What kind of blood moves through the systemic circulation. What color is venous blood and why is it darker than arterial blood?

Blood in medicine is usually divided into arterial and venous. It would be logical to think that the first flows in the arteries, and the second in the veins, but this is not entirely true. The fact is that in a large circle of blood circulation through the arteries, indeed, flows arterial blood(a.k.), and through the veins - venous (v.k.), but in a small circle, the opposite happens: c. to. comes from the heart to the lungs through the pulmonary arteries, gives carbon dioxide outside, enriched with oxygen, becomes arterial and returns from the lungs through the pulmonary veins.

What is the difference deoxygenated blood from arterial? A. to. saturated with O 2 and nutrients, it comes from the heart to organs and tissues. V. to. - “worked out”, it gives O 2 and nutrition to the cells, takes away CO 2 and metabolic products from them and returns from the periphery back to the heart.

Human venous blood differs from arterial blood in color, composition and functions.

by color

A. to. has a bright red or scarlet hue. This color is given to it by hemoglobin, which has attached O 2 and become oxyhemoglobin. V. to. contains CO 2, therefore its color is dark red, with a bluish tint.

Composition

In addition to gases, oxygen and carbon dioxide, other elements are contained in the blood. In a. to. a lot of nutrients, and in c. to. - mainly metabolic products, which are then processed by the liver and kidneys and excreted from the body. The pH level also differs: a. c. it is higher (7.4) than c. k. (7.35).

On the move

The circulation of blood in the arterial and venous systems differs significantly. A. to. moves from the heart to the periphery, and c. to. - in the opposite direction. When the heart contracts, blood is ejected from it at a pressure of approximately 120 mm Hg. pillar. When it passes through the capillary system, its pressure is significantly reduced and is approximately 10 mm Hg. pillar. Thus, a. to. moves under pressure with high speed, and in. It flows slowly under low pressure, overcoming gravity, and valves prevent its reverse flow.

How the transformation of venous blood into arterial and vice versa occurs can be understood if we consider the movement in the small and large circles of blood circulation.

The CO 2-rich blood travels through the pulmonary artery to the lungs, where the CO 2 is expelled to the outside. Then O 2 is saturated, and the blood already enriched with it through the pulmonary veins enters the heart. This is how movement occurs in the pulmonary circulation. After that, the blood makes a big circle: a. to. through the arteries carries oxygen and nutrition to the cells of the body. Giving O 2 and nutrients, it is saturated with carbon dioxide and metabolic products, becomes venous and returns to the heart through the veins. This completes the systemic circulation.

By function

Main function a. to. - the transfer of nutrition and oxygen to the cells through the arteries great circle circulation and small veins. Passing through all organs, it gives off O 2, gradually takes away carbon dioxide and turns into venous.

Through the veins, the outflow of blood is carried out, which took away the waste products of cells and CO 2. In addition, it contains nutrients that are absorbed digestive organs, and produced by glands internal secretion hormones.

By bleeding

Due to the peculiarities of the movement, bleeding will also differ. With arterial blood in full swing, such bleeding is dangerous and requires prompt first aid and medical attention. With a venous one, it calmly flows out in a jet and can stop on its own.

Other differences

• A. to. is located in the left side of the heart, c. to. - in the right, mixing of blood does not occur.
• Venous blood is warmer than arterial blood.
• V. to. flows closer to the surface of the skin.
• A. to. in some places comes close to the surface and here you can measure the pulse.
• The veins through which flows in. to., much more than the arteries, and their walls are thinner.
• A.K. movement is provided by a sharp ejection during heart contraction, outflow into. the valve system helps.
• The use of veins and arteries in medicine is also different - they are injected into a vein medications, it is from it that they take biological fluid for analysis.

Instead of a conclusion

Main differences a. to. and in. to. lie in the fact that the first is bright red, the second is burgundy, the first is saturated with oxygen, the second is carbon dioxide, the first moves from the heart to the organs, the second - from the organs to the heart.

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, through the arteries and capillaries, it spreads 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 and 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

Vessels in the human body form two closed circulatory systems. Allocate large and small circles of blood circulation. The vessels of the large circle supply blood to the organs, the vessels of the small circle provide gas exchange in the lungs.

Systemic circulation: arterial (oxygenated) blood flows from the left ventricle of the heart through the aorta, then through the arteries, arterial capillaries to all organs; from the organs, venous blood (saturated with carbon dioxide) flows through the venous capillaries into the veins, from there through the superior vena cava (from the head, neck and arms) and the inferior vena cava (from the trunk and legs) to right atrium.

Small circle of blood circulation: venous blood flows from the right ventricle of the heart through the pulmonary artery into a dense network of capillaries braiding the pulmonary vesicles, where the blood is saturated with oxygen, then arterial blood flows through the pulmonary veins into the left atrium. In the pulmonary circulation, arterial blood flows through the veins, venous blood through the arteries. It starts in the right ventricle and ends in the left atrium. The pulmonary trunk emerges from the right ventricle, carrying venous blood to the lungs. Here, the pulmonary arteries break up into vessels of smaller diameter, passing into the capillaries. Oxygenated blood flows through the four pulmonary veins into the left atrium.

Blood moves through the vessels due to the rhythmic work of the heart. During ventricular contraction, blood is pumped under pressure into the aorta and pulmonary trunk. Here develops the most high pressure- 150 mm Hg Art. As blood moves through the arteries, the pressure drops to 120 mm Hg. Art., and in the capillaries - up to 22 mm. The lowest pressure in the veins; in large veins it is below atmospheric.

Blood from the ventricles is ejected in portions, and the continuity of its flow is ensured by the elasticity of the walls of the arteries. At the moment of contraction of the ventricles of the heart, the walls of the arteries stretch, and then, due to elastic elasticity, return to the initial state before the next blood supply from the ventricles. Thanks to this, the blood moves forward. Rhythmic fluctuations in the diameter of arterial vessels caused by the work of the heart are called pulse. It is easily palpable in places where the arteries lie on the bone (radial, dorsal artery of the foot). By counting the pulse, you can determine the heart rate and their strength. In an adult healthy person at rest, the pulse rate is 60-70 beats per minute. With various diseases of the heart, arrhythmia is possible - interruptions in the pulse.

With the highest speed, blood flows in the aorta - about 0.5 m / s. In the future, the speed of movement decreases and in the arteries reaches 0.25 m / s, and in the capillaries - approximately 0.5 mm / s. The slow flow of blood in the capillaries and the large length of the latter favor metabolism ( total length capillaries in the human body reaches 100 thousand km, and the total surface of all body capillaries is 6300 m 2). The large difference in the speed of blood flow in the aorta, capillaries and veins is due to the unequal width of the total cross section. bloodstream in its various areas. The narrowest such area is the aorta, and the total lumen of the capillaries is 600-800 times greater than the lumen of the aorta. This explains the slowing down of blood flow in the capillaries.

The movement of blood through the vessels is regulated by neurohumoral factors. impulses sent to nerve endings, can cause either narrowing or expansion of the lumen of the vessels. To smooth muscle two types of vasomotor nerves fit the walls of blood vessels: vasodilating and vasoconstrictor.

The impulses going through these nerve fibers, arise in the vasomotor center of the medulla oblongata. In the normal state of the body, the walls of the arteries are somewhat tense and their lumen is narrowed. Impulses continuously flow from the vasomotor center along the vasomotor nerves, which cause a constant tone. Nerve endings in the walls of blood vessels react to changes in blood pressure and chemical composition, causing excitement in them. This excitation enters the central nervous system, resulting in a reflex change in the activity of the cardiovascular system. Thus, the increase and decrease in the diameters of the vessels occurs in a reflex way, but the same effect can also occur under the influence of humoral factors - chemicals that are in the blood and come here with food and from various internal organs. Among them, vasodilators and vasoconstrictors are important. For example, pituitary hormone - vasopressin, thyroid hormone - thyroxine, adrenal hormone - adrenaline constrict blood vessels, enhance all the functions of the heart, and histamine, which is formed in the walls of the digestive tract and in any working organ, acts in the opposite way: it expands capillaries without affecting other vessels . A significant effect on the work of the heart has a change in the content of potassium and calcium in the blood. Increasing the calcium content increases the frequency and strength of contractions, increases excitability and conduction of the heart. Potassium causes the exact opposite effect.

Expansion and narrowing of blood vessels in various organs significantly affects the redistribution of blood in the body. More blood is sent to a working organ, where the vessels are dilated, to a non-working organ - \ less. The depositing organs are the spleen, liver, subcutaneous fatty tissue.

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 of the great circle, gas exchange occurs: oxygen passes from the blood to the tissues, and carbon dioxide from the tissues into the blood. The blood becomes venous, through the vena cava enters the right atrium, and from there - into the right ventricle.

Small circle: From the right ventricle, venous blood flows through the pulmonary arteries to the lungs. 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 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) Venous blood is formed from arterial blood.

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 the arterial system averages 950 ml. Arteries gradually branch into smaller and smaller vessels - arterioles, which pass into capillaries.

capillaries(from lat. "capillus" - hair) - tiny vessels(the average diameter does not exceed 0.005 mm, or 5 microns), penetrating 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 the 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. AT 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 emerging from the aorta coronary arteries heart and ends in 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. one.

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 difference in pressure at the beginning and end venous system Therefore, 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.

AT 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 muscle, 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 exercises 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.