Circulation circles in humans. Structure and functions of the heart. Blood supply to the heart or coronary circulation

Human circulation

Human blood circulation diagram

Human blood circulation- a closed vascular pathway that provides continuous blood flow, carrying oxygen and nutrition to cells, carrying away carbon dioxide and metabolic products. It consists of two successively connected circles (loops), starting from the ventricles of the heart and flowing into the atria:

• systemic circulation begins in the left ventricle and ends in the right atrium;
• pulmonary circulation begins in the right ventricle and ends in the left atrium.

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

Systemic circulation video.

Both vena cavae bring blood to the right atrium, which also receives venous blood from the heart itself. This closes the circle of blood circulation. This blood path is divided into the pulmonary and systemic circulation.

Pulmonary circulation video

Pulmonary circulation(pulmonary) starts from the right ventricle of the heart with the pulmonary trunk, includes the branches of the pulmonary trunk to the capillary network of the lungs and the pulmonary veins flowing into left atrium.

Systemic circulation(bodily) starts from the left ventricle of the heart with the aorta, includes all its branches, capillary network and veins of organs and tissues of the whole body and ends in the right atrium.
Consequently, blood circulation occurs through two interconnected circulation circles.

The regular movement of blood flow in circles was discovered in the 17th century. Since then, the study of the heart and blood vessels has undergone significant changes due to the acquisition of new data and numerous studies. Today, there are rarely people who do not know what the circulatory circles of the human body are. However, not everyone has detailed information.

In this review, we will try to briefly but succinctly describe the importance of blood circulation, consider the main features and functions of blood circulation in the fetus, and the reader will also receive information about what the circle of Willis is. The data presented will allow everyone to understand how the body works.

Additional questions that may arise as you read will be answered by competent portal specialists.

Consultations are carried out online and free of charge.

In 1628, a physician from England, William Harvey, made the discovery that blood moves along a circular path - the systemic circulation and the pulmonary circulation. The latter includes blood flow to the lung respiratory system, and the large one circulates throughout the body. In view of this, the scientist Harvey is a pioneer and made the discovery of blood circulation. Of course, Hippocrates, M. Malpighi, as well as other famous scientists made their contribution. Thanks to their work, the foundation was laid, which became the beginning of further discoveries in this area.

general information

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

• The heart has two atria and two ventricles.
• The systemic circulation begins from the ventricle of the left chamber, and the blood is called arterial. From this point, blood flows through the arteries to each organ. As they travel through the body, the arteries transform into capillaries, which exchange gases. Next, the blood flow turns into venous. Then it enters the atrium of the right chamber and ends in the ventricle.
• The pulmonary circulation is formed in the ventricle of the right chamber and goes through the arteries to the lungs. There the blood exchanges, giving off gas and taking up oxygen, exits through the veins into the atrium of the left chamber, and ends in the ventricle.

Diagram No. 1 clearly shows how the blood circulation operates.

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

The circulatory organs are as follows:

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

Circulatory system

In addition to the minor and major pathways of blood circulation, there is also a peripheral pathway.

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

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

• Arteries leaving the heart carry blood circulation. Arterioles perform a similar function.
• Veins, like venules, help return blood to the heart.

Arteries are tubes through which a large circle of blood flows. They have a fairly large diameter. Able to withstand high pressure due to thickness and ductility. They have three shells: inner, middle and outer. Thanks to their elasticity, they independently regulate depending on the physiology and anatomy of each organ, its needs and the temperature of the external environment.

The system of arteries can be imagined as a bush-like bundle, which becomes smaller the further from the heart. As a result, in the limbs they look like capillaries. Their diameter is no larger than a hair, and they are connected by arterioles and venules. Capillaries have thin walls and have one epithelial layer. This is where the exchange of nutrients takes place.

Therefore, the importance of each element should not be underestimated. Violation of the functions of one leads to diseases of the entire system. Therefore, to maintain the functionality of the body, you should lead a healthy lifestyle.

Heart third circle

As we found out, the pulmonary circulation and the systemic circulation are not all components of the heart. vascular system. There is also a third path along which blood flow occurs and it is called the cardiac circulation circle.

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

Coronary circulation has the following properties:

• increased blood circulation;
• supply occurs in the diastolic state of the ventricles;
• There are few arteries here, so dysfunction of one gives rise to myocardial diseases;
• excitability of the central nervous system increases blood flow.

Diagram No. 2 shows how the coronary circulation functions.

The circulatory system includes the little-known circle of Willis. Its anatomy is such that it is presented in the form of a system of vessels that are located at the base of the brain. Its importance is difficult to overestimate, because... its main function is to compensate for the blood that it transfers from other “pools”. The vascular system of the circle of Willis is closed.

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

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

The Willis vascular system is designed not only to supply blood flow to the brain, but also to compensate for thrombosis. In view of this, treatment of the Willis pathway is practically not carried out, because no health hazard.

Blood supply in the human fetus

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

Diagram No. 3 shows how blood flows in the fetus.

Features of fetal blood circulation:

1. Blood moves due to the contractile function of the organ.
2. Starting from the 11th week, breathing affects blood supply.
3. Great importance is given to the placenta.
4. The fetal pulmonary circulation does not function.
5. Mixed blood flow enters the organs.
6. Identical pressure in the arteries and aorta.

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

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Tests

27-01. In which chamber of the heart does the pulmonary circulation conventionally begin?
A) in the right ventricle
B) in the left atrium
B) in the left ventricle
D) in the right atrium

27-02. Which statement correctly describes the movement of blood through the pulmonary circulation?
A) begins in the right ventricle and ends in the right atrium
B) begins in the left ventricle and ends in the right atrium
B) begins in the right ventricle and ends in the left atrium
D) begins in the left ventricle and ends in the left atrium

27-03. Which chamber of the heart receives blood from the veins of the systemic circulation?
A) left atrium
B) left ventricle
B) right atrium
D) right ventricle

27-04. Which letter in the figure indicates the chamber of the heart in which the pulmonary circulation ends?

27-05. The picture shows the human heart and large blood vessels. What letter represents the inferior vena cava?

27-06. What numbers indicate the vessels through which venous blood flows?

A) 2.3
B) 3.4
B) 1.2
D) 1.4

27-07. Which statement correctly describes the movement of blood through big circle blood circulation?
A) begins in the left ventricle and ends in the right atrium
B) begins in the right ventricle and ends in the left atrium
B) begins in the left ventricle and ends in the left atrium
D) begins in the right ventricle and ends in the right atrium

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 various body functions.

Circulatory system includes the heart and - aorta, arteries, arterioles, capillaries, venules, veins etc. 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 () 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 provides neutralization toxic substances, which 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 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 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 circulatory system. The force of the blood pressure gradient is used to overcome 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 changes little in an adult, 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 muscle-type vessels can change quickly 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 2 times. 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 enters 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% - in the vessels of the pulmonary circulation and about 7% - 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 area cross section vessel.

Rice. 1. Changes in blood pressure, linear velocity of blood flow 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 speed 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 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 predominantly in the central part of the blood flow and move in it with a relatively high speed. Leukocytes, on the contrary, are located predominantly 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.

CIRCLES OF BLOOD CIRCULATION

Arterial and venous vessels are not isolated and independent, but are interconnected as one system 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 arteries is higher than in 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 blood circulation circles, it is necessary to answer the questions: (WHERE? and WHAT?). For example: WHERE does it end?, begin? – (in which ventricle or atrium).

WHAT does it end with?, begins with? - (with what vessels) ..

The small circle of blood circulation delivers blood to the lungs where gas exchange occurs.

It begins in the right ventricle of the heart with the pulmonary trunk, into which venous blood enters during ventricular systole. The pulmonary trunk is divided into right and left pulmonary arteries. Each artery enters the lung through its gate and, accompanying the structures of the “bronchial tree”, reaches the structural functional units lung - (acnus) - dividing to 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 ends in the left atrium with four pulmonary veins.

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

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

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

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

ventriculus dexter

truncus pulmonalis

,Towith which vessels the pulmonary circulation begins and endsI.

originates from the right ventricle through the pulmonary trunk

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vessels forming the pulmonary circulation:

truncus pulmonalis

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

Atrium sinistrum

The circulatory system delivers blood to all organs of the body.

From the left ventricle of the heart, arterial blood flows into the aorta during systole. Arteries of elastic and muscular types, intraorgan arteries, which divide into arterioles and blood capillaries, depart from the aorta. Venous blood flows through the system of venules, then intraorgan veins, extraorgan veins form the superior and inferior vena cava. They head towards the heart and empty 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 ---

intraorgan veins ---veins---superior and inferior vena cava---

in which chamber of the heartbeginssystemic circulationand how

vesselohm .

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v. cava superior

v. cava inferior

Which vessels and in which chamber of the heart will the systemic circulation end:

v. cava inferior

Circulation circles represent a structural system of vessels and components of the heart, within which blood constantly moves.

Circulation plays one of the essential functions human body, it carries blood flows enriched with oxygen and nutrients necessary for tissues, removing metabolic decay products, as well as carbon dioxide, from the tissues.

Transportation of blood through vessels is a critical process, so its deviations lead to the most serious complications.

The circulation of blood flows is divided into a small and large circle of blood circulation. They are also called systemic and pulmonary, respectively. Initially, the systemic circle comes from the left ventricle, through the aorta, and entering the cavity of the right atrium, it ends its journey.

The pulmonary circulation of blood starts from the right ventricle, and enters the left atrium and ends its journey.

Who first identified the circles of blood circulation?

Due to the fact that in the past there were no instruments for hardware research of the body, the study physiological characteristics living organism was not possible.

The studies were carried out on corpses, in which doctors of that time studied only anatomical features, since the corpse’s heart was no longer beating, and circulatory processes remained a mystery to specialists and scientists of past times.

They simply had to speculate on some physiological processes, or use their imagination.

The first assumptions were the theories of Claudius Galen, back in the 2nd century. He was trained in the science of Hippocrates, and put forward the theory that the arteries inside themselves carry air cells, and not masses of blood. As a result, for many centuries they tried to prove this physiologically.

All scientists were aware of what the structural system of blood circulation looks like, but could not understand on what principle it functions.

A big step in organizing data on the functioning of the heart was made by Miguel Servet and William Harvey already in the 16th century.

The latter, for the first time in history, described the existence of systemic and pulmonary circulation circles, back in one thousand six hundred and sixteen, but was never able to explain in his works how they are connected to each other.

Already in the 17th century, Marcello Malpighi, the one who began to use the microscope for practical purposes, one of the first people in the world, discovered and described that there are small capillaries that are not visible with the naked eye, they connect two circles of blood circulation.

This discovery was disputed by the geniuses of those times.

How did blood circulation circles evolve?

As the class “vertebrates” developed more and more both anatomically and physiologically, an increasingly developed structure of the cardiovascular system was formed.

The formation of a vicious circle of blood movement occurred to increase the speed of movement of blood flows in the body.

When compared with other classes of animal beings (let’s take arthropods), chordates show the initial formation of blood movement in a vicious circle. The class of lancelets (a genus of primitive marine animals) does not have a heart, but has an abdominal and dorsal aorta.

The formation of two circulation circles is the evolution of the cardiovascular system, which adapted to its environment.

Types of vessels

The entire blood circulation system consists of the heart, which is responsible for pumping blood and its constant movement in the body, and the vessels inside which the pumped blood is distributed.

Many arteries, veins, as well as small capillaries form a closed circle of blood circulation with their multiple structure.

Mostly large vessels, which have the shape of a cylinder and are responsible for moving blood from the heart to the feeding organs, make up the systemic circulatory system.

All arteries have elastic walls that contract, resulting in blood moving evenly and in a timely manner.

The vessels have their own structure:

• Inner endothelial membrane. It is strong and elastic, it interacts directly with the blood;
• Smooth muscle elastic tissue. They make up the middle layer of the vessel, are more durable and protect the vessel from external damage;
• Connective tissue membrane. It is the outermost layer of the vessel, covering them along the entire length, protects the vessels from external influence on them.

The veins of the systemic circle help blood flow from small capillaries directly to the tissues of the heart. They have the same structure as arteries, but are more fragile, since their middle layer contains less tissue and is less elastic.

In view of this, the speed of blood movement through the veins is influenced by the tissues located in close proximity to the veins, and especially the skeletal muscles. Almost all veins contain valves that prevent blood from flowing in the opposite direction. The only exception is the vena cava.

The smallest components of the structure of the vascular system are capillaries, the covering of which is a single-layer endothelium. They are the smallest and shortest types of vessels.

It is they who enrich the tissues with useful elements and oxygen, removing from them the remnants of metabolic decay, as well as processed carbon dioxide.

Blood circulation in them occurs more slowly, in the arterial part of the vessel water is transported to the intercellular zone, and in the venous part the pressure drops and water rushes back into the capillaries.

On what principle are arteries located?

The placement of vessels on the way to the organs occurs along the shortest path to them. The vessels located in our limbs pass from the inside, since from the outside, their path would be longer.

Also, the pattern of vessel formation is definitely related to the structure of the human skeleton. An example is that according to upper limbs The brachial artery runs, which is called accordingly to the bone near which it passes - the brachial artery.

Other arteries are also called according to this principle: the radial artery - directly next to radius, ulnar - in the vicinity of the elbow, etc.

With the help of connections between nerves and muscles, networks of vessels are formed in the joints, in the systemic blood circulation. That is why when the joints move, they constantly support blood circulation.

The functional activity of an organ affects the size of the vessel leading to it; in this case, the size of the organ does not play a role. The more important and functional the organs, the more arteries leading to them.

Their placement around the organ itself is influenced solely by the structure of the organ.

System circle

The main task of the large circle of blood circulation is gas exchange in any organs except the lungs. It starts from the left ventricle, blood from it enters the aorta, spreading further throughout the body.

Components of the systemic circulatory system from the aorta, with all its branches, arteries of the liver, kidneys, brain, skeletal muscles and other organs. After the large vessels, it continues with small vessels and the beds of the veins of the above organs.

The right atrium is its final point.

Directly from the left ventricle, arterial blood enters the vessels through the aorta, it contains the majority of oxygen and a small proportion of carbon. The blood in it is taken from the pulmonary circulation, where it is enriched with oxygen by the lungs.

The aorta is the largest vessel in the body, and consists of a main canal and many branching, smaller arteries leading to the organs for their saturation.

Arteries leading to organs are also divided into branches and deliver oxygen directly to the tissues of certain organs.

With further branches, the vessels become smaller and smaller, eventually forming a great many capillaries, which are the smallest vessels in human body. Capillaries do not have a muscular layer, but are represented only by the inner lining of the vessel.

Many capillaries form a capillary network. They are all covered with endothelial cells, which are located at a sufficient distance from each other for nutrients to penetrate into the tissues.

This promotes gas exchange between small vessels and the area between cells.

They supply oxygen and take away carbon dioxide. The entire exchange of gases occurs constantly; after each contraction of the heart muscle in some part of the body, oxygen is delivered to tissue cells and hydrocarbons flow out of them.

The vessels that collect hydrocarbons are called venules. They subsequently join into larger veins and form one large vein. Large veins form the superior and inferior vena cava, ending in the right atrium.

Features of the systemic circulation

A special difference between the systemic circulatory system is that in the liver there is not only a hepatic vein, which removes venous blood from it, but also a portal vein, which in turn supplies blood to it, where blood purification is performed.

After this, the blood enters the hepatic vein and is transported to the systemic circle. The blood in the portal vein comes from the intestines and stomach, which is why harmful products nutrition has such a detrimental effect on the liver - they undergo cleansing in it.

The tissues of the kidneys and pituitary gland also have their own characteristics. Directly in the pituitary gland there is its own capillary network, which involves the division of arteries into capillaries and their subsequent connection into venules.

After this, the venules again divide into capillaries, then a vein is formed, which drains blood from the pituitary gland. Regarding the kidneys, the arterial network is divided according to a similar pattern.

How does blood circulation occur in the head?

One of the most complex structures of the body is blood circulation in the cerebral vessels. The sections of the head are fed by the carotid artery, which is divided into two branches (read). More details about

The arterial vessel enriches the face, temporal zone, mouth, nasal cavity, thyroid gland and other parts of the face.

This is how most of the systemic circle is formed, which ends in cerebral artery.

The main arteries supplying the brain are the subclavian and carotid arteries, which are connected together.

With the support of the vascular network, the brain functions with minor disruptions in blood flow.

Small circle

The main purpose of the pulmonary circulation is the exchange of gases in the tissues, saturating the entire area of ​​the lungs in order to enrich the already exhausted blood with oxygen.

The pulmonary circle of blood circulation starts from the right ventricle, where blood enters from the right atrium, with a low concentration of oxygen and a high concentration of hydrocarbons.

From there, the blood enters the pulmonary trunk, bypassing the valve. Next, the blood moves through a network of capillaries located throughout the lungs. Similar to the capillaries of the systemic circle, small vessels of the pulmonary tissues carry out gas exchange.

The only difference is that oxygen enters the lumen of small vessels, and not carbon dioxide, which here penetrates the cells of the alveoli. The alveoli, in turn, are enriched with oxygen with each inhalation of a person, and remove hydrocarbons from the body with exhalation.

Oxygen saturates the blood, making it arterial. After which it is transported through the venules and reaches the pulmonary veins, which end in the left atrium. This explains that the left atrium contains arterial blood, and the right atrium contains venous blood, and in a healthy heart they do not mix.

Lung tissue contains a double-level capillary network. The first is responsible for gas exchange to enrich the venous blood with oxygen (connection with the pulmonary blood circulation), and the second maintains the saturation of the lung tissues themselves (connection with the systemic blood circulation).

This is an additional protection for the brain from lack of oxygen. Its components are the following vessels: internal carotid arteries, the initial part of the anterior and posterior cerebral arteries, as well as the anterior and posterior communicating arteries.

Also, in pregnant women, an additional circle of blood circulation is formed, called the placental. Its main task is to maintain the child’s breathing. Its formation occurs in 1-2 months of gestation.

IN full force it starts working after the twelfth week. Since the fetal lungs are not yet functioning, oxygen enters the blood through the umbilical vein of the fetus with the arterial blood flow.

Nutrition of tissues with oxygen, important elements, as well as removal of carbon dioxide and metabolic products from cells in the body are the functions of blood. The process is a closed vascular path - human blood circulation circles, through which a continuous flow of vital fluid passes, its sequence of movement is ensured by special valves.

There are several circles of blood circulation in the human body

How many circles of blood circulation does a person have?

Human blood circulation or hemodynamics is a continuous flow of plasma fluid through the vessels of the body. This is a closed path of a closed type, that is, it does not come into contact with external factors.

Hemodynamics has:

• main circles – large and small;
• additional loops - placental, coronal and Willis.

The circulation cycle is always complete, which means that mixing of arterial and venous blood does not occur.

The heart, the main organ of hemodynamics, is responsible for plasma circulation. It is divided into 2 halves (right and left), where the internal sections are located - the ventricles and atria.

The heart is the main organ in the human circulatory system

Direction of liquid moving current connective tissue identify cardiac bridges or valves. They control the flow of plasma from the atria (cuspid) and prevent arterial blood from returning back into the ventricle (lunate).

The blood moves in circles in a certain order - first the plasma circulates in a small loop (5-10 seconds), and then in a large ring. Specific regulators control the functioning of the circulatory system - humoral and nervous.

Big circle

The large circle of hemodynamics has 2 functions:

• saturate the entire body with oxygen, distribute the necessary elements into the tissues;
• remove gas dioxide and toxic substances.

Here pass the superior and inferior vena cava, venules, arteries and artioles, as well as the largest artery, the aorta, which emerges from the left ventricle of the heart.

The placental circulation saturates the baby’s organs with oxygen and necessary elements

Heart circle

Due to the fact that the heart continuously pumps blood, it needs increased blood supply. Therefore, an integral part of the great circle is the coronal circle. It starts with coronary arteries, which surround the main organ as if with a crown (hence the name of the additional ring).

The cardiac circle supplies the muscular organ with blood

The role of the cardiac circle is to increase the supply of blood to the hollow muscular organ. A feature of the coronary ring is that the contraction of the coronary vessels is influenced by the vagus nerve, while the contractility of other arteries and veins is affected by the sympathetic nerve.

The circle of Willis is responsible for the complete supply of blood to the brain. The purpose of such a loop is to compensate for the lack of blood circulation in case of blockage of blood vessels. in such a situation, blood from other arterial basins will be used.

The structure of the arterial ring of the brain includes such arteries as:

• anterior and posterior brain;
• front and back connecting.

The circle of Willis circulation supplies the brain with blood

The human circulatory system has 5 circles, of which 2 are main and 3 are additional, thanks to which the body is supplied with blood. The small ring carries out gas exchange, and the large one is responsible for transporting oxygen and nutrients to all tissues and cells. Additional circles play an important role during pregnancy, reduce the load on the heart and compensate for the lack of blood supply to the brain.

In the human body, the movement of blood through the systemic and pulmonary circulation is provided so that the liquid tissue successfully copes with its responsibilities: transporting substances necessary for their development to the cells and carrying away decay products. Despite the fact that such concepts as “large and small circle” are rather arbitrary, since they are not completely closed systems(the first goes into the second and vice versa), each of them has its own task and purpose in the work of the cardiovascular system.

The human body contains from three to five liters of blood (women have less, men have more), which continuously moves through the vessels. It is a liquid tissue that contains a huge number of different substances: hormones, proteins, enzymes, amino acids, blood cells and other components (their number is in the billions). Such a high content of them in plasma is necessary for the development, growth and successful functioning of cells.

Blood transmits nutrients and oxygen to tissues through capillary walls. Then it takes carbon dioxide and decay products from the cells and carries them to the liver, kidneys, and lungs, which neutralize them and remove them outside. If for some reason the blood flow is stopped, the person will die within the first ten minutes: this time is enough for the brain cells deprived of nutrition to die, and the body to be poisoned by toxins.

The substance moves through the vessels, which is a vicious circle consisting of two loops, each of which originates in one of the ventricles of the heart and ends in the atrium. Each circle has veins and arteries, and the composition of the substance that is in them is one of the differences between the circulatory circles.

The arteries of the large loop contain tissue enriched with oxygen, while the veins contain tissue saturated with carbon dioxide. In the small loop, the opposite picture is observed: blood that needs purification is in the arteries, while fresh blood is in the veins.

The small and large circles perform two different tasks in the functioning of the cardiovascular system. In a large loop, human plasma flows through the vessels, transfers the necessary elements to the cells and takes away waste. In a small circle, the substance is cleared of carbon dioxide and saturated with oxygen. In this case, the plasma flows through the vessels only forward: the valves prevent the reverse movement of the liquid tissue. This system, consisting of two loops, allows different types blood do not mix with each other, which greatly facilitates the task of the lungs and heart.

How is blood purified?

The functioning of the cardiovascular system depends on the work of the heart: contracting rhythmically, it forces blood to move through the vessels. It consists of four hollow chambers located one after another according to the following scheme:

• right atrium;
• right ventricle;
• left atrium;
• left ventricle

Both ventricles are significantly larger than the atria. This is due to the fact that the atria simply collect and send the substance that enters them into the ventricles, and therefore do less work (the right one collects blood with carbon dioxide, the left one – saturated with oxygen).

According to the diagram, the right side of the heart muscle does not touch the left. The small circle originates inside the right ventricle. From here, the blood with carbon dioxide is sent to the pulmonary trunk, which subsequently diverges in two: one artery goes to the right, the second to the left lung. Here the vessels are divided into a huge number of capillaries, which lead to the pulmonary vesicles (alveoli).

Further, gas exchange occurs through the thin walls of the capillaries: red blood cells, which are responsible for transporting gas through the plasma, detach carbon dioxide molecules from themselves and combine with oxygen (blood is transformed into arterial blood). Then the substance leaves the lungs through four veins and ends up in the left atrium, where the pulmonary circulation ends.

It takes the blood four to five seconds to complete the small circle. If the body is at rest, this time is enough to provide it with the required amount of oxygen. For physical or emotional stress The pressure on the human cardiovascular system increases, which causes blood circulation to accelerate.

Features of blood flow in a large circle

Purified blood enters from the lungs into the left atrium, then goes into the cavity of the left ventricle (this is where the systemic circulation begins). This chamber has the thickest walls, due to which, when contracted, it is able to eject blood with a force sufficient for it to reach the farthest parts of the body in a few seconds.

During contraction, the ventricle releases liquid tissue into the aorta (this vessel is the largest in the body). Then the aorta diverges into smaller branches (arteries). Some of them go up to the brain, neck, upper limbs, some go down and serve the organs that are located below the heart.

In the systemic circulation, the purified substance moves through the arteries. Their distinctive feature are elastic but thick walls. Then the substance flows into smaller vessels - arterioles, and from them into capillaries, whose walls are so thin that gases and nutrients easily pass through them.

When the exchange ends, the blood, due to the added carbon dioxide and breakdown products, acquires a darker color, transforms into venous blood and is sent through the veins to the heart muscle. The walls of the veins are thinner than the arterial ones, but are characterized by a large lumen, so much more blood is placed in them: about 70% of the liquid tissue is in the veins.

If the movement of arterial blood is mainly influenced by the heart, then venous blood moves forward due to the contraction of skeletal muscles, which pushes it forward, as well as breathing. Since most of the plasma in the veins moves upward, to prevent it from flowing in the opposite direction, the vessels are equipped with valves to hold it back. At the same time, the blood that flows to the heart muscle from the brain moves through veins that do not have valves: this is necessary to avoid blood stagnation.

Approaching the heart muscle, the veins gradually converge with each other. Therefore, only two large vessels enter the right atrium: the superior and inferior vena cava. A large circle is completed in this chamber: from here the liquid tissue flows into the cavity of the right ventricle, then gets rid of carbon dioxide.

The average speed of blood flow in a large circle when a person is in a calm state is a little less than thirty seconds. At physical exercise, stress, and other factors that excite the body, blood flow can accelerate, since the cells need oxygen and nutrients during this period increases significantly.

Any diseases of the cardiovascular system negatively affect blood circulation, blocking blood flow, destroying vascular walls, which leads to starvation and cell death. Therefore, you need to be very careful about your health. If you experience pain in the heart, tumors in the limbs, arrhythmia and other health problems, be sure to consult a doctor so that he can determine the cause of circulatory problems or malfunctions cardiovascular system and prescribed a treatment regimen.