstrictor zone. Vasodilation occurs and the tone of the veins decreases. The arterial vessels are dilated (arterioles) and the veins will dilate, the pressure will decrease. The sympathetic influence decreases, the vagus increases, and the rhythm frequency decreases. High blood pressure returns to normal. Dilatation of arterioles increases blood flow in the capillaries. Some of the fluid will pass into the tissues - the blood volume will decrease, which will lead to a decrease in pressure.

They arise from chemoreceptors pressor reflexes. An increase in the activity of the vasoconstrictor zone along the descending pathways stimulates the sympathetic system, and the vessels constrict. The pressure increases through the sympathetic centers of the heart and the heart rate increases. The sympathetic system regulates the release of hormones from the adrenal medulla. Blood flow in the pulmonary circulation will increase. The respiratory system reacts by increasing breathing - releasing carbon dioxide from the blood. The factor that caused the pressor reflex leads to normalization of blood composition. In this pressor reflex, a secondary reflex to changes in heart function is sometimes observed. Against the background of increased blood pressure, a decrease in heart function is observed. This change in the work of the heart is in the nature of a secondary reflex.

38. Reflex influences on the heart from the vena cava (Bainbridge reflex). Reflexes from receptors of internal organs (Goltz reflex). Oculocardiac reflex (Aschner reflex).

Bainbridge injected 20 ml of saline into the venous part of the mouth. Solution or the same volume of blood. After this, a reflex increase in heart rate occurred, followed by an increase in blood pressure. The main component in this reflex is an increase in the frequency of contractions, and the pressure rises only secondarily. This reflex occurs when blood flow to the heart increases. When there is more blood inflow than outflow. In the area of ​​the mouth of the genital veins there are sensitive receptors that respond to an increase in venous pressure. These sensory receptors are the endings of afferent fibers of the vagus nerve, as well as afferent fibers of the dorsal spinal roots. Excitation of these receptors leads to the fact that impulses reach the nuclei of the vagus nerve and cause a decrease in the tone of the vagus nerve nuclei, while at the same time the tone of the sympathetic centers increases. The heart rate increases and blood from the venous part begins to be pumped into the arterial part. The pressure in the vena cava will decrease. Under physiological conditions, this condition can increase with physical exertion, when blood flow increases and with heart defects, blood stagnation is also observed, which leads to increased heart function.

Goltz discovered that stretching the stomach, intestines, or lightly tapping the intestines of a frog is accompanied by a slowdown in the heart, even to a complete stop. This is due to the fact that impulses are sent from the receptors to the nuclei of the vagus nerves. Their tone increases and the heart slows down or even stops.

39. Reflex effects on the cardiovascular system from the vessels of the pulmonary circulation (Parin reflex).

In the vessels of the pulmonary circulation there are receptors that respond to increased pressure in the pulmonary circulation. When the pressure in the pulmonary circulation increases, a reflex occurs, which causes the dilation of the vessels in the systemic circle; at the same time, the work of the heart slows down and an increase in the volume of the spleen is observed. Thus, a kind of unloading reflex arises from the pulmonary circulation. This reflex was discovered by V.V. Parin. He worked a lot in terms of development and research of space physiology, and headed the Institute of Medical and Biological Research. An increase in pressure in the pulmonary circulation is a very dangerous condition, because it can cause pulmonary edema. Because The hydrostatic pressure of the blood increases, which contributes to the filtration of blood plasma and, thanks to this condition, the liquid enters the alveoli.

40. The importance of the reflexogenic zone of the heart in the regulation of blood circulation and circulating blood volume.

For normal blood supply to organs and tissues and maintaining constant blood pressure, a certain ratio is necessary between the volume of circulating blood (CBV) and the total capacity of the entire vascular system. This correspondence is achieved through a number of neural and humoral regulatory mechanisms.

Let's consider the body's reactions to a decrease in blood volume during blood loss. In such cases, blood flow to the heart decreases and blood pressure levels decrease. In response to this, reactions occur aimed at restoring normal blood pressure levels. First of all, a reflex narrowing of the arteries occurs. In addition, during blood loss, a reflex increase in the secretion of vasoconstrictor hormones is observed: adrenaline - by the adrenal medulla and vasopressin - by the posterior lobe of the pituitary gland, and increased secretion of these substances leads to a narrowing of the arterioles. The important role of adrenaline and vasopressin in maintaining blood pressure during blood loss is evidenced by the fact that death with blood loss occurs earlier than after removal of the pituitary gland and adrenal glands. In addition to the sympathoadrenal influences and the action of vasopressin, the renin-angiotensin-aldosterone system is involved in maintaining blood pressure and blood volume at normal levels during blood loss, especially in the later stages. The decrease in blood flow in the kidneys that occurs after blood loss leads to increased release of renin and greater than normal formation of angiotensin II, which maintains blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which, firstly, helps maintain blood pressure by increasing the tone of the sympathetic division of the autonomic nervous system, and secondly, enhances the reabsorption of sodium in the kidneys. Sodium retention is an important factor in increasing water reabsorption in the kidneys and restoring blood volume.

To maintain blood pressure during open blood loss, the transfer into the vessels of tissue fluid and into the general blood flow of the amount of blood that is concentrated in the so-called blood depots is also important. The equalization of blood pressure is also facilitated by the reflex acceleration and strengthening of heart contractions. Thanks to these neurohumoral influences, with a rapid loss of 20— 25% In the blood, a fairly high level of blood pressure may remain for some time.

There is, however, a certain limit of blood loss, after which no regulatory devices (neither narrowing of blood vessels, nor ejection of blood from the depot, nor increased work of the heart, etc.) can keep blood pressure at a normal level: if the body quickly loses more than 40-50% of the blood contained in it, then blood pressure drops sharply and can drop to zero, which leads to death.

These mechanisms for regulating vascular tone are unconditional, innate, but during the individual life of animals, vascular conditioned reflexes are developed on their basis, thanks to which the cardiovascular system is included in the reactions necessary for the body under the action of only one signal preceding one or another environmental changes. Thus, the body turns out to be pre-adapted to the upcoming activity.

41. Humoral regulation of vascular tone. Characteristics of true, tissue hormones and their metabolites. Vasoconstrictor and vasodilator factors, mechanisms for realizing their effects when interacting with various receptors.

Some humoral agents narrow and others expand the lumen of arterial vessels.

Vasoconstrictor substances. These include adrenal medulla hormones - adrenalin And norepinephrine, as well as the posterior lobe of the pituitary gland - vasopressin.

Adrenaline and norepinephrine constrict arteries and arterioles of the skin, abdominal organs and lungs, and vasopressin acts primarily on arterioles and capillaries.

Adrenaline, norepinephrine and vasopressin affect blood vessels in very low concentrations. Thus, vasoconstriction in warm-blooded animals occurs at a concentration of adrenaline in the blood of 1*10 7 g/ml. The vasoconstrictor effect of these substances causes a sharp increase in blood pressure.

Humoral vasoconstrictor factors include serotonin (5-hydroxytryptamine), produced in the intestinal mucosa and in some areas of the brain. Serotonin is also formed during the breakdown of platelets. The physiological significance of serotonin in this case is that it constricts blood vessels and prevents bleeding from the affected vessel. In the second phase of blood coagulation, which develops after the formation of a blood clot, serotonin dilates blood vessels.

A special vasoconstrictor factor - renin, is formed in the kidneys, and in greater quantities, the lower the blood supply to the kidneys. For this reason, after partial compression of the renal arteries in animals, a persistent increase in blood pressure occurs due to narrowing of the arterioles. Renin is a proteolytic enzyme. Renin itself does not cause vasoconstriction, but, entering the blood, it breaks down α Plasma 2-globulin - angiotensinogen and converts it into a relatively inactive deca-peptide - angiotensin I. The latter, under the influence of the enzyme dipeptide carboxypeptidase, is converted into a very active vasoconstrictor substance angiotensin II. Angiotensin II is rapidly destroyed in the capillaries by angiotensinase.

Under conditions of normal blood supply to the kidneys, a relatively small amount of renin is formed. It is produced in large quantities when blood pressure levels drop throughout the vascular system. If you lower a dog's blood pressure by bloodletting, the kidneys will release an increased amount of renin into the blood, which will help normalize blood pressure.

The discovery of renin and the mechanism of its vasoconstrictive action is of great clinical interest: it explained the cause of high blood pressure accompanying some kidney diseases (hypertension of renal origin).

42. Coronary circulation. Features of its regulation. Features of blood circulation in the brain, lungs, and liver.

The heart receives its blood supply from the right and left coronary arteries, which arise from the aorta, at the level of the upper edges of the semilunar valves. The left coronary artery divides into the anterior descending and circumflex arteries. The coronary arteries usually function as ring arteries. And between the right and left coronary arteries, the anastomoses are very poorly developed. But if there is a slow closure of one artery, then the development of anastomoses between the vessels begins and which can pass from 3 to 5% from one artery to another. This is when the coronary arteries slowly close. Rapid overlap leads to a heart attack and is not compensated for from other sources. The left coronary artery supplies the left ventricle, the anterior half of the interventricular septum, the left and partly the right atrium. The right coronary artery supplies the right ventricle, right atrium, and the posterior half of the interventricular septum. Both coronary arteries participate in the blood supply to the conduction system of the heart, but in humans the right one is larger. The outflow of venous blood occurs through veins that run parallel to the arteries and these veins empty into the coronary sinus, which opens into the right atrium. From 80 to 90% of venous blood flows through this pathway. Venous blood from the right ventricle in the interatrial septum flows through the smallest veins into the right ventricle and these veins are called ven tibezia, which directly drain venous blood into the right ventricle.

200-250 ml flows through the coronary vessels of the heart. blood per minute, i.e. this represents 5% of minute volume. For 100 g of myocardium, from 60 to 80 ml flows per minute. The heart extracts 70-75% of oxygen from arterial blood, therefore in the heart there is a very large arterio-venous difference (15%) In other organs and tissues - 6-8%. In the myocardium, capillaries densely entwine each cardiomyocyte, which creates the best conditions for maximum blood extraction. The study of coronary blood flow is very difficult because... it varies with the cardiac cycle.

Coronary blood flow increases in diastole, in systole, blood flow decreases due to compression of blood vessels. At diastole - 70-90% of coronary blood flow. Regulation of coronary blood flow is primarily regulated by local anabolic mechanisms and quickly responds to a decrease in oxygen. A decrease in oxygen levels in the myocardium is a very powerful signal for vasodilation. A decrease in oxygen content leads to the fact that cardiomyocytes secrete adenosine, and adenosine is a powerful vasodilator. It is very difficult to assess the influence of the sympathetic and parasympathetic systems on blood flow. Both vagus and sympathicus change the functioning of the heart. It has been established that irritation of the vagus nerves causes a slowdown in the heart, increases the continuation of diastole, and the direct release of acetylcholine will also cause vasodilation. Sympathetic influences contribute to the release of norepinephrine.

In the coronary vessels of the heart there are 2 types of adrenoceptors - alpha and beta adrenoceptors. In most people, the predominant type is beta adrenergic receptors, but some have a predominance of alpha receptors. Such people will feel a decrease in blood flow when excited. Adrenaline causes an increase in coronary blood flow due to increased oxidative processes in the myocardium and increased oxygen consumption and due to its effect on beta adrenergic receptors. Thyroxine, prostaglandins A and E have a dilating effect on the coronary vessels, vasopressin narrows the coronary vessels and reduces coronary blood flow.

Blood circulation is the process of constant blood circulation in the body, which ensures its vital functions. The body's circulatory system is sometimes combined with the lymphatic system to form the cardiovascular system.

The blood is moved by the contractions of the heart and circulates through the vessels. It provides the body's tissues with oxygen, nutrients, hormones and delivers metabolic products to the organs of their excretion. Enrichment of blood with oxygen occurs in the lungs, and saturation with nutrients occurs in the digestive organs. In the liver and kidneys, metabolic products are neutralized and eliminated. Blood circulation is regulated by hormones and the nervous system. There are small (through the lungs) and large (through organs and tissues) circulation.

Blood circulation is an important factor in the life of the human and animal body. Blood can perform its various functions only by being in constant motion.

The circulatory system of humans and many animals consists of the heart and vessels through which blood moves to tissues and organs and then returns to the heart. Large vessels through which blood moves to organs and tissues are called arteries. The arteries branch into smaller arteries called arterioles, and finally into capillaries. Vessels called veins carry blood back to the heart.

The circulatory system of humans and other vertebrates is of a closed type—blood does not leave the body under normal conditions. Some species of invertebrates have an open circulatory system.

The movement of blood is ensured by the difference in blood pressure in different vessels.

History of the study

Even ancient researchers assumed that in living organisms all organs are functionally connected and influence each other. Various assumptions have been made. Hippocrates is the “father of medicine,” and Aristotle, the greatest Greek thinker who lived almost 2,500 years ago, was interested in and studied circulatory issues. However, ancient ideas were imperfect, and in many cases erroneous. They presented venous and arterial blood vessels as two independent systems, not connected to each other. It was believed that blood moves only through the veins, in the arteries, but there is air. This was justified by the fact that during autopsies of human and animal corpses, there was blood in the veins, but the arteries were empty, without blood.

This belief was refuted by the work of the Roman explorer and physician Claudius Galen (130 - 200). He experimentally proved that blood moves through the heart and arteries, as well as veins.

After Galen, until the 17th century, it was believed that blood from the right atrium somehow entered the left atrium through the septum.

In 1628, the English physiologist, anatomist and physician William Harvey (1578 - 1657) published his work “An Anatomical Study of the Movement of the Heart and Blood in Animals,” in which for the first time in the history of medicine he experimentally showed that blood moves from the ventricles of the heart through the arteries and returns to the atria veins. Undoubtedly, the circumstance that more than any other prompted William Harvey to realize that blood circulates was the presence of valves in the veins, the functioning of which indicates a passive hydrodynamic process. He realized that this could only make sense if the blood in the veins flowed towards the heart, and not away from it, as Galen had suggested and as European medicine believed in Harvey's time. Harvey was also the first to quantify cardiac output in humans, and it was largely because of this that, despite a huge underestimation (1020.6 g/min, that is, about 1 L/min instead of 5 L/min), skeptics became convinced that arterial blood cannot be continuously created in the liver, and, therefore, it must circulate. Thus, he constructed a modern diagram of the blood circulation of humans and other mammals, which includes two circles. The question of how blood gets from arteries to veins remained unclear.

It was in the year of publication of Harvey's revolutionary work (1628) that Malpighi was born, who 50 years later discovered capillaries - a link of blood vessels that connects arteries and veins - and thus completed the description of a closed vascular system.

The first quantitative measurements of mechanical phenomena in the blood circulation were made by Stephen Hales (1677 - 1761), who measured arterial and venous blood pressure, the volume of individual chambers of the heart, and the flow rate of blood from several veins and arteries, thus demonstrating that most of the resistance to blood flow occurs to the area of ​​microcirculation. He believed that as a result of the elasticity of the arteries, the flow of blood in the veins remains more or less constant, and does not pulsate, as in the arteries.

Later, in the 18th and 19th centuries, a number of famous fluid mechanics became interested in the issues of blood circulation and made significant contributions to the understanding of this process. Among them were Leonhard Euler, Bernoulli (who was actually a professor of anatomy) and Jean Louis Marie Poiseuille (also a physician, his example especially shows how the attempt to solve a partial applied problem can lead to the development of basic science). One of the most universal scientists was Thomas Young (1773 - 1829), also a physician, whose research in optics led to the establishment of the wave theory of light and an understanding of color perception. Another important area of ​​Jung's research concerns the nature of elasticity, in particular the properties and function of elastic arteries; his theory of wave propagation in elastic tubes is still considered a fundamentally correct description of pulse pressure in arteries. It is in his lecture on this subject to the Royal Society in London that the explicit statement is made that "the question of how and to what extent the circulation of the blood depends on the muscular and elastic forces of the heart and arteries, on the assumption that the nature of these forces is known, must become simply a matter of the very branches of theoretical hydraulics.”

Harvey's circulatory scheme was expanded when the hemodynamic scheme was created in the 20th century by Arinchinim N. I. It turned out that the skeletal muscle in the blood circulation is not only a flow vascular system and a consumer of blood, a “dependent” of the heart, but also an organ that, self-supporting, is a powerful pump - peripheral "heart". Due to the blood pressure developed by the muscle, it is not only not inferior, but even exceeds the pressure maintained by the central heart, and serves as its effective assistant. Due to the fact that there are a lot of skeletal muscles, more than 1000, their role in moving blood in a healthy and sick person is undoubtedly great.

Human circulation

Blood circulation occurs along two main paths called circles: the small and large circles of blood circulation.

In a small circle, blood circulates through the lungs. The movement of blood in this circle begins with the contraction of the right atrium, after which the blood enters the right ventricle of the heart, the contraction of which pushes the blood into the pulmonary trunk. Blood circulation in this direction is regulated by the atrioventricular septum and two valves: the tricuspid valve (between the right atrium and the right ventricle), which prevents blood from returning to the atrium, and the pulmonary valve, which prevents blood from returning from the pulmonary trunk to the right ventricle. The pulmonary trunk branches into a network of pulmonary capillaries, where the blood is oxygenated by ventilation of the lungs. The blood then returns from the lungs through the pulmonary veins to the left atrium.

The systemic circulation supplies oxygenated blood to organs and tissues. The left atrium contracts simultaneously with the right and pushes blood into the left ventricle. From the left ventricle, blood enters the aorta. The aorta branches into arteries and arterioles, which are the bicuspid (mitral) valve and the aortic valve.

Thus, the blood moves through the systemic circulation from the left ventricle to the right atrium, and then through the pulmonary circulation from the right ventricle to the left atrium.

There are also two more circles of blood circulation:

1. Cardiac circulatory circle - this circulatory circle begins from the aorta with two coronoid cardiac arteries, through which blood flows to all layers and parts of the heart, and then collects in small veins in the venous coronary sinus and ends with the veins of the heart flowing into the right atrium.
2. Placental - Occurs in a closed system, isolated from the mother’s circulatory system. The placental circulation begins from the placenta, which is a provisional (temporary) organ through which the fetus receives oxygen, nutrients, water, electrolytes, vitamins, antibodies from the mother and releases carbon dioxide and waste products.

Mechanism of blood circulation

This statement is completely true for arteries and arterioles, capillaries and veins, auxiliary mechanisms appear in the capillaries and veins, which are discussed below. The movement of arterial blood by the ventricles occurs at the isophygmic points of the capillaries, where water and salts are released into the interstitial fluid and blood pressure is unloaded to a pressure in the interstitial fluid, the value of which is about 25 mm Hg. Art.. Next, reabsorption (reverse absorption) of water, salts and cell waste products occurs from the interstitial fluid into the postcapillaries under the action of the suction force of the atria (liquid vacuum - movement of the atrioventricular septa, AVP down) and then by gravity under the influence of gravitational forces to the atria. The upward movement of the AVP leads to atrial systole and at the same time to ventricular diastole. The difference in pressure is created by the rhythmic work of the atria and ventricles of the heart, pumping blood from the veins to the arteries.

Cardiac cycle

The right half of the heart and the left work synchronously. For convenience of presentation, the work of the left half of the heart will be considered here. The cardiac cycle includes general diastole (relaxation), atrial systole (contraction), and ventricular systole. During general diastole, the pressure in the cavities of the heart is close to zero, in the aorta it slowly decreases from systolic to diastolic, normally in humans they are 120 and 80 mm Hg, respectively. Art. Because the pressure in the aorta is higher than in the ventricle, the aortic valve is closed. The pressure in the large veins (central venous pressure, CVP) is 2-3 mm Hg, that is, slightly higher than in the cavities of the heart, so that blood enters the atria and, in transit, into the ventricles. The atrioventricular valves are open at this time. During atrial systole, the circular muscles of the atria compress the entrance from the veins to the atria, which prevents the reverse flow of blood, the pressure in the atria rises to 8-10 mm Hg, and the blood moves into the ventricles. At the next ventricular systole, the pressure in them becomes higher than the pressure in the atria (which begin to relax), which leads to the closure of the atrioventricular valves. The external manifestation of this event is the first heart sound. Then the pressure in the ventricle exceeds the aortic pressure, as a result of which the aortic valve opens and blood begins to be forced out of the ventricle into the arterial system. The relaxed atrium fills with blood at this time. The physiological significance of the atria lies mainly in the role of an intermediate reservoir for blood coming from the venous system during ventricular systole. At the beginning of general diastole, the pressure in the ventricle drops below the aortic (closing of the aortic valve, II tone), then below the pressure in the atria and veins (opening of the atrioventricular valves), the ventricles begin to fill with blood again. The volume of blood ejected by the ventricle of the heart for each systole is 60-80 ml. This quantity is called stroke volume. The duration of the cardiac cycle is 0.8-1 s, giving a heart rate (HR) of 60-70 per minute. Hence, the minute volume of blood flow, as it is easy to calculate, is 3-4 liters per minute (minute volume of the heart, MVR).

Arterial system

Arteries, which contain almost no smooth muscle, but have a powerful elastic membrane, perform mainly a “buffer” role, smoothing out pressure differences between systolic and diastolic. The walls of the arteries are elastically stretchable, which allows them to accept an additional volume of blood, which is “thrown in” by the heart during systole, and only moderately, by 50-60 mm Hg, increase the pressure. During diastole, when the heart is not pumping anything, it is the elastic stretching of the arterial walls that maintains the pressure, preventing it from falling to zero, and thereby ensuring the continuity of blood flow. It is the stretching of the vessel wall that is perceived as a pulse beat. Arterioles have developed smooth muscles, thanks to which they are able to actively change their lumen and, thus, regulate resistance to blood flow. It is the arterioles that account for the greatest pressure drop, and they determine the relationship between blood flow volume and blood pressure. Accordingly, arterioles are called resistive vessels.

Capillaries

Capillaries are characterized by the fact that their vascular wall is represented by one layer of cells, so that they are highly permeable to all low-molecular substances dissolved in the blood plasma. Here the exchange of substances between tissue fluid and blood plasma occurs. When blood passes through capillaries, blood plasma is completely renewed with interstitial (tissue) fluid 40 times; the volume of diffusion alone through the total exchange surface of the body's capillaries is about 60 l/min or approximately 85,000 l/day; the pressure at the beginning of the arterial part of the capillary is 37.5 mm Hg. V.; the effective pressure is about (37.5 - 28) = 9.5 mmHg. V.; the pressure at the end of the venous part of the capillary, directed outward of the capillary, is 20 mmHg. V.; effective reabsorption pressure - close (20 - 28) = - 8 mm Hg. Art.

Venous system

From the organs, blood returns through postcapillaries into venules and veins into the right atrium through the superior and inferior vena cava, as well as the coronary veins (veins that return blood from the heart muscle). Venous return occurs through several mechanisms. Firstly, the basic mechanism due to the pressure difference at the end of the venous part of the capillary, directed outwards of the capillary is about 20 mmHg. Art., in the TG - 28 mm Hg. Art.,.) and atria (about 0), the effective reabsorption pressure is close (20 - 28) = - 8 mm Hg. Art. Secondly, for the veins of skeletal muscles it is important that when the muscle contracts, the pressure “outside” exceeds the pressure in the vein, so that the blood is “squeezed” out of the veins by muscle contraction. The presence of venous valves determines the direction of blood movement in this case - from the arterial end to the venous end. This mechanism is especially important for the veins of the lower extremities, since here the blood rises through the veins, overcoming gravity. Third, sucking the role of the chest. During inspiration, the pressure in the chest drops below atmospheric pressure (which we take to be zero), which provides an additional mechanism for blood return. The size of the lumen of the veins, and accordingly their volume, significantly exceeds those of the arteries. In addition, the smooth muscles of the veins ensure a change in their volume within a fairly wide range, adapting their capacity to the changing volume of circulating blood. Therefore, from the point of view of their physiological role, veins can be defined as “capacitive vessels”.

Quantitative indicators and their relationship

Stroke volume of the heart is the volume that the left ventricle ejects into the aorta (and the right into the pulmonary trunk) in one contraction. In humans it is 50-70 ml. Minute volume of blood flow (V minute) is the volume of blood passing through the cross section of the aorta (and pulmonary trunk) per minute. In an adult, the minute volume is approximately 5-7 liters. Heart rate (Freq) - the number of heart contractions per minute. Blood pressure is the pressure of blood in the arteries. Systolic pressure is the highest pressure during the cardiac cycle, reached towards the end of systole. Diastolic pressure is the lowest pressure during the cardiac cycle, achieved at the end of ventricular diastole. Pulse pressure is the difference between systolic and diastolic. Mean arterial pressure (P mean) is most easily determined as a formula. So, if blood pressure during the cardiac cycle is a function of time, then (2) where t begin and t end are the start and end times of the cardiac cycle, respectively. The physiological meaning of this value: this is such an equivalent pressure that, if it were constant, the minute volume of blood flow would not differ from what is actually observed. Total peripheral resistance is the resistance the vascular system provides to blood flow. It cannot be measured directly, but can be calculated based on cardiac output and mean arterial pressure. (3) Minute volume of blood flow is equal to the ratio of mean arterial pressure to peripheral resistance. This statement is one of the central laws of hemodynamics. The resistance of one vessel with rigid walls is determined by Poiseuille's law: (4) where η is the viscosity of the liquid, R is the radius and L is the length of the vessel. For series-connected vessels, the resistances add up: (5) for parallel ones, the conductivities add up: (6) Thus, the total peripheral resistance depends on the length of the vessels, the number of parallel-connected vessels and the radius of the vessels. It is clear that there is no practical way to know all these quantities, in addition, the walls of blood vessels are not rigid, and blood does not behave like a classical Newtonian fluid with constant viscosity. Because of this, as V. A. Lishchuk noted in “The Mathematical Theory of Blood Circulation,” “Poiseuille’s law has an illustrative rather than a constructive role for blood circulation.” However, it is clear that of all the factors that determine peripheral resistance, the radius of the vessels is of greatest importance (the length in the formula is in the 1st power, while the radius is in the 4th power), and this same factor is the only one capable of physiological regulation. The number and length of vessels are constant, the radius can vary depending on the tone of the vessels, mainly arterioles. Taking into account formulas (1), (3) and the nature of peripheral resistance, it becomes clear that mean arterial pressure depends on volumetric blood flow, which is determined mainly by the heart (see (1)) and vascular tone, mainly arterioles.

Stroke volume of the heart(V contr) - the volume that the left ventricle ejects into the aorta (and the right into the pulmonary trunk) in one contraction. In humans it is 50-70 ml.

Minute volume of blood flow(V minute) - the volume of blood passing through the cross section of the aorta (and pulmonary trunk) per minute. In an adult, the minute volume is approximately 5-7 liters.

Heart rate(Freq) - the number of heart contractions per minute.

Blood pressure- blood pressure in the arteries.

Systolic pressure- the highest pressure during the cardiac cycle is reached towards the end of systole.

Diastolic pressure- low pressure during the cardiac cycle, achieved at the end of ventricular diastole.

Pulse pressure- difference between systolic and diastolic.

(P mean) is most easily defined as a formula. So, if blood pressure during the cardiac cycle is a function of time, then

where t begin and t end are the start and end times of the cardiac cycle, respectively.

The physiological meaning of this value: this is the equivalent pressure, if constant, the minute volume of blood flow would not differ from that observed in reality.

Total peripheral resistance is the resistance the vascular system provides to blood flow. Resistance cannot be measured directly, but it can be calculated from cardiac output and mean arterial pressure.

The minute volume of blood flow is equal to the ratio of mean arterial pressure to peripheral resistance.

This statement is one of the central laws of hemodynamics.

The resistance of one vessel with rigid walls is determined by Poiseuille's law:

where (\Displaystyle \eta) (\Displaystyle \eta) is the viscosity of the liquid, R is the radius and L is the length of the vessel.

For vessels connected in series, the resistance is determined:

For parallel, conductivity is measured:

Thus, the total peripheral resistance depends on the length of the vessels, the number of parallel vessels and the radius of the vessels. It is clear that there is no practical way to know all these quantities, in addition, the walls of blood vessels are not solid, and blood does not behave like a classical Newtonian fluid with constant viscosity. Because of this, as V. A. Lishchuk noted in “The Mathematical Theory of Blood Circulation,” “Poiseuille’s law has an illustrative rather than a constructive role for blood circulation.” However, it is clear that of all the factors that determine peripheral resistance, the radius of the vessels is of greatest importance (length in the formula to the 1st power, radius to the fourth), and this same factor is the only one capable of physiological regulation. The number and length of vessels are constant, but the radius can vary depending on the tone of the vessels, mainly arterioles.

Taking into account formulas (1), (3) and the nature of peripheral resistance, it becomes clear that average arterial pressure depends on volumetric blood flow, which is determined mainly by the heart (see (1)) and vascular tone, mainly arterioles.

After all, it is a shame for future doctors not to know the basis of the basics - the blood circulation. Without having this information and an understanding of how blood moves through the body, it is impossible to understand the mechanism of development of vascular and heart diseases, or to explain the pathological processes that occur in the heart with a particular lesion. Without knowing the blood circulation it is impossible to work as a doctor. This information will not hurt the common man, because knowledge about one’s own body is never superfluous.

1 Big trip

To better understand how the systemic circulation works, let’s imagine a little. Let's imagine that all the vessels of the body are rivers, and the heart is a bay, into the bay of which all the river channels flow. Let's go on a journey: our ship begins a long voyage. From the left ventricle we swim to the aorta - the main vessel of the human body. This is where the great circle of blood circulation begins.

Blood saturated with oxygen flows in the aorta, because aortic blood is distributed throughout the human body. The aorta gives off branches, like a river, tributaries that supply blood to the brain and all organs. Arteries branch to arterioles, which in turn give off capillaries. Bright, arterial blood gives oxygen and nutrients to cells, and takes away metabolic products of cellular life.

The capillaries are organized into venules, which carry dark, cherry-colored blood, because it has given oxygen to the cells. Venules collect into larger veins. Our ship completes its journey along the two largest “rivers” - the superior and inferior vena cava - and ends up in the right atrium. The journey is over. A large circle can be schematically represented as follows: the beginning is the left ventricle and the aorta, the end is the vena cava and the right atrium.

2 Small trip

What is the pulmonary circulation? Let's go on our second journey! Our ship originates from the right ventricle, from which the pulmonary trunk arises. Remember that when completing the systemic circulation, we moored in the right atrium? From it, venous blood flows into the right ventricle, and then, with cardiac contraction, is pushed into a vessel that extends from it - the pulmonary trunk. This vessel goes to the lungs, where it bifurcates into pulmonary arteries and then into capillaries.

Capillaries envelop the bronchi and alveoli of the lungs, give off carbon dioxide and metabolic products and are enriched with life-giving oxygen. Capillaries organize into venules as they exit the lungs and then into larger pulmonary veins. We are accustomed to the fact that venous blood flows in the veins. Just not in the lungs! These veins are rich in arterial, bright scarlet, O2-rich blood. Through the pulmonary veins, our ship sails into the bay, where its journey ends - in the left atrium.

So, the beginning of the small circle is the right ventricle and the pulmonary trunk, the end is the pulmonary veins and the left atrium. A more detailed description is as follows: the pulmonary trunk is divided into two pulmonary arteries, which in turn branch into a network of capillaries, like a web, encircling the alveoli, where gas exchange occurs, then the capillaries collect into venules and pulmonary veins, which flow into the left upper cardiac chamber of the heart.

3 Historical facts

Having dealt with the sections of the blood circulation, it seems that there is nothing complicated in their structure. Everything is simple, logical, understandable. Blood leaves the heart, collects metabolic products and CO2 from the cells of the whole body, saturates them with oxygen, venous blood returns to the heart, which, passing through the natural “filters” of the body - the lungs, becomes arterial again. But it took many centuries to study and understand the movement of blood flow in the body. Galen mistakenly assumed that the arteries contained air rather than blood.

This position today can be explained by the fact that in those days they studied vessels only on corpses, and in a dead body the arteries are bloodless, and the veins, on the contrary, are full of blood. It was believed that blood was produced in the liver, and was consumed in the organs. Miguel Servet in the 16th century suggested that “the spirit of life originates in the left cardiac ventricle, this is facilitated by the lungs, where the mixing of air and blood coming from the right cardiac ventricle occurs,” thus, the scientist recognized and described for the first time the small circle.

But practically no attention was paid to Servetus' discovery. Harvey is considered the father of the circulatory system, who already in 1616 wrote in his writings that the blood “circles throughout the body.” For many years he studied the movement of blood, and in 1628 he published a work that became a classic, and crossed out all Galen’s ideas about blood circulation; in this work, blood circulation circles were outlined.

Harvey did not discover only capillaries, discovered later by the scientist Malpighi, who supplemented the knowledge about the “circles of life” with a connecting capillary link between arterioles and venules. The scientist was helped to open the capillaries by a microscope, which provided magnification up to 180 times. Harvey's discovery was met with criticism and challenge by the great minds of those times, many scientists did not agree with Harvey's discovery.

But even today, reading his works, you are surprised at how accurately and in detail for that time the scientist described the work of the heart and the movement of blood through the vessels: “The heart, while doing work, first moves, and then rests in all animals while they are still alive. At the moment of contraction, it squeezes blood out of itself, the heart empties at the moment of contraction.” The blood circulation was also described in detail, except that Harvey could not observe the capillaries, but he accurately described that blood collects from the organs and flows back to the heart?

But how does the transition from arteries to veins occur? This question haunted Harvey. Malpighi revealed this secret of the human body by discovering capillary blood circulation. It’s a shame that Harvey did not live several years to see this discovery, because the discovery of capillaries confirmed with 100% certainty the veracity of Harvey’s teachings. The great scientist did not have the opportunity to feel the full triumph of his discovery, but we remember him and his enormous contribution to the development of anatomy and knowledge about the nature of the human body.

4 From largest to smallest

I would like to dwell on the main elements of the circulatory circles, which are their framework through which the blood moves - the vessels. Arteries are vessels that carry blood from the heart. The aorta is the most important and important artery of the body, it is the largest - about 25 mm in diameter, it is through it that blood flows to other vessels extending from it and is delivered to organs, tissues, and cells.

Exception: the pulmonary arteries do not carry O2-rich blood, but CO2-rich blood to the lungs.

Veins are vessels that carry blood to the heart, their walls are easily stretchable, the diameter of the vena cava is about 30 mm, and the diameter of small veins is 4-5 mm. Their blood is dark, the color of ripe cherry, rich in metabolic products.

Exception: the pulmonary veins are the only veins in the body through which arterial blood flows.

Capillaries are the thinnest vessels, consisting of only one layer of cells. The single-layer structure allows gas exchange, the exchange of useful and harmful products between cells and directly capillaries.

The diameter of these vessels is only 0.006 mm on average, and the length is no more than 1 mm. That's how small they are! However, if we sum up the length of all the capillaries together, we get a very significant figure - 100 thousand km... Our body inside is shrouded in them like a cobweb. And it’s not surprising - after all, every cell of the body needs oxygen and nutrients, and capillaries can provide the supply of these substances. All vessels, both the largest and smallest capillaries, form a closed system, or rather two systems - the above-mentioned circulatory circles.

5 Important features

Why are blood circulation circles needed? Their role cannot be overestimated. Just as life on Earth is impossible without water resources, human life is impossible without the circulatory system. The main role of the large circle is:

1. Providing oxygen to every cell of the human body;
2. The flow of nutrients from the digestive system into the blood;
3. Filtration of waste products from the blood into the excretory organs.

The role of the small circle is no less important than those described above: removing CO2 from the body and metabolic products.

Knowledge about the structure of one’s own body is never superfluous; knowledge of how the circulatory sections function leads to a better understanding of the body’s functioning, and also forms an idea of ​​the unity and integrity of organs and systems, the connecting link of which is undoubtedly the bloodstream, organized in circulatory circles.

The small circle is intended for gas exchange with the external environment. It originates in the right ventricle. From there, the blood, saturated with carbon dioxide after passing through the entire body, is sent to the lungs, passes through the capillaries, gives off carbon dioxide and is saturated with oxygen from the external environment. It then goes into the veins and flows to the left atrium, where the circle ends. Briefly, the movement pattern is as follows: right ventricle, arteries, capillaries, veins, left atrium.

Important! Speaking about the pulmonary circle and the types of blood in its parts, you can get confused:

• venous blood is saturated with carbon dioxide, it is located in the arteries of the circle;
• arterial blood is saturated with oxygen, and it is in the veins in this circle.

This is easy to remember if you understand that the type of blood is determined by its composition, and not by the vessels where it moves.

Systemic circulation

The second - a large circle, carries all the functions mentioned above, and provides respiration and nutrition of tissues, humoral regulation, and also removes metabolic products from tissues. Structure:

• The great circle begins with the left ventricle, a larger part of the heart that has a thick and strong muscle, because it is this muscle that must push blood through the body.
• The aorta emerges from the ventricle - the widest vessel. The pressure in it is the strongest in the entire circle, so it has a thick muscle wall that can contract. The aorta gives rise to the remaining arteries: the carotid ones go to the head, and the vertebral ones go to the arms. The aorta itself descends along the spine, and along this path it gives rise to the arteries of the internal organs, muscles of the trunk and legs.
• Arteries give rise to arterioles, and they branch and form capillaries, in which the transfer of substances from the blood to the tissues occurs, and vice versa. Blood cells exchange oxygen and carbon dioxide with tissue cells and then move with the bloodstream to the heart.
• Capillaries flow into veinswhich are becoming increasingly larger. As a result, they enter the vena cava (located above and below the heart). These veins lead to the right atrium.

Schematically, the large circle includes: the left ventricle, the aorta, the carotid arteries, the vertebral arteries, the organs’ own arteries, their capillaries, the veins emerging from them, the vena cava and the right atrium. In addition to those mentioned, there are other vessels, they also belong to a large circle, but there are too many of them to list all the names; a general idea of ​​the anatomy of the circulatory system will suffice for us (Fig. 1).

Important! The liver and kidneys have their own characteristics of blood supply. The liver is a kind of filter that can neutralize toxins and cleanse the blood. Therefore, blood from the stomach, intestines, and other organs goes into the portal vein and then passes through the capillaries of the liver. Only then does it flow to the heart. But it is worth noting that not only the portal vein goes to the liver, but also the hepatic artery, which feeds the liver in the same way as the arteries of other organs. What are the features of the blood supply to the kidneys? They also purify the blood, so the blood supply in them is divided into two stages: first, the blood passes through the capillaries of the Malpighian glomeruli, where it is cleared of toxins, and then it is collected in an artery, which again branches into capillaries that feed the kidney tissue.

“Additional” circulation circles

The third, coronal circle, is part of a larger circle, but in the literature it is often highlighted additionally. This is the circle of blood supply to the heart. From the aorta, in addition to those mentioned, two coronary arteries depart, giving rise to the coronary vessels that supply the heart muscle.

Important! The heart muscle consumes a lot of oxygen, and this is not surprising if you know how much the total length of the vessels is - about 100,000 km.

This entire path is overcome by reducing it, and this requires a lot of energy. Since our cells can only get energy with the participation of oxygen, the flow of a large amount of blood is very important for the proper functioning of this muscle. Otherwise, the cells die and the work of the heart is disrupted.

The fourth circle is the placental circle, formed during pregnancy. It is, in fact, the blood supply system to the fetus in the uterus. The mother's blood enters the capillaries of the placenta, where it releases substances to the baby's circulatory system. Through the arteries in the umbilical cord, blood, saturated with all the necessary substances, flows back to the fetus and is included in the child’s circulatory system. In addition to the arteries, the umbilical cord contains the umbilical vein, through which blood flows to the placenta. On the way to the fetus, blood passes through a special filter, which should trap substances that are undesirable for the developing child. It is worth remembering that this filter works well, but not perfectly, and cannot protect the fetus from absolutely all toxins. For this reason, pregnant women need to carefully study the composition of foods, medications and even nutritional supplements so as not to affect the development of the child. The circulatory system is a kind of transport through which nutrients and biologically active substances are transferred from one organ and tissue to another. Blood participates in the processes of cellular nutrition, respiration and regulation (through hormones secreted into it). The human circulatory system is a complex and very well-organized system, which takes into account all the needs of tissues, including the protection of the most important organs from toxic substances and the removal of waste products. We also recommend that you watch the thematic video for a better understanding of the material presented.

The vessels in the human body form two closed circulatory systems. There are large and small circles of blood circulation. The vessels of the great circle supply blood to the organs, the vessels of the small circle provide gas exchange in the lungs.

Systemic circulation: arterial (oxygenated) blood flows from the left ventricle of the heart through the aorta, then through the arteries, arterial capillaries to all organs; from the organs, venous blood (saturated with carbon dioxide) flows through the venous capillaries into the veins, from there through the superior vena cava (from the head, neck and arms) and the inferior vena cava (from the torso and legs) into the right atrium.

Pulmonary circulation: venous blood flows from the right ventricle of the heart through the pulmonary artery into a dense network of capillaries entwining the pulmonary vesicles, where the blood is saturated with oxygen, then arterial blood flows through the pulmonary veins into the left atrium. In the pulmonary circulation, arterial blood flows through the veins, venous blood through the arteries. It begins in the right ventricle and ends in the left atrium. The pulmonary trunk emerges from the right ventricle, carrying venous blood to the lungs. Here the pulmonary arteries break up into vessels of smaller diameter, which turn into capillaries. Oxygenated blood flows through the four pulmonary veins into the left atrium.

Blood moves through the vessels due to the rhythmic work of the heart. During ventricular contraction, blood is forced under pressure into the aorta and pulmonary trunk. The highest pressure develops here - 150 mm Hg. Art. As blood moves through the arteries, the pressure drops to 120 mm Hg. Art., and in capillaries - up to 22 mm. Lowest venous pressure; in large veins it is below atmospheric.

Blood is ejected from the ventricles in portions, and the continuity of its flow is ensured by the elasticity of the artery walls. At the moment of contraction of the ventricles of the heart, the walls of the arteries stretch, and then, due to elastic elasticity, return to their original state even before the next flow of blood from the ventricles. Thanks to this, the blood moves forward. Rhythmic fluctuations in the diameter of arterial vessels caused by the work of the heart are called pulse. It can be easily palpated in places where the arteries lie on the bone (radial, dorsal artery of the foot). By counting the pulse, you can determine the frequency of heart contractions and their strength. In a healthy adult, the pulse rate at rest is 60-70 beats per minute. With various heart diseases, arrhythmia is possible - interruptions in the pulse.

Blood flows at the highest speed in the aorta - about 0.5 m/s. Subsequently, the speed of movement drops and in the arteries reaches 0.25 m/s, and in the capillaries - approximately 0.5 mm/s. The slow flow of blood in the capillaries and the large extent of the latter favor metabolism (the total length of capillaries in the human body reaches 100 thousand km, and the total surface of all capillaries in the body is 6300 m2). The large difference in the speed of blood flow in the aorta, capillaries and veins is due to the unequal width of the overall cross-section of the bloodstream in its different sections. The narrowest such section is the aorta, and the total lumen of the capillaries is 600-800 times greater than the lumen of the aorta. This explains the slowdown in blood flow in the capillaries.

The movement of blood through the vessels is regulated by neurohumoral factors. Impulses sent along nerve endings can cause either a narrowing or expansion of the lumen of blood vessels. Two types of vasomotor nerves approach the smooth muscles of the walls of blood vessels: vasodilators and vasoconstrictors.

The impulses traveling along these nerve fibers arise in the vasomotor center of the medulla oblongata. In the normal state of the body, the walls of the arteries are somewhat tense and their lumen is narrowed. From the vasomotor center, impulses continuously flow through the vasomotor nerves, which determine constant tone. Nerve endings in the walls of blood vessels react to changes in pressure and chemical composition of the blood, causing excitement in them. This excitation enters the central nervous system, resulting in a reflex change in the activity of the cardiovascular system. Thus, an increase and decrease in the diameters of blood vessels occurs in a reflex way, but the same effect can also occur under the influence of humoral factors - chemical substances that are in the blood and come here with food and from various internal organs. Among them, vasodilators and vasoconstrictors are important. For example, the pituitary hormone - vasopressin, the thyroid hormone - thyroxine, the adrenal hormone - adrenaline, constrict blood vessels, enhance all functions of the heart, and histamine, formed in the walls of the digestive tract and in any working organ, acts in the opposite way: dilates capillaries without affecting other vessels . A significant effect on the functioning of the heart is exerted by changes in the content of potassium and calcium in the blood. An increase in calcium content increases the frequency and strength of contractions, increases the excitability and conductivity of the heart. Potassium causes exactly the opposite effect.

The expansion and contraction of blood vessels in various organs significantly affects the redistribution of blood in the body. More blood is sent to a working organ, where the vessels are dilated, and to a non-working organ - \ less. The depositing organs are the spleen, liver, and subcutaneous fat.