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

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

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

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

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

The function of the heart is to rhythmically pump blood into the arteries, which comes to it through the veins. The heart contracts about once per minute when the body is at rest (1 time per 0.8 s). More than half of this time it rests - relaxes. The continuous activity of the heart consists of cycles, each of which consists of contraction (systole) and relaxation (diastole).

There are three phases of cardiac activity:

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

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

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

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

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

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

Veins are 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 the pulmonary veins, which carry arterial blood). The wall of a vein is much thinner and more elastic than the wall of an artery. Small and medium-sized veins are equipped with valves that prevent blood from flowing back into these vessels. In humans, the volume of blood in the venous system averages 3200 ml.

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

William Harvey () - English physician and naturalist. He created and introduced into the practice of scientific research the first experimental method - vivisection (live section).

In 1628, he published the book “Anatomical Studies on the Movement of the Heart and Blood in Animals,” in which he described the systemic and pulmonary circulation and formulated the basic principles of blood movement. The date of publication of this work is considered the year of the birth of physiology as an independent science.

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

The large circle starts from the left ventricle, carries blood throughout the body through the aorta, gives oxygen to tissues in the capillaries, takes up carbon dioxide, turns from arterial to venous and returns through the superior and inferior vena cava to the right atrium.

The pulmonary circulation begins from the right ventricle and carries blood through the pulmonary artery to the pulmonary capillaries. Here the blood releases carbon dioxide, is saturated with oxygen and flows through the pulmonary veins to the left atrium. From the left atrium, through the left ventricle, blood again enters the systemic circulation.

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

From the right ventricle of the heart, venous blood enters 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 the capillary networks that weave around the pulmonary vesicles, the blood gives up carbon dioxide and receives in return a new supply of oxygen (pulmonary respiration). Blood saturated with oxygen acquires a scarlet color, becomes arterial and flows from the capillaries into the veins, which, merging into four pulmonary veins (two on each side), flow into the left atrium of the heart. The pulmonary circulation ends in the left atrium, and arterial blood entering the atrium passes through the left atrioventricular opening into the left ventricle, where the systemic circulation begins. Consequently, venous blood flows in the arteries of the pulmonary circulation, and arterial blood flows in its veins.

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

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

The aorta branches into arteries, which go to all organs and tissues of the body and pass through them into arterioles and then into capillaries. The capillaries, in turn, gather into venules and then into veins. Through the capillary wall, metabolism and gas exchange occurs between the blood and body tissues. Arterial blood flowing in the capillaries gives off nutrients and oxygen and in return receives metabolic products and carbon dioxide (tissue respiration). As a result, the blood entering the venous bed is poor in oxygen and rich in carbon dioxide and therefore has a dark color - venous blood; When bleeding, you can determine by the color of the blood which vessel is damaged - an artery or a vein. The veins merge into two large trunks - the superior and inferior vena cava, which flow into the right atrium of the heart. This section of the heart ends the systemic (bodily) circulation.

In the systemic circulation, arterial blood flows through arteries, and venous blood flows through veins.

In a small circle, on the contrary, venous blood flows through the arteries from the heart, and arterial blood returns through the veins to the heart.

The complement to the great circle is third (cardiac) circle of blood circulation, serving the heart itself. It begins with the coronary arteries of the heart emerging from the aorta and ends with the veins of the heart. The latter merge into the coronary sinus, which flows into the right atrium, and the remaining veins open directly into the atrium cavity.

Movement of blood through vessels

Any liquid flows from a place where the pressure is higher to where it is lower. The greater the pressure difference, the higher the flow speed. Blood in the vessels of the systemic and pulmonary circulation also moves due to the pressure difference created by the heart through its contractions.

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

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

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

Arterial blood pressure is not a constant value. In healthy people at rest, a maximum, or systolic, blood pressure is distinguished - the level of pressure in the arteries during heart systole is about 120 mmHg, and a minimum, or diastolic - the level of pressure in the arteries during diastole of the heart is about 80 mmHg. Those. arterial blood pressure pulsates in time with the contractions of the heart: at the moment of systole it rises to 100 mHg. Art., and during diastole the domm Hg decreases. Art. These pulse pressure fluctuations occur simultaneously with pulse fluctuations of the arterial wall.

Pulse- periodic jerk-like expansion of the walls of the arteries, synchronous with the contraction of the heart. The pulse determines the number of heart contractions per minute. An adult's heart rate averages beats per minute. During physical activity, the heart rate may increase to a beat. In places where the arteries are located on the bone and lie directly under the skin (radial, temporal), the pulse is easily palpable. The pulse wave propagation speed is about 10 m/s.

Blood pressure is affected by:

1. heart function and force of cardiac contraction;
2. the size of the lumen of blood vessels and the tone of their walls;
3. the amount of blood circulating in the vessels;
4. blood viscosity.

A person's blood pressure is measured in the brachial artery, comparing it with atmospheric pressure. To do this, a rubber cuff connected to a pressure gauge is placed on the shoulder. Air is inflated into the cuff until the pulse at the wrist disappears. This means that the brachial artery is compressed by great pressure and blood does not flow through it. Then, gradually releasing air from the cuff, watch for the appearance of a pulse. At this moment, the pressure in the artery becomes slightly higher than the pressure in the cuff, and the blood, and with it the pulse wave, begins to reach the wrist. The pressure gauge readings at this time characterize the blood pressure in the brachial artery.

A persistent increase in blood pressure above these figures at rest is called hypertension, and a decrease in blood pressure is called hypotension.

The level of blood pressure is regulated by nervous and humoral factors (see table).

(diastolic)

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 speed here is maximum mm/s (see Table 1). As the arteries branch, their diameter decreases, but the total cross-sectional area of ​​all arteries increases and the speed of blood movement decreases, reaching 0.5 mm/s in the capillaries. Due to such a low speed of blood flow in the capillaries, the blood has time to give oxygen and nutrients to the tissues and accept their waste products.

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

The veins on the way from the capillaries, as they approach the heart, enlarge and merge, their number and the total lumen of the bloodstream decrease, and the speed of blood movement increases compared to the capillaries. From the table 1 also shows that 3/4 of all blood is in the veins. This is due to the fact that the thin walls of the veins are able to stretch easily, 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 of the chest (“respiratory pump”) and the contraction of skeletal muscles (“muscle pump”). During inhalation, the pressure in the chest decreases. In this case, the pressure difference at the beginning and end of the venous system increases, and blood is directed through the veins to the heart. Skeletal muscles contract and compress the veins, which also helps move blood to the heart.

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

Redistribution of blood in the body

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

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

Blood circulation time

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

The principle of measuring the time of blood circulation is that a substance that is not usually found in the body is injected into a vein, and it is determined after what period of time it appears in the vein of the same name on the other side or causes its characteristic effect. For example, a solution of the alkaloid lobeline, which acts through the blood on the respiratory center of the medulla oblongata, is injected into the cubital vein, and the time from the moment of administration of the substance to the moment when a short-term breath holding or cough appears is determined. This occurs when lobeline molecules, having circulated in the circulatory system, affect the respiratory center and cause a change in breathing or cough.

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

The blood circulation time in humans is on average approximately 27 heart systoles. As the heart beats per minute, the complete circulation of blood occurs in approximately seconds. We must not forget, however, that the speed of blood flow along the axis of the vessel is greater than at its walls, and also that not all vascular areas have the same length. Therefore, not all blood circulates so quickly, and the time indicated above is the shortest.

Studies on dogs have shown that 1/5 of the time of complete blood circulation is in the pulmonary circulation and 4/5 in the systemic circulation.

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

In addition, the functioning of the heart is affected by the adrenal hormone - adrenaline, which enters the heart with the blood and increases its contractions. The regulation of organ function with the help of substances carried by the blood is called humoral.

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

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

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

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

Cardiac hygiene

Normal activity of the human body is possible only if there is a well-developed cardiovascular system. The speed of blood flow will determine the degree of blood supply to organs and tissues and the rate of removal of waste products. During physical work, the organs' need 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 work activities, it is important to train the heart and increase the strength of its muscles.

Physical labor and physical education develop the heart muscle. To ensure normal function of the cardiovascular system, a person should start his day with morning exercises, especially people whose professions do not involve physical labor. To enrich the blood with oxygen, it is better to perform physical exercises in the fresh air.

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

First aid for wounds and bleeding

Injuries are often accompanied by bleeding. There are capillary, venous and arterial bleeding.

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

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

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

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

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Blood flows through the arteries of the pulmonary circulation

1. Establish a correspondence between human blood vessels and the direction of blood movement in them: 1-from the heart, 2-to the heart

A) veins of the pulmonary circulation

B) veins of the systemic circulation

B) arteries of the pulmonary circulation

D) arteries of the systemic circulation

2. A person has blood from the left ventricle of the heart

A) when it contracts, it enters the aorta

B) when it contracts, it enters the left atrium

B) supplies body cells with oxygen

D) enters the pulmonary artery

D) under high pressure enters the large circulation circle

E) enters the pulmonary circulation under low pressure

3. Establish the sequence in which blood moves through the systemic circulation in the human body

A) veins of the great circle

B) arteries of the head, arms and torso

D) capillaries of a large circle

D) left ventricle

E) right atrium

4. Establish the sequence in which blood passes through the pulmonary circulation in the human body

A) left atrium

B) pulmonary capillaries

B) pulmonary veins

D) pulmonary arteries

D) right ventricle

5. Blood flows through the arteries of the pulmonary circulation in humans

D) saturated with oxygen

D) faster than in the pulmonary capillaries

E) slower than in the pulmonary capillaries

6. Veins are blood vessels through which blood flows.

B) under greater pressure than in the arteries

D) under less pressure than in the arteries

D) faster than in capillaries

E) slower than in capillaries

7. Blood flows through the arteries of the systemic circulation in humans

B) saturated with carbon dioxide

D) saturated with oxygen

D) faster than in other blood vessels

E) slower than in other blood vessels

8. Establish the sequence of blood movement through the systemic circulation

A) Left ventricle

B) Right atrium

9. Establish the order in which the blood vessels should be arranged in order of decreasing blood pressure in them

10. Establish a correspondence between the type of human blood vessels and the type of blood they contain: 1 - arterial, 2 - venous

11. In mammals and humans, venous blood, unlike arterial blood,

A) poor in oxygen

B) flows in a small circle through the veins

B) fills the right half of the heart

D) saturated with carbon dioxide

D) enters the left atrium

E) provides body cells with nutrients

12. Arrange the blood vessels in order of decreasing speed of blood movement in them

Is the blood in the pulmonary arteries venous or arterial?

Venous blood is saturated with carbon dioxide.

Arteries are vessels that carry blood away from the heart.

Veins are vessels that carry blood to the heart.

(In the pulmonary circulation, venous blood flows through the arteries, and arterial blood flows through the veins.)

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

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

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

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

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

Systemic and pulmonary circulation

The vessels in the human body form two closed circulatory systems. There are 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 torso and legs) into the right atrium.

Pulmonary circulation: venous blood flows from the right ventricle of the heart through the pulmonary artery into a dense network of capillaries entwining 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 begins 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, which turn into 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 forced under pressure into the aorta and pulmonary trunk. The highest pressure develops here - 150 mm Hg. Art. As blood moves through the arteries, the pressure drops to 120 mmHg. Art., and in capillaries - up to 22 mm. Lowest venous pressure; in large veins it is below atmospheric.

Blood is ejected from the ventricles in portions, and the continuity of its flow is ensured by the elasticity of the artery walls. At the moment of contraction of the ventricles of the heart, the walls of the arteries are stretched, and then, due to elastic elasticity, return to their original state even before the next flow of blood 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 can be easily palpated in places where the arteries lie on the bone (radial, dorsal artery of the foot). By counting the pulse, you can determine the frequency of heart contractions and their strength. In a healthy adult, the pulse rate at rest is 60-70 beats per minute. With various heart diseases, arrhythmia is possible - interruptions in the pulse.

Blood flows at the highest speed in the aorta - about 0.5 m/s. Subsequently, the speed of movement drops 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 extent of the latter favor metabolism (the total length of capillaries in the human body reaches 100 thousand km, and the total surface of all capillaries in the body is 6300 m2). The large difference in the speed of blood flow in the aorta, capillaries and veins is due to the unequal width of the overall cross-section of the bloodstream in its different sections. The narrowest such section is the aorta, and the total lumen of the capillaries is 600-800 times greater than the lumen of the aorta. This explains the slowdown in blood flow in the capillaries.

The movement of blood through the vessels is regulated by neurohumoral factors. Impulses sent along nerve endings can cause either a narrowing or expansion of the lumen of blood vessels. Two types of vasomotor nerves approach the smooth muscles of the walls of blood vessels: vasodilators and vasoconstrictors.

The impulses traveling along 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. From the vasomotor center, impulses continuously flow through the vasomotor nerves, which determine constant tone. Nerve endings in the walls of blood vessels react to changes in pressure and chemical composition of the blood, causing excitement in them. This excitation enters the central nervous system, resulting in a reflex change in the activity of the cardiovascular system. Thus, an increase and decrease in the diameters of blood vessels occurs in a reflex way, but the same effect can also occur under the influence of humoral factors - chemical substances that are in the blood and come here with food and from various internal organs. Among them, vasodilators and vasoconstrictors are important. For example, the pituitary hormone - vasopressin, the thyroid hormone - thyroxine, the adrenal hormone - adrenaline, constrict blood vessels, enhance all functions of the heart, and histamine, formed in the walls of the digestive tract and in any working organ, acts in the opposite way: it dilates the capillaries without affecting other vessels . A significant effect on the functioning of the heart is exerted by changes in the content of potassium and calcium in the blood. An increase in calcium content increases the frequency and strength of contractions, increases the excitability and conductivity of the heart. Potassium causes exactly the opposite effect.

The expansion and contraction 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, and to a non-working organ - \ less. The depositing organs are the spleen, liver, and subcutaneous fat.

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k.), and along the veins - venous (v. k.), but in the small circle the opposite happens: v. It enters from the heart to the lungs through the pulmonary arteries, releases carbon dioxide to the outside, is enriched with oxygen, becomes arterial, and returns from the lungs through the pulmonary veins.

How does venous blood differ from arterial blood? A.K. is saturated with O 2 and nutrients; it flows from the heart to organs and tissues. V. k. - “spent”, it gives O 2 and nutrition to the cells, takes 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.K. has a bright red or scarlet tint. This color is given to it by hemoglobin, which added O 2 and became oxyhemoglobin. V.K. contains CO 2, so its color is dark red, with a bluish tint.

By composition

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

By movement

Blood circulation in the arterial and venous systems is significantly different. A. K. moves from the heart to the periphery, and c. k. - in the opposite direction. When the heart contracts, blood is ejected from it under a pressure of approximately 120 mmHg. pillar As it passes through the capillary system, its pressure decreases significantly and is approximately 10 mmHg. pillar Thus, a. k. moves under pressure at high speed, and c. It flows slowly under low pressure, overcoming the force of gravity, and its reverse flow is prevented by valves.

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

Blood saturated with CO 2 enters the lungs through the pulmonary artery, from where CO 2 is excreted. Then saturation with O 2 occurs, and the blood already enriched with it enters the heart through the pulmonary veins. This is how movement occurs in the pulmonary circulation. After this, the blood makes a large circle: a. It carries oxygen and nutrition through the arteries to the cells of the body. Giving up O 2 and nutrients, it is saturated with carbon dioxide and metabolic products, becomes venous and returns through the veins to the heart. This completes the large circle of blood circulation.

By functions performed

The veins carry out the outflow of blood, which has taken away cell waste products and CO 2 . In addition, it contains nutrients that are absorbed by the digestive organs and hormones produced by the endocrine glands.

By bleeding

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

Other differences

• A.K. is located on the left side of the heart, in. k. – in the right, blood mixing does not occur.
• Venous blood, unlike arterial blood, is warmer.
• V. k. flows closer to the surface of the skin.
• A.K. in some places comes close to the surface and here the pulse can be measured.
• The veins through which the v. flows. to., much more than arteries, and their walls are thinner.
• Movement a.k. is ensured by a sharp release during contraction of the heart, outflow into the. the valve system helps.
• The use of veins and arteries in medicine also differs - drugs are injected into the vein, and it is from it that biological fluid is taken for analysis.

Instead of a conclusion

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

Blood circulation in humans

Arterial blood is blood saturated with oxygen.

Venous blood is saturated with carbon dioxide.

Arteries are vessels that carry blood away from the heart.

Veins are vessels that carry blood to the heart.

(In the pulmonary circulation, venous blood flows through the arteries, and arterial blood flows through the veins.)

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

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

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

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

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

ASSIGNMENTS ON THIS TOPIC: Heart

Tests and assignments

Establish a correspondence between the sections of the circulatory system and the circle of blood circulation to which they belong: 1) Systemic circulation, 2) Pulmonary circulation. Write numbers 1 and 2 in the correct order.

A) Right ventricle

B) Carotid artery

B) Pulmonary artery

D) Superior vena cava

D) Left atrium

E) Left ventricle

Choose three correct answers out of six and write down the numbers under which they are indicated. Large circle of blood circulation in the human body

1) begins in the left ventricle

2) originates in the right ventricle

3) is saturated with oxygen in the alveoli of the lungs

4) supplies organs and tissues with oxygen and nutrients

5) ends in the right atrium

6) brings blood to the left side of the heart

1. Establish the sequence of human blood vessels in order of decreasing blood pressure in them. Write down the corresponding sequence of numbers.

1) inferior vena cava

3) pulmonary capillaries

4) pulmonary artery

2. Establish the order in which the blood vessels should be arranged in order of decreasing blood pressure in them

Establish a correspondence between the vessels and human circulatory circles: 1) pulmonary circulation, 2) systemic circulation. Write numbers 1 and 2 in the correct order.

B) pulmonary veins

B) carotid arteries

D) capillaries in the lungs

D) pulmonary arteries

E) hepatic artery

Choose one, the most correct option. Why can't blood get from the aorta to the left ventricle of the heart?

1) the ventricle contracts with great force and creates high pressure

2) semilunar valves fill with blood and close tightly

3) leaflet valves are pressed against the walls of the aorta

4) leaflet valves are closed and semilunar valves are open

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

Choose one, the most correct option. Arterial blood flows through the human body

1) renal veins

2) pulmonary veins

4) pulmonary arteries

Choose one, the most correct option. In mammals, blood is enriched with oxygen in

1) arteries of the pulmonary circulation

2) capillaries of the great circle

3) arteries of the great circle

4) capillaries of the small circle

1. Establish the sequence of blood movement through the vessels of the systemic circulation. Write down the corresponding sequence of numbers.

1) portal vein of the liver

3) gastric artery

4) left ventricle

5) right atrium

6) inferior vena cava

2. Determine the correct sequence of blood circulation in the systemic circulation, starting with the left ventricle. Write down the corresponding sequence of numbers.

2) Superior and inferior vena cava

3) Right atrium

4) Left ventricle

5) Right ventricle

6) Tissue fluid

3. Establish the correct sequence of blood passage through the systemic circulation. Write down the corresponding sequence of numbers in the table.

1) right atrium

2) left ventricle

3) arteries of the head, limbs and torso

5) inferior and superior vena cava

4. Establish the sequence of blood movement in the human body, starting with the left ventricle. Write down the corresponding sequence of numbers.

1) left ventricle

4) pulmonary veins

5) right atrium

Arrange the blood vessels in order of decreasing speed of blood movement in them

1) superior vena cava

3) brachial artery

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

Choose one, the most correct option. Valves prevent blood from flowing back from the pulmonary artery and aorta into the ventricles.

1. Establish the sequence of blood movement in a person through the pulmonary circulation. Write down the corresponding sequence of numbers.

1) pulmonary artery

2) right ventricle

4) left atrium

2. Establish the sequence of circulatory processes, starting from the moment when blood moves from the lungs to the heart. Write down the corresponding sequence of numbers.

1) blood from the right ventricle enters the pulmonary artery

2) blood moves through the pulmonary vein

3) blood moves through the pulmonary artery

4) oxygen comes from the alveoli to the capillaries

5) blood enters the left atrium

6) blood enters the right atrium

3. Establish the sequence of movement of arterial blood in a person, starting from the moment it is saturated with oxygen in the capillaries of the pulmonary circle. Write down the corresponding sequence of numbers.

1) left ventricle

2) left atrium

3) veins of the small circle

4) small circle capillaries

5) arteries of the great circle

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

4) pulmonary veins

5) capillaries of the lungs

Establish the sequence of events that occur in the cardiac cycle after blood enters the heart. Write down the corresponding sequence of numbers.

1) contraction of the ventricles

2) general relaxation of the ventricles and atria

3) blood flow into the aorta and artery

4) blood flow into the ventricles

5) atrial contraction

Establish a correspondence between human blood vessels and the direction of blood movement in them: 1) from the heart, 2) to the heart

A) veins of the pulmonary circulation

B) veins of the systemic circulation

B) arteries of the pulmonary circulation

D) arteries of the systemic circulation

Choose three options. A person has blood from the left ventricle of the heart

1) when it contracts, it enters the aorta

2) when it contracts, it enters the left atrium

3) supplies body cells with oxygen

4) enters the pulmonary artery

5) under high pressure enters the large circulation circle

6) under slight pressure enters the pulmonary circulation

Choose three options. Blood flows through the arteries of the pulmonary circulation in humans

4) oxygenated

5) faster than in the pulmonary capillaries

6) slower than in the pulmonary capillaries

Choose three options. Veins are blood vessels through which blood flows

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

Choose three options. Blood flows through the arteries of the systemic circulation in humans

3) saturated with carbon dioxide

4) oxygenated

5) faster than in other blood vessels

6) slower than in other blood vessels

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

2. Establish a correspondence between a vessel of the human circulatory system and the type of blood that flows through it: 1) arterial, 2) venous. Write numbers 1 and 2 in the order corresponding to the letters.

A) femoral vein

B) brachial artery

B) pulmonary vein

D) subclavian artery

D) pulmonary artery

Choose three options. In mammals and humans, venous blood, unlike arterial,

1) poor in oxygen

2) flows in a small circle through the veins

3) fills the right half of the heart

4) saturated with carbon dioxide

5) enters the left atrium

6) provides body cells with nutrients

Analyze the table “The work of the human heart.” For each cell indicated by a letter, select the corresponding term from the list provided.

2) Superior vena cava

4) Left atrium

5) Carotid artery

6) Right ventricle

7) Inferior vena cava

8) Pulmonary vein

Choose three correct answers out of six and write down the numbers under which they are indicated. Elements of the human circulatory system containing venous blood are

1) pulmonary artery

4) right atrium and right ventricle

5) left atrium and left ventricle

6) pulmonary veins

Choose three correct answers out of six and write down the numbers under which they are indicated. Blood leaks from the right ventricle

5) towards the lungs

6) towards the cells of the body

Establish a correspondence between the processes and the blood circulation circles for which they are characteristic: 1) small, 2) large. Write numbers 1 and 2 in the order corresponding to the letters.

A) Arterial blood flows through the veins.

B) The circle ends in the left atrium.

B) Arterial blood flows through the arteries.

D) The circle begins in the left ventricle.

D) Gas exchange occurs in the capillaries of the alveoli.

E) Venous blood is formed from arterial blood.

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

Circulatory system. Circulation circles

Question 1. What kind of blood flows through the arteries of the systemic circle, and what kind of blood flows through the arteries of the small circle?

Arterial blood flows through the arteries of the systemic circle, and venous blood flows through the arteries of the small circle.

Question 2. Where does the systemic circulation begin and end, and where does the pulmonary circulation end?

All vessels form two circles of blood circulation: large and small. The great circle begins in the left ventricle. The aorta departs from it, which forms an arch. Arteries arise from the aortic arch. The coronary vessels depart from the initial part of the aorta, which supply blood to the myocardium. The part of the aorta located in the chest is called the thoracic aorta, and the part located in the abdominal cavity is called the abdominal aorta. The aorta branches into arteries, arteries into arterioles, and arterioles into capillaries. From the capillaries of a large circle, oxygen and nutrients flow to all organs and tissues, and carbon dioxide and metabolic products flow from the cells into the capillaries. Blood turns from arterial to venous.

Purification of the blood from toxic breakdown products occurs in the vessels of the liver and kidneys. Blood from the digestive tract, pancreas and spleen enters the portal vein of the liver. In the liver, the portal vein branches into capillaries, which then unite again into the common trunk of the hepatic vein. This vein drains into the inferior vena cava. Thus, all blood from the abdominal organs, before entering the systemic circle, passes through two capillary networks: through the capillaries of these organs themselves and through the capillaries of the liver. The portal system of the liver ensures the neutralization of toxic substances that are formed in the large intestine. The kidneys also have two capillary networks: the network of the renal glomeruli, through which the blood plasma containing harmful metabolic products (urea, uric acid) passes into the cavity of the nephron capsule, and the capillary network intertwining the convoluted tubules.

Capillaries merge into venules, then into veins. Then, all the blood flows into the superior and inferior vena cava, which flow into the right atrium.

The pulmonary circulation begins in the right ventricle and ends in the left atrium. Venous blood from the right ventricle enters the pulmonary artery, then into the lungs. Gas exchange occurs in the lungs, venous blood turns into arterial blood. The four pulmonary veins carry arterial blood to the left atrium.

Question 3. Is the lymphatic system a closed or open system?

The lymphatic system should be classified as open. It blindly begins in the tissues with lymphatic capillaries, which then unite to form lymphatic vessels, which in turn form lymphatic ducts that empty into the venous system.

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Which vein carries arterial blood?

Which vein carries arterial blood?

In principle, arterial blood does not flow through the veins! It (as the name suggests) flows through the arteries! Arteries run deeper than veins. Blood pressure is always higher than venous pressure, since the main artery (aorta) comes from the heart, which pumps blood into it under pressure. The aorta is divided into smaller arteries, which in turn also branch, and so on, right up to the capillaries that carry oxygen to every cell of the body. This is how the cells “inhale”. Arterial blood is scarlet, saturated with oxygen.

Venous blood flows through the veins; it carries waste (exhalation) from each cell “to be released.” The veins are located closer to the surface, the pressure in them is less (here the heart creates not pressure, but “discharge”), the blood is dark.

I don't agree with the answer above. Everything that is written there is completely applicable to the systemic circulation. And in the pulmonary circulation, it is through the pulmonary veins that arterial blood flows from the lungs to the left atrium.

Arterial blood is the blood that flows through the arteries, and venous blood is the blood that flows through the veins.

This is one of the most common misconceptions.

It arose due to the consonance of words in the pairs “artery - arterial” and “vein - venous” (blood) and due to ignorance of these terms.

Firstly, the vessels are divided into arteries and veins depending on where they carry blood.

Arteries are efferent vessels, and blood flows through them from the heart to the organs.

Veins are afferent vessels; they carry blood from the organs to the heart.

Thirdly, the conclusion from these differences is the question: “Can arterial blood flow through the veins, and venous blood through the arteries?” and the seemingly paradoxical answer to it: “Maybe!” In the pulmonary circulation, in which the blood is saturated with oxygen in the lungs, this is exactly what happens.

Blood saturated with carbon dioxide (venous) flows from the heart to the lungs through the efferent vessels (arteries). Conversely, from the lungs to the heart, oxygen-rich blood (arterial) enters the heart through the afferent vessels (veins). In a large circle, which “serves” all the organs of the body and distributes oxygen, arterial (“oxygen”) blood runs through the arteries (from the heart), and venous (“carbon dioxide”) blood flows back through the veins (to the heart).

Blood circulation is a continuous flow of blood that moves through the vessels and cavities of the heart. This system is responsible for metabolic processes in the organs and tissues of the human body. Circulating blood transports oxygen and nutrients to the cells, taking carbon dioxide and metabolites from there. That is why any circulatory disorders threaten with dangerous consequences.

The blood circulation consists of a large (systemic) and a small (pulmonary) circle. Each turn has a complex structure and functions. The systemic circle originates from the left ventricle and ends in the right atrium, and the pulmonary circle originates from the right ventricle and ends in the left atrium.

Blood circulation is a complex system that consists of the heart and blood vessels. The heart constantly contracts, pushing blood through the vessels to all organs and tissues. The circulatory system consists of arteries, veins, and capillaries.

The circulatory system is formed by arteries, veins and capillaries

The arteries of the systemic circulation are the largest vessels; they have a cylindrical shape and transport blood from the heart to the organs.

Structure of the walls of arterial vessels:

• outer connective tissue membrane;
• middle layer of smooth muscle fibers with elastic veins;
• strong elastic inner endothelial membrane.

Arteries have elastic walls that constantly contract, allowing blood to move evenly.

With the help of the veins of the systemic circulation, blood moves from the capillaries to the heart. Veins have the same structure as arteries, but they are less strong, since their middle layer contains less smooth muscle and elastic fibers. That is why the speed of blood movement in the venous vessels is largely influenced by nearby tissues, especially skeletal muscles. All veins, except the vena cava, are equipped with valves that prevent the backflow of blood.

Capillaries are small vessels that consist of endothelium (a single layer of flat cells). They are quite thin (about 1 micron) and short (from 0.2 to 0.7 mm). Due to their structure, microvessels saturate tissues with oxygen and useful substances, carrying away carbon dioxide, as well as metabolic products. Blood moves slowly through them; in the arterial part of the capillaries, water is removed into the intercellular space. In the venous part, blood pressure decreases and water flows back into the capillaries.

Structure of the systemic circulation

The aorta is the largest vessel of the great circle, with a diameter of 2.5 cm. This is a kind of source from which all other arteries emerge. The vessels branch, their size decreases, they go to the periphery, where they give oxygen to organs and tissues.

The largest vessel of the systemic circulation is the aorta

The aorta is divided into the following sections:

• ascending;
• descending;
• the arc that connects them.

The ascending section is the shortest, its length is no more than 6 cm. The coronary arteries emanate from it, which supply oxygen-rich blood to the myocardial tissues. Sometimes the term “cardiac circulation” is used to name the ascending section. From the most convex surface of the aortic arch, arterial branches depart that supply blood to the arms, neck, and head: on the right side there is the brachiocephalic trunk, divided in two, and on the left there is the common carotid, subclavian artery.

The descending aorta is divided into 2 groups of branches:

• Parietal arteries that supply blood to the chest, spinal column, and spinal cord.
• Visceral (splanchnic) arteries that transport blood and nutrients to the bronchi, lungs, esophagus, etc.

Under the diaphragm is the abdominal aorta, the parietal branches of which supply the abdominal cavity, the lower surface of the diaphragm, and the spine.

The internal branches of the abdominal aorta are divided into paired and unpaired. The vessels that extend from the unpaired trunks transport oxygen to the liver, spleen, stomach, intestines, and pancreas. The unpaired branches include the celiac trunk, as well as the superior and inferior mesenteric arteries.

There are only two paired trunks: renal, ovarian or testicular. These arterial vessels are adjacent to the organs of the same name.

The aorta ends with the left and right iliac arteries. Their branches extend to the pelvic organs and legs.

Many people are interested in the question of how the systemic circulatory system works. In the lungs, the blood is saturated with oxygen, after which it is transported to the left atrium, and then to the left ventricle. The iliac arteries supply blood to the legs, and the remaining branches supply blood to the chest, arms, and organs of the upper half of the body.

The veins of the systemic circulation carry oxygen-poor blood. The systemic circle ends with the superior and inferior vena cava.

The diagram of the veins of the systemic circle is quite clear. The femoral veins in the legs unite to form the iliac vein, which becomes the inferior vena cava. In the head, venous blood collects in the jugular veins, and in the arms - in the subclavian veins. The jugular as well as the subclavian vessels unite to form the innominate vein, which gives rise to the superior vena cava.

Blood supply to the head

The circulatory system of the head is the most complex structure of the body. The carotid artery, which is divided into 2 branches, is responsible for the blood supply to the parts of the head. The external carotid arterial vessel saturates the face, temporal region, oral cavity, nose, thyroid gland, etc. with oxygen and useful substances.

The main vessel supplying blood to the head is the carotid artery

The internal branch of the carotid artery goes deeper, forming the Circle of Wallisian, which transports blood to the brain. In the cranium, the internal carotid artery branches into the ophthalmic, anterior, middle cerebral, and communicating arteries.

This is how only ⅔ of the systemic circle is formed, which ends with the posterior cerebral arterial vessel. It has a different origin, the scheme of its formation is as follows: subclavian artery - vertebral - basilar - posterior cerebral. In this case, the brain is supplied with blood by the carotid and subclavian arteries, which are connected to each other. Thanks to anastomoses (vascular anastomoses), the brain survives minor disturbances in blood flow.

Principle of placement of arteries

The circulatory system of each body structure is approximately similar to that described above. Arterial vessels always approach organs along the shortest path. The vessels in the limbs pass precisely along the flexion side, since the extensor part is longer. Each artery originates at the embryonic site of the organ, and not at its actual location. For example, the arterial vessel of the testicle emerges from the abdominal aorta. Thus, all vessels are connected to their organs from the inside.

The arrangement of vessels resembles the structure of the skeleton

The placement of arteries is also related to the structure of the skeleton. For example, the brachial branch runs along the upper limb, which corresponds to the humerus; the ulnar and radial arteries also pass next to the bones of the same name. And in the skull there are openings through which arterial vessels transport blood to the brain.

Arterial vessels of the systemic circulation form networks in the joint area using anastomoses. Thanks to this scheme, the joints are continuously supplied with blood during movement. The size of the vessels and their number depend not on the size of the organ, but on its functional activity. Organs that work more intensively are saturated with a large number of arteries. Their placement around the organ depends on its structure. For example, the diagram of the vessels of parenchymal organs (liver, kidneys, lungs, spleen) corresponds to their shape.

Structure and functions of the pulmonary circulation

The pulmonary circulation originates from the right ventricle, from which several pulmonary arterial vessels emerge. A small circle closes in the left atrium, to which the pulmonary veins adjoin.

The pulmonary circulation is so called because it is responsible for gas exchange between the pulmonary capillaries and the alveoli of the same name. It consists of the common pulmonary artery, right and left branches with branches, pulmonary vessels, which unite into 2 right and 2 left veins and enter the left atrium.

The common pulmonary artery (diameter from 26 to 30 mm) emerges from the right ventricle; it runs diagonally (up and to the left), dividing into 2 branches that approach the lungs. The right pulmonary arterial vessel goes to the right to the medial surface of the lung, where it divides into 3 branches, which also have branches. The left vessel is shorter and thinner, it passes from the point of division of the common pulmonary artery to the medial part of the left lung in the transverse direction. Near the middle part of the lung, the left artery is divided into 2 branches, which in turn are divided into segmental branches.

Venules emanate from the capillary vessels of the lungs, which pass into the veins of the small circle. There are 2 veins coming out of each lung (upper and lower). When the common basal vein connects with the superior vein of the lower lobe, the right inferior pulmonary vein is formed.

The superior pulmonary trunk has 3 branches: apical-posterior, anterior, and lingular vein. It takes blood from the upper part of the left lung. The left upper trunk is larger than the lower one; it collects blood from the lower lobe of the organ.

The superior and inferior vena cava transport blood from the upper and lower parts of the body to the right atrium. From there, the blood is sent to the right ventricle, and then through the pulmonary artery to the lungs.

Under the influence of high pressure, blood rushes to the lungs, and under negative pressure, to the left atrium. For this reason, blood always moves slowly through the capillary vessels of the lungs. Thanks to this pace, the cells have time to become saturated with oxygen, and carbon dioxide penetrates into the blood. When a person plays sports or does hard work, the need for oxygen increases, then the heart increases pressure and blood flow accelerates.

Based on the foregoing, blood circulation is a complex system that provides vital functions to the entire body. The heart is a muscular pump, and arteries, veins, capillaries are systems of channels that transport oxygen and nutrients to all organs and tissues. It is important to monitor the state of the cardiovascular system, as any violation can have dangerous consequences.

Questions at the beginning of the paragraph.

Question 1. What are the functions of the systemic circulation?

The function of the systemic circulation is to saturate organs and tissues with oxygen and transfer carbon dioxide from tissues and organs.

Question 2. What happens in the pulmonary circulation?

When the right ventricle contracts, venous blood is directed into the two pulmonary arteries. The right artery leads to the right lung, the left - to the left lung. Please note: venous blood moves through the pulmonary arteries! In the lungs, the arteries branch, becoming thinner and thinner. They approach the pulmonary vesicles - the alveoli. Here the thin arteries divide into capillaries, weaving around the thin wall of each vesicle. The carbon dioxide contained in the veins goes into the alveolar air of the pulmonary vesicle, and oxygen from the alveolar air passes into the blood. Here it combines with hemoglobin. The blood becomes arterial: hemoglobin again turns into oxyhemoglobin and the blood changes color - from dark it becomes scarlet. Arterial blood returns to the heart through the pulmonary veins. From the left and from the right lungs, two pulmonary veins carrying arterial blood are directed to the left atrium. The pulmonary circulation ends in the left atrium.

Question 3. What function do lymphatic capillaries and lymph nodes perform?

The outflow of lymph carries away from the tissue fluid everything that is formed during the life of cells. Here are microorganisms that have entered the internal environment, dead parts of cells, and other residues unnecessary for the body. In addition, some nutrients from the intestines enter the lymphatic system. All these substances enter the lymphatic capillaries and are sent to the lymphatic vessels. Passing through the lymph nodes, the lymph is cleansed and, freed from foreign impurities, flows into the neck veins.

Questions at the end of the paragraph.

Question 1. What kind of blood flows through the arteries of the systemic circle, and what kind of blood flows through the arteries of the small circle?

Arterial blood flows through the arteries of the systemic circle, and venous blood flows through the arteries of the small circle.

Question 2. Where does the systemic circulation begin and end, and where does the pulmonary circulation end?

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

Question 3. Is the lymphatic system a closed or open system?

The lymphatic system should be classified as open. It blindly begins in the tissues with lymphatic capillaries, which then unite to form lymphatic vessels, which in turn form lymphatic ducts that empty into the venous system.

Following the diagram shown in Figures 51 and 42, follow the path of the lymph from the moment of its formation to the flow into the bed of the blood vessel. Specify the function of the lymph nodes.

The human lymphatic system is a huge network of tiny vessels that combine into larger ones and are directed to the lymph nodes. Lymphatic capillaries penetrate all human tissues, as well as blood vessels. Connecting with each other, the capillaries form a tiny network. Through it, fluid, protein substances, metabolic products, microbes, as well as foreign substances and toxins are removed from the tissues.

Lymph, which fills the lymphatic system, contains cells that protect the body from invading microbes as well as foreign substances. By combining, capillaries form vessels of various diameters. The largest lymphatic duct flows into the circulatory system.

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

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

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

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

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

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

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

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

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

Choose one, the most correct option. Valves prevent blood from flowing back from the pulmonary artery and aorta into the ventricles.
1) tricuspid
2) venous
3) double-leaf
4) semilunar

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

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

Answer

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

Answer

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

Answer

1. Establish a correspondence between the type of human blood vessels and the type of blood they contain: 1) arterial, 2) venous
A) pulmonary arteries
B) veins of the pulmonary circulation
B) aorta and arteries of the systemic circulation
D) superior and inferior vena cava

Answer

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

Answer

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

Answer

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

Answer

Analyze the table “The work of the human heart.” For each cell indicated by a letter, select the corresponding term from the list provided.
1) Arterial
2) Superior vena cava
3) Mixed
4) Left atrium
5) Carotid artery
6) Right ventricle
7) Inferior vena cava
8) Pulmonary vein

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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