Large and small circle of blood circulation diagram. Circles of human circulation - a diagram of the circulatory system

The life and health of a person largely depend on the normal functioning of his heart. It pumps blood through the vessels of the body, maintaining the viability of all organs and tissues. The evolutionary structure of the human heart - the scheme, circles of blood circulation, the automatism of the cycles of contractions and relaxation of the muscle cells of the walls, the operation of the valves - everything is subordinated to the fulfillment of the main task of uniform and sufficient blood circulation.

The structure of the human heart - anatomy

The organ, thanks to which the body is saturated with oxygen and nutrients, is an anatomical formation of a cone-shaped shape, located in chest, mostly on the left. Inside the organ, a cavity divided into four unequal parts by partitions is two atria and two ventricles. The former collect blood from the veins flowing into them, while the latter push it into the arteries outgoing from them. Normally, in the right side of the heart (atrium and ventricle) there is oxygen-poor blood, and in the left - oxygenated.

atrium

Right (PP). It has a smooth surface, the volume is 100-180 ml, including an additional formation - the right ear. Wall thickness 2-3 mm. Vessels flow into the PP:

• superior vena cava,
• cardiac veins - through the coronary sinus and pinholes of small veins,
• inferior vena cava.

Left (LP). The total volume, including the ear, is 100-130 ml, the walls are also 2-3 mm thick. The LP receives blood from four pulmonary veins.

The atria are separated by the interatrial septum (IAS), which normally does not have any openings in adults. They communicate with the cavities of the corresponding ventricles through openings equipped with valves. On the right - tricuspid tricuspid, on the left - bicuspid mitral.

Ventricles

Right (RV) cone-shaped, base facing upwards. Wall thickness up to 5 mm. The inner surface in the upper part is smoother, closer to the top of the cone it has a large number of muscle cords-trabeculae. In the middle part of the ventricle, there are three separate papillary (papillary) muscles, which, by means of tendinous filaments-chords, keep the cusps of the tricuspid valve from deflecting them into the atrial cavity. The chords also depart directly from the muscular layer of the wall. At the base of the ventricle are two openings with valves:

• serving as an outlet for blood into the pulmonary trunk,
• connecting the ventricle to the atrium.

Left (LV). This section of the heart is surrounded by the most impressive wall, the thickness of which is 11-14 mm. The LV cavity is also cone-shaped and has two openings:

• atrioventricular with bicuspid mitral valve,
• outlet to the aorta with a tricuspid aortic.

Muscle cords in the region of the apex of the heart and papillary muscles supporting the leaflets mitral valve here are more powerful than similar structures in the pancreas.

shells of the heart

To protect and ensure the movements of the heart in the chest cavity, it is surrounded by a heart shirt - the pericardium. Directly in the wall of the heart there are three layers - epicardium, endocardium, myocardium.

• The pericardium is called the heart bag, it is loosely attached to the heart, its outer leaf is in contact with neighboring organs, and the inner one is the outer layer of the heart wall - the epicardium. Composition - connective tissue. A small amount of fluid is normally present in the pericardial cavity for better glide of the heart.
• The epicardium also has a connective tissue base, accumulations of fat are observed in the region of the apex and along the coronal sulci, where the vessels are located. In other places, the epicardium is firmly connected with the muscle fibers of the main layer.
• The myocardium makes up the main thickness of the wall, especially in the most loaded zone - the region of the left ventricle. Muscle fibers located in several layers run both longitudinally and in a circle, ensuring uniform contraction. The myocardium forms trabeculae in the region of the apex of both ventricles and papillary muscles, from which tendon chords extend to the valve leaflets. The muscles of the atria and ventricles are separated by a dense fibrous layer, which also serves as a framework for the atrioventricular (atrioventricular) valves. The interventricular septum consists of 4/5 of the length of the myocardium. In the upper part, called membranous, its basis is connective tissue.
• Endocardium - a sheet that covers all the internal structures of the heart. It is three-layered, one of the layers is in contact with the blood and is similar in structure to the endothelium of the vessels that enter and exit the heart. Also in the endocardium there is connective tissue, collagen fibers, smooth muscle cells.

All heart valves are formed from the folds of the endocardium.

Human heart structure and functions

The pumping of blood by the heart into the vascular bed is provided by the features of its structure:

• the heart muscle is capable of automatic contraction,
• the conducting system guarantees the constancy of the cycles of excitation and relaxation.

How does the cardiac cycle work?

It consists of three consecutive phases: general diastole (relaxation), atrial systole (contraction), and ventricular systole.

• General diastole is a period of physiological pause in the work of the heart. At this time, the heart muscle is relaxed, and the valves between the ventricles and atria are open. From the venous vessels, blood freely fills the cavities of the heart. The valves of the pulmonary artery and aorta are closed.
• Atrial systole occurs when the pacemaker is automatically excited in sinus node atrium. At the end of this phase, the valves between the ventricles and the atria close.
• The systole of the ventricles takes place in two stages - isometric tension and expulsion of blood into the vessels.
• The period of tension begins with an asynchronous contraction of the muscle fibers of the ventricles until the moment of complete closure of the mitral and tricuspid valves. Then, in the isolated ventricles, tension begins to grow, pressure rises.
• When it becomes higher than in the arterial vessels, the period of exile is initiated - the valves open, releasing blood into the arteries. At this time, the muscle fibers of the walls of the ventricles are intensively reduced.
• Then the pressure in the ventricles decreases, the arterial valves close, which corresponds to the beginning of diastole. During the period of complete relaxation, the atrioventricular valves open.

The conduction system, its structure and the work of the heart

The conduction system of the heart provides contraction of the myocardium. Its main feature is the automatism of cells. They are able to self-excite in a certain rhythm, depending on the electrical processes that accompany cardiac activity.

As part of the conduction system, the sinus and atrioventricular nodes, the underlying bundle and branchings of His, Purkinje fibers are interconnected.

• sinus node. Normally generates an initial impulse. It is located in the area of ​​the mouth of both hollow veins. From it, excitation passes to the atria and is transmitted to the atrioventricular (AV) node.
• The atrioventricular node propagates the impulse to the ventricles.
• The bundle of His is a conductive "bridge" located in the interventricular septum, where it is also divided into the right and left legs, which transmit excitation to the ventricles.
• Purkinje fibers are the terminal part of the conduction system. They are located near the endocardium and are in direct contact with the myocardium, causing it to contract.

The structure of the human heart: diagram, circles of blood circulation

The task of the circulatory system, the main center of which is the heart, is the delivery of oxygen, nutrients and bioactive components to the tissues of the body and the elimination of metabolic products. To do this, the system provides a special mechanism - the blood moves through the circles of blood circulation - small and large.

small circle

From the right ventricle at the time of systole, venous blood is pushed into the pulmonary trunk and enters the lungs, where it is saturated with oxygen in the microvessels of the alveoli, becoming arterial. It flows into the cavity of the left atrium and enters the system of a large circle of blood circulation.

big circle

From the left ventricle into systole, arterial blood through the aorta and further through vessels of different diameters enters various organs, giving them oxygen, transferring nutrients and bioactive elements. In small tissue capillaries, the blood turns into venous blood, as it is saturated with metabolic products and carbon dioxide. Through the system of veins, it flows to the heart, filling its right sections.

Nature has worked hard to create such a perfect mechanism, giving it a margin of safety for many years. Therefore, you should carefully treat it so as not to create problems with blood circulation and your own health.

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

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

Systemic circulation

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

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

“Additional” circles of blood circulation

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

CIRCULATION CIRCLES

Arterial and venous vessels are not isolated and independent, but are interconnected as a single system of blood vessels. The circulatory system forms two circles of blood circulation: LARGE and SMALL.

The movement of blood through the vessels is also possible due to the difference in pressure at the beginning (artery) and end (vein) of each circle of blood circulation, which is created by the work of the heart. The pressure in the arteries is higher than in the veins. During contractions (systole), the ventricle ejects an average of 70-80 ml of blood each. Blood pressure rises and their walls stretch. During diastole (relaxation), the walls return to their original position, pushing the blood further, ensuring its uniform flow through the vessels.

Speaking about the circles of blood circulation, it is necessary to answer the questions: (WHERE? and WHAT?). For example: WHERE does it end?, does it begin? - (in which ventricle or atrium).

WHAT ends?, begins? - (what vessels) ..

The pulmonary circulation delivers blood to the lungs where gas exchange takes place.

It begins in the right ventricle of the heart with the pulmonary trunk, into which venous blood enters during ventricular systole. The pulmonary trunk divides into the right and left pulmonary arteries. Each artery enters the lung through its gates and, accompanying the structures " bronchial tree» reaches the structural and functional units of the lung - (acnus) - dividing to the blood capillaries. Gas exchange occurs between the blood and the contents of the alveoli. Venous vessels form two pulmonary vessels in each lung.

veins that carry arterial blood to the heart. The pulmonary circulation in the left atrium ends with four pulmonary veins.

right ventricle heart --- pulmonary trunk --- pulmonary arteries ---

division of intrapulmonary arteries --- arterioles --- blood capillaries ---

venules --- fusion of intrapulmonary veins --- pulmonary veins --- left atrium.

in which vessel and in which chamber of the heart does the pulmonary circulation begin:

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originates from the right ventricle in the pulmonary trunk

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vessels that form the pulmonary circulation:

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what vessels and in what chamber of the heart does the pulmonary circulation end:

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The systemic circulation delivers blood to all organs of the body.

From the left ventricle of the heart, arterial blood is sent to the aorta during systole. Arteries of the elastic and muscular types, intraorgan arteries, which divide into arterioles and blood capillaries, depart from the aorta. Venous blood through the system of venules, then intraorgan veins, extraorganic veins form the superior, inferior vena cava. They go to the heart and flow into the right atrium.

sequentially it looks like this:

left ventricle of the heart --- aorta --- arteries (elastic and muscular) ---

intraorgan arteries --- arterioles --- blood capillaries --- venules ---

intraorganic veins --- veins --- superior and inferior vena cava ---

which chamber of the heartstartssystemic circulationand how

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v. cava superior

v. cava inferior

what vessels and in what chamber of the heart does the systemic circulation end:

v. cava inferior

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

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 takes place in a closed system consisting of small and large circles:

• A large circle of blood circulation provides all organs and tissues with blood with nutrients contained in it.
• The small, or pulmonary, circle of blood circulation is designed to enrich the blood with oxygen.

Circulatory 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.

Small circle of blood circulation It 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 through the pulmonary veins enters the left atrium, where the small 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 flows through the venules and veins into the right atrium, where the large 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 off, carrying blood to the head (carotid arteries) and to upper limbs(vertebral arteries). The aorta runs down along the spine, where branches depart 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 cells of organs and tissues necessary for their activity. nutrients and oxygen, and in the capillary system turns into venous blood. Venous blood, saturated with carbon dioxide and cellular metabolic products, 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. Scheme of small and large circles of blood circulation

It should be noted 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 a common trunk of the hepatic vein, which flows into the inferior vena cava. All the blood of 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 unabsorbed in small intestine amino acids 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 branches off from the abdominal artery.

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

Rice. Scheme of blood circulation

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. The difference between blood flow in the systemic and pulmonary circulation

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

Patterns of the movement of blood through the 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, the science of the movement of fluids, are taken into account.

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 fluid encounters along its path.

The pressure difference contributes to the movement of the fluid: the greater it is, the more intense this movement. Resistance in the vascular system, which reduces the speed of blood flow, 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 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. Blood flow velocity is characterized by three indicators: volumetric blood flow velocity, linear blood flow velocity 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 blood flow velocity - 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 large and small circles of blood circulation. Normally, it is 17-25 s. Passing through a small circle takes about 1/5, and passing through a large circle - 4/5 of this time

The driving force of blood flow in the vascular system of each of the circles of blood circulation 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 ( R2) is the driving force of blood flow through any vessel of the circulatory system. The force of the blood pressure gradient is used to overcome the resistance to blood flow ( R) in the vascular system and in each individual vessel. The higher the blood pressure gradient in the circulation or in a separate vessel, the greater the volumetric blood flow in them.

The most important indicator of the movement of blood 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 section of an individual vessel per unit time. The volumetric 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 circulation. Since the entire volume of blood ejected by the left ventricle during this time flows through the aorta and other vessels of the systemic circulation per unit of time (minute), the concept of systemic volumetric blood flow is synonymous with the concept of (MOC). The IOC of an adult at rest is 4-5 l / min.

Distinguish also volumetric blood flow in the body. In this case, they mean the total blood flow flowing per unit of time through all the afferent arterial or efferent venous vessels of the organ.

Thus, the volume 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 an 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 current resistance blood.

The total (systemic) minute blood flow in a large circle is calculated taking into account the values ​​of 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 calculation Q or IOC value is substituted R equal to the mean hydrodynamic 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 due to 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 heart systole, when blood pressure reaches its maximum level, blood flow increases, and during diastole, when blood pressure is at its lowest, 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 rapidly, since they have a large 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, evaluating the results of measuring blood pressure and its deviations. Factors affecting the resistance of the vessel, for fluid flow, are described by Poiseuille's law, according to which

where R- resistance; L is the length of the vessel; η - blood viscosity; Π - number 3.14; r is the 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 changing values ​​of the radius of the vessels r and blood viscosity η ).

It has already been mentioned that the radius of muscle-type vessels can change rapidly and have a significant effect on the amount of resistance to blood flow (hence their name - resistive vessels) and the amount of blood flow through organs and tissues. Since the resistance depends on the magnitude of the radius to the 4th power, even small fluctuations in the radius of the vessels greatly affect the resistance to blood flow and blood flow. So, for example, if the radius of the 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 is doubled. At a constant average hemodynamic pressure, blood flow in one organ can increase, in another - decrease depending on contraction or relaxation. smooth muscle afferent arterial vessels and veins of this organ.

The viscosity of the blood depends on the content in the blood 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, the viscosity of the blood does not change as quickly as the lumen of the vessels. After blood loss, with erythropenia, hypoproteinemia, blood viscosity decreases. With significant erythrocytosis, leukemia, increased erythrocyte aggregation and hypercoagulability, blood viscosity can increase significantly, which leads to an increase in blood flow resistance, an increase in the load on the myocardium and may be accompanied by a violation of blood flow in the vessels of the microvasculature.

In the established regime of blood circulation, 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 part of the systemic circulation. This volume of blood returns to the right atrium and enters the right ventricle. From it, blood is expelled into the pulmonary circulation and then through the pulmonary veins returns to left heart. Since the IOCs of the left and right ventricles are the same, and the systemic and pulmonary circulations are connected in series, the volumetric blood flow velocity in the vascular system remains the same.

However, during changes in blood flow conditions, such as when changing from horizontal to vertical position When gravity causes a temporary accumulation of blood in the veins of the lower torso and legs, for a short time the cardiac output of the left and right ventricles may become different. Soon, intracardiac and extracardiac mechanisms of regulation of the work of the heart equalize the volume of blood flow through the small and large circles of blood circulation.

With a sharp decrease in venous return of blood to the heart, causing a decrease in stroke volume, the arterial pressure blood. With a pronounced decrease in it, blood flow to the brain can decrease. This explains the feeling of dizziness that can occur with a sharp transition of a person from a horizontal to a vertical position.

Volume and linear velocity of blood flow in the vessels

The total volume of blood 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% - in the vessels of the pulmonary circulation, and about 7% - in the cavities of the heart.

Most of the blood is contained in the veins (about 75%) - this indicates their role in the deposition of blood in both the systemic and pulmonary circulation.

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

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

V \u003d Q / Pr 2

where V— linear blood flow velocity, mm/s, cm/s; Q - volumetric blood flow velocity; P- a number equal to 3.14; r is the radius of the vessel. Value 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 different parts of the vascular system

Rice. 2. Hydrodynamic characteristics of the vascular bed

From the expression of the dependence of the magnitude of the linear velocity on the volume in the vessels of the circulatory system, it can be seen 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 cm 2), the linear velocity of blood largest and is at rest about 20- 30 cm/s. At physical activity it can increase by 4-5 times.

In the direction of 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 part of the vessels of the great circle (500-600 times the cross-section of the aorta), the linear velocity of blood flow becomes minimal (less than 1 mm/s). The slow flow of blood in the capillaries creates best conditions for the flow of metabolic processes between blood and tissues. In 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 under 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 stream. There is a laminar type of blood flow, in which the blood flow can be conditionally divided into layers. In this case, the linear velocity of the movement of blood layers (mainly plasma), close to or adjacent to the vessel wall, is the smallest, and the layers in the center of the flow are the largest. Friction forces arise between the vascular endothelium and the parietal layers of blood, creating shear stresses on the vascular endothelium. These stresses play a role in the production of vasoactive factors by the endothelium, which regulate the lumen of the vessels and the rate of blood flow.

Erythrocytes in vessels (with the exception of capillaries) are located mainly in the central part of the blood stream 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 a low speed. This allows them to bind to adhesion receptors at sites 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 velocity of blood movement in the narrowed part of the vessels, in places where its branches depart from the vessel, the laminar nature of blood movement can change to turbulent. In this case, the layering of the movement of its particles in the blood flow may be disturbed, and between the vessel wall and the blood, greater friction forces and shear stresses may occur than with laminar movement. Vortex blood flows develop, the likelihood of damage to the endothelium and the deposition of cholesterol and other substances in the intima of the vessel wall increases. This can lead to mechanical disruption of the structure of the vascular wall and initiation of the development of parietal thrombi.

The time of a complete blood circulation, i.e. the return of a blood particle to the left ventricle after its ejection and passage through the large and small circles of blood circulation, is 20-25 s in mowing, or after about 27 systoles of the ventricles of the heart. Approximately a quarter of this time is spent on moving blood through the vessels of the small circle and three quarters - through the vessels of the systemic circulation.

Small circle of blood circulation begins in the right ventricle, from which the pulmonary trunk emerges, and ends in the left atrium, where the pulmonary veins flow. The pulmonary circulation is also called pulmonary, it provides gas exchange between the blood of the pulmonary capillaries and the air of the pulmonary alveoli. It consists of the pulmonary trunk, the right and left pulmonary arteries with their branches, the vessels of the lungs, which are collected in two right and two left pulmonary veins, flowing into the left atrium.

Pulmonary trunk(truncus pulmonalis) originates from the right ventricle of the heart, diameter 30 mm, goes obliquely upwards, to the left and at the level of the IV thoracic vertebra is divided into the right and left pulmonary arteries, which go to the corresponding lung.

Right pulmonary artery with a diameter of 21 mm goes to the right to the gates of the lung, where it is divided into three lobar branches, each of which, in turn, is divided into segmental branches.

Left pulmonary artery shorter and thinner than the right one, runs from the bifurcation of the pulmonary trunk to the hilum of the left lung in the transverse direction. On its way, the artery crosses with the left main bronchus. In the gate, respectively, to the two lobes of the lung, it is divided into two branches. Each of them breaks up into segmental branches: one - within the boundaries of the upper lobe, the other - the basal part - with its branches provides blood to the segments of the lower lobe of the left lung.

Pulmonary veins. Venules begin from the capillaries of the lungs, which merge into larger veins and form two pulmonary veins in each lung: the right upper and right lower pulmonary veins; left superior and left inferior pulmonary veins.

Right superior pulmonary vein collects blood from the upper and middle lobe right lung, but lower right - from the lower lobe of the right lung. The common basal vein and superior vein of the lower lobe form the right inferior pulmonary vein.

Left superior pulmonary vein collects blood from the upper lobe of the left lung. It has three branches: apical-posterior, anterior and reed.

Left lower pulmonary the vein carries blood from the lower lobe of the left lung; it is larger than the upper one, consists of superior vein and the common basal vein.

Vessels of the systemic circulation

Systemic circulation begins in the left ventricle, from where the aorta exits, and ends in the right atrium.

The main purpose of the vessels of the systemic circulation is the delivery of oxygen and nutrients, hormones to organs and tissues. The exchange of substances between the blood and tissues of organs occurs at the level of capillaries, the excretion of metabolic products from the organs occurs through the venous system.

The blood vessels of the systemic circulation include the aorta with the arteries of the head, neck, torso and extremities extending from it, branches of these arteries, small vessels of organs, including capillaries, small and large veins, which then form the superior and inferior vena cava.

Aorta(aorta) - the largest unpaired arterial vessel of the human body. It is divided into the ascending aorta, the aortic arch and the descending aorta. The latter, in turn, is divided into the thoracic and abdominal parts.

Ascending aorta begins with an extension - a bulb, leaves the left ventricle of the heart at the level of the III intercostal space on the left, behind the sternum goes up and at the level of the II costal cartilage passes into the aortic arch. The length of the ascending aorta is about 6 cm. The right and left coronary arteries depart from it, which supply the heart with blood.

Aortic arch starts from the II costal cartilage, turns to the left and back to the body of the IV thoracic vertebra, where it passes into the descending part of the aorta. In this place there is a slight narrowing - isthmus of the aorta. Large vessels depart from the aortic arch (brachiocephalic trunk, left common carotid and left subclavian arteries), which provide blood to the neck, head, upper body and upper limbs.

Descending aorta - the longest part of the aorta, starts from the level of the IV thoracic vertebra and goes to the IV lumbar, where it is divided into the right and left iliac arteries; this place is called aortic bifurcation. The descending aorta is divided into the thoracic and abdominal aorta.