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 erythrocytes, 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, saturated with platelets, and when damaged venous bleeding easier to stop.
2. The pressure in the veins is lower, so when the vessel is damaged, the volume of blood loss is lower.
3. Its temperature is higher, so it additionally prevents quick 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, the blood moves through them in jerks.

Arterial and venous blood do not mix in the heart. The first passes on the left side of the heart, the second - on the right. They only mix serious pathologies heart, which leads to 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 spreads through the arteries and capillaries throughout the body, carrying oxygen and nutrients.

The aorta is the largest artery, which then divides into superior and inferior. Each of them supplies blood to the upper and lower part bodies, respectively. Since the arterial “flows around” absolutely all organs, is supplied to them with the help of an extensive system of capillaries, this circle of blood circulation is called large. But the volume of the arterial at the same time is about 1/3 of the total.

Blood flows through the pulmonary circulation, which gave up all the oxygen, and "took" metabolic products from the organs. It flows through the veins. The pressure in them is lower, the blood flows evenly. Through the veins, it returns 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 rate of blood flow in order to deliver oxygen to the organs as quickly as possible. The walls of the veins are thinner, more elastic. This is due to a lower blood flow rate, as well as a large volume (venous is about 2/3 of the total volume).

What kind of blood is in the pulmonary vein?

The pulmonary arteries provide oxygenated blood to the aorta and its further circulation through the systemic circulation. The pulmonary vein returns some of the oxygenated blood to the heart to feed the heart muscle. It is called a vein because it brings blood to the heart.

What is saturated in venous blood?

Coming to the organs, the blood 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.

Venous blood flow depends on its saturation and density. The closer to the heart, the thicker it is.

Why are tests taken from a vein?

This is due to the kind of blood in the veins - saturated with products metabolism and vital activity of organs. If a person is sick, it contains certain groups of substances, the remains of bacteria and other pathogenic cells. In a healthy person, these impurities are not found. By the nature of impurities, as well as by the level of concentration of carbon dioxide and other gases, it is possible to determine the nature of the pathogenic process.

The second reason is that venous bleeding during a vessel puncture is much easier to stop. But there are times when bleeding from a vein for a long time does not stop. This is a symptom of hemophilia low content platelets. In this case, even a small injury can be very dangerous for a person.

How to distinguish venous bleeding from arterial:

1. Assess the volume and nature of the flowing blood. The venous one flows out in a uniform stream, the arterial one is thrown out in portions and even "fountains".
2. Assess 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 the venous fold faster?

It is thicker, contains a large number of platelets. A low blood flow rate allows the formation of a fibrin network at the site of damage to the vessel, for which platelets “cling”.

How to stop venous bleeding?

With a slight damage to the veins of the limbs, it is 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 applied to the area above the injured vein to limit the amount of blood flowing to the injury site. In summer it can be kept for about 2 hours, in winter - for an hour, a maximum of one and a half. During this time, you need to have time to deliver the victim to the hospital. If you keep the tourniquet longer than the specified time, tissue nutrition will be disturbed, which threatens with necrosis.

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

Video

arterial blood is oxygenated blood.
Deoxygenated blood- saturated with carbon dioxide.

arteries are the vessels carrying blood from the heart.
Vienna 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, blood is arterial, 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 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 in the left ventricle, because it pushes blood through the systemic circulation. With the contraction of the left ventricle, a pulse wave is created, as well as maximum blood pressure.

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

big circle blood circulation: from the left ventricle, arterial blood travels through the arteries to all organs of the body. in the capillaries great circle gas exchange occurs: oxygen moves from the blood to the tissues, and carbon dioxide from tissues to blood. The blood becomes venous, through the vena cava enters right atrium and from there to the right ventricle.

Small circle: From the right ventricle, venous blood flows through the pulmonary arteries to the lungs. In the capillaries of the lungs, gas exchange occurs: 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.

Establish a correspondence between the sections of the circulatory system and the circle of blood circulation to which they belong: 1) the systemic circle of blood circulation, 2) the small circle of blood circulation. Write the 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 from six and write down the numbers under which they are indicated. The systemic circulation in the human body
1) begins in the left ventricle
2) originates in the right ventricle
3) 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 into left half hearts

Answer

1. Set the sequence of human blood vessels in decreasing order in them 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 place blood vessels in order of decreasing blood pressure
1) Veins
2) Aorta
3) Arteries
4) Capillaries

Answer

Establish a correspondence between the vessels and circles of human circulation: 1) pulmonary circulation, 2) systemic circulation. Write the 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 most 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) the semilunar valves fill with blood and close tightly
3) leaf valves are pressed against the walls of the aorta
4) the cuspid valves are closed and the 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 in the human body flows through
1) renal veins
2) pulmonary veins
3) vena cava
4) pulmonary arteries

Answer

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

Answer

1. Establish the 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) right atrium
6) inferior vena cava

Answer

2. Determine 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 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 blood movement in the human body, starting from 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 flow 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. Backflow of blood from pulmonary artery and the aorta to the ventricles obstruct the valves
1) tricuspid
2) venous
3) double-leaf
4) semilunar

Answer

1. Establish the sequence of blood flow in a person in 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 blood circulation 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 flows 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 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 the small circle
4) small circle capillaries
5) arteries of a large 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. Set the correct sequence for the 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

Set the sequence of events that take place 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) the flow of blood into the aorta and artery
4) the flow of blood into the ventricles
5) atrial contraction

Answer

Establish a correspondence between 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 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) supply the cells of the body with oxygen
4) enters the pulmonary artery
5) under great 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 pulmonary capillaries
6) slower than in 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 the 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
B) pulmonary vein
D) subclavian artery
D) pulmonary artery
E) aorta

Answer

Choose three options. In mammals and humans, venous blood, in contrast to 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 from six and write down the numbers under which they are indicated. Veins as opposed to arteries
1) have valves in the walls
2) can subside
3) have walls from one layer of cells
4) carry blood from the 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 marked with a letter, 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 from six and write down the numbers under which they are indicated. Elements of the human circulatory system that contain 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 from six and write down the numbers under which they are indicated. Blood flowing from the right ventricle
1) arterial
2) venous
3) along 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 circles of blood circulation 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.
D) Gas exchange occurs in the capillaries of the alveoli.
E) education is taking place venous blood from arterial.

Answer

Find three errors in the given text. Specify the numbers of 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 resilient and elastic; the walls of the veins, on the contrary, are inelastic. (3) When the atria contract, blood is pushed out 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) The blood in the human body moves in two circles of blood circulation.

Answer

Choose three correctly labeled captions for the figure, which depicts 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 marked captions for the picture, which shows 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, which ensures 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 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 that has given oxygen to organs and tissues enters the right half of the heart and is sent to the pulmonary (pulmonary) circulation, where the blood is saturated with oxygen, returns to the heart, entering its left half, and again spreads throughout the body (large circulation) .

Heart - main body circulatory systems. It is a hollow muscular organ, consisting of four chambers: two atria (right and left), separated atrial septum, and two ventricles (right and left), separated interventricular septum. The right atrium communicates with the right ventricle through the tricuspid ventricle, and the left atrium communicates with the left ventricle through butterfly valve. The mass of the heart of an adult is on average about 250 g in women and about 330 g in men. Heart length 10-15 cm, transverse dimension 8-11 cm and anteroposterior - 6-8.5 cm. The volume of the heart 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 cardiac muscle, which is similar in structure to the striated muscles. However, the heart muscle is distinguished by the ability to automatically contract rhythmically due to impulses that occur 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 contracts 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
• total 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 ejected from the left ventricle into the aorta enters the arteries departing from it, which feed the heart.

arteries- blood vessels that carry oxygenated blood from the heart to organs and tissues (only the pulmonary artery carries venous blood).

The wall of the artery is represented by three layers: the outer connective tissue membrane; middle, 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 arterial system averages 950 ml. Arteries gradually branch into a tree-like small vessels- arterioles that pass into the capillaries.

capillaries(from 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 with 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.

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

Circles of blood circulation

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

In humans and mammals, blood moves 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 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 the 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, braiding the pulmonary vesicles, the blood gives off carbon dioxide and receives in return a new supply of oxygen (pulmonary respiration). Oxygenated blood acquires a scarlet color, becomes arterial and flows from the capillaries into the veins, which, having merged 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 that enters 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 with the right atrium.

From the left ventricle of the heart, blood enters the largest arterial vessel- aorta. Arterial blood contains nutrients and oxygen necessary for the life 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. Capillaries, in turn, are collected in venules and further into veins. Through the wall of the capillaries there is a metabolism and gas exchange 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, the color of the blood 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 (corporeal) circle of blood circulation.

The addition to the great circle is third (cardiac) 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 atrial cavity.

The movement of blood through the vessels

Any fluid 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 systemic and pulmonary circulation also moves due to the pressure difference that the heart creates with 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 highest pressure is in the aorta and large arteries (blood pressure). Arterial blood pressure is not a constant value [show]

Blood pressure- this is the blood pressure on the walls of the blood vessels and chambers of the heart, resulting from the contraction of the heart, which pumps blood into the vascular system, and the resistance of the vessels. 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. At healthy people at rest, the maximum, or systolic, blood pressure is distinguished - the level of pressure in the arteries during the 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 oscillations occur simultaneously with the pulse oscillations 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 provide the greatest resistance to the movement of blood. In the veins, blood pressure continues to gradually decrease, and in the vena cava it is atmospheric pressure or even below it. 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 out, their diameter decreases, but the total cross-sectional area of ​​all 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 slowing down of blood flow in the capillaries is explained by their huge amount(about 40 billion) and a large total lumen (800 times the lumen of the aorta). The movement of blood in the capillaries is carried out by changing the lumen of the supply small arteries: their expansion increases the blood flow in the capillaries, and their 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 decrease, and the speed of blood movement increases compared to the capillaries. From Table. 1 also shows that 3/4 of all blood is in the veins. This is due to the fact that thin walls 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 occurs in the direction of the heart. This is facilitated by the suction action chest("respiratory pump") and skeletal muscle contraction ("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 through the veins is sent to the heart. Skeletal muscles, contracting, compress the veins, which also contributes to the movement of blood to the heart.

The relationship between the speed of blood flow, the width of the bloodstream and blood pressure is illustrated in Fig. 3. The amount of blood flowing per unit of time through the vessels is equal to the product of the speed of blood movement by the cross-sectional area of ​​the 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 any organ, due to the relaxation of its smooth muscles, expands, 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. As a result of redistribution, more blood flows to the working organs at the expense of the organs that are currently at rest.

The redistribution of blood is regulated nervous system: simultaneously with the expansion of blood vessels in the working organs, the blood vessels of the 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 reduce the speed of blood movement in the vessels.

Blood circulation time

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

The principle of measuring the time of the blood circulation is that some substance that is not usually found in the body is injected into the 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 an action characteristic of it. For example, in cubital 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 the substance is administered to the moment when a short-term breath holding or cough appears. This happens when the lobelin molecules, having completed the circuit in circulatory system, will act on the respiratory center and cause a change in breathing or coughing.

IN last 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 isotope of sodium and an electron counter. To do this, several of these counters are placed on different parts bodies near large vessels and in the region of the heart. After the introduction of a radioactive isotope of sodium into the cubital vein, the time of appearance of radioactive radiation in the region of the heart and the studied vessels is determined.

The circulation time of the blood in humans is on average about 27 systoles of the heart. At 70-80 heartbeats per minute, a complete blood circulation occurs in about 20-23 seconds. We must not forget, however, that the speed of blood flow along the axis of the vessel is greater than that of 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 a complete blood circulation occurs in the pulmonary circulation and 4/5 in the systemic circulation.

Regulation of blood circulation

Innervation of the heart. Heart like others internal organs, innervated by the autonomic nervous system and receives dual 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 heart.

In addition, the work of the heart is affected by the hormone of the adrenal glands - adrenaline, which enters the heart with blood and increases its contractions. 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 provide an accurate adaptation of activity. of cardio-vascular system to the needs of the body and environmental conditions.

Innervation of blood vessels. Blood vessels are innervated by sympathetic nerves. Excitation propagating through them causes contraction of smooth muscles in the walls of blood vessels and constricts blood vessels. If you cut the sympathetic nerves going to a certain part of the body, the corresponding vessels will expand. Consequently, the sympathetic nerves to the blood vessels constantly receive excitation, which keeps these vessels in a state of some constriction - vascular tone. When the excitement increases, the frequency nerve impulses increases and the vessels narrow more strongly - the vascular tone increases. On the contrary, with a decrease in the frequency of nerve impulses 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 vasoconstrictor, vasodilating nerves are also suitable. These nerves become excited and dilate the blood vessels of the organs as they work. Substances that are carried by the blood also affect the lumen of the vessels. Adrenaline constricts 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 of the organs varies 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 circulation is to maintain a 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 the center to sympathetic nerves a weaker excitation than before begins to flow to the vessels and the heart, and the blood vessels dilate, and the heart weakens its work. As a result of these changes, blood pressure decreases. And if for some reason the pressure falls below the norm, then the irritation of the receptors stops completely and the vasomotor center, without receiving inhibitory influences from the receptors, intensifies its activity: it sends more nerve impulses per second to the heart and blood vessels, the vessels constrict, the heart contracts, more often and stronger, blood pressure rises.

Hygiene of cardiac activity

Normal activity human body possible only in the presence of a well-developed cardiovascular system. The rate 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 need of organs 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 a variety of labor activity, it is important to train the heart, increase the strength of its muscles.

Physical labor, 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 best done outdoors.

It must be remembered that excessive physical and mental stress may cause disruption normal operation heart disease. Especially bad influence alcohol, nicotine, and drugs affect the cardiovascular system. Alcohol and nicotine poison the heart muscle and nervous system, cause severe violations regulation of vascular tone and activity of the heart. 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 develop spasms of the heart vessels, causing 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 microbes from entering the wound.

Venous bleeding is characterized by a significantly higher rate of blood flow. The flowing blood is 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 has stopped, the wound is treated disinfectant (3% peroxide solution hydrogen, vodka), bandage 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 your finger in the place where it comes close to the surface of the body. It is also necessary to apply a rubber tourniquet above the wound site, i.e. closer to the heart (you can use a bandage, a rope for this) and tighten it tightly to completely stop the bleeding. The tourniquet must not be kept tightened for more than 2 hours. When it is applied, a note must be attached in which the time of applying the tourniquet should be indicated.

It should be remembered that venous, and even more arterial bleeding can lead to significant blood loss and even death. Therefore, when injured, 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 lose consciousness. Loss of consciousness (fainting) is a consequence of inhibition of the vasomotor center, a drop in blood pressure and insufficient supply of blood to the brain. The unconscious person should be allowed to smell some non-toxic strong smell substance (eg. ammonia), wet the face cold water or lightly pat him on the cheeks. When olfactory or skin receptors are stimulated, excitation from them enters the brain and relieves inhibition of the vasomotor center. Blood pressure rises, the brain receives adequate nutrition and consciousness returns.

Provides lymph and blood flow 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 cell systems and tissues, saturated with carbon dioxide, containing metabolic products.

Medical manipulations and research are carried out mainly with such blood, which contains the end products of metabolism 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 through the veins of the pulmonary circulation.

The structure of the veins

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

The large circle originates in the left ventricle of the heart, and the aorta with a diameter of up to three centimeters emerges from it. Further, the oxygenated blood of the arteries flows through vessels decreasing in diameter to all organs. giving 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 again filled with oxygen. Through the veins, arterial blood enters the left atrium, which is then pushed out 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 smaller, superior and inferior hollow vessels branching off 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:

• veins of the heart that go directly into the cavity of the heart;
• coronary sinus;
• large cardiac vein;
• left ventricular 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 supplied by the heart, as well as the difference in pressure in the sections of the vessels.

Superior vena cava system

The superior vena cava takes venous blood from the upper body - the head, neck, sternum and partially abdominal cavity and enters the right atrium. Vessel valves are absent. The process is as follows: carbonated blood superior vein flows into the region of the pericardium, lower - into the region of the right atrium. The system of the superior vena cava is divided into the following parts:

1. Upper hollow - a small vessel, 5-8 cm long, 2.5 cm in diameter.
2. Unpaired - continuation of the right ascending lumbar vein.
3. Semi-unpaired - 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. Shoulderheads - the roots of the upper hollow.
7. Vertebral - location in the diametrical openings of the cervical vertebrae.
8. Deep cervical - collection of venous blood of the occipital region along the carotid artery.
9. Internal chest.

Inferior vena cava system

The inferior vena cava is a connection of the iliac veins on both sides in the region of 4-5 lumbar vertebrae, it takes venous blood lower divisions body. 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, blood outflows from the legs, pelvis and abdomen from the lower hollow. 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 vessel is 500-600 mm long and 110-180 mm in diameter.

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

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

Upper mesenteric vein accumulates blood in the roots of the mesentery small intestine from ileum, pancreatic, right and middle colic, iliac colic and right ventricular-omental 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 venous system

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

Veins coming from the external jugular:

• posterior auricular - collection of venous blood behind auricle;
• occipital branch - collection from the venous plexus of the head;
• suprascapular - taking blood from the 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 maxillo-hyoid and sternothyroid muscles.

The internal jugular vein originates 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 provided:

• transportation of substances to ensure the functions of cells and tissues;
• - transport necessary chemical substances for metabolic reactions in cells;
• collection of metabolites of cells and tissues;
• the 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 circle of blood circulation are an extensive network that provides blood to all organs, in contrast to the small circle. The optimal functioning of the system of the superior and inferior vena cava leads to proper 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 excreted through the veins.

Arteries of the systemic circulation move blood from the left ventricle down 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. Excretion of metabolic products occurs through the veins and capillaries. In the pulmonary circulation, the main function is the process of gas exchange in the lungs.

Arterial blood, which moves through the arteries, having passed its way, passes into 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.