How long does it take for blood to complete a full circle? Systemic and pulmonary circulation

Circulation- this is the movement of blood through the vascular system, ensuring gas exchange between the body and the external environment, metabolism between organs and tissues and humoral regulation of various body functions.

Circulatory system includes and - aorta, arteries, arterioles, capillaries, venules, veins and. Blood moves through the vessels due to the contraction of the heart muscle.

Blood circulation occurs in a closed system consisting of small and large circles:

• The systemic circulation supplies all organs and tissues with blood and the nutrients it contains.
• The pulmonary, or pulmonary, circulation is designed to enrich the blood with oxygen.

Circulation circles were first described by the English scientist William Harvey in 1628 in his work “Anatomical Studies on the Movement of the Heart and Vessels.”

Pulmonary circulation begins from the right ventricle, during the contraction of which venous blood enters the pulmonary trunk and, flowing through the lungs, gives off carbon dioxide and is saturated with oxygen. Oxygen-enriched blood from the lungs flows through the pulmonary veins into the left atrium, where the pulmonary circle ends.

Systemic circulation begins from the left ventricle, during the contraction of which blood enriched with oxygen is pumped into the aorta, arteries, arterioles and capillaries of all organs and tissues, and from there it flows through the venules and veins into the right atrium, where the great circle ends.

The largest vessel in the systemic circulation is the aorta, which emerges from the left ventricle of the heart. The aorta forms an arch from which arteries branch, carrying blood to the head (carotid arteries) and to the upper extremities (vertebral arteries). The aorta runs down along the spine, where branches branch off from it, carrying blood to the abdominal organs, to the muscles of the trunk and lower extremities.

Arterial blood, rich in oxygen, passes throughout the body, delivering the nutrients and oxygen necessary for the cells of organs and tissues for their activities, and in the capillary system it turns into venous blood. Venous blood, saturated with carbon dioxide and products of cellular metabolism, returns to the heart and from it enters the lungs for gas exchange. The largest veins of the systemic circulation are the superior and inferior vena cava, which flow into the right atrium.

Rice. Diagram of the pulmonary and systemic circulation

You should pay attention to how the circulatory systems of the liver and kidneys are included in the systemic circulation. All blood from the capillaries and veins of the stomach, intestines, pancreas and spleen enters the portal vein and passes through the liver. In the liver, the portal vein branches into small veins and capillaries, which then reconnect into the common trunk of the hepatic vein, which flows into the inferior vena cava. All blood from the abdominal organs, before entering the systemic circulation, flows through two capillary networks: the capillaries of these organs and the capillaries of the liver. The portal system of the liver plays an important role. It ensures the neutralization of toxic substances that are formed in the large intestine during the breakdown of amino acids that are not absorbed in the small intestine and are absorbed by the colon mucosa into the blood. The liver, like all other organs, also receives arterial blood through the hepatic artery, which arises from the abdominal artery.

The kidneys also have two capillary networks: there is a capillary network in each Malpighian glomerulus, then these capillaries are connected to form an arterial vessel, which again breaks up into capillaries intertwining the convoluted tubules.

Rice. Circulation diagram

A feature of blood circulation in the liver and kidneys is the slowing down of blood flow, which is determined by the function of these organs.

Table 1. Differences in blood flow in the systemic and pulmonary circulation

Blood flow in the body	Systemic circulation	Pulmonary circulation
In which part of the heart does the circle begin?	In the left ventricle	In the right ventricle
In which part of the heart does the circle end?	In the right atrium	In the left atrium
Where does gas exchange occur?	In capillaries located in the organs of the chest and abdominal cavities, the brain, upper and lower extremities	In the capillaries located in the alveoli of the lungs
What kind of blood moves through the arteries?	Arterial	Venous
What kind of blood moves through the veins?	Venous	Arterial
Time it takes for blood to circulate
Circle function	Supply of organs and tissues with oxygen and transfer of carbon dioxide	Saturation of blood with oxygen and removal of carbon dioxide from the body

Blood circulation time - the time of a single passage of a blood particle through the major and minor circles of the vascular system. More details in the next section of the article.

Patterns of blood movement through vessels

Basic principles of hemodynamics

Hemodynamics is a branch of physiology that studies the patterns and mechanisms of blood movement through the vessels of the human body. When studying it, terminology is used and the laws of hydrodynamics are taken into account - the science of the movement of fluids.

The speed at which blood moves through the vessels depends on two factors:

• from the difference in blood pressure at the beginning and end of the vessel;
• from the resistance that the liquid encounters along its path.

The pressure difference promotes fluid movement: the larger it is, the more intense this movement. Resistance in the vascular system, which reduces the speed of blood movement, depends on a number of factors:

• the length of the vessel and its radius (the longer the length and the smaller the radius, the greater the resistance);
• blood viscosity (it is 5 times greater than the viscosity of water);
• friction of blood particles against the walls of blood vessels and among themselves.

Hemodynamic parameters

The speed of blood flow in the vessels is carried out according to the laws of hemodynamics, common with the laws of hydrodynamics. The speed of blood flow is characterized by three indicators: volumetric speed of blood flow, linear speed of blood flow and blood circulation time.

Volumetric blood flow velocity - the amount of blood flowing through the cross section of all vessels of a given caliber per unit of time.

Linear speed of blood flow - the speed of movement of an individual blood particle along a vessel per unit of time. In the center of the vessel, the linear velocity is maximum, and near the vessel wall it is minimum due to increased friction.

Blood circulation time - the time during which blood passes through the systemic and pulmonary circulation. Normally it is 17-25 s. It takes about 1/5 to pass through a small circle, and 4/5 of this time to pass through a large circle.

The driving force of blood flow in the vascular system of each circulatory system is the difference in blood pressure ( ΔР) in the initial section of the arterial bed (aorta for the great circle) and the final section of the venous bed (vena cava and right atrium). Blood pressure difference ( ΔР) at the beginning of the vessel ( P1) and at the end of it ( P2) is the driving force of blood flow through any vessel of the circulatory system. The force of the blood pressure gradient is spent on overcoming resistance to blood flow ( R) in the vascular system and in each individual vessel. The higher the blood pressure gradient in the blood circulation or in a separate vessel, the greater the volumetric blood flow in them.

The most important indicator of blood movement through the vessels is volumetric blood flow velocity, or volumetric blood flow (Q), which is understood as the volume of blood flowing through the total cross-section of the vascular bed or the cross-section of an individual vessel per unit time. Blood flow rate is expressed in liters per minute (l/min) or milliliters per minute (ml/min). To assess the volumetric blood flow through the aorta or the total cross-section of any other level of the vessels of the systemic circulation, the concept is used volumetric systemic blood flow. Since in a unit of time (minute) the entire volume of blood ejected by the left ventricle during this time flows through the aorta and other vessels of the systemic circulation, the concept of systemic volumetric blood flow is synonymous with the concept (IOC). The IOC of an adult at rest is 4-5 l/min.

Volumetric blood flow in an organ is also distinguished. In this case, we mean the total blood flow flowing per unit of time through all the afferent arterial or efferent venous vessels of the organ.

Thus, volumetric blood flow Q = (P1 - P2) / R.

This formula expresses the essence of the basic law of hemodynamics, which states that the amount of blood flowing through the total cross-section of the vascular system or individual vessel per unit time is directly proportional to the difference in blood pressure at the beginning and end of the vascular system (or vessel) and inversely proportional to the resistance to flow blood.

The total (systemic) minute blood flow in the systemic circle is calculated taking into account the average hydrodynamic blood pressure at the beginning of the aorta P1, and at the mouth of the vena cava P2. Since in this section of the veins the blood pressure is close to 0 , then into the expression for calculating Q or MOC value is substituted R, equal to the average hydrodynamic arterial blood pressure at the beginning of the aorta: Q(IOC) = P/ R.

One of the consequences of the basic law of hemodynamics - the driving force of blood flow in the vascular system - is determined by the blood pressure created by the work of the heart. Confirmation of the decisive importance of blood pressure for blood flow is the pulsating nature of blood flow throughout the cardiac cycle. During cardiac systole, when blood pressure reaches its maximum level, blood flow increases, and during diastole, when blood pressure is minimal, blood flow decreases.

As blood moves through the vessels from the aorta to the veins, blood pressure decreases and the rate of its decrease is proportional to the resistance to blood flow in the vessels. The pressure in arterioles and capillaries decreases especially quickly, since they have great resistance to blood flow, having a small radius, a large total length and numerous branches, creating an additional obstacle to blood flow.

The resistance to blood flow created in the entire vascular bed of the systemic circulation is called total peripheral resistance(OPS). Therefore, in the formula for calculating volumetric blood flow, the symbol R you can replace it with an analogue - OPS:

Q = P/OPS.

From this expression a number of important consequences are derived that are necessary for understanding the processes of blood circulation in the body, assessing the results of measuring blood pressure and its deviations. Factors influencing the resistance of a vessel to fluid flow are described by Poiseuille’s law, according to which

Where R- resistance; L— length of the vessel; η - blood viscosity; Π - number 3.14; r— radius of the vessel.

From the above expression it follows that since the numbers 8 And Π are permanent L in an adult changes little, then the value of peripheral resistance to blood flow is determined by the changing values ​​of the radius of blood vessels r and blood viscosity η ).

It has already been mentioned that the radius of muscular-type vessels can quickly change and have a significant impact on the amount of resistance to blood flow (hence their name - resistive vessels) and the amount of blood flow through organs and tissues. Since resistance depends on the value of the radius to the 4th power, even small fluctuations in the radius of the vessels greatly affect the values ​​of resistance to blood flow and blood flow. So, for example, if the radius of a vessel decreases from 2 to 1 mm, then its resistance will increase by 16 times and, with a constant pressure gradient, the blood flow in this vessel will also decrease by 16 times. Reverse changes in resistance will be observed when the radius of the vessel increases by a factor of 2. With a constant average hemodynamic pressure, blood flow in one organ can increase, in another - decrease, depending on the contraction or relaxation of the smooth muscles of the afferent arterial vessels and veins of this organ.

Blood viscosity depends on the content of the number of red blood cells (hematocrit), protein, lipoproteins in the blood plasma, as well as on the aggregate state of the blood. Under normal conditions, blood viscosity does not change as quickly as the lumen of blood vessels. After blood loss, with erythropenia, hypoproteinemia, blood viscosity decreases. With significant erythrocytosis, leukemia, increased erythrocyte aggregation and hypercoagulation, blood viscosity can increase significantly, which entails an increase in resistance to blood flow, an increase in the load on the myocardium and may be accompanied by impaired blood flow in the vessels of the microvasculature.

In a steady-state circulatory regime, the volume of blood expelled by the left ventricle and flowing through the cross-section of the aorta is equal to the volume of blood flowing through the total cross-section of the vessels of any other section of the systemic circulation. This volume of blood returns to the right atrium and flows into the right ventricle. From it, blood is expelled into the pulmonary circulation and then returns to the left heart through the pulmonary veins. Since the IOC of the left and right ventricles are the same, and the systemic and pulmonary circulations are connected in series, the volumetric velocity of blood flow in the vascular system remains the same.

However, during changes in blood flow conditions, for example when moving from a horizontal to a vertical position, when gravity causes a temporary accumulation of blood in the veins of the lower torso and legs, the MOC of the left and right ventricles may become different for a short time. Soon, intracardiac and extracardiac mechanisms regulating the work of the heart equalize the volume of blood flow through the pulmonary and systemic circulation.

With a sharp decrease in venous return of blood to the heart, causing a decrease in stroke volume, blood pressure may decrease. If it is significantly reduced, blood flow to the brain may decrease. This explains the feeling of dizziness that can occur when a person suddenly moves from a horizontal to a vertical position.

Volume and linear speed of blood flow in vessels

The total blood volume in the vascular system is an important homeostatic indicator. Its average value is 6-7% for women, 7-8% of body weight for men and is in the range of 4-6 liters; 80-85% of the blood from this volume is in the vessels of the systemic circulation, about 10% is in the vessels of the pulmonary circulation, and about 7% is in the cavities of the heart.

The most blood is contained in the veins (about 75%) - this indicates their role in depositing blood in both the systemic and pulmonary circulation.

The movement of blood in the vessels is characterized not only by volume, but also linear speed of blood flow. It is understood as the distance a particle of blood moves per unit of time.

There is a relationship between the volumetric and linear velocity of blood flow, described by the following expression:

V = Q/Pr 2

Where V— linear blood flow velocity, mm/s, cm/s; Q - volumetric blood flow velocity; P- number equal to 3.14; r— radius of the vessel. Magnitude Pr 2 reflects the cross-sectional area of ​​the vessel.

Rice. 1. Changes in blood pressure, linear blood flow velocity and cross-sectional area in various parts of the vascular system

Rice. 2. Hydrodynamic characteristics of the vascular bed

From the expression of the dependence of the linear velocity on the volumetric velocity in the vessels of the circulatory system, it is clear that the linear velocity of blood flow (Fig. 1) is proportional to the volumetric blood flow through the vessel(s) and inversely proportional to the cross-sectional area of ​​this vessel(s). For example, in the aorta, which has the smallest cross-sectional area in the systemic circulation (3-4 cm2), linear speed of blood movement the largest and at rest is about 20-30 cm/s. With physical activity it can increase 4-5 times.

Towards the capillaries, the total transverse lumen of the vessels increases and, consequently, the linear velocity of blood flow in the arteries and arterioles decreases. In capillary vessels, the total cross-sectional area of ​​which is greater than in any other section of the vessels of the great circle (500-600 times larger than the cross-section of the aorta), the linear velocity of blood flow becomes minimal (less than 1 mm/s). Slow blood flow in the capillaries creates the best conditions for metabolic processes between blood and tissues. In the veins, the linear velocity of blood flow increases due to a decrease in their total cross-sectional area as they approach the heart. At the mouth of the vena cava it is 10-20 cm/s, and with loads it increases to 50 cm/s.

The linear speed of plasma movement depends not only on the type of vessel, but also on their location in the blood flow. There is a laminar type of blood flow, in which the flow of blood can be divided into layers. In this case, the linear speed of movement of the layers of blood (mainly plasma) close or adjacent to the wall of the vessel is the lowest, and the layers in the center of the flow are the highest. Friction forces arise between the vascular endothelium and the parietal blood layers, creating shear stresses on the vascular endothelium. These tensions play a role in the endothelium’s production of vasoactive factors that regulate the lumen of blood vessels and the speed of blood flow.

Red blood cells in vessels (with the exception of capillaries) are located mainly in the central part of the blood flow and move in it at a relatively high speed. Leukocytes, on the contrary, are located mainly in the parietal layers of the blood flow and perform rolling movements at low speed. This allows them to bind to adhesion receptors in places of mechanical or inflammatory damage to the endothelium, adhere to the vessel wall and migrate into tissues to perform protective functions.

With a significant increase in the linear speed of blood movement in the narrowed part of the vessels, in the places where its branches depart from the vessel, the laminar nature of blood movement can be replaced by turbulent one. In this case, the layered movement of its particles in the blood flow may be disrupted; greater frictional forces and shear stresses may arise between the vessel wall and the blood than during laminar movement. Eddy blood flows develop, increasing the likelihood of damage to the endothelium and deposition of cholesterol and other substances into the intima of the vessel wall. This can lead to mechanical disruption of the structure of the vascular wall and initiation of the development of wall thrombi.

Time of complete blood circulation, i.e. The return of a blood particle to the left ventricle after its ejection and passage through the systemic and pulmonary circulation is 20-25 seconds per mow, or after approximately 27 systoles of the ventricles of the heart. Approximately a quarter of this time is spent moving blood through the vessels of the pulmonary circulation and three quarters through the vessels of the systemic circulation.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The cardiac cycle consists of 3 phases:

Atrial systole - 0.1 s

Ventricular systole - 0.3 s

Total pause 0.4 s

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

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

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

tension period

1. phase of asynchronous contraction - 0.05 s

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

period of exile

1. rapid expulsion phase 0.12s

2. slow phase 0.13 s.

The expulsion phase begins end systolic volume protodiastolic period

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

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

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

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

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

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

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

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

Systolic (during 1st systole);

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

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

V syst avg.=70ml, ν avg=70 beats/min,

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

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

An indirect method based on gas exchange was proposed.

Fick method (method for determining IOC).

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

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

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

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

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

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

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

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

IOC distribution.

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

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

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

-Ppacemaker cells

-transitional cells

-Purkinje cells

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

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

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

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

The conduction system includes:

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

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

These two nodes are connected by intraatrial tracts.

3. Atrial tracts

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

Middle tract (Wenckebach)

Posterior tract (Torel)

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

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

6. Purkinje fibers

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Excitation speed

Myocardium - 1 m/s 0.035

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

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

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

Ventricular myocardium - 0.8-0.9 m/s

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Formation of various ECG components:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Standard leads.

1 lead. Right and left forearms

2 lead. Right hand - left shin.

3 lead. Left hand - left foot.

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

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

2 lead. AVL Left hand - right hand right leg

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

Chest leads. They are single-pole.

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

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

4 lead. Projection of the apex of the heart

3 lead. Midway between second and fourth.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Features of the circulatory system:

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

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

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

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

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

Types of blood vessels:

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

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

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

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

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

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

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

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

Q=(p1—p2) /R= ∆p/R,

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

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

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

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

Hagen Poiselle's Law:

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

Q=∆pπr 4 /8ηl.

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

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

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

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

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

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

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

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

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

R=1/R1 + 1/R2+…+ 1/Rn,

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

Physiological processes obey general physical laws.

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

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

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

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

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

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

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

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

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

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

There are:

Blood pressure;

Venous pressure;

Intracardiac pressure;

Capillary pressure.

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

E = P+ ρV 2 /2 + ρgh,

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

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

Systolic blood volume;

Heart rate and rhythm;

Elasticity of artery walls;

Resistance of resistive vessels;

Blood velocity in capacitance vessels;

Circulating blood speed;

Blood viscosity;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

depressor.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Encyclopedic YouTube

1 / 5

✪ Circulation circles. Big and small, their interaction.

✪ Circulatory circles, easy diagram

✪ Human Circulatory Circles in 60 seconds

✪ Structure and work of the heart. Circulation circles

✪ Two circles of blood circulation

Subtitles

Systemic (systemic) circulation

Structure

Functions

The main task of the small circle is gas exchange in the pulmonary alveoli and heat transfer.

“Additional” circulation circles

Depending on the physiological state of the body, as well as practical expediency, additional circles of blood circulation are sometimes distinguished:

• placental
• cordial

Placental circulation

The mother's blood enters the placenta, where it gives oxygen and nutrients to the capillaries of the fetal umbilical vein, which runs along with two arteries in the umbilical cord. The umbilical vein gives off two branches: most of the blood flows through the ductus venosus directly into the inferior vena cava, mixing with unoxygenated blood from the lower part of the body. A smaller portion of the blood enters the left branch of the portal vein, passes through the liver and hepatic veins and then also enters the inferior vena cava.

After birth, the umbilical vein empties and turns into the round ligament of the liver (ligamentum teres hepatis). The ductus venosus also turns into a scar cord. In premature infants, the ductus venosus may function for some time (it usually becomes scarred after some time. If not, there is a risk of developing hepatic encephalopathy). In portal hypertension, the umbilical vein and the Arantian duct can recanalize and serve as bypass pathways (porto-caval shunts).

Mixed (arterial-venous) blood flows through the inferior vena cava, the oxygen saturation of which is about 60%; Venous blood flows through the superior vena cava. Almost all the blood from the right atrium flows through the foramen ovale into the left atrium and then into the left ventricle. From the left ventricle, blood is ejected into the systemic circulation.

A smaller portion of the blood flows from the right atrium into the right ventricle and pulmonary trunk. Since the lungs are in a collapsed state, the pressure in the pulmonary arteries is greater than in the aorta, and almost all the blood passes through the ductus arteriosus into the aorta. The ductus arteriosus flows into the aorta after the arteries of the head and upper extremities depart from it, which provides them with more enriched blood. A very small part of the blood enters the lungs, which subsequently enters the left atrium.

Part of the blood (about 60%) from the systemic circulation enters the placenta through the two umbilical arteries of the fetus; the rest goes to the organs of the lower body.

With a normally functioning placenta, the blood of the mother and fetus never mixes - this explains the possible difference in blood groups and Rh factor of the mother and fetus(es). However, determining the blood type and Rh factor of a newborn child from umbilical cord blood is often erroneous. During the birth process, the placenta experiences “overload”: pushing and the passage of the placenta through the birth canal contribute to pushing maternal blood into the umbilical cord (especially if the birth took place “unusually” or there was a pathology of pregnancy). To accurately determine the blood type and Rh factor of a newborn, blood should be taken not from the umbilical cord, but from the child.

Blood supply to the heart or coronary circulation

It is part of a large circle of blood circulation, but due to the importance of the heart and its blood supply, you can sometimes find mention of this circle in the literature.

Arterial blood enters the heart through the right and left coronary arteries, originating from the aorta above its semilunar valves. The left coronary artery is divided into two or three, rarely four arteries, of which the most clinically significant are the anterior descending (LAD) and circumflex branches (OB). The anterior descending branch is a direct continuation of the left coronary artery and descends to the apex of the heart. The circumflex branch departs from the left coronary artery at its beginning at approximately a right angle, bends around the heart from front to back, sometimes reaching the posterior wall of the interventricular groove. The arteries enter the muscle wall, branching to the capillaries. The outflow of venous blood occurs mainly into 3 veins of the heart: large, middle and small. Merging, they form the coronary sinus, which opens into the right atrium. The rest of the blood flows through the anterior cardiac veins and the Tebasian veins.

Ring of Willis or Circle of Willis

The circle of Willis is an arterial ring formed by the arteries of the vertebral and internal carotid arteries, located at the base of the brain, helps compensate for insufficient blood supply. Normally, the circle of Willis is closed. The anterior communicating artery, the initial segment of the anterior cerebral artery (A-1), the supraclinoid part of the internal carotid artery, the posterior communicating artery, the initial segment of the posterior cerebral artery (P-1) participate in the formation of the circle of Willis.

The vascular system consists of two circles of blood circulation - large and small (Fig. 17).

Systemic circulation starts from the left ventricle of the heart, from where blood enters the aorta. From the aorta, the path of arterial blood continues through the arteries, which branch as they move away from the heart and the smallest of them break up into capillaries, which permeate the entire body in a dense network. Through the thin walls of the capillaries, the blood releases nutrients and oxygen into the tissue fluid, and the waste products of cells from the tissue fluid enter the blood. From the capillaries, blood flows into small veins, which, merging, form larger veins and flow into the superior and inferior vena cava. The superior and inferior vena cava bring venous blood to the right atrium, where the systemic circulation ends.

Rice. 17. Blood circulation diagram.

Pulmonary circulation starts from the right ventricle of the heart by the pulmonary artery. Venous blood is carried through the pulmonary artery to the capillaries of the lungs. In the lungs, gases are exchanged between the venous blood of the capillaries and the air in the alveoli of the lungs. From the lungs, arterial blood returns through four pulmonary veins to the left atrium. The pulmonary circulation ends in the left atrium. From the left atrium, blood enters the left ventricle, where the systemic circulation begins.

Closely related to the circulatory system lymphatic system. It serves to drain fluid from tissues, in contrast to the circulatory system, which creates both inflow and outflow of fluid. The lymphatic system begins with a network of closed capillaries, which turn into lymphatic vessels, which flow into the left and right lymphatic ducts, and from there into large veins. On the way to the veins, lymph flowing from various organs and tissues passes through the lymph nodes, which act as biological filters that protect the body from foreign bodies and infections. The formation of lymph is associated with the transition of a number of substances dissolved in the blood plasma from capillaries to tissues and from tissues to lymphatic capillaries. During the day, the human body produces 2-4 liters of lymph.

During normal functioning of the body, there is a balance between the rate of lymph formation and the rate of outflow of lymph, which returns through the veins to the bloodstream. Lymphatic vessels penetrate almost all organs and tissues, there are especially many of them in the liver and small intestine. In structure, lymphatic vessels are similar to veins, just like veins, they are equipped with valves that create conditions for the movement of lymph in only one direction.

The flow of lymph through the vessels is carried out due to the contraction of the walls of blood vessels and muscle contraction. The movement of lymph is also facilitated by negative pressure in the chest cavity, especially during inhalation. At the same time, the thoracic lymphatic duct, which lies on the way to the veins, expands, which facilitates the flow of lymph into the bloodstream.

10.4.3. The structure of the heart and its age-related features. The main pump of the circulatory system - the heart - is a muscular bag divided into 4 chambers: two atria and two ventricles (Fig. 18). The left atrium is connected to the left ventricle by an opening in the cusp of which there is mitral valve. The right atrium is connected to the right ventricle by an opening that closes tricuspid valve. The right and left halves are not connected to each other, therefore the “venous” half of the heart is always located in the right half of the heart, i.e. oxygen-poor blood, and in the left - “arterial”, saturated with oxygen. The exit from the right (pulmonary artery) and left (aorta) ventricles is closed with similar designs semilunar valves. They prevent blood from these large exiting vessels from returning to the heart during the period of its relaxation.

Although the bulk of the heart walls is the muscle layer (myocardium), there are several additional layers of tissue that protect the heart from external influences and strengthen its walls, which experience enormous pressure during operation. These protective layers are called pericardium. The inner surface of the heart cavity is lined endocardium, the properties of which allow it not to harm blood cells during contractions. The heart is located on the left side of the chest (although in some cases there is a different location) with the “top” down.

The weight of the heart in an adult is 0.5% of body weight, i.e. 250-300 g for men and about 200 g for women. In children, the relative size of the heart is slightly larger - approximately 0.7% of body weight. The heart as a whole increases in proportion to the increase in body size. For the first 8 months. after birth, the weight of the heart doubles, by 3 years - three times, by 5 years - 4 times, and by 16 years - 11 times compared to the weight of the heart of a newborn. Boys usually have slightly larger hearts than girls; Only during puberty do girls who begin to mature earlier have larger hearts.

The atrial myocardium is much thinner than the ventricular myocardium. This is understandable: the work of the atria is to pump a portion of blood through the valves into the adjacent ventricle, while the ventricles need to give the blood such an acceleration that will force it to reach the most distant parts of the capillary network from the heart. For the same reason, the myocardium of the left ventricle is 2.5 times thicker than the myocardium of the right ventricle: pushing blood through the pulmonary circulation requires much less effort than through the systemic circulation.

The heart muscle consists of fibers similar to those of skeletal muscles. However, along with structures that have contractile activity, the heart also contains another - conductive - structure, which ensures rapid conduction of excitation to all parts of the myocardium and its synchronous periodic contraction. Each part of the heart is, in principle, capable of independent (spontaneous) periodic contractile activity, but normally heart contraction is controlled by a certain part of the cells, which is called pacemaker and is located in the upper part of the right atrium (sinus node). The impulse automatically generated here with a frequency of approximately 1 time per second (in adults; in children - much more often) spreads across conducting system heart, which includes atriumno-ventricular node, bundle of Hiss, splitting into right and left legs, branching in the mass of the ventricular myocardium (Fig. 19). Most cardiac arrhythmias are the result of certain damage to the fibers of the conduction systems

Rice. 18. Structure of the heart.

10.4.4. Properties of the heart muscle. The bulk of the heart wall is made up of a powerful muscle - the myocardium, consisting of a special kind of striated muscle tissue. The thickness of the myocardium varies in different parts of the heart. It is thinnest in the atria (2-3 mm), the left ventricle has the most powerful muscular wall, it is 2.5 times thicker than in the right ventricle.

The bulk of the cardiac muscle is represented by fibers typical of the heart, which ensure contraction of the heart’s parts. Their main function is contractility. This is the working muscle of the heart. In addition, there are atypical fibers in the heart muscle. The activity of atypical fibers is associated with the occurrence of excitation in the heart and its conduction from the atria to the ventricles.

These fibers form conduction system of the heart. The conduction system consists of the sinoatrial node, atriogastric node, atrioventricular bundle and its branches (Fig. 19). The sinoatrial node is located in the right atrium and is the pacemaker of the heart; automatic excitation impulses are generated here that determine the contraction of the heart. The atrioventricular node is located between the right atrium and the ventricles. In this area, excitation from the atria spreads to the ventricles. Under normal conditions, the atrioventricular node is excited by impulses coming from the sinoatrial node, but it is also capable of automatic excitation and in some pathological cases provokes excitation in the ventricles and their contraction, which does not follow the rhythm created by the sinoatrial node. A so-called extrasystole occurs. From the atrioventricular node, excitation is transmitted through the atrioventricular bundle (bundle of His), which, passing along the interventricular septum, branches into the left and right legs. The legs pass into a network of conducting myocytes (atypical muscle fibers), which cover the working myocardium and transmit excitation to it.

Cardiac cycle. The heart contracts rhythmically: contractions of the heart parts alternate with their relaxation. Contraction of the heart is called systole, and relaxation is called diastole.

Rice. 19. Schematic representation of the conduction system of the heart.

1- sinus node; 2 - atrioventricular node; 3-bundle of Hiss; 4 and 5 - right and left legs of the Hiss bundle; 6 - terminal branches of the conductive system.

The period covering one contraction and relaxation of the heart is called the cardiac cycle. In a state of relative rest, the cardiac cycle lasts about 0.8 s.

Cordial cycle (lasts 0.8s)		First phase:		Second phase:		Third phase:
		atrial contraction - atrial systole (lasts 0.1 s)		contraction of the ventricles ventricular systole (lasts 0.3s)		general pause (0.4 s)

When the heart contracts, blood is pumped into the vascular system. The main force of contraction occurs during ventricular systole, during the phase of expulsion of blood from the left ventricle into the aorta.

The work of all body systems does not stop even during a person’s rest and sleep. Cell regeneration, metabolism, and brain activity at normal levels continue regardless of human activity.

The most active organ in this process is the heart. Its constant and uninterrupted operation ensures blood circulation sufficient to maintain all human cells, organs, and systems.

Muscular work, the structure of the heart, as well as the mechanism of blood movement throughout the body, its distribution to various parts of the human body is a rather extensive and complex topic in medicine. As a rule, such articles are filled with terminology that is incomprehensible to a person without a medical education.

This edition describes the blood circulation briefly and clearly, which will allow many readers to expand their knowledge in health matters.

Please note. This topic is interesting not just for general development; knowledge of the principles of blood circulation and the mechanisms of the heart can be useful if it is necessary to provide first aid for bleeding, injuries, heart attacks and other incidents before the arrival of doctors.

Many of us underestimate the significance, complexity, high accuracy, coordination of the heart and blood vessels, as well as human organs and tissues. Day and night without stopping, all elements of the system communicate with each other in one way or another, providing the human body with nutrition and oxygen. A number of factors can upset the balance of blood circulation, after which, in a chain reaction, all areas of the body that are directly and indirectly dependent on it will be affected.

Studying the circulatory system is impossible without basic knowledge of the structure of the heart and human anatomy. Considering the complexity of the terminology and the vastness of the topic, upon first acquaintance with it, for many it becomes a discovery that a person’s blood circulation goes through two whole circles.

Complete blood circulation in the body is based on the synchronization of the work of the muscular tissues of the heart, the difference in blood pressure created by its work, as well as the elasticity and patency of arteries and veins. Pathological manifestations affecting each of the above factors impair the distribution of blood throughout the body.

It is its circulation that is responsible for the delivery of oxygen and useful substances to organs, as well as the removal of harmful carbon dioxide, metabolic products harmful to their functioning.

The heart is a muscular organ of the human body, divided into four parts by partitions that form cavities. By contracting the heart muscle, different blood pressure is created inside these cavities, ensuring the operation of valves that prevent accidental reflux of blood back into the vein, as well as the outflow of blood from the artery into the ventricular cavity.

At the top of the heart there are two atria, named according to their location:

1. Right atrium. Dark blood comes from the superior vena cava, after which, due to the contraction of muscle tissue, it splashes into the right ventricle under pressure. Contraction begins at the point where the vein connects to the atrium, which provides protection against blood flowing back into the vein.
2. Left atrium. The cavity is filled with blood through the pulmonary veins. By analogy with the mechanism of myocardium described above, the blood squeezed out by contraction of the atrium muscle enters the ventricle.

The valve between the atrium and the ventricle opens under blood pressure and allows it to freely pass into the cavity, after which it closes, limiting its ability to return back.

The ventricles are located at the bottom of the heart:

1. Right ventricle. The blood pushed out from the atrium enters the ventricle. Next, it contracts, closes the three leaflet valves and opens the pulmonary valve under blood pressure.
2. Left ventricle. The muscle tissue of this ventricle is significantly thicker than the right one, and therefore, during contraction, it can create stronger pressure. This is necessary to ensure the force of blood release into the systemic circulation. As in the first case, the pressure force closes the atrium valve (mitral) and opens the aortic valve.

Important. The full functioning of the heart depends on the synchronicity and rhythm of contractions. Dividing the heart into four separate cavities, the entrances and exits of which are separated by valves, ensures the movement of blood from the veins to the arteries without the risk of mixing. Anomalies in the development of the structure of the heart and its components disrupt the mechanics of the heart, and therefore the blood circulation itself.

The structure of the circulatory system of the human body

In addition to the rather complex structure of the heart, the structure of the circulatory system itself has its own characteristics. Blood is distributed throughout the body through a system of hollow interconnected vessels of various sizes, wall structure, and purpose.

The structure of the vascular system of the human body includes the following types of vessels:

1. Arteries. The vessels, which do not contain smooth muscles in their structure, have a durable shell with elastic properties. When additional blood is released from the heart, the walls of the artery expand, which allows you to control the blood pressure in the system. During the pause, the walls stretch and narrow, reducing the lumen of the inner part. This prevents the pressure from falling to critical levels. The function of arteries is to transport blood from the heart to the organs and tissues of the human body.
2. Vienna. The flow of venous blood is ensured by its contractions, the pressure of the skeletal muscles on its membrane, and the pressure difference at the pulmonary vena cava during lung function. A feature of its functioning is the return of waste blood to the heart for further gas exchange.
3. Capillaries. The structure of the wall of the thinnest vessels consists of only one layer of cells. This makes them vulnerable, but at the same time highly permeable, which determines their function. The exchange between tissue cells and plasma that they provide saturates the body with oxygen, nutrition, and cleanses it of metabolic products through filtration in the network of capillaries of the relevant organs.

Each type of vessel forms its own so-called system, which can be examined in more detail in the presented diagram.

Capillaries are the thinnest of vessels; they dot all parts of the body so densely that they form so-called networks.

The pressure in the vessels created by the muscle tissue of the ventricles varies, depending on their diameter and distance from the heart.

Types of blood circulation, functions, characteristics

The circulatory system is divided into two closed systems that communicate thanks to the heart, but perform different tasks. We are talking about the presence of two circles of blood circulation. Medical experts call them circles because of the closedness of the system, distinguishing two main types: large and small.

These circles have fundamental differences in both structure, size, number of vessels involved, and functionality. The table below will help you learn more about their main functional differences.

Table No. 1. Functional characteristics, other features of the systemic and pulmonary circulation:

As can be seen from the table, circles perform completely different functions, but have the same importance for blood circulation. While the blood cycles through the large circle once, inside the small circle it completes 5 cycles in the same period of time.

In medical terminology, the term “additional circulation circles” is sometimes encountered:

• cardiac - passes from the coronary arteries of the aorta, returns through the veins to the right atrium;
• placental – circulates in the fetus developing in the uterus;
• Willis - located at the base of the human brain, acts as a reserve blood supply in case of blockage of blood vessels.

One way or another, all additional circles are part of the larger one or are directly dependent on it.

Important. Both circles of blood circulation maintain balance in the functioning of the cardiovascular system. Poor circulation due to the occurrence of various pathologies in one of them leads to an inevitable impact on the other.

Big circle

From the name itself you can understand that this circle differs in size and, accordingly, in the number of vessels involved. All circles begin with the contraction of the corresponding ventricle and end with the return of blood to the atrium.

The large circle originates when the strongest left ventricle contracts, pushing blood into the aorta. Passing along its arc, thoracic, abdominal segment, it is redistributed along the network of vessels through arterioles and capillaries to the corresponding organs and parts of the body.

It is through the capillaries that oxygen, nutrients, and hormones are released. When it flows into the venules, it takes with it carbon dioxide, harmful substances formed by metabolic processes in the body.

Then, through the two largest veins (superior and inferior hollow veins), the blood returns to the right atrium, completing the cycle. You can visually see the pattern of blood circulating in a large circle in the figure below.

As can be seen in the diagram, the outflow of venous blood from the unpaired organs of the human body does not occur directly to the inferior vena cava, but bypass. Having saturated the abdominal organs with oxygen and nutrition, the spleen rushes to the liver, where it is cleansed through capillaries. Only after this the filtered blood enters the inferior vena cava.

The kidneys also have filtering properties; the double capillary network allows venous blood to directly enter the vena cava.

Despite the relatively short cycle, coronary circulation is of great importance. The coronary arteries leaving the aorta branch into smaller ones and go around the heart.

Entering its muscle tissue, they are divided into capillaries that feed the heart, and the outflow of blood is provided by three cardiac veins: small, middle, large, as well as the thymus and anterior cardiac veins.

Important. The constant work of heart tissue cells requires a large amount of energy. About 20% of the total amount of blood pushed out of the organ, enriched with oxygen and nutrients into the body, passes through the coronary circle.

Small circle

The structure of the small circle includes much fewer involved vessels and organs. In the medical literature it is more often called pulmonary and for good reason. This organ is the main one in this chain.

Carrying out through the blood capillaries entwining the pulmonary vesicles, gas exchange is of utmost importance for the body. It is the small circle that subsequently makes it possible for the large circle to saturate the entire human body with enriched blood.

Blood flow through the small circle is carried out in the following order:

1. By contraction of the right atrium, venous blood, darkened due to excess carbon dioxide in it, is pushed into the cavity of the right ventricle of the heart. The atriogastric septum is closed at this moment to prevent blood from returning into it.
2. Under pressure from the muscle tissue of the ventricle, it is pushed into the pulmonary trunk, while the tricuspid valve separating the cavity from the atrium is closed.
3. After blood enters the pulmonary artery, its valve closes, which eliminates the possibility of its return to the ventricular cavity.
4. Passing through a large artery, the blood enters the area where it branches into capillaries, where carbon dioxide is removed and oxygenated.
5. Scarlet, purified, enriched blood through the pulmonary veins ends its cycle at the left atrium.

As you can see when comparing two blood flow patterns, in a large circle dark venous blood flows through the veins to the heart, and in a small circle purified scarlet blood flows and vice versa. The arteries of the pulmonary circle are filled with venous blood, while the arteries of the large circle carry enriched scarlet blood.

Circulatory disorders

In 24 hours, the heart pumps more than 7,000 liters through human vessels. blood. However, this figure is relevant only if the entire cardiovascular system is stable.

Only a few can boast of excellent health. Under real life conditions, due to many factors, almost 60% of the population has health problems, the cardiovascular system is no exception.

Its work is characterized by the following indicators:

• efficiency of the heart;
• vascular tone;
• condition, properties, blood mass.

The presence of deviations in even one of the indicators leads to disruption of the blood flow of two circulatory circles, not to mention the detection of their entire complex. Specialists in the field of cardiology distinguish between general and local disorders that impede the movement of blood through the circulation; a table with a list of them is presented below.

Table No. 2. List of disorders of the circulatory system:

The above-described disorders are also divided into types depending on the circulatory system which it affects:

1. Disorders of the central circulation. This system includes the heart, aorta, vena cava, pulmonary trunk and veins. Pathologies of these elements of the system affect its other components, which threatens a lack of oxygen in the tissues and intoxication of the body.
2. Peripheral circulation disorders. It implies a pathology of microcirculation, manifested by problems with blood supply (arterial/venous anemia), rheological characteristics of blood (thrombosis, stasis, embolism, disseminated intravascular coagulation), and vascular permeability (blood loss, plasmorrhagia).

The main risk group for the manifestation of such disorders is primarily genetically predisposed people. If parents have problems with blood circulation or heart function, there is always a chance to pass on a similar diagnosis by inheritance.

However, even without genetics, many people expose their body to the risk of developing pathologies in both the systemic and pulmonary circulation:

• bad habits;
• sedentary lifestyle;
• harmful working conditions;
• constant stress;
• predominance of junk food in the diet;
• uncontrolled use of medications.

All this gradually affects not only the condition of the heart, blood vessels, blood, but also the entire body. The result is a decrease in the protective functions of the body, the immune system weakens, which provides opportunities for the development of various diseases.

Important. Changes in the structure of the walls of blood vessels, muscle tissue of the heart, and other pathologies can be caused by infectious diseases, some of which are sexually transmitted.

World medical practice considers atherosclerosis, hypertension, and ischemia to be the most common diseases of the cardiovascular system.

Atherosclerosis usually has a chronic form and progresses quite quickly. Violation of protein-fat metabolism leads to structural changes, mainly in large and medium-sized arteries. The proliferation of connective tissue is provoked by lipid-protein deposits on the walls of blood vessels. Atherosclerotic plaque closes the lumen of the artery, preventing blood flow.

Hypertension is dangerous due to constant stress on blood vessels, accompanied by oxygen deprivation. As a result, dystrophic changes occur in the walls of the vessel, and the permeability of their walls increases. Plasma leaks through the structurally altered wall, forming edema.

Coronary heart disease (ischemic) is caused by a violation of the cardiac circulation. Occurs when there is a deficiency of oxygen sufficient for the full functioning of the myocardium or a complete stop of blood flow. Characterized by dystrophy of the heart muscle.

Prevention of circulatory problems, treatment

The best option for preventing diseases and maintaining proper blood circulation in the systemic and pulmonary circles is prevention. Following simple but quite effective rules will help a person not only strengthen the heart and blood vessels, but will also prolong the youth of the body.

Basic steps to prevent cardiovascular disease:

• quitting smoking, alcohol;
• maintaining a balanced diet;
• playing sports, hardening;
• compliance with the work and rest regime;
• healthy sleep;
• regular preventive examinations.

An annual examination by a medical professional will help with early detection of signs of poor circulation. If a disease at an early stage of development is detected, experts recommend drug treatment with drugs from the appropriate groups. Following your doctor's instructions increases your chances of a positive outcome.

Important. Quite often, the disease is asymptomatic for a long time, which gives it the opportunity to progress. In such cases, surgery may be necessary.

Quite often, for the prevention and treatment of the pathologies described by the editors, patients use traditional methods of treatment and recipes. Such methods require prior consultation with your doctor. Based on the patient’s medical history and the individual characteristics of his condition, the specialist will give detailed recommendations.