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

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

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

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

The function of the heart is to rhythmically pump blood into the arteries, which comes to it through the veins. The heart beats about 70-75 times per minute when the body is at rest (1 time per 0.8 s). More than half of this time it rests - relaxes. Continuing activities The heart consists of cycles, each of which consists of contraction (systole) and relaxation (diastole).

There are three phases of cardiac activity:

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

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

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

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

In humans, the diameter of the arteries ranges from 0.4 to 2.5 cm. The total 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) - the smallest vessels (average diameter does not exceed 0.005 mm, or 5 microns), penetrating the organs and tissues of animals and humans, having a closed circulatory system. They connect small arteries - arterioles with small veins - venules. Through the walls of capillaries, consisting of endothelial cells, gases and other substances are exchanged between the blood and various tissues.

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

Circulation circles

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

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

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

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

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

Movement of blood through vessels

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

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

The most high pressure 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 blood vessels and chambers of the heart, resulting from 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, the maximum, or systolic, blood pressure is distinguished - the level of pressure in the arteries during heart systole is about 120 mm Hg, and the minimum, or diastolic - the level of pressure in the arteries during diastole of the heart is about 80 mm Hg. Those. arterial blood pressure pulsates in time with the contractions of the heart: at the moment of systole it rises to 120-130 mm Hg. Art., and during diastole it decreases to 80-90 mm Hg. Art. These pulse pressure fluctuations occur simultaneously with pulse fluctuations of the arterial wall.

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

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

The 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 vein. venous system, so the blood moves through the veins towards the heart. This is facilitated by the suction action chest(“breathing pump”) and contraction skeletal muscles(“muscle pump”). During inhalation, the pressure in the chest decreases. In this case, the pressure difference at the beginning and end of the venous system increases, and blood through the veins is directed to the heart. Skeletal muscles contract and compress the veins, which also helps move blood to the heart.

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

Redistribution of blood in the body

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

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

Blood circulation time

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

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

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

The blood circulation time in humans is on average approximately 27 heart systoles. At 70-80 heart beats per minute, complete blood circulation occurs in approximately 20-23 seconds. We must not forget, however, that the speed of blood flow along the axis of the vessel is greater than at its walls, and also that not all vascular areas have the same length. Therefore, not all blood circulates so quickly, and the time indicated above is the shortest.

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

Regulation of blood circulation

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

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

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 the excitation increases, the frequency nerve impulses increases and the vessels narrow more strongly - vascular tone increases. On the contrary, when the frequency of nerve impulses decreases due to inhibition of sympathetic neurons, vascular tone decreases and blood vessels dilate. To the vessels of some organs (skeletal muscles, salivary glands) in addition to vasoconstrictors, vasodilator nerves are also suitable. These nerves are stimulated and dilate the blood vessels of the organs as they work. The lumen of blood vessels is also affected by substances carried by the blood. Adrenaline constricts blood vessels. Another substance, acetylcholine, secreted by the endings of some nerves, dilates them.

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

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

Cardiac hygiene

Normal activity 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. At physical work The organs' need for oxygen increases simultaneously with the strengthening and acceleration of heart contractions. Only a strong heart muscle can provide such work. To be resilient to diversity labor activity, it is important to train the heart, increase the strength of its muscles.

Physical labor and physical education develop the heart muscle. To 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. Especially bad influence Alcohol, nicotine, and drugs affect the cardiovascular system. Alcohol and nicotine poison the heart muscle and nervous system, causing sudden violations regulation of vascular tone and cardiac activity. They lead to development serious illnesses cardiovascular system and can cause sudden death. Young people who smoke and drink alcohol are more likely than others to experience heart spasms, which can cause severe heart attacks and sometimes death.

First aid for wounds and bleeding

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

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

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

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

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

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

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

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