The passage of blood through the heart. Circles of blood circulation in humans: who discovered and what types exist

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

Circulatory system includes and - aorta, arteries, arterioles, capillaries, venules, veins, etc. 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:

• The systemic circulation provides all organs and tissues with blood containing nutrients.
• The small, or pulmonary, circle of blood circulation is designed to enrich the blood with oxygen.

Circles of blood circulation were first described by the English scientist William Harvey in 1628 in the work "Anatomical studies on the movement of the heart and blood vessels."

Small circle of blood circulation starts from the right ventricle, with the contraction of which venous blood enters the pulmonary trunk and, flowing through the lungs, gives off carbon dioxide and is saturated with oxygen. Blood enriched with oxygen from the lungs through the pulmonary veins enters the left atrium, where the small circle ends.

A large circle of blood circulation begins from the left ventricle, with the contraction of which oxygen-enriched blood 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 great circle ends.

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

Arterial blood, rich in oxygen, flows 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.

Fig. The 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 are then reunited into the 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 provides the neutralization of toxic substances that are formed in the large intestine during the breakdown of non-absorbed into 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 extends 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 an arterial vessel, which again disintegrates into capillaries that encircle the convoluted tubules.

Fig. Circulation diagram

A feature of blood circulation in the liver and kidneys is a slowdown in blood flow due to the function of these organs.

Table 1. The difference between blood flow in the systemic and pulmonary circulation

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

Regularities of the movement of blood through the vessels

Basic principles of hemodynamics

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

The speed at which blood flows 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 liquid meets on its way.

The pressure difference promotes the movement of the liquid: the larger it is, the more intense this movement. The 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 greater the length and the smaller the radius, the greater the resistance);
• blood viscosity (it is 5 times higher than the viscosity of water);
• friction of blood particles against the walls of blood vessels and among themselves.

Hemodynamic indicators

The blood flow velocity in the vessels is carried out according to the laws of hemodynamics, in common with the laws of hydrodynamics. Blood flow velocity is characterized by three parameters: 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 the 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 the blood passes through the large and small circles of blood circulation. Normally, it is 17-25 seconds. It takes about 1/5 to go through the small circle, and 4/5 of this time to go through the big one.

The driving force of blood flow through 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). Difference in blood pressure ( ΔР) at the beginning of the vessel ( Р1) and at the end of it ( P2) is the driving force of blood flow through any vessel of the circulatory system. The force of the blood pressure gradient is spent on overcoming the resistance to blood flow ( R) in the vascular system and in each individual vessel. The higher the gradient of blood pressure in the circle of blood circulation or in an individual 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 rate, 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 of time. The volumetric 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, use the concept 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 (MOC). The IOC of an adult at rest is 4-5 l / min.

There are also volumetric blood flow in the organ. In this case, they mean the total blood flow flowing per unit of time through all the arterial or outflowing venous vessels of the organ.

Thus, the volumetric blood flow Q \u003d (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 of time is directly proportional to the difference in blood pressure at the beginning and at the end of the vascular system (or vessel) and inversely proportional to the resistance to current blood.

The total (systemic) minute blood flow in the great circle is calculated taking into account the values \u200b\u200bof the mean hydrodynamic blood pressure at the beginning of the aorta P1, and at the mouth of the vena cava P2. Since in this part of the veins the blood pressure is close to 0 , then in the expression for calculating Q or the IOC is substituted with the value 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 due to the blood pressure generated by the work of the heart. Confirmation of the decisive value of the blood pressure value for blood flow is the pulsating nature of the blood flow throughout the cardiac cycle. During 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 the arterioles and capillaries decreases especially quickly, since they have great resistance to blood flow, having a small radius, large total length and numerous branches, which create 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 the volumetric blood flow, the symbol R you can replace it with an analogue - OPS:

Q \u003d P / OPS.

A number of important consequences are derived from this expression, necessary for understanding the processes of blood circulation in the body, assessing the results of measuring blood pressure and its deviations. The factors influencing the resistance of the vessel for the fluid flow are described by Poiseuille's law, according to which

where R - resistance; L - 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, little changes, the value of peripheral resistance to blood flow is determined by changing values \u200b\u200bof 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 degree, then even small fluctuations in the radius of the vessels strongly affect the values \u200b\u200bof 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 16 times and with a constant pressure gradient the blood flow in this vessel will also decrease 16 times. Reverse changes in resistance will be observed when the vessel radius is doubled. With a constant average hemodynamic pressure, the blood flow in one organ can increase, in the other it can decrease, depending on the contraction or relaxation of the smooth muscles of the bringing arterial vessels and veins of this organ.

The viscosity of blood depends on the content in the blood of the number of erythrocytes (hematocrit), protein, lipoproteins in the blood plasma, as well as the state of aggregation of the blood. Under normal conditions, blood viscosity 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 aggregation of erythrocytes 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 the established 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 part of the systemic circulation. This volume of blood returns to the right atrium and enters the right ventricle. From it, the blood is expelled into the pulmonary circulation and then through the pulmonary veins returns to the left heart. Since the MVC of the left and right ventricles are the same, and the large and small circles of blood circulation are connected in series, the volumetric blood flow velocity in the vascular system remains the same.

However, during a change in blood flow conditions, for example, during the transition from a horizontal to a vertical position, when gravity causes a temporary accumulation of blood in the veins of the lower trunk and legs, for a short time the MVC 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, arterial blood pressure may decrease. With a pronounced decrease in it, blood flow to the brain may decrease. This explains the feeling of dizziness that can occur with a sharp transition of a person from horizontal to vertical position.

Volume and linear velocity of blood currents in vessels

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

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

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

There is a relationship between volumetric and linear blood flow velocity, 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 - number equal to 3.14; r Is the radius of the vessel. The quantity Pr 2 reflects the cross-sectional area of \u200b\u200bthe vessel.

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

Fig. 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 can be seen that the linear blood flow velocity (Fig. 1) is proportional to the volumetric blood flow through the vessel (s) and inversely proportional to the cross-sectional area of \u200b\u200bthis vessel (s). For example, in the aorta having the smallest cross-sectional area in the systemic circulation (3-4 cm 2), linear blood velocity the largest and is alone about 20-30 cm / s... When physical activity it can increase by 4-5 times.

Towards the capillaries, the total transverse lumen of the vessels increases and, therefore, the linear velocity of blood flow in the arteries and arterioles decreases. In capillary vessels, the total cross-sectional area of \u200b\u200bwhich is greater than in any other part of the great circle vessels (500-600 times the cross-section of the aorta), the linear blood flow velocity becomes minimal (less than 1 mm / s). The slow blood flow in the capillaries creates the best conditions for metabolic processes between blood and tissues. In veins, the linear velocity of blood flow increases due to a decrease in the area of \u200b\u200btheir total cross-section as they approach the heart. At the mouth of the hollow veins, it is 10-20 cm / s, and under loads it increases to 50 cm / s.

The linear velocity 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 notes of blood can be conditionally divided into layers. In this case, the linear velocity of movement of blood layers (mainly plasma), close to or adjacent to the vessel wall, 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 layers of blood, creating shear stresses on the vascular endothelium. These stresses play a role in the production of vasoactive factors by the endothelium that regulate vascular lumen and blood flow velocity.

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 make rolling movements at a 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 velocity 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 change to turbulent. In this case, the layer-by-layer movement of its particles can be disturbed in the blood flow; greater frictional and shear forces can arise between the vessel wall and the blood than with laminar motion. Vortex blood flows develop, the likelihood of damage to the endothelium and the deposition of cholesterol and other substances into the intima of the vessel wall increases. This can lead to mechanical disruption of the structure of the vascular wall and the initiation of the development of parietal thrombi.

Time of complete blood circulation, i.e. The return of a blood particle to the left ventricle after its ejection and passing 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 the movement of blood through the vessels of the small circle and three quarters - through the vessels of the systemic circulation.

Arterial blood is blood saturated with oxygen.
Deoxygenated blood - saturated with carbon dioxide.

Arteries - these are the vessels that carry blood from the heart.
Veins are the vessels that carry blood to the heart.
(In the pulmonary circulation, venous blood flows through the arteries, and arterial blood flows through the veins.)

In humans, in all other mammals, as well as in birds four-chambered heart, consists of two atria and two ventricles (in the left half of the heart, the blood is arterial, in the right - venous, mixing does not occur due to the complete septum in the ventricle).

Between the ventricles and the atria are flap valves, and between the arteries and ventricles - lunar.The valves prevent blood from flowing backward (from the ventricle to the atrium, from the aorta to the ventricle).

The thickest wall is at the left ventricle; he pushes blood on a large circle blood circulation. When the left ventricle contracts, a pulse wave is created, as well as maximum arterial pressure.

Blood pressure: in the arteries the largest, in the capillaries the average, in the veins the smallest. Blood speed: the largest in the arteries, the smallest in the capillaries, medium in the veins.

Big circle blood circulation: from the left ventricle, arterial blood flows through the arteries to all organs of the body. Gas exchange occurs in the capillaries of the great circle: oxygen passes from the blood to the tissues, and carbon dioxide from the tissues to the blood. The blood becomes venous, through the vena cava it enters the right atrium, and from there - into the right ventricle.

Small circle: from the right ventricle, venous blood flows through the pulmonary arteries to the lungs. Gas exchange occurs in the capillaries of the lungs: carbon dioxide passes from the blood into the air, and oxygen from the air into the blood, the blood becomes arterial and enters the left atrium through the pulmonary veins, and from there into the left ventricle.

1. Establish a correspondence between the sections of the circulatory system and the circulatory system to which they belong: 1) The systemic circulatory system, 2) The pulmonary circulatory system. Write down the numbers 1 and 2 in the correct order.
A) Right ventricle
B) Carotid artery
C) Pulmonary artery
D) Superior vena cava
E) Left atrium
E) Left ventricle

Answer

2. Establish a correspondence between the vessels and the human circulation: 1) the pulmonary circulation, 2) the systemic circulation. Write down the numbers 1 and 2 in the correct order.
A) aorta
B) pulmonary veins
C) carotid arteries
D) capillaries in the lungs
D) pulmonary arteries
E) hepatic artery

Answer

3. Establish a correspondence between the structures of the circulatory system and the human circulation circles: 1) small, 2) large. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) aortic arch
B) portal vein of the liver
C) left atrium
D) right ventricle
D) carotid artery
E) alveolar capillaries

Answer

Choose three correct answers out of six and write down the numbers under which they are indicated. A large circle of blood circulation in the human body
1) begins in the left ventricle
2) originates in the right ventricle
3) is saturated with oxygen in the alveoli of the lungs
4) supplies organs and tissues with oxygen and nutrients
5) ends in the right atrium
6) brings blood to the left side of the heart

Answer

1. Set the sequence of the person's blood vessels in order of decreasing blood pressure. Write down the corresponding sequence of numbers.
1) inferior vena cava
2) aorta
3) pulmonary capillaries
4) pulmonary artery

Answer

2. Establish the sequence in which the blood vessels should be placed in the order of decreasing blood pressure in them
1) Veins
2) Aorta
3) Arteries
4) Capillaries

Answer

3. Set the sequence of the blood vessels in the order of increasing blood pressure. Write down the corresponding sequence of numbers.
1) inferior vena cava
2) aorta
3) pulmonary artery
4) alveolar capillaries
5) arterioles

Answer

Choose the one that is most correct. Why blood cannot get from the aorta to the left ventricle of the heart
1) the ventricle contracts with great force and creates high pressure
2) the semilunar valves fill with blood and close tightly
3) the leaflet valves are pressed against the walls of the aorta
4) the flap valves are closed and the lunar ones are open

Answer

Choose the one that is most correct. In the pulmonary circulation, blood comes from the right ventricle along
1) pulmonary veins
2) pulmonary arteries
3) carotid arteries
4) aorta

Answer

Choose the one that is most correct. Arterial blood in the human body flows through
1) renal veins
2) pulmonary veins
3) vena cava
4) pulmonary arteries

Answer

Choose the one that is most correct. In mammals, blood oxygenation occurs in
1) arteries of the pulmonary circulation
2) large circle capillaries
3) arteries of a large circle
4) small circle capillaries

Answer

1. Establish a sequence of blood flow through the vessels of the systemic circulation. Write down the corresponding sequence of numbers.
1) portal vein of the liver
2) aorta
3) gastric artery
4) left ventricle
5) the right atrium
6) inferior vena cava

Answer

2. Determine the correct sequence of blood circulation in the systemic circulation, starting with the left ventricle. Write down the corresponding sequence of numbers.
1) Aorta
2) Superior and inferior vena cava
3) Right atrium
4) Left ventricle
5) Right ventricle
6) Tissue fluid

Answer

3. Establish the correct sequence of blood flow through the systemic circulation. Write down the corresponding sequence of numbers in the table.
1) right atrium
2) left ventricle
3) arteries of the head, limbs and trunk
4) aorta
5) inferior and superior vena cava
6) capillaries

Answer

4. Establish the sequence of movement of blood in the human body, starting with the left ventricle. Write down the corresponding sequence of numbers.
1) left ventricle
2) hollow veins
3) aorta
4) pulmonary veins
5) the right atrium

Answer

5. Establish the sequence of passage of a portion of blood in a person, starting from the left ventricle of the heart. Write down the corresponding sequence of numbers.
1) right atrium
2) aorta
3) left ventricle
4) lungs
5) left atrium
6) the right ventricle

Answer

6ph. Establish the sequence of blood movement along the systemic circulation in a person, starting from the ventricle. Write down the corresponding sequence of numbers.
1) left ventricle
2) capillaries
3) right atrium
4) arteries
5) veins
6) aorta

Answer

Arrange the blood vessels in the order of decreasing blood flow rate in them
1) superior vena cava
2) aorta
3) brachial artery
4) capillaries

Answer

Choose the one that is most correct. The hollow veins in the human body flow into
1) left atrium
2) the right ventricle
3) left ventricle
4) right atrium

Answer

Choose the one that is most correct. Reverse blood flow from pulmonary artery and the aorta in the ventricles obstruct valves
1) tricuspid
2) venous
3) double-leaf
4) lunar

Answer

1. Establish the sequence of blood flow in a person along the pulmonary circulation. Write down the corresponding sequence of numbers.
1) pulmonary artery
2) the right ventricle
3) capillaries
4) left atrium
5) veins

Answer

2. Establish a sequence of blood circulation processes, starting with the moment when blood moves from the lungs to the heart. Write down the corresponding sequence of numbers.
1) blood from the right ventricle enters the pulmonary artery
2) blood moves through the pulmonary vein
3) blood moves through the pulmonary artery
4) oxygen enters the capillaries from the alveoli
5) blood enters the left atrium
6) blood enters the right atrium

Answer

3. Establish the sequence of movement of arterial blood in a person, starting from the moment of its saturation with oxygen in the capillaries of the small circle. Write down the corresponding sequence of numbers.
1) left ventricle
2) left atrium
3) veins of a small circle
4) small circle capillaries
5) arteries of a large circle

Answer

4. Establish a sequence of movement of arterial blood in the human body, starting with the capillaries of the lungs. Write down the corresponding sequence of numbers.
1) left atrium
2) left ventricle
3) aorta
4) pulmonary veins
5) lung capillaries

Answer

5. Establish the correct sequence for the flow of blood from the right ventricle to the right atrium. Write down the corresponding sequence of numbers.
1) pulmonary vein
2) left ventricle
3) pulmonary artery
4) the right ventricle
5) the right atrium
6) aorta

Answer

Establish the sequence of events that occur in the cardiac cycle after the entry of blood into the heart. Write down the corresponding sequence of numbers.
1) contraction of the ventricles
2) general relaxation of the ventricles and atria
3) blood supply to the aorta and artery
4) blood supply to the ventricles
5) contraction of the atria

Answer

Establish a correspondence between the human blood vessels and the direction of blood flow in them: 1) from the heart, 2) to the heart
A) veins of the pulmonary circulation
B) veins of a large circle of blood circulation
C) arteries of the pulmonary circulation
D) arteries of a large circle of blood circulation

Answer

Choose three options. A person has blood from the left ventricle of the heart
1) when it contracts, it enters the aorta
2) when it contracts, it enters the left atrium
3) supplies body cells with oxygen
4) enters the pulmonary artery
5) under high pressure enters a large circle of blood circulation
6) under low pressure enters the pulmonary circulation

Answer

Choose three options. Blood flows through the arteries of the pulmonary circulation of a person
1) from the heart
2) to the heart

4) oxygenated
5) faster than in pulmonary capillaries
6) slower than in the pulmonary capillaries

Answer

Choose three options. Veins are blood vessels through which blood flows
1) from the heart
2) to the heart
3) under greater pressure than in the arteries
4) under less pressure than in the arteries
5) faster than capillaries
6) slower than in capillaries

Answer

Choose three options. Blood flows through the arteries of a person's systemic circulation
1) from the heart
2) to the heart
3) saturated with carbon dioxide
4) oxygenated
5) faster than other blood vessels
6) slower than other blood vessels

Answer

1. Establish a correspondence between the type of human blood vessels and the type of blood they contain: 1) arterial, 2) venous
A) pulmonary arteries
B) veins of the pulmonary circulation
C) aorta and arteries of a large circle of blood circulation
D) upper and lower vena cava

Answer

2. Establish a correspondence between a vessel of the human circulatory system and the type of blood that flows through it: 1) arterial, 2) venous. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) femoral vein
B) brachial artery
C) pulmonary vein
D) subclavian artery
D) pulmonary artery
E) aorta

Answer

Establish a correspondence between signs and blood vessels: 1) vein 2) artery. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) has a thin muscle layer
B) has valves
C) carries blood from the heart
D) brings blood to the heart
D) has elastic elastic walls
E) withstands high blood pressure

Answer

Choose three options. In mammals, animals and humans, venous blood, in contrast to arterial,
1) poor in oxygen
2) flows in a small circle through the veins
3) fills the right half of the heart
4) saturated with carbon dioxide
5) enters the left atrium
6) provides body cells with nutrients

Answer

1. Choose three correct answers out of six and write down the numbers under which they are indicated. Veins as opposed to arteries
1) have valves in the walls
2) may subside
3) have walls of one layer of cells
4) carry blood from organs to the heart
5) withstand high blood pressure
6) always carry blood that is not saturated with oxygen

Answer

2. Choose three correct answers out of six and write down the numbers under which they are indicated. Veins, unlike arteries, are characterized by
1) flap valves
2) transfer of blood to the heart
3) semilunar valves
4) high blood pressure
5) thin muscle layer
6) fast blood flow

Answer

Analyze the table "Human Heart Work". For each letter cell, select the appropriate term from the list provided.
1) Arterial
2) Superior vena cava
3) Mixed
4) Left atrium
5) Carotid artery
6) Right ventricle
7) Inferior vena cava
8) Pulmonary vein

Answer

Choose three correct answers out of six and write down the numbers under which they are indicated. Elements of the human circulatory system containing venous blood are
1) pulmonary artery
2) aorta
3) hollow veins
4) right atrium and right ventricle
5) left atrium and left ventricle
6) pulmonary veins

Answer

Choose three correct answers out of six and write down the numbers under which they are indicated. Blood flows from the right ventricle
1) arterial
2) venous
3) through the arteries
4) through the veins
5) towards the lungs
6) towards the cells of the body

Answer

Establish a correspondence between the processes and circulatory systems for which they are characteristic: 1) small, 2) large. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) Arterial blood flows through the veins.
B) The circle ends in the left atrium.
C) Arterial blood flows through the arteries.
D) The circle begins in the left ventricle.
E) Gas exchange occurs in the capillaries of the alveoli.
E) Venous blood is formed from arterial blood.

Answer

Find three mistakes in the above text. Indicate the numbers of the proposals in which they are made.(1) The walls of the arteries and veins have a three-layer structure. (2) The walls of the arteries are very resilient and elastic; the walls of the veins, on the other hand, are inelastic. (3) With atrial contraction, blood is pushed into the aorta and pulmonary artery. (4) The blood pressure in the aorta and vena cava is the same. (5) The speed of blood movement in the vessels is not the same, in the aorta it is maximum. (6) The speed of movement of blood in the capillaries is higher than in the veins. (7) Blood in the human body moves in two circles of blood circulation.

Choose three correct answers out of six and write down the numbers under which they are indicated. What parts of the circulatory system belong to the systemic circulation?
1) pulmonary artery
2) superior vena cava
3) right atrium
4) left atrium
5) left ventricle
6) the right ventricle

Answer

Choose three correct answers out of six and write down the numbers under which they are indicated. Human pulse
1) is not related to the blood flow rate
2) depends on the elasticity of the walls of blood vessels
3) palpable on large arteries close to the body surface
4) speeds up blood flow
5) due to the rhythmic oscillation of the veins
6) not associated with heartbeat

Answer

Establish the sequence of transport of carbon dioxide from the moment it enters the bloodstream. Write down the corresponding sequence of numbers.
1) left ventricle
2) capillaries of internal organs
3) vena cava
4) alveolar capillaries

Answer

© D.V. Pozdnyakov, 2009-2019

In the human body, the circulatory system is designed to fully meet its internal needs. An important role in the advancement of blood is played by the presence of a closed system in which arterial and venous blood flows are separated. And this is done through the presence of circles of blood circulation.

Historical reference

In the past, when scientists did not yet have informative devices at hand capable of studying physiological processes on a living organism, the greatest scientists were forced to search for anatomical features in corpses. Naturally, the heart of a deceased person does not contract, so some of the nuances had to be conjectured on their own, and sometimes just fantasized. So, back in the second century AD Claudius Galen, student on the works of himself Hippocrates, assumed that the arteries contain air instead of blood in their lumen. Over the next centuries, many attempts have been made to combine and link together the available anatomical data from the standpoint of physiology. All scientists knew and understood how the circulatory system works, but how does it work?

Scientists have made a colossal contribution to the systematization of data on the work of the heart Miguel Servet and William Harvey in the 16th century. Harvey, the scientist who first described the large and small circles of blood circulation , in 1616 determined the presence of two circles, but how the arterial and venous channels are connected, he could not explain in his writings. And only later, in the 17th century, Marcello Malpighi, one of the first who began to use the microscope in his practice, discovered and described the presence of the smallest capillaries invisible to the naked eye, which serve as a connecting link in the circles of blood circulation.

Phylogenesis, or the evolution of the circulation

Due to the fact that, with evolution, animals of the class of vertebrates became more and more progressive in anatomical and physiological terms, they required a complex structure of the cardiovascular system. So, for a faster movement of the liquid internal environment in the body of a vertebrate animal, it became necessary to have a closed blood circulation system. Compared with other classes of the animal kingdom (for example, with arthropods or with worms), in chordates, the rudiments of a closed vascular system appear. And if the lancelet, for example, lacks a heart, but there is an abdominal and dorsal aorta, then in fish, amphibians (amphibians), reptiles (reptiles), a two- and three-chambered heart appears, respectively, and in birds and mammals - a four-chambered heart, a feature of which it is the focus of two circles of blood circulation, not mixing with each other.

Thus, the presence in birds, mammals and humans, in particular, of two separate circles of blood circulation is nothing more than the evolution of the circulatory system necessary for better adaptation to environmental conditions.

Anatomical features of the circulatory system

Circles of blood circulation is a collection of blood vessels, which is a closed system for entering internal organs oxygen and nutrients through gas and nutrient exchange, as well as for the removal of carbon dioxide and other metabolic products from cells. The human body is characterized by two circles - the systemic, or large circle, and also the pulmonary, also called a small circle.

Video: circulatory circles, mini-lecture and animation

A large circle of blood circulation

The main function of the great circle is to ensure gas exchange in all internal organs, except for the lungs. It starts in the left ventricular cavity; represented by the aorta and its branches, the arterial bed of the liver, kidneys, brain, skeletal muscles and other organs. Further, this circle continues with the capillary network and the venous bed of the listed organs; and by the confluence of the vena cava into the cavity of the right atrium ends in the latter.

So, as already mentioned, the beginning of the great circle is the cavity of the left ventricle. This is where the arterial blood stream is directed, which contains most oxygen rather than carbon dioxide. This flow enters the left ventricle directly from the circulatory system of the lungs, that is, from the small circle. The arterial flow from the left ventricle is pushed through the aortic valve into the largest great vessel, the aorta. The aorta can be figuratively compared to a kind of tree, which has many branches, because arteries branch off from it to internal organs (to the liver, kidneys, gastrointestinal tract, to the brain - through the system carotid arteries, to skeletal muscles, to subcutaneous fat, etc.). Organ arteries, also having numerous ramifications and bearing the names corresponding to the anatomy, carry oxygen to each organ.

In the tissues of internal organs, arterial vessels are subdivided into vessels of smaller and smaller diameters, and as a result, a capillary network is formed. Capillaries are the smallest vessels that practically do not have a middle muscle layer, but are represented by an inner membrane - an intima lined with endothelial cells. The gaps between these cells at the microscopic level are so large compared to other vessels that they allow proteins, gases and even formed elements to freely penetrate into the intercellular fluid of the surrounding tissues. Thus, between the capillary with arterial blood and the liquid intercellular medium in one or another organ, there is an intense gas exchange and the exchange of other substances. Oxygen penetrates from the capillary, and carbon dioxide, as a product of cell metabolism, into the capillary. The cellular stage of respiration is carried out.

After more oxygen has passed into the tissues, and all carbon dioxide has been removed from the tissues, the blood becomes venous. All gas exchange is carried out with each new inflow of blood, and during that period of time while it moves along the capillary towards the venule - a vessel that collects venous blood. That is, with each cardiac cycle in one or another part of the body, oxygen is supplied to the tissues and carbon dioxide is removed from them.

These venules are combined into larger veins, and a venous bed is formed. Veins, similar to arteries, bear the names in which organ they are located (renal, cerebral, etc.). From the large venous trunks, tributaries of the superior and inferior vena cava are formed, and the latter then flow into the right atrium.

Features of blood flow in the organs of a large circle

Some of the internal organs have their own characteristics. So, for example, in the liver there is not only the hepatic vein, which "carries" the venous flow from it, but also the portal vein, which, on the contrary, brings blood to the hepatic tissue, where the blood is purified, and only then the blood is collected into the tributaries of the hepatic vein to get to the big circle. The portal vein brings blood from the stomach and intestines, so everything that a person has eaten or drunk must undergo a kind of "cleaning" in the liver.

In addition to the liver, certain nuances exist in other organs, for example, in the tissues of the pituitary gland and kidneys. So, in the pituitary gland, the presence of the so-called "miraculous" capillary network is noted, because the arteries that bring blood to the pituitary gland from the hypothalamus are divided into capillaries, which are then collected in venules. Venules, after the blood with molecules of releasing hormones is collected, are again divided into capillaries, and then veins are already formed that carry blood from the pituitary gland. In the kidneys, the arterial network is divided twice into capillaries, which is associated with the processes of excretion and reabsorption in kidney cells - in the nephrons.

Small circle of blood circulation

Its function is to carry out gas exchange processes in the lung tissue in order to saturate the "spent" venous blood with oxygen molecules. It begins in the cavity of the right ventricle, where from the right atrial chamber (from the "end point" of the great circle) venous blood flow enters with an extremely small amount of oxygen and a high content of carbon dioxide. This blood moves through the valve of the pulmonary artery into one of the large vessels called the pulmonary trunk. Further, the venous flow moves along the arterial bed in the lung tissue, which also breaks down into a network of capillaries. By analogy with capillaries in other tissues, gas exchange takes place in them, only oxygen molecules enter the lumen of the capillary, and carbon dioxide penetrates into the alveolocytes (alveolar cells). Air from the environment enters the alveoli with each act of breathing, from which oxygen penetrates through the cell membranes into the blood plasma. With exhaled air during exhalation, carbon dioxide that has entered the alveoli is removed to the outside.

After saturation with O 2 molecules, the blood acquires arterial properties, flows through the venules and eventually reaches the pulmonary veins. The latter, consisting of four or five pieces, open into the cavity of the left atrium. As a result, venous blood flow flows through the right half of the heart, and arterial blood flows through the left half; and normally these streams should not mix.

The lung tissue has a double network of capillaries. With the help of the first, gas exchange processes are carried out in order to enrich the venous flow with oxygen molecules (interconnection directly with the small circle), and in the second, the lung tissue itself is nourished with oxygen and nutrients (interrelation with the large circle).

Additional circles of blood circulation

With these concepts, it is customary to highlight the blood supply to individual organs. So, for example, to the heart, which needs oxygen more than others, arterial inflow is carried out from the branches of the aorta at its very beginning, which are called the right and left coronary (coronary) arteries. In the capillaries of the myocardium, there is an intense gas exchange, and venous outflow carried out in the coronary veins. The latter are collected in the coronary sinus, which opens directly into the right atrial chamber. In this way, cardiac, or coronary circulation.

coronary (coronary) circle of blood circulation in the heart

Circle of willisis a closed arterial network of cerebral arteries. The brain circle provides additional blood supply to the brain in case of disturbance of cerebral blood flow through other arteries. This protects so important organ from lack of oxygen, or hypoxia. The cerebral circulation is represented by the initial segment of the anterior cerebral artery, the initial segment of the posterior cerebral artery, the anterior and posterior communicating arteries, and the internal carotid arteries.

circle of Willis in the brain (classic version of the structure)

Placental circulation functions only during gestation by a woman and performs the function of "breathing" in a child. The placenta forms from 3-6 weeks of gestation and begins to function at full strength from the 12th week. Due to the fact that the lungs of the fetus do not work, the flow of oxygen into its blood is carried out through the flow of arterial blood into the umbilical vein of the child.

fetal circulation before birth

Thus, the entire human circulatory system can be conditionally divided into separate interconnected areas that perform their functions. The correct functioning of such areas, or circles of blood circulation, is the key to the healthy functioning of the heart, blood vessels and the whole organism as a whole.

What is a pulmonary circulation?

From the right ventricle, blood is pumped into the capillaries of the lungs. Here it "gives off" carbon dioxide and "takes" oxygen, after which it goes back to the heart, namely to the left atrium.

What is the small circle of blood circulation for?

How does the pulmonary circulation function?

Heart valves:

Positive and negative pressure:

The alveoli are located on the branches of the bronchial tree (bronchioles).

How is blood flow in the pulmonary circulation regulated?

What is the systemic circulation?

The circulatory system: through the arteries, blood saturated with oxygen is carried out of the heart and enters the organs; through the veins, blood saturated with carbon dioxide returns to the heart.

100,000 km of blood vessels:

How does the systemic circulation work?

Where are the blood vessels located?

Main blood vessels:

Portal vein:

Connections:

Air embolism:

ON A NOTE:

This is a continuous movement of blood through a closed cardiovascular system, ensuring the exchange of gases in the lungs and body tissues.

In addition to providing tissues and organs with oxygen and removing carbon dioxide from them, blood circulation delivers nutrients, water, salts, vitamins, hormones to the cells and removes metabolic end products, and also maintains the constancy of body temperature, ensures humoral regulation and interconnection of organs and organ systems in organism.

The circulatory system consists of the heart and blood vessels that permeate all organs and tissues of the body.

Blood circulation begins in the tissues, where metabolism takes place through the walls of the capillaries. The blood, which has given oxygen to organs and tissues, enters the right half of the heart and is sent to the small (pulmonary) circle of blood circulation, where the blood is saturated with oxygen, returns to the heart, entering its left half, and again spreads throughout the body (large circle of blood circulation) ...

A heart - the main organ of the circulatory system. It is a hollow muscular organ consisting of four chambers: two atria (right and left), separated by an interatrial septum, and two ventricles (right and left), separated by an interventricular septum. The right atrium communicates with the right ventricle through the tricuspid valve, and the left atrium communicates with the left ventricle through the bicuspid valve. The weight of the heart of an adult is on average about 250 g in women and about 330 g in men. The length of the heart is 10-15 cm, the transverse size is 8-11 cm and the anteroposterior dimension is 6-8.5 cm. The heart volume in men is on average 700-900 cm 3, and in women - 500-600 cm 3.

The outer walls of the heart are formed by the heart muscle, which is similar in structure to the striated muscles. However, the heart muscle is distinguished by its ability to automatically rhythmically contract due to impulses that arise in the heart itself, regardless of external influences (heart automation).

The function of the heart consists in the rhythmic pumping of blood in the artery, coming to it through the veins. The heart beats about 70-75 times per minute at rest (1 time per 0.8 s). More than half of this time, it rests - relaxes. The continuous activity of the heart consists of cycles, each of which consists of contraction (systole) and relaxation (diastole).

There are three phases of cardiac activity:

• atrial contraction - atrial systole - takes 0.1 s
• ventricular contraction - ventricular systole - takes 0.3 s
• general pause - diastole (simultaneous relaxation of the atria and ventricles) - takes 0.4 s

Thus, during the entire cycle, the atria work 0.1 s and rest 0.7 s, the ventricles work 0.3 s and rest 0.5 s. This explains the ability of the heart muscle to work without fatigue throughout life. The high efficiency of the heart muscle is due to the increased blood supply to the heart. Approximately 10% of the blood that is expelled by the left ventricle into the aorta enters the arteries that feed the heart.

Arteries - blood vessels carrying oxygen-rich blood from the heart to organs and tissues (only the pulmonary artery carries venous blood).

The artery wall is represented by three layers: the outer connective tissue sheath; medium, consisting of elastic fibers and smooth muscles; internal, formed by the endothelium and connective tissue.

In humans, the diameter of the arteries ranges from 0.4 to 2.5 cm. The total volume of blood in the arterial system averages 950 ml. Arteries gradually branch out in a tree-like manner into smaller and smaller vessels - arterioles, which pass into capillaries.

Capillaries (from the Latin "capillus" - hair) - the smallest vessels (the average diameter does not exceed 0.005 mm, or 5 microns), penetrating the organs and tissues of animals and humans, which have a closed circulatory system. They connect small arteries - arterioles with small veins - venules. Through the walls of the capillaries, consisting of endothelial cells, there is an exchange of gases and other substances between the blood and various tissues.

Veins - blood vessels carrying blood saturated with carbon dioxide, metabolic products, hormones and other substances from tissues and organs to the heart (except for the pulmonary veins carrying arterial blood). The vein wall is much thinner and more elastic than the artery wall. Small and medium veins are equipped with valves that prevent the reverse flow of blood in these vessels. In humans, the volume of blood in the venous system averages 3200 ml.

Circles of blood circulation

The movement of blood through the vessels was first described in 1628 by the English physician W. Harvey.

In humans and mammals, blood flows through a closed cardiovascular system, consisting of a large and small circles of blood circulation (Fig.).

Small circle of blood circulation - pulmonary circle - serves to enrich blood with oxygen in the lungs. It starts from the right ventricle and ends with the left atrium.

From the right ventricle of the heart, venous blood enters the pulmonary trunk (common pulmonary artery), which soon divides into two branches - carrying blood to the right and left lungs.

In the lungs, the arteries branch out into capillaries. In the capillary networks that surround the pulmonary vesicles, the blood gives off carbon dioxide and receives a new supply of oxygen in return (pulmonary respiration). Oxygenated blood becomes scarlet, becomes arterial and flows from the capillaries into the veins, which, merging into four pulmonary veins (two on each side), flow into the left atrium of the heart. In the left atrium, the small (pulmonary) circle of blood circulation ends, and the arterial blood entering the atrium passes through the left atrioventricular opening into the left ventricle, where the systemic circulation begins. Consequently, venous blood flows in the arteries of the pulmonary circulation, and arterial blood flows in its veins.

A large circle of blood circulation - corporal - collects venous blood from the upper and lower half of the body and similarly distributes arterial blood; starts from the left ventricle and ends with the right atrium.

From the left ventricle of the heart, blood enters the largest arterial vessel - the aorta. Arterial blood contains nutrients and oxygen necessary for the vital activity of the body and has a bright scarlet color.

The aorta branches into arteries that go to all organs and tissues of the body and pass in their thickness into arterioles and further into capillaries. The capillaries, in turn, collect into venules and further into veins. Metabolism and gas exchange between blood and body tissues take place through the wall of the capillaries. The arterial blood flowing in the capillaries gives up nutrients and oxygen and in return receives metabolic products and carbon dioxide (tissue respiration). As a result, the blood entering the venous bed is poor in oxygen and rich in carbon dioxide and therefore has a dark color - venous blood; when bleeding, by the color of the blood, you can determine which vessel is damaged - an artery or a vein. The veins merge into two large trunks - the superior and inferior vena cava, which flow into the right atrium of the heart. This part of the heart ends with a large (bodily) circle of blood circulation.

The addition to the large circle is third (cardiac) circle of blood circulationserving the very heart. It begins with the coronary arteries of the heart extending from the aorta and ends with the veins of the heart. The latter merge into the coronary sinus, which flows into the right atrium, and the rest of the veins open into the atrial cavity directly.

The movement of blood through the vessels

Any liquid flows from a place where the pressure is higher to where it is lower. The greater the pressure difference, the higher the flow rate. The blood in the vessels of the large and small circle of blood circulation also moves due to the pressure difference that the heart creates by its contractions.

In the left ventricle and aorta, blood pressure is higher than in the vena cava ( negative pressure) and in the right atrium. The difference in pressure in these areas ensures the movement of blood in the systemic circulation. High pressure in the right ventricle and pulmonary artery and low pressure in the pulmonary veins and left atrium ensure the movement of blood in the pulmonary circulation.

The highest pressure in the aorta and large arteries (blood pressure). Arterial blood pressure is not constant [show]

Blood pressure - This is the pressure of blood on the walls of blood vessels and chambers of the heart, resulting from the contraction of the heart, pumping blood into the vascular system, and vascular resistance. The most important medical and physiological indicator of the state of the circulatory system is the pressure in the aorta and large arteries - blood pressure.

Arterial blood pressure is not constant. Have healthy people at rest, maximum, or systolic, blood pressure is distinguished - the level of pressure in the arteries during systole of the heart is about 120 mm Hg, and the minimum, or diastolic, is the level of pressure in the arteries during the diastole of the heart about 80 mm Hg. Those. arterial blood pressure pulsates in time with the contractions of the heart: at the time of systole, it rises to 120-130 mm Hg. Art., and during diastole decreases to 80-90 mm Hg. Art. These pulse pressure fluctuations occur simultaneously with the pulse fluctuations of the arterial wall.

As the blood moves through the arteries, part of the pressure energy is used to overcome the friction of the blood against the vessel walls, so the pressure gradually drops. A particularly significant drop in pressure occurs in the smallest arteries and capillaries - they provide the greatest resistance to the movement of blood. In the veins, the blood pressure continues to decrease gradually, and in the vena cava it is equal to or even lower than the atmospheric pressure. Indicators of blood circulation in different parts of the circulatory system are given in table. 1.

The speed of blood movement depends not only on the pressure difference, but also on the width of the bloodstream. Although the aorta is the widest vessel, but in the body it is one and all the blood flows through it, which is pushed out by the left ventricle. Therefore, the maximum speed here is 500 mm / s (see Table 1). As the arteries branch out, their diameter decreases, but the total cross-sectional area of \u200b\u200ball arteries increases and the blood velocity decreases, reaching 0.5 mm / s in the capillaries. Due to such a low rate of blood flow in the capillaries, the blood has time to give oxygen and nutrients to the tissues and take their waste products.

The slowdown in blood flow in the capillaries is explained by their huge number (about 40 billion) and a large total lumen (800 times more than the aortic lumen). The movement of blood in the capillaries is carried out by changing the lumen of the supplying small arteries: their expansion increases the blood flow in the capillaries, and the narrowing decreases it.

The veins on the way from the capillaries as they approach the heart enlarge, merge, their number and the total lumen of the bloodstream decreases, and the speed of blood movement in comparison with the capillaries increases. From table. 1 also shows that 3/4 of all blood is in the veins. This is due to the fact that the thin walls of the veins are able to easily stretch, so they can contain significantly more blood than the corresponding arteries.

The main reason for the movement of blood through the veins is the pressure difference at the beginning and end of the venous system, so the movement of blood through the veins is towards the heart. This is facilitated by the suction action of the chest ("breathing pump") and the contraction of skeletal muscles ("muscle pump"). During inhalation, the pressure in the chest decreases. In this case, the pressure difference at the beginning and at the end of the venous system increases, and the blood is directed through the veins to the heart. Skeletal muscles contract and constrict the veins, which also facilitates the movement of blood to the heart.

The relationship between the speed of blood movement, the width of the bloodstream and blood pressure is illustrated in Fig. 3. The amount of blood flowing through the vessels per unit of time is equal to the product of the blood velocity by the cross-sectional area of \u200b\u200bthe vessels. This value is the same for all parts of the circulatory system: how much blood pushes the heart into the aorta, how much it flows through the arteries, capillaries and veins, and the same amount returns back to the heart, and is equal to the minute volume of blood.

Redistribution of blood in the body

If the artery extending from the aorta to some organ expands due to the relaxation of its smooth muscles, then the organ will receive more blood. At the same time, other organs will receive less blood due to this. This is the redistribution of blood in the body. Due to the redistribution, more blood flows to the working organs due to the organs that are currently at rest.

The redistribution of blood is regulated by the nervous system: simultaneously with the expansion of the vessels in the working organs, the blood vessels of the non-working ones narrow and the blood pressure remains unchanged. But if all the arteries expand, it will lead to a fall blood pressure and to a decrease in the speed of blood flow in the vessels.

Blood circulation time

Blood circulation time is the time it takes for blood to pass through the entire circulation. A number of methods are used to measure the time of blood circulation. [show]

The principle of measuring the time of blood circulation is that a substance that is not usually found in the body is injected into a vein, and it is determined after what period of time it appears in the vein of the same name on the other side or causes its characteristic action. For example, a solution of the alkaloid lobeline is injected into the ulnar vein, acting through the blood on the respiratory center of the medulla oblongata, and the time from the moment of administration of the substance to the moment when a short-term breath holding or cough appears. This happens when lobelin molecules, having made a circuit in circulatory system, will act on the respiratory center and cause breathing changes or coughing.

In recent years, the rate of blood circulation in both circles of blood circulation (or only in a small, or only in a large circle) is determined using a radioactive sodium isotope and an electron counter. To do this, several such counters are placed on different parts of the body near large vessels and in the region of the heart. After the introduction of a radioactive sodium isotope into the cubital vein, the time of the appearance of radioactive radiation in the region of the heart and the studied vessels is determined.

The time of blood circulation in humans averages about 27 heart systoles. With 70-80 heartbeats per minute, a complete blood circulation occurs in approximately 20-23 seconds. It should not be forgotten, however, that the blood flow rate along the axis of the vessel is greater than at its walls, and also that not all vascular regions have the same length. Therefore, not all blood circulates so quickly, and the time indicated above is the shortest.

Studies on dogs have shown that 1/5 of the time of the complete blood circulation falls on the pulmonary circulation and 4/5 - on the great circle.

Regulation of blood circulation

Innervation of the heart... The heart, like other internal organs, is innervated by the autonomic nervous system and receives double innervation. The sympathetic nerves approach the heart, which intensify and accelerate its contractions. The second group of nerves - parasympathetic - acts on the heart in the opposite way: it slows down and weakens the heart contractions. These nerves regulate the heart.

In addition, the adrenal hormone, adrenaline, which enters the heart with blood and enhances its contractions, affects the work of the heart. The regulation of the work of organs with the help of substances carried by the blood is called humoral.

Nervous and humoral regulation of the heart in the body act in concert and ensure the precise adaptation of the activity of the cardiovascular system to the needs of the body and environmental conditions.

Innervation of blood vessels. The blood vessels are initiated by the sympathetic nerves. Excitation spreading through them causes a contraction of smooth muscles in the walls of blood vessels and constricts the blood vessels. If you cut the sympathetic nerves to a specific part of the body, the corresponding vessels will dilate. Consequently, along the sympathetic nerves to the blood vessels, excitement comes all the time, which keeps these vessels in a state of some constriction - vascular tone. When the arousal increases, the frequency of nerve impulses increases and the vessels narrow more - vascular tone increases. On the contrary, with a decrease in the frequency of nerve impulses due to inhibition of sympathetic neurons, the vascular tone decreases and the blood vessels expand. To the vessels of some organs (skeletal muscles, salivary glands) in addition to vasoconstrictor, vasodilating nerves are also suitable. These nerves are excited and dilate the blood vessels of the organs as they work. The lumen of the vessels is also affected by substances that are carried by the blood. Adrenaline constricts the blood vessels. Another substance - acetylcholine - secreted by the endings of some nerves, expands them.

Regulation of the activity of the cardiovascular system. The blood supply to the organs changes depending on their needs due to the described redistribution of blood. But this redistribution can only be effective if the pressure in the arteries does not change. One of the main functions of the nervous regulation of blood circulation is to maintain a constant blood pressure. This function is carried out reflexively.

There are receptors in the wall of the aorta and carotid arteries that become more irritated if the blood pressure is above normal levels. Excitation from these receptors goes to the vasomotor center, located in the medulla oblongata, and inhibits its work. From the center along the sympathetic nerves to the vessels and heart, a weaker excitation begins to flow than before, and the blood vessels dilate, and the heart weakens its work. As a result of these changes, blood pressure drops. And if the pressure for some reason falls below normal, then the irritation of the receptors stops completely and the vaso-motor center, without receiving inhibitory influences from the receptors, intensifies its activity: it sends more nerve impulses to the heart and blood vessels per second, the vessels narrow, the heart contracts, more often and stronger, blood pressure rises.

Cardiac hygiene

Normal activity of the human body is possible only with a well-developed cardiovascular system. The blood flow rate will determine the degree of blood supply to organs and tissues and the rate of removal of waste products. During physical work, the organs' demand for oxygen increases simultaneously with the intensification and acceleration of heart contractions. Only a strong heart muscle can provide such work. To be resilient to varied labor activity, it is important to train the heart, to increase the strength of its muscles.

Physical labor, physical education develop the heart muscle. To ensure the normal function of the cardiovascular system, a person should start his day with morning exercises, especially people whose professions are not associated with physical labor. To enrich the blood with oxygen, exercise is best done outdoors.

It must be remembered that excessive physical and mental stress can cause disruption of the normal functioning of the heart, its diseases. Special bad influence alcohol, nicotine, drugs affect the cardiovascular system. Alcohol and nicotine poison the heart muscle and nervous system, cause sharp disturbances in the regulation of vascular tone and heart activity. They lead to the development of severe diseases of the cardiovascular system and can cause sudden death. Young people who smoke and drink alcohol are more likely than others to have spasms of the heart vessels, causing severe heart attacks and sometimes death.

First aid for injuries and bleeding

Trauma is often accompanied by bleeding. Distinguish between capillary, venous and arterial bleeding.

Capillary bleeding occurs even with a minor injury and is accompanied by a slow flow of blood from the wound. Such a wound should be treated with a solution of brilliant green (brilliant green) for disinfection and a clean gauze bandage should be applied. The dressing stops bleeding, promotes blood clot formation, and prevents germs from entering the wound.

Venous bleeding is characterized by a significantly higher rate of blood flow. The leaking blood is dark in color. To stop bleeding, it is necessary to apply a tight bandage below the wound, that is, further from the heart. After stopping bleeding, the wound is treated with a disinfectant (3% solution of peroxide hydrogen, vodka), bandaged with a sterile pressure bandage.

With arterial bleeding, scarlet blood gushes from the wound. This is the most dangerous bleeding. If the artery of the limb is damaged, it is necessary to raise the limb as high as possible, bend it and press the wounded artery with a finger in the place where it is close to the surface of the body. It is also necessary above the wound site, that is, closer to the heart, to apply a rubber band (you can use a bandage, rope for this) and tighten it tightly to completely stop the bleeding. The tourniquet should not be kept tightened for more than 2 hours. When applying it, you must attach a note in which you should indicate the time of the tourniquet application.

It should be remembered that venous, and even more so arterial bleeding can lead to significant blood loss and even death. Therefore, in case of injury, it is necessary to stop the bleeding as soon as possible, and then take the victim to the hospital. Strong pain or fright can cause the person to pass out. Loss of consciousness (fainting) is the result of inhibition of the vasomotor center, a drop in blood pressure, and insufficient blood supply to the brain. The unconscious person should be given a sniff of some non-toxic substance with a strong odor (for example, ammonia), moisten his face with cold water or lightly pat his cheeks. When olfactory or skin receptors are irritated, excitation from them enters the brain and removes the inhibition of the vasomotor center. Blood pressure rises, the brain receives adequate nutrition, and consciousness returns.