How blood flows through the circulation. Circulation

Blood constantly circulates throughout the body, providing transport various substances. It consists of plasma and suspension various cells(the main ones are red blood cells, leukocytes and platelets) and moves along a strict route - the system of blood vessels.

Venous blood - what is it?

Venous – blood that returns to the heart and lungs from organs and tissues. It circulates through the pulmonary circulation. The veins through which it flows lie close to the surface of the skin, so the venous pattern is clearly visible.

This is partly due to a number of factors:

1. It is thicker, rich in platelets, and when damaged venous bleeding easier to stop.
2. The pressure in the veins is lower, so if a vessel is damaged, the amount of blood loss is lower.
3. Its temperature is higher, so it additionally prevents rapid loss heat through the skin.

The same blood flows in both arteries and veins. But its composition is changing. From the heart it enters the lungs, where it is enriched with oxygen, which it transfers to the internal organs, providing them with nutrition. The veins that carry arterial blood are called arteries. They are more elastic, blood moves through them in spurts.

Arterial and venous blood do not mix in the heart. The first passes along the left side of the heart, the second - along the right. They mix only when serious pathologies heart, which entails a significant deterioration in well-being.

What is the systemic and pulmonary circulation?

From the left ventricle, the contents are pushed out and enter the pulmonary artery, where they are saturated with oxygen. Then it is carried throughout the body through arteries and capillaries, carrying oxygen and nutrients.

The aorta is the largest artery, which is then divided into superior and inferior. Each of them supplies blood to the upper and bottom part bodies accordingly. Since the arterial system “flows around” absolutely all organs and is supplied to them with the help of a branched system of capillaries, this circle of blood circulation is called large. But the arterial volume is about 1/3 of the total.

Blood flows through the pulmonary circulation, which has given up all the oxygen and “taken away” metabolic products from the organs. It flows through the veins. The pressure in them is lower, the blood flows evenly. It returns through the veins to the heart, from where it is then pumped to the lungs.

How are veins different from arteries?

Arteries are more elastic. This is due to the fact that they need to maintain a certain speed of blood flow in order to deliver oxygen to the organs as quickly as possible. The walls of the veins are thinner and more elastic. This is due to the lower speed of blood flow, as well as the large volume (venous is about 2/3 of the total volume).

What kind of blood is in the pulmonary vein?

The pulmonary arteries ensure the flow of oxygenated blood into the aorta and its further circulation throughout the systemic circulation. The pulmonary vein returns some of the oxygenated blood to the heart to nourish the heart muscle. It is called a vein because it supplies blood to the heart.

What is venous blood rich in?

When the blood reaches the organs, it gives them oxygen, in return it is saturated with metabolic products and carbon dioxide, and acquires a dark red hue.

A large amount of carbon dioxide is the answer to the question why venous blood is darker than arterial blood and why veins are blue. It also contains nutrients that are absorbed into digestive tract, hormones and other substances synthesized by the body.

Its saturation and density depend on which vessels the venous blood flows through. The closer to the heart, the thicker it is.

Why are tests taken from a vein?

This is due to the type of blood in the veins - rich in products metabolism and vital functions of organs. If a person is sick, it contains certain groups of substances, remains of bacteria and other pathogenic cells. In a healthy person, these impurities are not detected. By the nature of the impurities, as well as by the level of concentration of carbon dioxide and other gases, the nature of the pathogenic process can be determined.

The second reason is that venous bleeding when a vessel is punctured is much easier to stop. But there are times when bleeding from a vein for a long time doesn't stop. This is a sign of hemophilia, low content platelets. In this case, even a minor injury can be very dangerous for a person.

How to distinguish venous bleeding from arterial bleeding:

1. Assess the volume and nature of leaking blood. The venous flows out in a uniform stream, the arterial flows out in portions and even in “fountains”.
2. Determine what color the blood is. Bright scarlet points to arterial bleeding, dark burgundy - for venous.
3. Arterial is more liquid, venous is thicker.

Why does venous clot faster?

It is thicker and contains a large number of platelets. The low speed of blood flow allows the formation of a fibrin mesh at the site of vessel damage, to which platelets “cling.”

How to stop venous bleeding?

With minor damage to the veins of the extremities, it is often enough to create an artificial outflow of blood by raising an arm or leg above the level of the heart. A tight bandage should be applied to the wound itself to minimize blood loss.

If the injury is deep, a tourniquet should be placed above the damaged vein to limit the amount of blood flowing to the injury site. In summer you can keep it for about 2 hours, in winter - for an hour, maximum one and a half. During this time, you need to have time to deliver the victim to the hospital. If you hold the tourniquet longer than the specified time, tissue nutrition will be disrupted, which threatens necrosis.

It is advisable to apply ice to the area around the wound. This will help slow down your blood circulation.

Video

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

Arteries- these are vessels, blood bearers from the heart.
Vienna- These are 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 there is arterial blood, in the right - venous, mixing does not occur due to a complete septum in the ventricle).

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

The thickest wall is at the left ventricle, because it pushes blood through the systemic circulation. When the left ventricle contracts, a pulse wave is created, as well as maximum blood pressure.

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

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

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

Answer

Choose three correct answers out of six and write down the numbers under which they are indicated. 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 left half hearts

Answer

1. Establish the sequence of human blood vessels in order of decreasing size blood pressure. Write down the corresponding sequence of numbers.
1) inferior vena cava
2) aorta
3) pulmonary capillaries
4) pulmonary artery

Answer

2. Set the order in which to arrange blood vessels in order of decreasing blood pressure
1) Veins
2) Aorta
3) Arteries
4) Capillaries

Answer

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

Answer

Choose the one that suits you best correct option. Why can't blood get from the aorta to the left ventricle of the heart?
1) the ventricle contracts with great strength and creates high pressure
2) semilunar valves fill with blood and close tightly
3) leaflet valves are pressed against the walls of the aorta
4) leaflet valves are closed and semilunar valves are open

Answer

Choose one, the most correct option. Blood enters the pulmonary circulation from the right ventricle through
1) pulmonary veins
2) pulmonary arteries
3) carotid arteries
4) aorta

Answer

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

Answer

Choose one, the most correct option. In mammals, blood is enriched with oxygen in
1) arteries of the pulmonary circulation
2) capillaries of the great circle
3) arteries of the great circle
4) capillaries of the small circle

Answer

1. Establish the sequence of blood movement 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) right atrium
6) inferior vena cava

Answer

2. Define correct sequence blood circulation in the systemic circulation, starting from 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 passage 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 torso
4) aorta
5) inferior and superior vena cava
6) capillaries

Answer

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

Answer

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

Answer

Choose one, the most correct option. The vena cava in the human body drains into
1) left atrium
2) right ventricle
3) left ventricle
4) right atrium

Answer

Choose one, the most correct option. Reverse flow of blood from pulmonary artery and the aortas into the ventricles are prevented by valves
1) tricuspid
2) venous
3) double-leaf
4) semilunar

Answer

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

Answer

2. Establish the sequence of circulatory processes, starting from 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 comes from the alveoli to the capillaries
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 it is saturated with oxygen in the capillaries of the pulmonary circle. Write down the corresponding sequence of numbers.
1) left ventricle
2) left atrium
3) veins of the small circle
4) small circle capillaries
5) arteries of the great circle

Answer

4. Establish the 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) capillaries of the lungs

Answer

5. Establish the correct sequence of passage of a portion 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) right ventricle
5) right atrium
6) aorta

Answer

Establish the sequence of events occurring in cardiac cycle after blood enters the heart. Write down the corresponding sequence of numbers.
1) contraction of the ventricles
2) general relaxation of the ventricles and atria
3) blood flow into the aorta and artery
4) blood flow into the ventricles
5) atrial contraction

Answer

Establish a correspondence between human blood vessels and the direction of blood movement in them: 1) from the heart, 2) to the heart
A) veins of the pulmonary circulation
B) veins of the systemic circulation
B) arteries of the pulmonary circulation
D) arteries of the systemic 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 the greater circulation
6) under slight pressure enters the pulmonary circulation

Answer

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

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

Answer

Choose three options. Blood flows through the arteries of the systemic circulation in humans
1) from the heart
2) to the heart
3) saturated with carbon dioxide
4) oxygenated
5) faster than in other blood vessels
6) slower than in 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
B) aorta and arteries of the systemic circulation
D) superior and inferior 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 numbers 1 and 2 in the order corresponding to the letters.
A) femoral vein
B) brachial artery
B) pulmonary vein
D) subclavian artery
D) pulmonary artery
E) aorta

Answer

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

Answer

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 fall off
3) have walls made 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

Analyze the table “The work of the human heart.” For each cell indicated by a letter, select the corresponding 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) vena cava
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 leaks 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 the circles of blood circulation for which they are characteristic: 1) small, 2) large. Write 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.
B) Arterial blood flows through the arteries.
D) The circle begins in the left ventricle.
D) Gas exchange occurs in the capillaries of the alveoli.
E) Education occurs venous blood from the arterial

Answer

Find three errors in the given text. Indicate the numbers of the proposals in which they are made.(1) The walls of arteries and veins have a three-layer structure. (2) The walls of the arteries are very elastic and elastic; The walls of the veins, on the contrary, are inelastic. (3) When the atria contract, 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 blood movement in capillaries is higher than in veins. (7) Blood in the human body moves through two circulation circles.

Answer

Choose three correctly labeled captions for the picture that shows internal structure hearts. Write down the numbers under which they are indicated.
1) superior vena cava
2) aorta
3) pulmonary vein
4) left atrium
5) right atrium
6) inferior vena cava

Answer

Choose three correctly labeled captions for the picture that depicts the structure of the human heart. Write down the numbers under which they are indicated.
1) superior vena cava
2) flap valves
3) right ventricle
4) semilunar valves
5) left ventricle
6) pulmonary artery

Answer

© D.V. Pozdnyakov, 2009-2019

This is the 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 cells and removes metabolic end products, and also maintains a constant body temperature, ensures humoral regulation and the interconnection of organs and organ systems in body.

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

Blood circulation begins in the tissues where metabolism occurs through the walls of the capillaries. The blood, which has given oxygen to the organs and tissues, enters the right half of the heart and is sent by it to the pulmonary circulation, where the blood is saturated with oxygen, returns to the heart, entering its left half, and is again distributed throughout the body (systemic circulation) .

Heart - main body circulatory system. It is a hollow muscular organ, consisting of four chambers: two atria (right and left), separated interatrial septum, and two ventricles (right and left), separated interventricular septum. The right atrium communicates with the right ventricle through the tricuspid, and the left atrium communicates with the left ventricle through bicuspid valve. The average weight of an adult human heart is about 250 g in women and about 330 g in men. Heart length 10-15 cm, cross dimension 8-11 cm and anteroposterior - 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 cardiac muscle, which is similar in structure to striated muscles. However, the heart muscle is distinguished by its ability to contract rhythmically automatically due to impulses arising in the heart itself, regardless of external influences(automatic heart).

The function of the heart is to rhythmically pump blood into the arteries, which comes to it through the veins. The heart beats about 70-75 times per minute when the body is 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:

• contraction of the atria - atrial systole - takes 0.1 s
• contraction of the ventricles - 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 for 0.1 s and rest for 0.7 s, the ventricles work for 0.3 s and rest for 0.5 s. This explains the ability of the heart muscle to work without getting tired throughout life. The high performance of the heart muscle is due to increased blood supply to the heart. Approximately 10% of the blood ejected by the left ventricle into the aorta enters the arteries that branch from it, which supply the heart.

Arteries- blood vessels that carry oxygenated 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 membrane; middle, consisting of elastic fibers and smooth muscles; internal, formed by endothelium and connective tissue.

In humans, the diameter of the arteries ranges from 0.4 to 2.5 cm. The total blood volume in arterial system averages 950 ml. The arteries gradually branch into trees into more and more small vessels- arterioles that turn into capillaries.

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

Vienna- blood vessels carrying blood saturated with carbon dioxide, metabolic products, hormones and other substances from tissues and organs to the heart (with the exception of the pulmonary veins, which carry arterial blood). The wall of a vein is much thinner and more elastic than the wall of an artery. Small and medium-sized veins are equipped with valves that prevent blood from flowing back into these vessels. A person's blood volume is venous system averages 3200 ml.

Circulation circles

The movement of blood through vessels was first described in 1628. English doctor V. Harvey.

In humans and mammals, blood moves through a closed cardiovascular system, consisting of the systemic and pulmonary circulation (Fig.).

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

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

In the lungs, arteries branch into capillaries. IN capillary networks, entwining the pulmonary vesicles, the blood gives up carbon dioxide and receives in return a new supply of oxygen (pulmonary respiration). Blood saturated with oxygen acquires a scarlet color, 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. The pulmonary circulation ends in the left atrium, and 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.

Systemic circulation- bodily - collects venous blood from the upper and lower half of the body and similarly distributes arterial blood; starts from the left ventricle and ends at the right atrium.

From the left ventricle of the heart, blood enters the largest arterial vessel- aorta. Arterial blood contains the nutrients and oxygen necessary for the body to function and is bright scarlet in color.

The aorta branches into arteries that go to all organs and tissues of the body and pass through them into arterioles and then into capillaries. The capillaries, in turn, gather into venules and then into veins. Through the capillary wall, metabolism and gas exchange occurs between the blood and body tissues. Arterial blood flowing in the capillaries gives off 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, you can determine by the color of the blood 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 section of the heart ends the systemic (bodily) circulation.

The complement to the great circle is third (cardiac) circle of blood circulation, serving the heart itself. It begins with the coronary arteries of the heart emerging 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 remaining veins open directly into the atrium cavity.

Movement of blood through 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 speed. Blood in the vessels of the systemic and pulmonary circulation also moves due to the pressure difference created by the heart through 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 pressure difference 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 pressure is highest in the aorta and large arteries (blood pressure). Blood pressure is not constant [show]

Blood pressure- this is the pressure of blood on the walls of the 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 a constant value. U healthy people at rest, the maximum, or systolic, blood pressure is distinguished - the level of pressure in the arteries during heart systole is about 120 mmHg, and the minimum, or diastolic, is the level of pressure in the arteries during diastole of the heart is about 80 mmHg. Those. arterial blood pressure pulsates in time with the contractions of the heart: at the moment of systole it rises to 120-130 mm Hg. Art., and during diastole it decreases to 80-90 mm Hg. Art. These pulse pressure fluctuations occur simultaneously with pulse fluctuations of the arterial wall.

As blood moves through the arteries, part of the pressure energy is used to overcome the friction of the blood against the walls of the vessels, so the pressure gradually drops. A particularly significant drop in pressure occurs in the smallest arteries and capillaries - they offer the greatest resistance to blood movement. In the veins, blood pressure continues to gradually decrease, and in the vena cava it is equal to atmospheric pressure or even below it. Blood circulation indicators in different departments 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, it is the only one in the body 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, their diameter decreases, but the total cross-sectional area of ​​all arteries increases and the speed of blood movement decreases, reaching 0.5 mm/s in the capillaries. Due to such a low speed of blood flow in the capillaries, the blood has time to give oxygen and nutrients to the tissues and accept their waste products.

The slowing down of blood flow in the capillaries is explained by their a huge amount(about 40 billion) and a large total lumen (800 times larger than the lumen of the aorta). The movement of blood in the capillaries is carried out due to changes in the lumen of the supplying small arteries: their expansion increases blood flow in the capillaries, and narrowing decreases it.

The veins on the way from the capillaries, as they approach the heart, enlarge and merge, their number and the total lumen of the bloodstream decrease, and the speed of blood movement increases compared to the capillaries. From the table 1 also shows that 3/4 of all blood is in the veins. This is due to the fact that thin walls veins can 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 occurs in the direction of the heart. This is facilitated by the suction action chest(“respiratory pump”) and contraction of skeletal muscles (“muscle pump”). During inhalation, the pressure in the chest decreases. In this case, the pressure difference at the beginning and end of the venous system increases, and blood through the veins is directed to the heart. Skeletal muscles contract and compress the veins, which also helps move 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 per unit time through the vessels is equal to the product of the speed of blood movement and the cross-sectional area of ​​the vessels. This value is the same for all parts of the circulatory system: the amount of blood the heart pushes into the aorta, the same amount 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 how blood is redistributed in the body. Due to redistribution, more blood flows to working organs at the expense of organs that are currently at rest.

Blood redistribution is regulated nervous system: simultaneously with the dilation of blood vessels in working organs, the blood vessels of non-working organs narrow and blood pressure remains unchanged. But if all the arteries dilate, it will lead to a fall blood pressure and to a decrease in the speed of blood movement in the vessels.

Blood circulation time

Blood circulation time is the time required for blood to pass through the entire circulation. A number of methods are used to measure blood circulation time [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 effect. For example, in ulnar vein inject a solution of the alkaloid lobeline, which acts through the blood on respiratory center medulla oblongata, and determine the time from the moment of administration of the substance to the moment when a short-term breath holding or cough appears. This occurs when lobeline molecules, having completed a cycle in circulatory system, will affect the respiratory center and cause changes in breathing or coughing.

IN last years the speed of blood circulation in both circles of blood circulation (or only in the small, or only in the major circle) is determined using a radioactive sodium isotope and an electron counter. To do this, several such counters are placed on different parts bodies near large vessels and in the heart area. After introducing a radioactive sodium isotope into the cubital vein, the time of appearance of radioactive radiation in the area of ​​the heart and the vessels under study is determined.

The blood circulation time in humans is on average approximately 27 heart systoles. At 70-80 heart beats per minute, complete blood circulation occurs in approximately 20-23 seconds. We must not forget, however, that the speed of blood flow along the axis of the vessel is greater than at its walls, and also that not all vascular areas 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 complete blood circulation is in the pulmonary circulation and 4/5 in the systemic circulation.

Regulation of blood circulation

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

In addition, the functioning of the heart is influenced by the adrenal hormone - adrenaline, which enters the heart with the blood and increases its contractions. The regulation of organ function 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 precise adaptation of activity of cardio-vascular system to the needs of the body and environmental conditions.

Innervation of blood vessels. Blood vessels are supplied by sympathetic nerves. Excitation spreading through them causes contraction of smooth muscles in the walls of blood vessels and narrows the blood vessels. If you cut the sympathetic nerves going to a certain part of the body, the corresponding vessels will dilate. Consequently, excitation constantly flows through the sympathetic nerves to the blood vessels, which keeps these vessels in a state of certain constriction - vascular tone. When the excitation increases, the frequency nerve impulses increases and the vessels narrow more strongly - vascular tone increases. On the contrary, when the frequency of nerve impulses decreases due to inhibition of sympathetic neurons, vascular tone decreases and blood vessels dilate. To the vessels of some organs (skeletal muscles, salivary glands) in addition to vasoconstrictors, vasodilator nerves are also suitable. These nerves are stimulated and dilate the blood vessels of the organs as they work. The lumen of blood vessels is also affected by substances carried by the blood. Adrenaline constricts blood vessels. Another substance, acetylcholine, secreted by the endings of some nerves, dilates them.

Regulation of the cardiovascular system. The blood supply to 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 nervous regulation blood circulation is to maintain constant blood pressure. This function is carried out reflexively.

In the wall of the aorta and carotid arteries There are receptors that are more irritated if blood pressure exceeds normal level. Excitation from these receptors goes to the vasomotor center located in medulla oblongata, and slows down its work. From center to sympathetic nerves weaker excitation begins to flow to the vessels and heart than before, and the blood vessels dilate, and the heart weakens its work. Due to these changes, blood pressure decreases. And if the pressure for some reason drops below normal, then the irritation of the receptors stops completely and the vasomotor center, without receiving inhibitory influences from the receptors, increases its activity: it sends more nerve impulses per second to the heart and blood vessels, the vessels narrow, the heart contracts more often and stronger, blood pressure rises.

Cardiac hygiene

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

Physical labor and physical education develop the heart muscle. To provide normal function cardiovascular system, a person should start his day with morning exercises, especially people whose professions are not related to physical labor. To enrich the blood with oxygen physical exercise It's best to do it outdoors.

It must be remembered that excessive physical and mental stress may cause disruption normal operation heart and its diseases. Especially bad influence Alcohol, nicotine, and drugs affect the cardiovascular system. Alcohol and nicotine poison the heart muscle and nervous system, causing sudden violations regulation of vascular tone and cardiac activity. They lead to development serious illnesses cardiovascular system and can cause sudden death. Young people who smoke and drink alcohol are more likely than others to experience heart spasms, which can cause severe heart attacks and sometimes death.

First aid for wounds and bleeding

Injuries are often accompanied by bleeding. There are 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 apply a clean gauze bandage. The bandage stops bleeding, promotes the formation of a blood clot and prevents germs from entering the wound.

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

During arterial bleeding, scarlet blood gushes from the wound. This is the most dangerous bleeding. If an artery in a limb is damaged, you need to raise the limb as high as possible, bend it and press the wounded artery with your finger in the place where it comes 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 tourniquet (you can use a bandage or rope for this) and tighten it tightly to completely stop the bleeding. The tourniquet should not be kept tight for more than 2 hours. When applying it, you must attach a note in which you should indicate the time of application of the tourniquet.

It should be remembered that venous, and even more so, arterial bleeding can lead to significant blood loss and even death. Therefore, if injured, it is necessary to stop the bleeding as soon as possible, and then take the victim to the hospital. Strong pain or fear can cause a person to lose consciousness. Loss of consciousness (fainting) is a consequence of inhibition of the vasomotor center, a drop in blood pressure and insufficient blood supply to the brain. The person who has lost consciousness should be given some non-toxic substance to smell. strong odor substance (for example ammonia), wet your face cold water or lightly pat his cheeks. When olfactory or skin receptors are irritated, excitation from them enters the brain and relieves inhibition of the vasomotor center. Blood pressure rises, the brain receives adequate nutrition, and consciousness returns.

Ensures the flow of lymph and blood to the heart.

The veins of the systemic circulation are closed system vessels that collect oxygen-depleted blood from all body cells and tissues, united by the following subsystems:

• cardiac veins;
• superior vena cava;
• inferior vena cava.

Difference between venous and arterial blood

Venous blood is the blood that flows back from all cellular systems and tissues, saturated with carbon dioxide, containing metabolic products.

Medical manipulations and studies are carried out mainly with blood that contains metabolic end products and a smaller amount of glucose.

This is the blood that flows to all cells and tissues from the heart muscle, saturated with oxygen and hemoglobin, containing nutrients.

Oxygenated arterial blood circulates through the arteries of the systemic circulation and the veins of the pulmonary circulation.

Vein structure

The walls are much thinner than arterial ones, since the blood flow speed and pressure in them is lower. Their elasticity is lower than that of arteries. The valves of the vessels are usually located opposite, which prevents the reverse flow of blood. IN large quantities The valves of the veins are located in the lower extremities. The veins are also located from the folds of the inner membrane, which have special elasticity. In the arms and legs there are venous vessels located between the muscles, this, when muscle contraction, allows blood to return back to the heart.

The large circle originates in the left ventricle of the heart, and the aorta emerges from it with a diameter of up to three centimeters. Next, the oxygenated blood of the arteries flows through vessels of decreasing diameter to all organs. Having given everything useful material, the blood is saturated with carbon dioxide and goes back through the venous system through the smallest vessels - venules, while the diameter gradually increases, approaching the heart. Venous blood from the right atrium is pushed into the right ventricle, and the pulmonary circulation begins. Entering the lungs, the blood is filled with oxygen again. Arterial blood enters the left atrium through the veins, which is then pushed into the left ventricle of the heart, and the circle repeats again.

The arteries and veins of the systemic circulation include the aorta, as well as the smaller, superior and inferior hollow vessels branching from it.

Small capillaries make up an area of ​​about one and a half thousand square meters in the human body.

The veins of the systemic circulation carry depleted blood, except for the umbilical and pulmonary veins, which carry arterial, oxygenated blood.

Cardiac vein system

These include:

• cardiac veins, which go directly into the heart cavity;
• coronary sinus;
• great cardiac vein;
• left gastric posterior vein;
• left atrial oblique vein;
• anterior vessels of the heart;
• average and small vein;
• atrial and ventricular;
• the smallest venous vessels of the heart;
• atrioventricular.

The driving force of blood flow is the energy given by the heart, as well as the pressure difference in the sections of the vessels.

Superior vena cava system

The superior vena cava takes venous blood from the upper part of the body - head, neck, sternum and partially abdominal cavity and enters the right atrium. There are no vascular valves. The process is as follows: blood saturated with carbon dioxide superior vein flows into the pericardial region, lower - into the region of the right atrium. The superior vena cava system is divided into the following parts:

1. The upper hollow is a small vessel, 5-8 cm long, 2.5 cm in diameter.
2. The azygos is a continuation of the right ascending lumbar vein.
3. Hemizygos is a continuation of the left ascending lumbar vein.
4. Posterior intercostal - collection of veins of the back, its muscles, external and internal vertebral plexuses.
5. Intravertebral venous connections - located inside spinal canal.
6. Brachiocephalic - roots of the upper hollow.
7. Vertebral - location in the diametrical foramina of the cervical vertebrae.
8. Deep cervical - collection of venous blood from the occipital region along the carotid artery.
9. Inner chest.

Inferior vena cava system

The inferior vena cava is a connection of the iliac veins on both sides in the area of ​​4 - 5 lumbar vertebrae, takes venous blood lower sections bodies. The inferior vena cava is one of the largest veins in the body. It is about 20 cm long, up to 3.5 cm in diameter. Thus, from the lower hollow there is an outflow of blood from the legs, pelvis and abdomen. The system is divided into the following components:

Portal vein

Portal vein got its name due to the entry of the trunk into the gates of the liver, as well as the collection of venous blood from the digestive organs - the stomach, spleen, large and small intestines. Its vessels are located behind the pancreas. The length of the vessel is 500-600 mm, in diameter - 110-180 mm.

The tributaries of the visceral trunk are the superior mesenteric, inferior mesenteric and splenic vessels.

The system basically includes the vessels of the stomach, large intestine and fine sections, pancreas, gallbladder and spleen. In the liver it divides into right and left and then branches into smaller veins. Eventually they merge into central veins liver, sublobular veins of the liver. And eventually three or four hepatic vessels are formed. Thanks to this system, the blood of the digestive organs passes through the liver, entering the inferior vena cava subsystem.

Upper mesenteric vein accumulates blood in the roots of the mesentery small intestine from ileum, pancreatic, right and middle colon, ileal colon and right ventricular-epiploic veins.

The inferior mesenteric vein is formed from the superior rectal, sigmoid and left colic veins.

The splenic vein combines splenic blood, stomach blood, duodenum and pancreas.

Jugular vein system

The jugular vein vessel runs from the base of the skull to the supraclavicular cavity. The systemic circulation includes these veins, which are the key collectors of blood from the head and neck. In addition to the internal blood, the external one also collects blood from the head and soft tissues. jugular vein. The external one begins in the area of ​​the auricle and goes down along the sternocleidomastoid muscle.

Veins coming from the external jugular:

• posterior ear - collection of venous blood for auricle;
• occipital branch - collection from the venous plexus of the head;
• suprascapular - receiving blood from formations of the periosteal cavity;
• transverse veins of the neck - satellites of the transverse cervical arteries;
• anterior jugular - consists of the mental veins, veins of the maxillohyoid and sternothyroid muscles.

The internal jugular vein begins in the jugular cavity of the skull, being a satellite of the external and internal carotid arteries.

Great circle functions

It is thanks to the continuous movement of blood in the arteries and veins of the systemic circulation that the main functions of the system are ensured:

• transportation of substances to ensure the functions of cells and tissues;
• -transport necessary chemical substances for metabolic reactions in cells;
• sampling of cell and tissue metabolites;
• connection of tissues and organs with each other through blood;
• transport to cells protective equipment;
• fence harmful substances from the body;
• heat exchange.

The vessels of this circulatory circle represent an extensive network that supplies blood to all organs, in contrast to the small circle. Optimal functioning of the system of the superior and inferior vena cava leads to adequate blood supply to all organs and tissues.

In the human body, there are two circles of blood circulation: large (systemic) and small (pulmonary). The systemic circle originates in the left ventricle and ends in the right atrium. The arteries of the systemic circulation carry out metabolism, carry oxygen and nutrition. In turn, the arteries of the pulmonary circulation enrich the blood with oxygen. Metabolic products are removed through the veins.

Arteries of the systemic circulation moves blood from the left ventricle first through the aorta, then through the arteries to all organs of the body, and this circle ends in the right atrium. The main purpose of this system is to deliver oxygen and nutrients to the organs and tissues of the body. Metabolic products are removed through veins and capillaries. The main function of the pulmonary circulation is the process of gas exchange in the lungs.

Arterial blood, which moves through the arteries, having passed its path, passes into the venous. After most of the oxygen has been given away and carbon dioxide has passed from the tissues into the blood, it becomes venous. All small vessels (venules) are collected in large veins systemic circulation. They are the superior and inferior vena cava.