The small circle of blood circulation passes through. What is a small and large circle of blood circulation

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Circles of blood circulation (human anatomy)

The regularity of the movement of blood in the circles of blood circulation was discovered by W. Harvey (1628). Since that time, the study of the anatomy and physiology of blood vessels has been enriched by numerous data that have revealed the mechanism of general and regional blood supply. In the process of development in the circulatory system, especially in the heart, certain structural complications occurred, namely, in higher animals, the heart was divided into four chambers. The heart of fish has two chambers - the atrium and the ventricles, separated by a bicuspid valve. The venous sinus flows into the atrium, and the ventricle communicates with the arterial cone. In this two-chambered heart, venous blood flows, which is released into the aorta, and then to the branchial vessels for oxygenation. In animals, with the appearance of pulmonary respiration (two-breathing fish, amphibians), a septum with holes forms in the atrium. In this case, all venous blood enters the right atrium, and arterial blood enters the left atrium. Blood from the atria enters the common ventricle, where it mixes.

In the heart of reptiles, due to the presence of an incomplete interventricular septum (except for the crocodile, which has a complete septum), a more perfect separation of the arterial and venous blood currents is observed. Crocodiles have a four-chambered heart, but the mixing of arterial and venous blood occurs at the periphery due to the connection of arteries and veins.

Birds, like mammals, have a four-chambered heart and complete separation of blood currents is noted not only in the heart, but also in the vessels. A feature of the structure of the heart and large vessels in birds is the presence of the right aortic arch, while the left arch atrophies.

In higher animals and humans, which have a four-chambered heart, there are large, small and cardiac circles of blood circulation (Fig. 138). The heart is central to these circles. Regardless of the composition of the blood, all vessels entering the heart are considered to be veins, and those leaving it as arteries.

Rice. 138. Circulation scheme (according to Kishsh-Sentagotai).1 - a. carotis communis; 2 - arcus aortae; 3 - a. pulmonalis; 4 - v. pulmonalis; 5 - ventriculus sinister; 6 - ventriculus dexter; 7 - truncus coeliacus; 8 - a. mesenterica superior; 9 - a. mesenterica inferior; 10 - v. cava inferior; 11 - aorta; 12 - a. iliaca communis; 13 - vasa pelvina; 14 - a. femoralis; 15 - v. femoralis; 16 - v. iliaca communis; 17 - v. portae; 18 - vv. hepaticae; 19 - a. subclavia; 20 - v. subclavia; 21 - v. cava superior; 22 - v. jugularis interna

Small circle of blood circulation (pulmonary). Venous blood from the right atrium passes through the right atrioventricular opening into the right ventricle, which, by contracting, pushes blood into the pulmonary trunk. The latter is divided into right and left pulmonary arteries passing through the gate of the lungs. In the lung tissue, the arteries divide to form capillaries that surround each alveolus. After the release of carbon dioxide by erythrocytes and their enrichment with oxygen, venous blood turns into arterial. Arterial blood through four pulmonary veins (each lung has two veins) is collected in the left atrium, and then through the left atrioventricular opening passes into the left ventricle. The systemic circulation begins from the left ventricle.

A large circle of blood circulation ... Arterial blood from the left ventricle during its contraction is thrown into the aorta. The aorta splits into arteries that supply blood to the head, neck, limbs, trunk and all internal organs in which they end with capillaries. Nutrients, water, salts and oxygen are released from the blood of the capillaries into the tissues, metabolic products and carbon dioxide are resorbed. Capillaries collect in venules, where the venous vascular system representing the roots of the superior and inferior vena cava. Venous blood through these veins enters the right atrium, where the systemic circulation ends.

Blood provides normal human activity, saturating the body with oxygen and energy, while removing carbon dioxide and toxins.

The central organ of the circulatory system is the heart, which consists of four chambers separated by valves and partitions, which act as the main channels for blood circulation.

Today, it is customary to divide everything into two circles - large and small. They are united into one system and are closed on each other. The circulation is made up of arteries - the vessels that carry blood from the heart, and veins - the vessels that carry blood back to the heart.

Blood in the human body can be arterial and venous. The first carries oxygen into the cells and has the highest pressure and, accordingly, speed. The second removes carbon dioxide and delivers it to the lungs (low pressure and low speed).

Both circles of blood circulation are two loops connected in series. The main organs of blood circulation can be called the heart, which acts as a pump, the lungs, which exchange oxygen, and which cleanses the blood of harmful substances and toxins.

In the medical literature, you can often find a wider list, where the human circulation circles are presented in this form:

Big
Small
Cordial
Placental
Willisiev

A large circle of human blood circulation

The large circle originates from the left ventricle of the heart.

Its main function is to deliver oxygen and nutrients to organs and tissues through capillaries, total area which reaches 1500 sq. m.

In the process of passing through the arteries, the blood takes carbon dioxide and returns to the heart, through the vessels, closing the blood flow in the right atrium with two vena cava - the lower and upper.

The entire cycle of passage takes from 23 to 27 seconds.

Sometimes the name of the corporal circle is found.

Small circle of blood circulation

The small circle originates from the right ventricle, then passing through the pulmonary arteries, delivers venous blood to the lungs.

Through the capillaries, carbon dioxide is displaced (gas exchange) and the blood, having become arterial, returns to the left atrium.

The main task of the small circle of blood circulation is heat exchange and blood circulation

The main task of the small circle is heat exchange and circulation. The average blood circulation time is no more than 5 seconds.

It can also be called the pulmonary circulation.

"Additional" circles of blood circulation in humans

Through the placental circle, oxygen is supplied to the fetus in the womb. It has a displaced system and does not belong to any of the main circles. At the same time, arterial-venous blood flows along the umbilical cord with a ratio of oxygen and carbon dioxide of 60/40%.

The heart circle is part of the bodily (large) circle, but due to the importance of the heart muscle, it is often distinguished into a separate subcategory. At rest, up to 4% of the total cardiac output (0.8 - 0.9 mg / min) is involved in the bloodstream, with an increase in the load, the value increases up to 5 times. It is in this part of a person's blood circulation that there is a blockage of blood vessels by a thrombus and a lack of blood in the heart muscle.

The circle of Willis provides blood supply to the human brain, it also stands out separately from the large circle due to the importance of functions. With blockage of individual vessels, it provides additional oxygen delivery through other arteries. Often atrophied and has hypoplasia of individual arteries. A full-fledged circle of Willis is observed in only 25-50% of people.

Features of the blood circulation of individual human organs

Although the entire body is supplied with oxygen due to the large circle of blood circulation, some individual organs have their own unique oxygen exchange system.

The lungs have a double capillary network. The first belongs to the body circle and nourishes the organ with energy and oxygen, while taking away metabolic products. The second to the pulmonary - here there is a displacement (oxygenation) of carbon dioxide from the blood and its enrichment with oxygen.

The heart is one of the main organs of the circulatory system

Venous blood flows from the unpaired abdominal organs in a different way, it preliminarily passes through the portal vein. Vienna is so named because of its connection with the gate of the liver. Passing through them, it is cleansed of toxins and only after that it returns through the hepatic veins to the general circulation.

The lower third of the rectum in women does not pass through the portal vein and is connected directly to the vagina, bypassing hepatic filtration, which is used to administer some drugs.

Heart and brain. Their features were revealed in the section on additional circles.

Few facts

Up to 10,000 liters of blood pass through the heart per day, besides, it is the strongest muscle in the human body, contracting up to 2.5 billion times in a lifetime.

The total length of the vessels in the body reaches 100 thousand kilometers. This may be enough to get to the moon or wrap the earth around the equator several times.

The average amount of blood is 8% of the total body weight. With a weight of 80 kg, about 6 liters of blood flows in a person.

Capillaries have such "narrow" (no more than 10 microns) passages that blood cells can only pass through them one at a time.

Watch an informative video about the circles of blood circulation:

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general information

The human circulatory system consists of: a heart (4 chambers) and two circles of blood circulation.

The heart has two atria and two ventricles.
The systemic circulation starts from the left ventricle, and the blood is called arterial. From this point, blood flow moves through the arteries to each organ. As they travel through the body, the arteries are transformed into capillaries, in which the exchange of gas is formed. Further, the blood flow turns into venous. Then it enters the atrium of the right chamber, and ends in the ventricle.
The small circle of blood circulation is formed in the ventricle of the right chamber and goes through the arteries to the lungs. There, the blood is exchanged, giving off gas and taking oxygen, goes through the veins into the atrium of the left chamber, and ends in the ventricle.

Diagram # 1 clearly shows how the circulation circles work.

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It is also necessary to pay attention to the organs and clarify the basic concepts that are important in the functioning of the body.

The circulatory organs are as follows:

atria;
ventricles;
aorta;
capillaries, incl. pulmonary;
veins: hollow, pulmonary, blood;
arteries: pulmonary, coronary, blood;
alveolus.

Circulatory system

In addition to the small and large circulation pathways, there is also a peripheral pathway.

Peripheral circulation is responsible for the continuous process of blood flow between the heart and blood vessels. The muscle of the organ, contracting and relaxing, moves the blood through the body. Of course, the pumped volume, blood structure and other nuances are of great importance. The circulatory system works by pressure and impulses generated in the organ. How the heart pulsates depends on the systolic state and its change to diastolic.

Vessels of the systemic circulation carry blood flow to organs and tissues.

Types of blood vessels:

Arteries, departing from the heart, carry blood circulation. Arterioles perform a similar function.
Veins, like venules, facilitate the return of blood to the heart.

Arteries are tubes along which the systemic circulation moves. They have a fairly large diameter. They are able to withstand high pressure due to their thickness and ductility. They have three shells: inner, middle and outer. Due to their elasticity, they are independently regulated depending on the physiology and anatomy of each organ, its needs and the temperature of the external environment.

The system of arteries can be represented in the form of a bushy bundle, which become, the farther from the heart, the smaller. As a result, in the limbs they look like capillaries. Their diameter is not larger than a hair, but arterioles and venules connect them. Capillaries have thin walls and one epithelial layer. This is where the exchange of nutrients takes place.

Therefore, the importance of each element should not be underestimated. Dysfunction of one, leads to diseases of the entire system. Therefore, in order to maintain the functionality of the body, healthy image life.

Heart third circle

As we found out - a small circle of blood circulation and a large, these are not all components of the cardiovascular system. There is also a third path through which the blood flow moves and it is called the cardiac circle of blood circulation.

This circle originates from the aorta, or rather from the point where it divides into two coronary arteries. Blood through them penetrates through the layers of the organ, then passes through small veins into the coronary sinus, which opens into the atrium of the chamber of the right section. And some of the veins are directed to the ventricle. The path of blood flow through the coronary arteries is called coronary circulation. Collectively, these circles are the system that produces blood supply and nutrient saturation to the organs.

Coronary circulation has the following properties:

increased blood circulation;
supply occurs in the diastolic state of the ventricles;
there are few arteries, so dysfunction of one gives rise to myocardial diseases;
CNS excitability increases blood flow.

Diagram # 2 shows how the coronary circulation functions.

The circulatory system includes the little-known circle of Willisiev. Its anatomy is such that it is presented in the form of a system of vessels, which are located at the base of the brain. Its value can hardly be overestimated, tk. its main function is to compensate for the blood that it transfers from other "pools". The vascular system of the Willis circle is closed.

Normal development of the Way of Willis occurs in only 55%. A common pathology is aneurysm and underdevelopment of the arteries connecting it.

At the same time, underdevelopment does not affect a person's condition in any way, provided that there are no violations in other pools. Can be detected during MRI. Aneurysm of the arteries of the Willis blood circulation is performed as a surgical intervention in the form of ligation. If the aneurysm has opened, then the doctor prescribes conservative treatment methods.

Willisiev's vascular system is designed not only to supply blood flow to the brain, but also to compensate for thrombosis. In view of this, treatment of the Willis' way is practically not carried out, because there is no dangerous value for health.

Blood supply in the human fetus

The fetal circulation is the following system. The blood flow with an increased content of carbon dioxide from the upper region enters the atrium of the right chamber through the vena cava. Through the opening, blood enters the ventricle and then into the pulmonary trunk. Unlike the human blood supply, the small circle of blood circulation of the embryo does not go into the lungs of the respiratory tract, but into the duct of the arteries, and only then into the aorta.

Diagram # 3 shows how the blood flows in the fetus.

Features of the fetal circulation:

Blood moves through contractile function organ.
From the 11th week, respiration affects the blood supply.
The placenta is of great importance.
The small circle of blood circulation of the fetus does not function.
Mixed blood flow enters the organs.
Identical pressure in arteries and aorta.

Summing up the article, it should be emphasized how many circles are involved in supplying blood to the whole body. Information about how each of them works allows the reader to independently understand the intricacies of anatomy and functionality. human body... Do not forget that you can ask a question online and get an answer from competent specialists with medical education.

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1. The value 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 cardiac cavities and a network of blood vessels that provide all vital important functions organism.

The heart is the primary pump that energizes the movement of the blood. This is a difficult point of intersection of different blood streams. In a normal heart, these streams do not mix. The heart begins to contract about a month after conception, and from that moment on, its work does not stop until the last moment of life.

In a time equal to the average lifespan, the heart makes 2.5 billion contractions, and at the same time it pumps 200 million liters of blood. It is a unique pump, which is about the size of a man's fist, and the average weight for a man is 300g and for a woman is 220g. The heart looks like a blunt cone. Its length is 12-13 cm, width is 9-10.5 cm, and anteroposterior size equal to 6-7cm.

The blood vessel system is 2 circles of blood circulation.

A large circle of blood circulation begins in the left ventricle with the aorta. The aorta provides 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: the arteries pass into the arterioles, and the arterioles - into the capillaries. Capillaries provide the entire amount of metabolic processes in tissues. There the blood becomes venous, it flows from the organs. It flows to the right atrium through the inferior and superior vena cava.

Small circle of blood circulation begins in the right ventricle with the pulmonary trunk, which divides into the right and left pulmonary arteries. Arteries carry venous blood to the lungs, where gas exchange will take place. 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, the blood delivers oxygen, nutrients, water, salt to the cells, and removes carbon dioxide and end products of metabolism from the tissues.

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

2. Placental circulation. Features of the blood circulation of the newborn.

The fetal circulatory system is very different from that of the newborn. This is determined by both anatomical and functional characteristics of the fetus, reflecting its adaptive 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, which connects the pulmonary artery to the aorta. This allows a significant mass of blood to bypass the non-functional 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 the blood, enriched with oxygen and containing all the necessary nutrients, enters the vein of the umbilical cord. Then arterial blood through the venous (arantium) duct enters the liver. The fetal liver is a kind of blood depot. In the deposit of blood, its left lobe plays the greatest role. From the liver, through the same venous duct, blood enters the inferior vena cava, and from there - into the right atrium. The right atrium also receives blood from the superior vena cava. Between the place of confluence of the inferior and superior vena cava is the 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 a functioning foramen ovale. From the left atrium, blood enters the left ventricle, and from there to the aorta. From the ascending arch of the aorta, 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 portion of the blood flows to the non-functioning lungs. The bulk of blood from the pulmonary artery is directed through the arterial (botall) duct into the descending arch of the aorta. The blood of the descending aortic arch supplies the lower half of the trunk and lower limbs... After that, the blood, poor in oxygen, through the branches of the iliac arteries enters the paired arteries of the umbilical cord and through them into the placenta. Volumetric distributions of blood in fetal circulation are as follows: approximately half of the total blood volume from the right heart enters through the foramen ovale into the left heart, 30% is discharged through the arterial (botal) duct into the aorta, 12% enters the lungs. Such a distribution of blood is of very great physiological importance from the point of view of obtaining oxygen-rich blood by the individual organs of the fetus, namely, purely arterial blood is contained only in the vein of the umbilical cord, in the venous duct and blood vessels of the liver; mixed venous blood, containing a sufficient amount of oxygen, is located in the inferior vena cava and the ascending aortic arch, therefore the liver and top part the trunk of the fetus is supplied with arterial blood better than the lower half of the body. Later, as pregnancy progresses, there is a slight narrowing of the foramen ovale and a decrease in the size of the inferior vena cava. As a result, in the second half of pregnancy, the imbalance in the distribution of arterial blood decreases slightly.

The physiological features of the fetal circulation are important not only from the point of view of supplying it with oxygen. Fetal circulation is of no less importance for the implementation of the most important process of removing CO2 and other metabolic products from the fetus. Described above anatomical features fetal circulation create the prerequisites for the implementation of a very short pathway for the elimination of CO2 and metabolic products: aorta - umbilical arteries - placenta. The fetal cardiovascular system has pronounced adaptive responses 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 its body. This is due to the presence of various mechanisms of a neurogenic and humoral nature that regulate the heart rate, stroke volume of the heart, peripheral constriction and dilatation of the ductus arteriosus and other arteries. In addition, the fetal circulatory system is closely related to the hemodynamics of the placenta and mother. This relationship is clearly visible, for example, when the syndrome of compression of the inferior vena cava occurs. The essence of this syndrome lies in the fact that some women at the end of pregnancy are compressed by the uterus of the inferior vena cava and, apparently, partly of the aorta. As a result, in the position of a woman on her back, her blood is redistributed, while a large amount of blood is retained in the inferior vena cava, and the 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 the inferior vena cava compression syndrome clearly demonstrates the presence of a close relationship between the mother's vascular system, placental and fetal hemodynamics.

3. Heart, its hemodynamic functions. The cycle of the heart, 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 there is a complete contraction and relaxation of all parts of the heart. Contraction - systole, relaxation - diastole. The length of your cycle will depend on your heart rate. The normal frequency of contractions ranges from 60 to 100 beats per minute, but the average frequency is 75 beats per minute. To determine the duration of the cycle, divide 60s by the frequency. (60s / 75s = 0.8s).

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 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% full with blood. The heart cycle begins with

atrial systole... At this time, atrial contraction occurs, 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. provides the pumping of additional blood into the ventricles and the atrial systole completes the filling of the ventricles with blood. Blood cannot flow back, as the annular 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 is the systole of the ventricles.

Ventricular systole- the most difficult phase of the cardiac cycle, lasting 0.3 s. In systole, voltage period, it lasts 0.08 s and period of exile... Each period is subdivided into 2 phases -

voltage period

1.phase of asynchronous contraction - 0.05 s

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

period of exile

1.fast expulsion phase 0.12s

2. slow phase 0.13 s.

The expulsion phase begins end systolic volume protodiastolic period

4. Valve apparatus of the heart, its meaning. The mechanism of the valves. Changes in pressure in different parts of the heart in different phases of the cardiac cycle.

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

At the exit site of large vessels - the aorta and the pulmonary trunk - there are semilunar valves, represented by three pockets. When the blood is filled in the pockets, the valves close, so there is no reverse blood flow.

The purpose of the heart valve apparatus is to provide unilateral blood flow. Damage to the valve leaflets leads to valve failure. In this case, a reverse blood flow is observed as a result of a loose connection of the valves, which disrupts hemodynamics. The boundaries of the heart are changing. Signs of the development of insufficiency are obtained. The second problem associated with the area of valves, stenosis of the valves - (stenotic, for example, the venous ring) - the lumen decreases.When they talk about stenosis, it means either talking about atrioventricular valves, or about the place of vascular discharge. Above the semilunar valves of the aorta, from its bulb, the coronary vessels depart. 50% of people have more blood flow in the right than in the left, 20% have more blood flow 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 basins of the coronary arteries. Violation of the blood flow of the coronary vessels is accompanied by myocardial ischemia, angina pectoris, and complete blockage leads to necrosis - a heart attack. Venous outflow of blood goes through the superficial vein system, the so-called coronary sinus. There are also veins that open directly into the lumen of the ventricle and right atrium.

Ventricular systole begins with an asynchronous contraction phase. Some of the cardiomyocytes are excited and are involved in the excitation process. But the resulting tension in the ventricular myocardium provides 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 the tension of the cardiomyocytes occurs, it is impossible to compress the fluid. The length of the cardiomyocytes does not change. Isometric contraction phase. Shrinking at low length. This phase is called the isovalumic phase. During this phase, the volume of blood does not change. The space of the ventricles is closed, the pressure rises, in the right up to 5-12 mm Hg. in the left 65-75 mm Hg, while the pressure of the ventricles will become greater than the diastolic pressure in the aorta and pulmonary trunk and the excess of pressure in the ventricles over the pressure of blood 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, with the contraction of the ventricles, the blood is pushed into the aorta, into the pulmonary trunk, the length of the cardiomyocytes changes, the pressure also increases at the systole height in the left ventricle 115-125 mm, in the right 25-30 mm. At the beginning, the fast expulsion phase, and then the expulsion becomes slower. During the systole of the ventricles, 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 to increase systolic output if required. The ventricles complete the 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 meets the pockets of the semilunar valve, which fill up and close the valve. This period was named protodiastolic period- 0.04s. When the semilunar valves are closed, the flap valves are also closed, the isometric relaxation period ventricles. It lasts 0.08s. This is where the voltage drops without changing the length. This causes a drop in pressure. Blood has accumulated in the ventricles. The blood begins to press on the atrio-ventricular valves. They open at the beginning of ventricular diastole. The period of blood filling with blood begins - 0.25 s, while a phase of fast filling - 0.08 and a phase of slow filling - 0.17 s are distinguished. Blood flows freely from the atria into the ventricle. This is a passive process. The ventricles will be filled with blood by 70-80% 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 expelled by the heart per unit of time. Distinguish:

Systolic (during 1 systole);

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

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

V system av. = 70ml, ν avg = 70 beats / min,

V min = V system * ν = 4900 ml / 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's method (method for determining the IOC).

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

O2 consumption per minute is 300 ml;
O2 content in arterial blood = 20 vol%;
O2 content in venous blood = 14 vol%;
Arterio-venous oxygen difference = 6 vol% or 60 ml of blood.

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

The magnitude of the systolic volume can be defined as V min / ν. The systolic volume depends on the strength of the contractions of the ventricular myocardium, 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 the minute volume is determined by the change in ν and the systolic volume.

With physical exertion, the value of the minute volume can increase to 25-30 liters, the 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, untrained people - frequency, in children only due to frequency.

Distribution of the IOC.

	Aorta and large arteries
	Small arteries
	Arterioli
	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 arousal.

The heart muscle has a cellular structure and the cellular structure of the myocardium was established back in 1850 by Kelliker, but 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 contact area of cardiomyocytes is the insertion discs. Currently, the cells of the heart muscle are subdivided into the cells of the working myocardium - the cardiomyocytes of the working myocardium of the atria and ventricles and into the cells of the cardiac conduction system. Allocate:

-Pcells - pacemaker

-transition cells

- Purkinje cells

The cells of the working myocardium belong to striated muscle cells and cardiomyocytes have an elongated shape, reaching 50 μm in length, and 10-15 μm in diameter. The fibers are composed 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. In cardiomyocytes, there is also a longitudinal system of L tubules and transverse T tubules. However, T tubules, in contrast to the T-tubules of skeletal muscles, branch off at the level of Z membranes (in skeletal ones, at the border of discs A and I). Neighboring cardiomyocytes are connected by means of an intercalary disc - the membrane contact area. In this case, the structure of the insert disk is heterogeneous. A slit area (10-15 Nm) can be identified in the insert disk. The second zone of close contact is desmosomes. In the area of desmosomes, a thickening of the membrane is observed, and tonofibrils (threads connecting neighboring membranes) pass here. Desmosomes are 400 nm long. There are tight contacts, they are called nexuses, in which the outer layers of neighboring membranes merge, now they are found - conexons - bonding due to special proteins - connexins. 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. The myocardium is a functional sensidium. Cardiomyocytes are isolated from each other and come into contact in the area of the intercalated discs, where the membranes of neighboring cardiomyocytes come into contact.

7. Automation of the heart. Conductive system of the heart. Automation gradient. Stannius' experience. eight. Physiological properties heart muscle. Refractory phase. The ratio of the phases of the action potential, contraction and excitability in different phases of the cardiac cycle.

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

Connesxons are a compound in the membrane of neighboring cells. These structures are formed due to the proteins of the connexins. The Connexon is surrounded by 6 such proteins, a channel is formed inside the Connexon, which allows ions to pass, thus the electric current spreads from one cell to another. “F area has a resistance of 1.4 ohm per cm2 (low). Excitation covers cardiomyocytes at the same time. They function as functional sensitivities. Nexuses are very sensitive to lack of oxygen, to the action of catecholamines, to stressful situations, to physical exertion. This can cause a violation of the conduction of excitation in the myocardium. Under experimental conditions, breaking of tight contacts can be obtained by placing pieces of the myocardium in hypertonic solution sucrose. For the rhythmic activity of the heart, it is important cardiac conduction system- this system consists of a complex of muscle cells that form bundles and nodes and the cells of the conducting system differ from the cells of the working myocardium - they are poor in myofibrils, rich in sarcoplasm and contain high content glycogen. These features in light microscopy make them lighter with a small cross-striation and they were called atypical cells.

The conducting system includes:

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

2. The atrioventricular node (or Ashof-Tavara node), which lies in the right atrium on the border with the ventricle, is the posterior wall of the right atrium

These two nodes are connected by intra-atrial tracts.

3. Atrial tracts

Anterior - with a branch of Bachmen (to the left atrium)

Middle tract (Wenckebach)

Rear tract (Torelya)

4. Bundle of His (departs from the atrioventricular node. Passes through fibrous tissue and provides a connection between the atrial myocardium and the myocardium of the ventricle. Passes into the interventricular septum, where it is divided into the right and left leg of the His bundle)

5. The right and left legs of the bundle of His (they go 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 conducting system of the heart, which is formed by modified types of muscle cells, there are three types of cells: pacemaker (P), transitional cells and Purkinje cells.

1. P cells... They are located in the sino-arthrial node, less in the atrioventricular nucleus. These are the smallest cells, they have few t - fibrils and mitochondria, the t-system is absent, l. the system is poorly developed. The main function of these cells is to generate an action potential due to the innate property of slow diastolic depolarization. In them, there is a periodic decrease in the membrane potential, which leads them to self-excitation.

2. Transitional cells carry out the transfer of excitation in the area of the atrioventricular nucleus. They are found between P cells and Purkinje cells. These cells are elongated, they lack the sarcoplasmic reticulum. These cells have a slower conduction rate.

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 the emergence of action potential in the cells of the conducting 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. Decreased membrane potential in the diastolic period (50-70mV)

2. The fourth phase is not stable and there is a gradual decrease in the membrane potential to the threshold critical level of depolarization and in diastole it gradually slowly continues to decrease, reaching the 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 the ionic composition lead to the fact that the membrane potential in P-cells decreases to a threshold level and the P-cell self-excites providing the emergence of an action potential. The Plato phase is poorly expressed. Phase zero smoothly transition to the TB process of repolarization, which restores the diastolic membrane potential, and then the cycle repeats again and the P-cells go into a state of excitement. The cells of the sino-atrial node have the greatest excitability. The potential in it is especially 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 enhance automaticity. Humoral factors - adrenaline, norepinephrine. Physical factors- mechanical factor - stretching, stimulates the automatic, warming, also increases the automatic. All of this is used in medicine. This is the basis of the direct and indirect massage hearts. The area of the atrioventricular node is also automatic. The degree of automation 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 conducting system of the ventricles, impulses can also occur (20-30 per minute). In the course of the conducting system, a gradual decrease in the level of automation occurs, which is called the gradient of automation. 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 the phases of the action potential. The duration of AP, its ratio with the periods of refractoriness.

The action potential of the ventricular myocardium lasts about 0.3 s (more than 100 times longer than the AP 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 AP and the magnitude of its excitability are shown in Fig. 7.4. Distinguish the period absolute refractoriness(lasts 0.27 s, i.e., somewhat shorter than the duration of AP; the period relative refractoriness, during which the heart muscle can respond by contraction only to very strong irritations (lasts 0.03 s), and a short period supernormal excitability, when the heart muscle can respond by contraction to subthreshold stimulation.

Contraction (systole) of the myocardium lasts about 0.3 s, which roughly 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 prolonged refractory phase prevents the development of continuous shortening (tetanus) of the heart muscle, which would lead to the impossibility of the heart exercising its pumping function.

11. Reaction of the heart to additional irritation. 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 the relative refractoriness, there is a small period of increased excitability - the excitability becomes higher baseline- super normal excitability. In this phase, the heart is especially sensitive to the effects of other stimuli (other stimuli or extrasystoles, extraordinary systoles, may occur). The presence of a long refractory period should protect the heart from repeated excitations. The heart performs a pumping function. The gap between normal and extraordinary contractions is shortened. The pause can be normal or extended. An extended pause is called compensatory. The cause of extrasystoles is the emergence 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 localization, there are different extrasystoles - sinus, premedium, atrioventricular. Ventricular extrasystoles are accompanied by an extended compensatory phase. 3 additional irritation is the reason for the extraordinary contraction. In time, the extrasystole, the heart loses its excitability. Another impulse comes to them from the sinus node. A pause is needed to restore the normal rhythm. When a failure occurs in the heart, the heart skips one normal beat and then returns to its normal rhythm.

12. Conducting excitement in the heart. Atrioventricular delay. Blockade of the cardiac conduction system.

Conductivity- the ability to conduct arousal. The speed of the excitation in different departments is not the same. In the atrial myocardium - 1 m / s and the time of excitation takes 0.035 s

Excitation rate

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 sinus node to ventricular myocardium - 0.107 s

Ventricular myocardium - 0.8-0.9 m / s

Violation of the conduction of the heart leads to the development of blockades - sinus, atrioventricular, bundle of His and its legs. The sinus node may turn off. Will the AV node turn on as a pacemaker? Sinus blocks are rare. More in the atrioventricular nodes. The lengthening of the delay (more than 0.21 s), 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 inconsistently. A block of the legs and bundle is a blockade of the ventricles. accordingly, one ventricle lags behind the other).

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

Cardiomyocytes include fibrils, sarcomeres. There are longitudinal tubules and T tubules of the outer membrane, which enter inward at the level of the membrane I. They are wide. The contractile fugation of cardiomyocytes is associated with the proteins myosin and actin. On thin actin proteins - the troponin and tropomyosin system. This prevents the myosin heads from adhering to the myosin heads. Removal of blockage - with calcium ions. Calcium channels are opened through the t tubes. An increase in calcium in the sarcoplasm removes the inhibitory effect of actin and myosin. Myosin bridges move the filament tonic to the center. The myocardium obeys 2 laws of contractile function - all or nothing. The force of contraction depends on the initial length of the cardiomyocytes - Frank and Staraling. If the myocytes are pre-stretched, then they respond with a greater force of contraction. Stretching depends on the filling with blood. 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.

apical impulse is a rhythmic pulsation in the fifth intercostal space 1 cm inward from the mid-clavicular line, due to beats of the apex of the heart.

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

The apical impulse is better defined in a horizontal position with a slight turn to the left side. Examine the apical impulse by palpation, placing the palm of the right hand parallel to the intercostal space. In this case, the following are determined push properties: localization, area (1.5-2 cm2), height or amplitude of vibration and force of 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, sound manifestations in the shape of heart tones. To study heart sounds, the method of auscultation and graphic registration of tones using a microphone and a phonocardiograph amplifier is used.

15. Heart sounds, their origin, components, especially heart sounds in children. Methods for the study of heart sounds (auscultation, phonocardiography).

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

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

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

On the phonocardiogram, 2-4 oscillations correspond to it. Normally, in the inspiratory phase, you can sometimes hear the splitting of the second tone. In the inspiratory phase, blood flow to the right ventricle becomes lower due to a decrease in intrathoracic pressure and the systole of the right ventricle lasts a little longer than the left one, so the pulmonary valve closes a little more slowly. On exhalation, they close at the same time.

In pathology, splitting is present in both the inspiratory and expiratory phases.

Third tone occurs 0.13 s after the second. It is associated with vibrations of the walls of the ventricle in the phase of their rapid filling with blood. On the phonocardiogram, 1-3 fluctuations are recorded. 0.04s.

Fourth tone... Associated with atrial systole. It is recorded in the form of low-frequency vibrations that 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 suggested to listen to heart sounds at five points.

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

The second tone 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.

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

When listening, you can also hear noises. The appearance of noise is associated either with a narrowing of the valve openings, which is designated as stenosis, or with damage to the valve cusps and their loose closure, then valve failure occurs. By the time the murmurs appear, they can be systolic and diastolic.

16. Electrocardiogram, the origin of its teeth. Intervals and ECG segments... Clinical ECG value... Age features of the 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 generator of electricity. Body tissues, possessing a relatively high electrical conductivity, make it possible to register the electrical potentials of the heart from the surface of the body. This research technique electrical activity heart, introduced into practice by V. Einthoven, A. F. Samoilov, T. Lewis, V. F. Zelenin and others, was named electrocardiography, and the curve recorded with its help is called electrocardiogram (ECG). Electrocardiography is widely used in medicine as a diagnostic method that makes it possible to assess the dynamics of the propagation of excitation in the heart and to judge cardiac abnormalities with ECG changes.

Currently, they use special devices - electrocardiographs with electronic amplifiers and oscillographs. The curves are recorded on a moving paper tape. Devices have also been developed with the help of which the ECG is recorded during active muscular activity and at a distance from the subject. These devices - tele-electrocardiographs - are based on the principle of transmitting an ECG over a distance using radio communication. In this way, ECGs are recorded in athletes during competitions, in astronauts in space flight, etc. specialized center located at a great distance from the patient.

Due to a certain position of the heart in the chest and the peculiar shape of the human body, the electric lines of force that arise between the excited (-) and unexcited (+) areas of the heart are unevenly distributed over the surface of the body. For this reason, depending on the place of application of the electrodes, the shape of the ECG and the voltage of its teeth will be different. To register an ECG, the potentials are removed from the limbs and the surface of the chest. Usually they use three so-called standard limb leads: Lead I: right hand - left hand; Lead II: right hand - left leg; Lead III: left arm - left leg (Fig. 7.5). In addition, three unipolar enhanced Goldberger leads: aVR; aVL; aVF. When registering enhanced leads, two electrodes used to register 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 the registration of six chest leads.

Formation of various ECG components:

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

2) PQ interval - conducting PD along the cardiac conduction system from the CA to the AV node and further to the ventricular myocardium, including atrioventricular retention. 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) R wave - excitation of the bulk of the ventricles. Duration 0.03-0.09, amplitude 10-20 mm.

5) S wave - 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) Segment ST - reflects the process of full coverage of the excitation of the ventricles. The duration is highly dependent on the heart rate. Mixing this segment up or down by more than 1 mm may indicate myocardial ischemia.

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

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

17. Methods of ECG derivation in humans. Dependence of the size of the ECG teeth in various leads on the position of the electrical axis of the heart (Einthoven's triangle rule).

In general, the heart can also be seen as electric dipole(negatively charged base, positively charged tip). The line that connects the areas of the heart with the maximum potential difference - electrical heart line ... When projected, coincides with the anatomical axis. When the heart works, an electric field is generated. The lines of force of this electric field propagate in the human body as in a volumetric conductor. Different parts of the body will receive a different charge.

The orientation of the heart's electric field causes the upper half of the torso, right arm, head and neck to be negatively charged. Bottom half torso, both legs and left arm are positively charged.

If electrodes are placed on the surface of the body, then potential difference... To register the potential difference, there are various lead systems.

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

Standard leads.

1 lead. Right and left forearm

Lead 2. Right hand - left shin.

3 lead. Left hand - left leg.

Single pole leads... Measure the magnitude of the potentials at one point in relation to others.

1 lead. Right arm - left arm + left leg (ABP)

Lead 2. AVL Left arm - right arm right leg

3. Abduction of the AVF left leg - right arm + left arm.

Chest leads... They are unipolar.

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

Lead 2. 4 intercostal space to the left of the sternum.

4 lead. Apex projection

3 lead. The middle between the second and fourth.

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

6 lead. 5 intercostal space along the mid-axillary 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 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. Characterization of the effects of the sympathetic nervous system on the heart. Strengthening nerve I.P. Pavlov.

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

Like all autonomic nerves, the heart 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 conducting 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 upper five segments thoracic spinal cord. The processes of these neurons end in the cervical and upper thoracic sympathetic nodes. In these nodes are the second neurons, the processes of which go to the heart. Most of the sympathetic nerve fibers that innervate the heart extend from the stellate ganglion.

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

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

The inotropic effect of the "reinforcing" nerve is clearly visible when the intraventricular pressure is recorded with an electromagnometer. The pronounced effect of the "reinforcing" nerve on the contractility of the myocardium is manifested especially in violation of contractility. One of such extreme forms of impaired contractility is the alternation of heart contractions, when one "normal" contraction of the myocardium (pressure in the ventricle develops in excess of the pressure in the aorta and blood is ejected from the ventricle into the aorta) alternates with a "weak" contraction of the myocardium, in which the pressure in the ventricle during systole does not reach the pressure in the aorta and the ejection of blood does not occur. The "reinforcing" nerve not only enhances the usual ventricular contractions, but also eliminates the alternation, restoring ineffective contractions to normal (Fig. 7.13). According to I.P. Pavlov, these fibers are specially trophic, that is, they stimulate metabolic processes.

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

V last years Facts became known indicating the possibility of not only corrective, but also triggering influences of the nervous system on the heart rhythm, when signals coming along the nerves initiate heart contractions. This can be observed in experiments with stimulation of the vagus nerve in a mode close to natural impulses in it, that is, in "bursts" ("bundles") of impulses, and not in a continuous stream, as was traditionally done. When the vagus nerve is irritated by "bursts" of impulses, the heart contracts in the rhythm of these "bursts" (each "burst" corresponds to one contraction of the heart). Changing the frequency and characteristics of "volleys", you can control the heart rate within a wide range.

19. Characterization of influences vagus nerves on the heart. The tone of the centers of the vagus nerves. Proof of its presence, age-related changes in the tone of the vagus nerves. Factors supporting the tone of the vagus nerves. The phenomenon of "escape" of the heart 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 work of the heart until it stops completely in diastole. This was the first case of the discovery of the inhibitory effect of nerves in the body.

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

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

With prolonged irritation of the vagus nerve, the contractions of the heart that stopped at the beginning are restored, despite the continued irritation. This phenomenon is called the escape of the heart from the influence of the vagus nerve.

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

When sympathetic nerves are irritated, spontaneous depolarization of the pacemaker cells in diastole is accelerated, which leads to an increase in 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 batmotropic effect). The effect of irritation of the sympathetic nerve is observed after a long latency period (10 s or more) and continues long after the termination of the irritation of the nerve.

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

The chemical mechanism of transmission of nerve impulses to the heart. When the peripheral segments of the vagus nerves are irritated at their endings, ACh is released in the heart, and when the sympathetic nerves are irritated, norepinephrine is released. These substances are direct agents that inhibit or intensify the activity of the heart, and therefore are called mediators (transmitters) of nerve 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 exposed 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. The lower curves show the effects caused by the transferred Ringer's solution, which was in the heart during irritation.

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

The obtained data indicate that during excitation, along with the main mediator substance, other biologically active substances, in particular peptides, 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 irritation of the vagus nerve, 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 value of electrolytes in the work of the heart. Endocrine function of the heart.

Changes in the work of the heart are observed when a number of biologically active substances circulating in the blood act on it.

Catecholamines (adrenaline, norepinephrine) increase the strength and speed up the heart rate, which is of great biological importance. At physical activity or emotional stress, the adrenal medulla releases a large amount of adrenaline into the bloodstream, which leads to an increase in 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 (an energy source for the contracting myocardium). In addition, phosphorylase is necessary for the activation of Ca 2+ ions, an agent that implements the conjugation of 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 hand, 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.

The adrenal cortex hormones, angiotensin and serotonin, also increase the strength of myocardial contractions, and thyroxin increases the heart rate. Hypoxemia, hypercapnia and acidosis inhibit the contractile activity of the myocardium.

Atrial myocytes form atriopeptide, or natriuretic hormone. The secretion of this hormone is stimulated by the 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 carried out by increasing glomerular filtration and suppressing the reabsorption of water in the tubules. Natriuretic hormone suppresses renin secretion, inhibits the effects of angiotensin II and aldosterone. Na-triuretic hormone relaxes smooth muscle cells of small vessels, thereby helping to reduce blood pressure, as well as intestinal smooth muscles.

22. The meaning of the centers medulla oblongata and the hypothalamus in the regulation of the heart. The role of the limbic system and 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 step in the hierarchy of nerve centers that regulate the work of the heart. By integrating the reflex and influences descending from the higher parts of the brain, they form signals that control the activity of the heart, including determining the rhythm of its contractions. The 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, which in strength and severity are much superior to those that occur in natural conditions. With local point stimulation of some points of the hypothalamus, it was possible to observe isolated reactions: a change in the heart rate, 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 there are structures in the hypothalamus that can regulate separate 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 changes in 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. He - executive agency, providing an 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 in the cerebral cortex of the centers responsible for the occurrence of motor and cardiovascular reactions contributes to the optimal autonomic support of the body's behavioral reactions.

23. The movement of blood through the 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) the closedness of the vascular bed, which includes the pumping organ of the heart;

2) the 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 (unlike other hydrodynamic systems);

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

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

Types of blood vessels:

1) the main vessels of the elastic type: the aorta, large arteries extending 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 the pulsating blood flow into a smooth and continuous one;

2) vessels of resistance or resistive vessels - vessels of the muscle 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 course of the metabolic process, the performance of the respiratory function between blood and cells; the number of functioning capillaries depends on the functional and metabolic activity in the tissues;

4) shunt vessels or arteriovenular anastomoses directly connect arterioles and venules; if these shunts are open, then the blood is discharged from the arterioles to the venules, bypassing the capillaries, if they are closed, then the blood goes from the arterioles to 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, significantly affect the amount of venous return of blood to the heart.

24. The main parameters of hemodynamics. Poiseuille's formula. The nature of the movement of blood through the vessels, its features. The possibility of applying the laws of hydrodynamics to explain the movement of blood through the vessels.

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

The amount of blood flowing through the 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 the current, E is the voltage, R is the resistance.

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

Hagen Poisel's Law:

where η is the 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 values of pressures that matter, but the difference in pressure:

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 [Din * s / cm 5]. Relative units of resistance 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 elements of the vessels.

If the values of the resistances arising in series-connected vessels are considered, 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 by 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 values inverse to the resistance in each element.

Physiological processes obey general physical laws.

25. The speed of blood flow in different parts of the vascular system. The concept of volumetric and linear blood velocity. Time of blood circulation, methods of its determination. Age-related changes in the time of blood circulation.

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

Volumetric velocity- the amount of blood passing through the cross-section of the vascular bed per unit of 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 (through all vessels in a minute pass 5 l), but each organ receives different amount blood, as a result of this, Q is distributed in a% ratio, for a separate body it is necessary to know the pressure in the artery, the vein through which the blood supply is carried out, as well as the pressure inside the organ itself.

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

In the direction from the aorta, the total cross-sectional area increases, reaches a maximum at the level of capillaries, the total lumen of which is 800 times larger than the aortic lumen; 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 velocity is greater.

The blood flow in the vascular system is laminar, each layer moves parallel to the other without mixing. The wall layers experience great friction, as a result, the velocity tends to 0, towards the center of the vessel, the velocity increases, reaching its maximum value in the axial part. Laminar blood flow is silent. Sound phenomena occur when laminar blood flow turns into turbulent (eddies 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 are narrowed, when the velocity increases at the sites of the vessels' branching, or when obstacles arise in the way. Turbulent blood flow is noisy.

Blood circulation time- the time it takes for the blood to complete a full circle (both small and large). It is 25 s, which accounts for 27 systoles (1/5 for a small one - 5 s, 4/5 for a large one - 20 s). Normally, 2.5 liters of blood circulate, the circulation rate is 25 sec, which is enough to provide the IOC.

26. Blood pressure in various parts of the vascular system. Factors determining the value 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 muscles of the heart, which performs the pumping function.

Distinguish:

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 stream. This energy is made up of potential, kinetic energy and potential energy of gravity:

E = P + ρV 2/2 + ρgh,

where P - potential energy, ρV 2/2 - kinetic energy, ρgh - energy of a blood column or potential energy of gravity.

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

Systolic blood volume;

The frequency and rhythm of heart contractions;

Elasticity of the artery walls;

Resistance of resistive vessels;

Blood speed in capacitive 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 the value of blood pressure. Age-related changes in blood pressure in humans.

In arterial pressure, a distinction is made between lateral and terminal 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 pressures decrease, since the energy of the flow is spent on overcoming resistance, while maximum reduction occurs 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, in blood pressure they are distinguished:

Systolic or maximum pressure (pressure established during the period of ventricular systole);

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

The difference between the magnitude of the systolic and diastolic pressure is the pulse pressure;

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

In different departments, the pressure will take different meanings... In the left atrium, the systolic pressure is 8-12 mm Hg, the diastolic pressure is 0, in the left ventricle, syst = 130, diast = 4, in the aorta, syst = 110-125 mm Hg, diast = 80-85, in the brachial artery, syst = 110-120, diaste = 70-80, at the arterial end of the capillaries of syst 30-50, but there are no oscillations, at the venous end of the capillaries syst = 15-25, small veins syst = 78-10 (on 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, diastas = 5-14, in the pulmonary veins, syst = 4-8.

In the large and small circle, a gradual decrease in pressure occurs, which reflects the consumption of energy used to overcome resistance. The mean pressure is not the arithmetic mean, for example, 120 to 80, the mean 100 is an incorrect given, since the duration of the systole and diastole of the ventricles is different in time. To calculate the average pressure, two mathematical formulas were proposed:

Cp 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 mm Hg)

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, with changes in the tone of the liver arteries.

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

First order waves (pulse) the most common. They are synchronized with the contractions of the heart. During each systole, a portion of blood enters the arteries and increases their elastic stretching, while the pressure in the arteries rises. During diastole, the flow of blood from the ventricles to arterial system only the outflow of blood from the large arteries stops and occurs: the stretching of their walls decreases and the pressure decreases. Pressure fluctuations, gradually damping, spread from the aorta and pulmonary artery to all their branches. The highest value of pressure in the arteries (systolic, or maximum pressure) observed during the passage of the top of the pulse wave, and the least (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 first-order wave. 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 arterial pressure pulse waves in arterioles and capillaries.

In addition to systolic, diastolic and pulse blood pressure, the so-called mean arterial pressure. It is 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., mean arterial pressure is the resultant of all pressure changes in the vessels.

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

In addition to pulse fluctuations, the blood pressure curve shows waves of the second order, coinciding with breathing 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 waves of the third order. These are even slower increases and decreases in pressure, each of which covers several second-order respiratory waves. These waves are due to periodic changes in the tone of the vasomotor centers. They are observed most often with insufficient supply of oxygen to the brain, for example, when climbing 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 blood flow through it. For such a study, use sphygmomanometer Riva-Rocci. The examinee is put on the shoulder with a hollow rubber cuff, which is connected to a rubber bulb, which serves for air injection, and to a manometer. When inflated, the cuff compresses the shoulder, and the manometer shows the value of this pressure. To measure blood pressure using this device, at the suggestion of NS Korotkov, one listens to vascular tones arising in the artery to the periphery of the cuff imposed on the shoulder.

When blood moves in an uncompressed artery, there are no sounds. If the pressure in the cuff is raised above the level of systolic blood pressure, then the cuff completely compresses the lumen of the artery and blood flow in it stops. There are also no sounds. If now you 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 on the wall of the artery of a portion of blood moving through the compressed area with high velocity and kinetic energy, produces a sound heard below the cuff. The pressure in the cuff, at which the first sounds appear in the artery, arises at the moment the apex of the pulse wave passes and corresponds to the maximum, i.e., systolic, pressure. With a further decrease in pressure in the cuff, a moment comes when it becomes lower than diastolic, blood begins to flow through the artery both during the apex and base of the pulse wave. At this point, sounds in the artery below the cuff disappear. The pressure in the cuff at the time of the disappearance of sounds in the artery corresponds to the value of the minimum, i.e. di-astolic, pressure. The arterial pressure values determined by the Korotkov method and recorded in the same person by introducing a catheter connected to an electromometer into the artery do not differ significantly from each other.

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

V clinical practice Blood pressure is usually determined in the brachial artery. In healthy people aged 15-50 years, the maximum pressure measured by the Korotkov method is 110-125 mm Hg. Over the age of 50, it usually rises. 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 arterial pressure in middle-aged adults in the brachial artery is on average 60-80 mm Hg, the pulse pressure is 35-50 mm Hg, and the average is 90-95 mm Hg.

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

Capillaries are the thinnest vessels, 5-7 microns in diameter, 0.5-1.1 mm long. These vessels lie in the intercellular spaces, in close contact with the cells of organs and tissues of the body. The total length of all the capillaries of the human body is about 100,000 km, that is, a thread that could gird the earth three times along the equator. The physiological significance of capillaries lies in the fact that through their walls, the exchange of substances between blood and tissues is carried out. 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 blood flow velocity in the capillaries is low and amounts to 0.5-1 mm / s. Thus, each blood particle is in the capillary for about 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 metabolism between blood and tissue (intercellular) fluid.

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

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

The blood pressure in the capillaries is measured in a direct way: under the control of a binocular microscope, a thinnest cannula is inserted into the capillary, connected to an electromagnometer. In humans, the pressure at the arterial end of the capillary is 32 mm Hg, and at the venous end - 15 mm Hg, at the top of the capillary loop of the nail bed - 24 mm Hg. In the capillaries of the renal glomeruli, the pressure reaches 65-70 mm Hg, and in the capillaries that encircle the renal tubules - only 14-18 mm Hg. The pressure in the capillaries of the lungs is very low - an average of 6 mm Hg. Measurement of capillary pressure is carried out in the position of the body, in which the capillaries of the investigated area are at the same level with the heart. In the case of expansion of arterioles, the pressure in the capillaries increases, and with narrowing, it decreases.

Blood flows only in the "duty" capillaries. Some of the capillaries are cut off from the circulation. During the period of intensive activity of organs (for example, with muscle contraction or secretory activity of the glands), when the metabolism in them increases, the number of functioning capillaries increases significantly.

Regulation of capillary blood circulation by the nervous system, the effect on it of physiologically active substances - hormones and metabolites - are carried out when they are exposed to arteries and arterioles. Narrowing or dilation 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, that is, the ratio of erythrocytes to plasma. In this case, the total blood flow through the metarterioles and capillaries is determined by the contraction of 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 when it leaves the metaarterioles) determines which part of the blood will pass through true capillaries.

In some areas of the body, for example, in the skin, lungs and kidneys, there are direct connections of 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 open, then some of the blood can enter the veins, bypassing the capillaries.

Arteriovenous anastomoses play the role of shunts that regulate capillary circulation. An example of this is a change in capillary blood circulation in the skin with an increase (over 35 ° C) or a decrease (below 15 ° C) temperature environment... 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 complex of microvessels, relatively isolated in hemodynamic respect, supplying blood to a certain cell population of an organ. In this case, the specificity of vascularization of tissues of various organs takes place, which is manifested in the peculiarities of branching of microvessels, density of capillarization of tissues, etc. The presence of modules allows you to regulate local blood flow in individual microsections of tissues.

Microcirculation is a collective concept. It unites the mechanisms of blood flow in small vessels and the exchange of fluid 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 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 extensible 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 if the pressure in the veins rises by 10 mm Hg. the capacity of the venous system will increase 6 times. Vein capacity can also change when the smooth muscle of the venous 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. Vein pressure in a person can be measured by inserting a hollow needle into a superficial (usually ulnar) vein and connecting it to a sensitive electric manometer. In the veins outside chest 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 blood pressure, for example, in the veins of the legs in a standing position.

In the veins of the chest 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, that is, below atmospheric. When you exhale, the opposite changes occur and the pressure rises (during normal exhalation, it does not rise above 2-5 mm Hg). Injury to veins lying near the chest cavity (for example, the jugular veins) is dangerous, since the pressure in them at the time of inhalation is negative. When inhaling, it is possible for atmospheric air to enter the vein cavity and the development of air embolism, i.e., the transfer of air bubbles with blood and their subsequent blockage of arterioles and capillaries, which can lead to death.

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

The arterial pulse is called the rhythmic oscillations of the artery wall, caused by an increase in pressure during the period of the system. Pulsation of the arteries can be easily detected by touching any artery accessible to palpation: 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 pressure increase that occurs in the aorta at the time of expulsion of blood from the ventricles. At this time, the pressure in the aorta rises sharply and its wall is stretched. The wave of increased pressure and the vibrations of the vascular wall caused by this extension with a certain speed propagate from the aorta to the arterioles and capillaries, where the pulse wave is extinguished.

The speed of propagation of the pulse wave does not depend on the speed of blood movement. The maximum linear velocity of blood flow through the arteries does not exceed 0.3-0.5 m / s, and the velocity of pulse wave propagation in young and middle-aged people with normal arterial pressure and normal vascular elasticity is equal in the aorta 5,5 -8.0 m / s, and in the peripheral arteries - 6.0-9.5 m / s. With age, as the elasticity of the vessels decreases, the rate 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. Curve rise - anacrot - arises 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 the systole of the ventricle, when the pressure in it begins to fall, the pulse curve falls - catacroth. 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 the large arteries - incisura. The movement of blood back to the heart is obstructed, since the semilunar valves, under the influence of the reverse flow of blood, close and prevent it from entering the heart. The wave of blood is reflected from the valves and creates a secondary wave of pressure increase, causing the expansion again. arterial walls... As a result, a secondary appears on the sphygmogram, 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).

The study of the pulse, both palpable and instrumental, by registering a sphygmogram, provides valuable information about the functioning of the cardiovascular system. This study allows you to evaluate both the very fact of the presence of heartbeats, and the frequency of its contractions, rhythm (rhythmic or arrhythmic pulse). Rhythm fluctuations can also be of a physiological nature. So, "respiratory arrhythmia", manifested in an increase in the pulse rate on inspiration and a decrease on expiration, is usually expressed in young people. Tension (hard or soft pulse) is determined by the amount of effort that must be applied in order for the pulse in the distal part of the artery to disappear. The pulse voltage to a certain extent reflects the value of the average blood pressure.

Venous pulse. There are no pulse fluctuations in blood pressure in small and medium-sized veins. In large veins near the heart, pulse fluctuations are noted - a venous pulse, which has a different origin than arterial pulse... It is caused by the obstruction of blood flow from the veins into the heart during atrial and ventricular systole. During the systole of these parts of the heart, the pressure inside the veins rises and their walls vibrate. It is most convenient to record the venous pulse of the jugular vein.

On the curve of the venous pulse - phlebogram - there are three teeth: a, c, v (fig. 7.21). Barb a coincides with the systole of the right atrium and is due to the fact that at the time of atrial systole the mouths of the hollow veins are clamped by a ring muscle fibers, as a result of which the flow of blood from the veins to the atria is temporarily suspended. During diastole of the atria, the access to them of blood becomes free again, and at this time the curve of the venous pulse drops steeply. Soon, a small tooth appears on the curve of the venous pulse. c... It is caused by the impulse of the pulsating carotid artery, which lies 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 the systole of the ventricles of the atria are filled with blood, further blood flow into them is impossible, stagnation of blood in the veins and stretching of their walls occur. After the prong v there is a drop in the curve, which coincides with the diastole of the ventricles and the flow of blood into them from the atria.

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

With the enhanced function of any organ or tissue, the intensity of metabolic processes increases and the concentration of metabolic products (metabolites) - carbon monoxide (IV) CO 2 and carbonic acid, adenosine diphosphate, phosphoric and lactic acids and other substances - increases. The 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 vasodilation in the working organ. The smooth muscles of the vascular wall are very sensitive to the action of these metabolic products.

Getting into 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 arising from the central action of these substances leads to an increase in systemic blood pressure with a significant increase in blood flow through the working organs.

In skeletal muscle at rest, there are about 30 open, that is, functioning, capillaries per 1 mm 2 of the cross section, and at 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 by no more than 5-6 times, therefore, an increase in the blood supply to working muscles by 100 times is possible only as a result of blood redistribution. So, during the period of digestion, there is an increased blood flow to the digestive organs and a decrease in the blood supply to the skin and skeletal muscles. During mental stress, the blood supply to the brain increases.

Strenuous muscular work leads to narrowing of the vessels of the digestive organs and increased blood flow to the working skeletal muscles. The blood flow to these muscles increases as a result of the local vasodilating action of metabolic products formed in the working muscles, as well as due to reflex vasodilation. So, when one hand works, the vessels expand 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 the working organ, muscle tone decreases not only due to the accumulation of metabolic products, but also as a result 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, therefore, a significant increase in local blood circulation.

In addition to metabolic products that accumulate in working organs and tissues, other humoral factors also affect the muscles of the vascular wall: hormones, ions, etc. this is a significant rise in systemic blood pressure. Adrenaline also enhances cardiac activity, however, the vessels of the working skeletal muscles and the vessels of the brain do not narrow under the influence of adrenaline. Thus, the release into the blood of a large amount of adrenaline, formed during emotional stress, significantly increases the level of systemic blood pressure and at the same time improves the blood supply to the brain and muscles and thereby leads to the mobilization of the body's energy and plastic resources, which are necessary in emergency conditions, when - second, emotional stress arises.

The vessels of a number of internal organs and tissues have individual characteristics of regulation, 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 heat regulation. Their expansion with an increase in 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 position to a vertical one. At the same time, the venous outflow of blood from the legs becomes difficult and the amount of blood entering the heart through the inferior vena cava decreases (with fluoroscopy, a decrease in the size of the heart is clearly visible). As a result, venous blood flow to the heart can be significantly reduced.

In recent years, an important role of the vascular wall endothelium in the regulation of blood flow has been established. The vascular endothelium synthesizes and secretes factors that actively affect the tone of vascular smooth muscles. Endothelial cells - endotheliocytes under the influence of chemical stimuli brought by the blood, or under the influence of mechanical stimulation (stretching) are able to release substances that directly act on vascular smooth muscle cells, causing them to contract or relax. The life span 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 vascular relaxation are, apparently, nitrates and nitrites. A possible vasoconstrictor factor is a vasoconstrictor peptide endothelium, consisting of 21 amino acid residues.

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

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

The main vasoconstrictor nerves of the abdominal cavity organs are sympathetic fibers that run as part of the internal nerve (item splanchnicus). After cutting these nerves, the blood flow through the vessels of the abdominal cavity, devoid of vasoconstrictor sympathetic innervation, increases sharply due to the expansion of the arteries and arterioles. With irritation of the item splanchnicus, the vessels of the stomach and small intestine are narrowed.

Sympathetic vasoconstrictor nerves to the limbs are part of the spinal mixed nerves, as well as along the walls of the arteries (in their adventitia). Since the transection of the sympathetic nerves causes the vasodilation of the area that is 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 arterial vasoconstriction.

Vasodilatory effects (vasodilation) were first discovered during irritation of several nerve branches belonging to the parasympathetic division of the nervous system. For example, irritation of the drum string (chorda timpani) causes dilation of the vessels of the submandibular gland and tongue, n. Cavernosi penis - dilation of the vessels of the cavernous bodies of the penis.

In some organs, for example, in skeletal muscles, the dilation of arteries and arterioles occurs when the sympathetic nerves are irritated, which contain, in addition to vasoconstrictors, and vasodilators. In this case, activation α -adrenergic receptors leads to vasoconstriction (constriction). 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 vasodilating reactions. Vasodilator nerves, their importance in the regulation of regional blood circulation.

Expansion of blood vessels (mainly of the skin) can also be caused by irritation of the peripheral segments of the posterior roots of the spinal cord, which contain afferent (sensory) 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, whose bodies are located in the spinal nodes, have a dual function: they transmit afferent impulses to the spinal cord and efferent impulses to the vessels. The transmission of impulses in two directions is possible because afferent fibers, like all other nerve fibers, have two-way conduction.

According to another point of view, the expansion of the skin vessels with irritation of the dorsal roots occurs due to the fact that acetylcholine and histamine are formed in the receptor nerve endings, which diffuse through the tissues and expand nearby vessels.

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

VF Ovsyannikov (1871) found that the nerve center providing a certain degree of narrowing of the arterial bed - the vasomotor center - is located in the medulla oblongata. The localization of this center is determined by transection of the brainstem at different levels. If the transection is performed in a dog or cat above the quadruple, then the blood pressure does not change. If the brain is cut between the medulla oblongata and the spinal cord, then the maximum blood pressure in the carotid artery drops 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 vasodilation 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 section of the vasomotor center causes narrowing of the arteries and lifting, and irritation of the second - expansion of the arteries and a drop in blood pressure.

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

The 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 the vascular tone of certain parts of the body. The spinal centers are able, some time after turning off the vasoconstrictor center of the medulla oblongata, slightly increase the blood pressure, which has decreased due to the expansion of the arteries and arterioles.

In addition to the vasomotor centers of the medulla oblongata and spinal cord, the state of the 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, the arteries and arterioles are constantly in a state of constriction, 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 regions 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 is of both reflexive and humoral origin.

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

Own vascular reflexes. They are caused by signals from the receptors of the vessels themselves. The receptors concentrated in the aortic arch and in the area of the carotid artery branching into the 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 the blood pressure in the vessels rises, therefore they are called pressoreceptors, or baroreceptors. If the carotid and aortic nerves are cut on both sides, hypertension occurs, ie, a steady increase in blood pressure, reaching 200-250 mm Hg in the dog's carotid artery. instead of 100-120 mm Hg. fine.

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

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

In the reflexogenic zone of the carotid sinus (carotid sinus, sinus caroticus) there are receptors from which centripetal nerve fibers originate, forming the carotid sinus 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 the stretching of the carotid artery wall excites the receptors of the carotid sinus, reflexively lowers the tone of the vasoconstrictor center and increases the tone of the nuclei of the vagus nerves.

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

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

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

In response to an increase in pressure, baroreceptors stimulate the activity of the vasodilator zone. At the same time, they increase the tone of the nuclei of the vagus nerve. In response, reflex reactions develop, reflex changes occur. The vasodilator zone suppresses the vasoconstrictor tone. Vascular dilation 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 wandering increases, the rhythm frequency decreases. High blood pressure returns to normal. Dilation of arterioles increases blood flow in the capillaries. Part of the fluid will pass into the tissues - the volume of blood will decrease, which will lead to a decrease in pressure.

From chemoreceptors arise pressor reflexes... An increase in the activity of the vasoconstrictor zone along the descending pathways stimulates the sympathetic system, while the vessels are narrowed. The pressure rises through the sympathetic centers of the heart, the heart will work faster. The sympathetic system regulates the release of hormones by the adrenal medulla. Blood flow in the pulmonary circulation will increase. The respiratory system reacts with increased breathing - the release of blood from carbon dioxide. The factor that caused the pressor reflex leads to the normalization of the blood composition. In this pressor reflex, a secondary reflex to a change in the work of the heart is sometimes observed. Against the background of an increase in pressure, there is a tension in the work of the heart. 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 the receptors of internal organs (Goltz reflex). Eye-cardiac reflex (Ashner reflex).

Bainbridge injected into the venous part of the mouth 20 ml nat. Solution or the same volume of blood. After that, there was a reflex increase in heart rate, 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 a second time. This reflex occurs when there is an increase in blood flow to the heart. When the blood flow is greater than the outflow. In the area of the mouth of the genital veins - sensitive receptors that respond to an increase in venous pressure. These sensory receptors are the endings of the afferent fibers of the vagus nerve, as well as the afferent fibers of the posterior 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 nuclei of the vagus nerve, while the tone of the sympathetic centers increases. There is an increase in the work of the heart and blood from the venous part begins to be pumped into the arterial. The pressure in the vena cava will decrease. Under physiological conditions, this condition can increase with physical exertion, when the blood flow increases and with heart defects, blood stagnation is also observed, which leads to an increase in the work of the heart.

Goltz found that stretching of the stomach, intestines, or light beating of the intestines in a frog is accompanied by a slowdown in the work of the heart, up to a complete stop. This is due to the fact that from the receptors impulses arrive at the nuclei of the vagus nerves. Their tone rises and the work of the heart is inhibited, or even its arrest.

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

In the vessels of the pulmonary circulation, they are located in receptors that respond to an increase in pressure in the pulmonary circulation. With an increase in pressure in the small circle of blood circulation, a reflex arises, which causes the expansion of the vessels of the large circle, at the same time the work of the heart is strained and an increase in the volume of the spleen is observed. Thus, such a kind of unloading reflex arises from the small circle of blood circulation. This reflex was discovered by V.V. Parin... He worked very hard in the development and research of space physiology, headed the Institute for Biomedical Research. Increased 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 helps to filter the blood plasma and, due to this state, the liquid enters the alveoli.

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

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

Consider the body's response to a decrease in BCC in blood loss. In such cases, blood flow to the heart decreases and blood pressure decreases. In response to this, there are reactions aimed at restoring the normal level of blood pressure. First of all, there is a reflex narrowing of the arteries. In addition, with blood loss, there is a reflex increase in the secretion of vasoconstrictor hormones: adrenaline - by the adrenal medulla and vasopressin - by the posterior lobe of the pituitary gland, and an increase in the secretion of these substances leads to narrowing of 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 and adrenal glands. In addition to the sympathoadrenal effects and the action of vasopressin, in maintaining blood pressure and BCC at a normal level with blood loss, especially in late dates, the renin-angiotensin-aldosterone system is involved. The resulting decrease in blood flow in the kidneys after blood loss leads to an increased release of renin and a 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 part of the autonomic nervous system, and secondly, enhances sodium reabsorption in the kidneys. Sodium retention is important factor increasing the reabsorption of water in the kidneys and the restoration of the BCC.

To maintain blood pressure with open blood loss, the transition to the vessels of the 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. Reflex acceleration and intensification of heart contractions also contributes to the equalization of blood pressure. Thanks to these neurohumoral effects, with a rapid loss of 20— 25% blood pressure can remain high enough for some time.

There is, however, a certain limit of blood loss, after which no regulatory adaptations (neither vasoconstriction, 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 40-50% of the blood contained in it, then blood pressure drops sharply and can drop to zero, which leads to death.

These mechanisms of regulation of vascular tone are unconditioned, congenital, but during the individual life of animals, vascular conditioned reflexes are developed on their basis, due to which the cardiovascular system gets involved in reactions, necessary for the body with the action of only one signal, preceding one or another change in the environment. Thus, the body turns out to be adapted in advance for the forthcoming activity.

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

Some humoral agents constrict, while others dilate the lumen of arterial vessels.

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

Epinephrine and norepinephrine constrict the arteries and arterioles of the skin, abdominal organs and lungs, while vasopressin acts predominantly on arterioles and capillaries.

Epinephrine, norepinephrine and vasopressin affect the vessels at very low concentrations. Thus, vasoconstriction in warm-blooded animals occurs when the concentration of adrenaline to the blood is 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. Physiological significance of serotonin in this case consists in the fact that it narrows 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 the greater the amount, 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 bloodstream, breaks down α 2-plasma globulin - angiotensinogen and turns it into a relatively inactive deca-peptide - angiotensin I. The latter, under the influence of the enzyme dipeptide carboxypeptidase, turns into a very active vasoconstrictor substance angiotensin II. Angiotensin II is rapidly degraded in capillaries by angiotensinase.

In conditions of normal blood supply to the kidneys, a relatively small amount of renin is formed. In large quantities, it is produced when the blood pressure level drops throughout the vascular system. If you lower blood pressure in a dog 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 vasoconstrictor action is of great clinical interest: it explained the cause of high blood pressure accompanying some kidney diseases (renal hypertension).

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

The heart receives blood from the right and left coronary arteries, which extend from the aorta, at the level of the superior edges of the semilunar valves. The left coronary artery is divided into the anterior descending artery and the circumflex artery. Coronary arteries usually function as annular 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 are slowly closed. Rapid overlap leads to heart attack and is not compensated from other sources. The left coronary area supplies the left ventricle, the anterior half of the interventricular septum, the left and partly the right atrium. The right coronary artery feeds the right ventricle, right atrium, and the posterior half of the interventricular septum. Both coronary arteries are involved in the blood supply to the cardiac conduction system, 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 flow into the coronary sinus, which opens into the right atrium. Through this path, from 80 to 90% of the venous blood flows out. Venous blood from the right ventricle to atrial septum flows through the smallest veins into the right ventricle and these veins are called veins of tibesium, which directly remove venous blood into the right ventricle.

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

Increased coronary blood flow in diastole, systole, decreased blood flow, due to compression of blood vessels. Diastole accounts for 70-90% of coronary blood flow. The regulation of coronary blood flow is primarily regulated by local anabolic mechanisms and responds quickly to a decrease in oxygen. A decrease in the level of oxygen 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 effect of sympathetic and parasympathetic system on the bloodstream. Both vagus and sympathicus change the work of the heart. It has been established that irritation of the vagus nerves slows down the work of the heart, increases the continuation of diastole, and the direct release of acetylcholine will also cause vasodilation. Sympathetic influences promote the release of norepinephrine.

There are 2 types of adrenoceptors in the coronary vessels of the heart - alpha and beta adrenoceptors. For 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 with anxiety. Epinephrine causes an increase in coronary blood flow by increasing oxidative processes in the myocardium and an increase in oxygen consumption and due to the effect on beta-adrenergic receptors. Thyroxin, prostaglandins A and E have an expanding effect on coronary vessels, vasopressin narrows coronary vessels and reduces coronary blood flow.

In the human body, blood moves by two closed vascular systems connected to the heart - small and big circles of blood circulation.

Small circle of blood circulation - This is the path of blood from the right ventricle to the left atrium.

Venous, low-oxygen blood enters the right side of the heart. Shrinking, right ventricle throws it into pulmonary artery... Through the two branches into which the pulmonary artery is divided, this blood flows to easy... There, the branches of the pulmonary artery, dividing into smaller and smaller arteries, pass into capillaries, which densely entwine numerous pulmonary vesicles containing air. Passing through the capillaries, the blood is enriched with oxygen. At the same time, carbon dioxide from the blood passes into the air, which fills the lungs. Thus, in the capillaries of the lungs, venous blood is converted into arterial blood. It enters the veins, which, connecting with each other, form four pulmonary veins that fall into left atrium(fig. 57, 58).

The time of the blood circulation in the pulmonary circulation is 7-11 seconds.

A large circle of blood circulation - this is the path of blood from the left ventricle through the arteries, capillaries and veins to the right atrium.Material from the site

The left ventricle, contracting, pushes arterial blood into aorta- the largest human artery. Arteries branch off from it, which supply blood to all organs, in particular to the heart. Arteries in each organ gradually branch out, forming dense networks of smaller arteries and capillaries. Oxygen and nutrients are supplied from the capillaries of the systemic circulation to all tissues of the body, and carbon dioxide passes from the cells into the capillaries. In this case, the blood turns from arterial to venous. Capillaries merge into veins, first into small ones, and then into larger ones. Of these, all the blood is collected in two large hollow veins. Superior vena cava carries blood to the heart from the head, neck, hands, and inferior vena cava- from all other parts of the body. Both vena cava flows into the right atrium (Fig. 57, 58).

The time of blood circulation in the systemic circulation is 20-25 seconds.

Venous blood from the right atrium enters the right ventricle, from which it flows through the pulmonary circulation. At the exit of the aorta and pulmonary artery from the ventricles of the heart are placed semilunar valves(fig. 58). They look like pockets located on the inner walls of the blood vessels. When blood is pushed into the aorta and pulmonary artery, the semilunar valves are pressed against the vessel walls. When the ventricles relax, the blood cannot return to the heart due to the fact that, flowing into the pockets, it stretches them and they close tightly. Consequently, the semilunar valves provide the movement of blood in one direction - from the ventricles to the arteries.