Summary: The human circulatory system. General structure and significance of the circulatory system (heart, blood vessels)

Date: 15.04.2019

The content of the article

CIRCULATORY SYSTEM(circulatory system), a group of organs involved in the circulation of blood in the body. The normal functioning of any animal organism requires effective blood circulation, since it carries oxygen, nutrients, salts, hormones and other vital substances to all organs of the body. In addition, the circulatory system returns blood from tissues to those organs where it can be enriched with nutrients, as well as to the lungs, where it is saturated with oxygen and released from carbon dioxide (carbon dioxide). Finally, blood should wash a number of special organs, such as the liver and kidneys, which neutralize or excrete end products of metabolism. The accumulation of these foods can lead to chronic illness and even death.

This article discusses the human circulatory system. ( For circulatory systems in other species, see ANATOMY COMPARATIVE.)

The constituent parts of the circulatory system.

In its most general form, this transport system consists of a four-chamber muscle pump (heart) and many channels (vessels) whose function is to deliver blood to all organs and tissues and then return it to the heart and lungs. According to the main components of this system, it is also called cardiovascular, or cardiovascular.

Blood vessels are divided into three main types: arteries, capillaries and veins. Arteries carry blood from the heart. They branch into vessels of smaller diameter, through which blood enters all parts of the body. Closer to the heart, the arteries have the largest diameter (approximately with the thumb), in the limbs they are the size of a pencil. In the most distant parts of the body from the heart, the blood vessels are so small that they are visible only under a microscope. It is these microscopic vessels, capillaries, that supply cells with oxygen and nutrients. After their delivery, blood loaded with end products of metabolism and carbon dioxide is sent to the heart through a network of vessels called veins, and from the heart to the lungs, where gas exchange occurs, as a result of which the blood is freed from the load of carbon dioxide and saturated with oxygen.

During the passage through the body and its organs, some part of the liquid through the walls of the capillaries seeps into the tissue. This opalescent, plasma-like fluid is called lymph. Lymph is returned to the general circulatory system through the third system of channels - the lymphatic pathways, which merge into large ducts that flow into the venous system in the immediate vicinity of the heart. ( For a detailed description of lymph and lymphatic vessels, seeLYMPHATIC SYSTEM.)

WORK OF THE BLOOD SYSTEM

Pulmonary circulation.

It is convenient to begin the description of the normal movement of blood throughout the body from the moment when it returns to the right half of the heart through two large veins. One of them, the superior vena cava, brings blood from the upper half of the body, and the second, inferior vena cava, from the inferior. Blood from both veins enters the collective section of the right side of the heart, the right atrium, where it mixes with the blood brought by the coronary veins opening into the right atrium through the coronary sinus. The coronary arteries and veins circulate the blood necessary for the work of the heart itself. The atrium fills, contracts and pushes blood into the right ventricle, which, while contracting, pumps blood through the pulmonary arteries into the lungs. A constant blood flow in this direction is supported by the operation of two important valves. One of them, the tricuspid located between the ventricle and the atrium, prevents the return of blood to the atrium, and the second, the pulmonary valve, closes when the ventricle relaxes and thereby prevents the return of blood from the pulmonary arteries. In the lungs, blood passes through the branching vessels, entering the network of thin capillaries, which are in direct contact with the smallest air sacs - the alveoli. Between capillary blood and alveoli, an exchange of gases occurs, which completes the pulmonary phase of blood circulation, i.e. phase of blood flow to the lungs ( see alsoBREATHING BODIES).

Systemic circulation.

From this moment, the systemic phase of blood circulation begins, i.e. blood transfer phase to all body tissues. Purified from carbon dioxide and enriched with oxygen (oxygenated), the blood returns to the heart through four pulmonary veins (two from each lung) and under low pressure enters the left atrium. The way the blood flows from the right ventricle of the heart to the lungs and returns from them to the left atrium is the so-called pulmonary circulation. The left atrium, filled with blood, contracts simultaneously with the right and pushes it into the massive left ventricle. The latter, having filled, contracts, sending blood under high pressure to the largest diameter artery - the aorta. All arterial branches supplying body tissues depart from the aorta. Like the right side of the heart, there are two valves on the left. A bicuspid (mitral) valve directs blood flow to the aorta and prevents the return of blood to the ventricle. The entire path of blood from the left ventricle until its return (through the upper and lower vena cava) to the right atrium is designated as a large circle of blood circulation.

Arteries.

In a healthy person, the aortic diameter is approximately 2.5 cm. This large vessel departs from the heart upward, forms an arc, and then descends through the chest into the abdominal cavity. Along the aorta, all large arteries that enter the large circle of blood circulation branch off from it. The first two branches extending from the aorta almost at the very heart are the coronary arteries that supply blood to the heart tissue. In addition to them, the ascending aorta (the first part of the arc) does not give branches. However, at the top of the arc, three important vessels depart from it. The first - the nameless artery - immediately divides into the right carotid artery, which supplies blood to the right half of the head and brain, and the right subclavian artery, passing under the collarbone into the right hand. The second branch from the aortic arch is the left carotid artery, the third is the left subclavian artery; along these branches blood flows to the head, neck and left arm.

From the aortic arch, a descending aorta begins, which supplies blood to the organs of the chest, and then through the hole in the diaphragm penetrates into the abdominal cavity. Two renal arteries that feed the kidneys are separated from the abdominal aorta, as well as the abdominal trunk with upper and lower mesenteric arteries extending to the intestine, spleen and liver. Then the aorta is divided into two iliac arteries that supply the pelvic organs with blood. In the groin area, the iliac arteries pass into the femoral; the latter, going down the hips, at the level of the knee joint pass into the popliteal arteries. Each of them, in turn, is divided into three arteries - the anterior tibial, posterior tibial and fibular arteries, which feed the tissues of the legs and feet.

Throughout the bloodstream, the arteries become smaller and smaller as they branch, and finally acquire a caliber that is only several times larger than the size of their blood cells. These vessels are called arterioles; continuing to divide, they form a diffuse network of vessels (capillaries), the diameter of which is approximately equal to the diameter of the red blood cell (7 μm).

The structure of the arteries.

Although the large and small arteries are somewhat different in structure, the walls of both of them consist of three layers. The outer layer (adventitia) is a relatively loose layer of fibrous, elastic connective tissue; the smallest blood vessels (the so-called vascular vessels) that feed the vascular wall, as well as the branches of the autonomic nervous system that regulate the lumen of the vessel, pass through it. The middle layer (media) consists of elastic tissue and smooth muscles, providing elasticity and contractility of the vascular wall. These properties are necessary to regulate blood flow and maintain normal blood pressure in changing physiological conditions. As a rule, the walls of large vessels, such as the aorta, contain more elastic tissue than the walls of the smaller arteries in which muscle tissue predominates. For this tissue feature, the arteries are divided into elastic and muscle. The inner layer (intima) rarely exceeds the diameter of several cells in thickness; it is this layer, lined with endothelium, that gives the inner surface of the vessel smoothness facilitating blood flow. Through it, nutrients enter the deep layers of the media.

As the diameter of the arteries decreases, their walls become thinner and the three layers become less and less distinguishable, while - at the arteriolar level - mainly spiral muscle fibers, some elastic tissue and the inner lining of endothelial cells remain in them.

Capillaries.

Finally, the arterioles quietly pass into the capillaries, the walls of which were sent only by the endothelium. Although these thinnest tubes contain less than 5% of the circulating blood volume, they are extremely important. Capillaries form an intermediate system between arterioles and venules, and their networks are so dense and wide that no part of the body can be pierced without piercing a huge number of them. It is in these networks that under the influence of osmotic forces, oxygen and nutrients pass into individual cells of the body, and in return products of cellular metabolism enter the bloodstream.

In addition, this network (the so-called capillary bed) plays a crucial role in regulating and maintaining body temperature. The constancy of the internal environment (homeostasis) of the human body depends on the preservation of body temperature within narrow limits of the norm (36.8–37 °). Typically, blood from arterioles enters the venules through the capillary bed, but in cold conditions, the capillaries close and blood flow decreases, primarily in the skin; while blood from arterioles enters the venules, bypassing the many branches of the capillary bed (bypass). On the contrary, if heat transfer is necessary, for example, in the tropics, all capillaries open and skin blood flow rises, which contributes to heat loss and maintaining a normal body temperature. Such a mechanism exists in all warm-blooded animals.

Veins.

On the opposite side of the capillary bed, the vessels merge into numerous small channels, venules, which are comparable in size to arterioles. They continue to connect, forming larger veins through which blood from all parts of the body flows back to the heart. The system of valves found in most veins contributes to constant blood flow in this direction. Venous pressure, in contrast to pressure in the arteries, does not directly depend on the muscle tension of the vascular wall, so the blood flow in the right direction is determined mainly by other factors: the pushing force created by the arterial pressure of a large circle of blood circulation; “Suction” effect of negative pressure that occurs in the chest during inspiration; pumping action of limb muscles, which during normal contractions push venous blood to the heart.

The walls of the veins are similar in structure to arterial in that they also consist of three layers, expressed, however, much weaker. Blood flow through the veins, which occurs almost without pulsation and at relatively low pressure, does not require such thick and elastic walls as arteries. Another important difference between veins and arteries is the presence of valves in them that maintain low blood pressure in one direction. The greatest number of valves is found in the veins of the limbs, where muscle contractions play a particularly important role in moving blood back to the heart; large veins, such as the hollow, portal, and iliac, are devoid of valves.

On the way to the heart, veins collect blood flowing from the gastrointestinal tract through the portal vein, from the liver through the hepatic veins, from the kidneys through the renal veins and from the upper limbs through the subclavian veins. Near the heart, two hollow veins form, through which blood enters the right atrium.

The vessels of the pulmonary circulation (pulmonary) resemble the vessels of the large circle, with the only exception that they lack valves, and the walls of both arteries and veins are much thinner. Unlike a large circle of blood circulation, venous, non-oxygenated blood flows into the lungs through the pulmonary arteries, and arterial blood flows through the pulmonary veins, i.e. saturated with oxygen. The terms "arteries" and "veins" correspond to the direction of blood flow in the vessels - from the heart or to the heart, and not to what kind of blood they contain.

Subsidiary organs.

A number of organs perform functions that complement the work of the circulatory system. Closest to it are the spleen, liver and kidneys.

Spleen.

With multiple passage through the circulatory system, red blood cells (red blood cells) are damaged. Such "spent" cells are removed from the blood in many ways, but the spleen plays the main role here. The spleen not only destroys damaged red blood cells, but also produces lymphocytes (related to white blood cells). In lower vertebrates, the spleen also plays the role of a erythrocyte reservoir, but in humans this function is weakly expressed. see alsoSPLEEN.

Liver.

To fulfill its more than 500 functions, the liver needs good blood supply. Therefore, it occupies an important place in the circulatory system and is provided by its own vascular system, which is called the portal system. A number of liver functions are directly related to blood, for example, the removal of spent red blood cells from it, the development of blood coagulation factors and the regulation of blood sugar by accumulating its excess in the form of glycogen. see alsoLIVER.

The kidneys.

BLOOD (ARTERIAL) PRESSURE

With each contraction of the left ventricle of the heart, the arteries fill with blood and stretch. This phase of the cardiac cycle is called the ventricular systole, and the phase of ventricular relaxation is called the diastole. During diastole, however, the elastic forces of large blood vessels come into play, maintaining blood pressure and preventing the flow of blood flowing to various parts of the body from being interrupted. A change in systole (contractions) and diastole (relaxation) makes the blood flow in the arteries pulsating. The pulse can be found on any large artery, but it is usually felt on the wrist. In adults, the pulse rate is usually 68–88, and in children 80–100 beats per minute. The existence of arterial pulsation is also evidenced by the fact that during transection of an artery, bright red blood flows with jerks, and with transection of a vein, bluish (due to lower oxygen content) blood flows evenly, without visible jerks.

To ensure proper blood supply to all parts of the body during both phases of the cardiac cycle, a certain level of blood pressure is needed. Although this value fluctuates significantly even in healthy people, normal blood pressure averages 100–150 mmHg. during systole and 60–90 mm Hg during diastole. The difference between these indicators is called pulse pressure. For example, in a person with a blood pressure of 140/90 mmHg. pulse pressure is 50 mmHg Another indicator - mean arterial pressure - can be approximately calculated by averaging systolic and diastolic pressure or adding half of the pulse pressure to the diastolic.

Normal blood pressure is determined, maintained and regulated by many factors, the main of which are the strength of the heart contractions, the elastic “return” of the walls of the arteries, the amount of blood in the arteries and the resistance of the small arteries (muscle type) and arterioles to the movement of blood. All these factors together determine the lateral pressure on the elastic walls of the arteries. It can be very accurately measured using a special electronic sensor inserted into the artery and recording the results on paper. Such devices, however, are quite expensive and are used only for special studies, and doctors, as a rule, make indirect measurements using the so-called. sphygmomanometer (tonometer).

A sphygmomanometer consists of a cuff that is wrapped around the limb where the measurement is made, and a recording device, which can be a mercury column or a simple aneroid manometer. Typically, the cuff is tightly wrapped around the arm above the elbow and inflated until the pulse on the wrist disappears. The brachial artery is found at the elbow level and a stethoscope is placed over it, after which air is slowly released from the cuff. When the pressure in the cuff drops to a level at which blood flow resumes through the artery, a sound is heard using a stethoscope. The readings of the measuring device at the time of the appearance of this first sound (tone) correspond to the level of systolic blood pressure. With the further release of air from the cuff, the character of the sound changes significantly or it completely disappears. This moment corresponds to the level of diastolic pressure.

In a healthy person, blood pressure fluctuates throughout the day, depending on the emotional state, stress, sleep, and many other physical and mental factors. These fluctuations reflect certain shifts of the fine balance existing in the norm, which is supported by both nerve impulses coming from the centers of the brain through the sympathetic nervous system, and changes in the chemical composition of the blood that have a direct or indirect regulatory effect on the blood vessels. With strong emotional stress, the sympathetic nerves cause a narrowing of the small arteries of the muscle type, which leads to an increase in blood pressure and heart rate. Chemical equilibrium is even more important, the effect of which is mediated not only by the brain centers, but also by the individual nerve plexuses associated with the aorta and carotid arteries. The sensitivity of this chemical regulation is illustrated, for example, by the effect of the accumulation of carbon dioxide in the blood. With an increase in its level, blood acidity increases; this both directly and indirectly causes a reduction in the walls of the peripheral arteries, which is accompanied by an increase in blood pressure. At the same time, the heart rate increases, but the vessels of the brain expand paradoxically. The combination of these physiological reactions ensures the stability of the supply of oxygen to the brain due to an increase in the volume of incoming blood.

It is the fine regulation of blood pressure that allows you to quickly change the horizontal position of the body to vertical without significant movement of blood to the lower extremities, which could cause fainting due to insufficient blood supply to the brain. In such cases, the walls of the peripheral arteries contract and the oxygenated blood is sent mainly to vital organs. Vasomotor (vasomotor) mechanisms are even more important for animals such as a giraffe, whose brain, when it raises its head after drinking, moves up by almost 4 m in a few seconds. A similar decrease in the blood content in the vessels of the skin, digestive tract and liver occurs moments of stress, emotional experiences, shock and trauma, which allows you to provide the brain, heart and muscles with more oxygen and nutrients.

Such fluctuations in blood pressure are normal, but changes in it are observed in a number of pathological conditions. In heart failure, the force of contraction of the heart muscle can drop so much that the blood pressure is too low (arterial hypotension). Similarly, loss of blood or other fluids due to a severe burn or bleeding can cause a decrease in both systolic and diastolic pressure to a dangerous level. With some congenital heart defects (for example, non-closure of the ductus arteriosus) and a number of lesions of the valvular apparatus of the heart (for example, aortic valve insufficiency), peripheral resistance drops sharply. In such cases, systolic pressure can remain normal, and diastolic pressure is significantly reduced, which means an increase in pulse pressure.

The regulation of blood pressure in the body and the maintenance of the necessary blood supply to the organs make it possible to understand the enormous complexity of the organization and operation of the circulatory system. This truly remarkable transport system is a real “way of life" of the body, since the lack of blood supply to any vital organ, especially the brain, for at least several minutes leads to irreversible damage and even death.

BLOOD VESSEL DISEASES

Blood vessel diseases (vascular diseases) are conveniently considered in accordance with the type of vessels in which pathological changes develop. Stretching the walls of blood vessels or the heart itself leads to the formation of aneurysms (saccular protrusions). Usually this is a consequence of the development of scar tissue in a number of diseases of the coronary vessels, syphilitic lesions or hypertension. Aneurysm of the aorta or ventricles of the heart is the most serious complication of cardiovascular disease; it can rupture spontaneously, causing fatal bleeding.

Aorta.

The largest artery, the aorta, must contain the blood ejected under pressure from the heart and, due to its elasticity, move it into smaller arteries. In the aorta, infectious (most often syphilitic) and arteriosclerotic processes can develop; aortic rupture is also possible due to trauma or congenital weakness of its walls. High blood pressure often leads to chronic aortic expansion. However, aortic diseases are less important than heart disease. Her most severe lesions are extensive atherosclerosis and syphilitic aortitis.

Atherosclerosis.

Aortic atherosclerosis is a form of simple arteriosclerosis of the inner lining of the aorta (intima) with granular (atheromatous) fatty deposits in this layer and under it. One of the serious complications of this aortic disease and its main branches (nameless, iliac, carotid and renal arteries) is the formation of blood clots in the inner layer, which can interfere with blood flow in these vessels and lead to a catastrophic disturbance in the blood supply to the brain, legs and kidneys. Such obstructive (obstructing blood flow) lesions of some large vessels can be eliminated surgically (vascular surgery).

Syphilitic aortitis.

A decrease in the prevalence of syphilis itself makes the aortic inflammation caused by it more rare. It manifests itself approximately 20 years after infection and is accompanied by a significant expansion of the aorta with the formation of aneurysms or the spread of infection to the aortic valve, which leads to its insufficiency (aortic regurgitation) and overload of the left ventricle of the heart. It is also possible narrowing of the mouth of the coronary arteries. Any of these conditions can lead to death, sometimes very quickly. The age at which aortitis and its complications is manifested ranges from 40 to 55 years; the disease is more often observed in men.

Arteriosclerosis

the aorta, accompanied by a loss of elasticity of its walls, is characterized by damage not only to intima (as in atherosclerosis), but also to the muscle layer of the vessel. This is an elderly disease, and with increasing life expectancy of the population, it occurs more often. Loss of elasticity reduces the effectiveness of blood flow, which in itself can lead to aortic enlargement similar to aneurysm and even rupture of it, especially in the abdominal region. Currently, sometimes it is possible to cope with this condition surgically ( see alsoANEURYSM).

Pulmonary artery.

Lesions of the pulmonary artery and its two main branches are few. In these arteries, arteriosclerotic changes sometimes occur, as well as congenital malformations. The two most important changes include: 1) expansion of the pulmonary artery due to an increase in pressure due to any obstruction of blood flow in the lungs or on the blood path to the left atrium, and 2) blockage (embolism) of one of its main branches due to the passage of a blood clot inflamed large veins of the leg (phlebitis) through the right half of the heart, which is a common cause of sudden death.

Arteries of medium caliber.

The most common disease of the middle arteries is arteriosclerosis. With its development in the coronary arteries of the heart, the inner layer of the vessel (intima) is affected, which can lead to complete blockage of the artery. Depending on the degree of damage and the general condition of the patient, balloon angioplasty or coronary artery bypass grafting is performed. In balloon angioplasty, a catheter with a balloon at the end is inserted into the affected artery; balloon inflation leads to flattening of deposits along the arterial wall and the expansion of the lumen of the vessel. During bypass operations, a portion of the vessel is cut out from another part of the body and sewn into the coronary artery, bypassing the narrowed place, restoring normal blood flow.

In case of damage to the arteries of the legs and arms, the middle, muscle, and blood vessels (media) are densified, which leads to their thickening and curvature. Damage to these arteries has relatively less severe consequences.

Arterioles.

The defeat of arterioles creates an obstacle to free blood flow and leads to an increase in blood pressure. However, even before arterioles are sclerosed, spasms of unknown origin may occur, which is a common cause of hypertension.

Veins.

Vein diseases are very common. The most common varicose veins of the lower extremities; this condition develops under the influence of gravity in obesity or pregnancy, and sometimes due to inflammation. In this case, the function of the venous valves is impaired, the veins are stretched and overflowed with blood, which is accompanied by swelling of the legs, the appearance of pain and even ulceration. Various surgical procedures are used for treatment. Relief of the disease is facilitated by the training of the muscles of the lower leg and weight loss. Another pathological process - inflammation of the veins (phlebitis) - is also most often noted in the legs. In this case, there are obstacles to blood flow with impaired local blood circulation, but the main danger of phlebitis is the separation of small blood clots (emboli) that can pass through the heart and cause circulation in the lungs to stop. This condition, called pulmonary embolism, is very severe and often fatal. The defeat of large veins is much less dangerous and is much less common.

The content of the article

This article discusses the human circulatory system. ( For circulatory systems in other species, see ANATOMY COMPARATIVE.)

The constituent parts of the circulatory system.

WORK OF THE BLOOD SYSTEM

Pulmonary circulation.

Systemic circulation.

Arteries.

The structure of the arteries.

Capillaries.

Veins.

Subsidiary organs.

A number of organs perform functions that complement the work of the circulatory system. Closest to it are the spleen, liver and kidneys.

Spleen.

Liver.

The kidneys.

BLOOD (ARTERIAL) PRESSURE

BLOOD VESSEL DISEASES

Aorta.

Atherosclerosis.

Syphilitic aortitis.

Arteriosclerosis

Pulmonary artery.

Arteries of medium caliber.

Arterioles.

Veins.

Circulatory system, or circulatory, or cardiovascular, Is a large, branched transport system. It continuously, throughout the life of a person, carries oxygen, nutrients, hormones throughout the body, taking from the cells, tissues and organs the waste products of the exchange of substances, that is, it carries out hemodynamics (blood movement in the body). Consequently, the circulatory system provides: body nutrition, gas exchange, its release from metabolic products and humoral regulation of the functioning of the body.

Blood moves through the blood vessels mainly due to heart contractions. And her path in the body is this: heart → arteries → capillaries → veins → heart. The circulatory system is a closed system. It consists of two circles of blood circulation — big and small.

They were first described by the eminent English scientist William Harvey.

Heart - hollow muscle organ. Its mass in an adult is 250-300 g. The heart is located in the chest cavity and is shifted to the left of the midline of the chest. It is contained in a pericardial sac formed by a connective tissue. On the inner surface of the pericardial sac, fluid is released that moisturizes the heart and reduces friction during its contractions.

The structure of the heart corresponds to its characteristic function. It is divided by a solid partition into two parts - left and right, and each of them is divided into two interconnected departments: the upper - atrium and lower - ventricle. Consequently, the human heart, like all mammals, has four chambers: it consists of two atria and two ventricles. The walls of the atria are much thinner than the walls of the ventricles. This is due to the fact that the work performed by the atria is relatively small. During their contraction, blood enters the ventricles, which do much more work: they push blood along the entire length of the vessels. Muscle wall ( myocardium) The left ventricle is thicker than the wall of the right ventricle because it does a lot of work. At the border between each atrium and ventricle, there are valves in the form of valves that are attached to the walls of the heart by tendon filaments. it flap valves (Fig. 58).

During atrial contraction, valve flaps hang inward in the ventricles. Blood flows freely from the atria into the ventricles. When the ventricles contract, the valve flaps rise and close the entrance to the atrium. Therefore, blood moves in only one direction: from the atria to the ventricles. From the ventricles, it is pushed into the vessels.

The whole human body is permeated blood vessels. In their structure, they are not the same.

Arteries - These are vessels through which blood moves from the heart. They have strong elastic walls, which include smooth muscles. Contracting, the heart ejects blood into the arteries under great pressure. Due to its density and elasticity, the walls of the arteries withstand this pressure and stretch.

Large arteries branch to the extent of distance from the heart. The smallest arteries ( arterioles) branch into thin capillaries (Fig. 59), which in the human body is approximately 150 billion. The walls of the capillaries are formed by a single layer of flat cells. Substances dissolved in blood plasma pass into the tissue fluid, and from it enter the cells through these walls. Vital products of cells penetrate through the walls of the capillaries from the tissue fluid into the blood. From the capillaries, blood flows into veins - vessels through which it flows to the heart. The pressure in the veins is small, their walls are much thinner than the walls of the arteries. Material from the site

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1 Circulatory system

2 Historical background

3 Circles of human blood circulation

4 The mechanism of blood circulation
5 Quantitative indicators and their relationship

6 Literature

Circulation - circulation blood in the body. Blood is driven by contractions hearts and circulates through vessels. Blood supplies the body tissues with oxygen, nutrients, hormones and delivers metabolic products to their organs of excretion. Blood enrichment with oxygen occurs in the lungs, and saturation with nutrients - digestive organs. In the liver and kidneys, neutralization and withdrawal of products metabolism. Blood circulation is regulated hormones and nervous system. There are small (through the lungs) and large (through organs and tissues) circles of blood circulation.

Blood circulation is an important factor in the life of the human body and a number of animals. Blood can perform its various functions only in constant motion.

Circulatory system

The circulatory system of humans and many animals consists of hearts and vesselsthrough which blood moves to tissues and organs, and then returns to the heart. Large vessels through which blood moves to organs and tissues are called arteries. Arteries branch into smaller arteries, arteriolesand finally on capillaries. By vessels called veins, blood returns to the heart. The heart is four-chamber and has two circles of blood circulation.

Historical reference

Researchers of ancient times assumed that in living organisms all organs are functionally connected and exert influence on each other. A variety of assumptions were made. Yet Hippocrates - the father of medicine, and Aristotle - The largest Greek thinker who lived almost 2500 years ago, was interested in blood circulation issues and studied it. However, their ideas were not perfect and in many cases erroneous. They presented venous and arterial blood vessels as two independent systems that were not interconnected. It was believed that blood moves only through the veins, while in the arteries there is air. This was justified by the fact that at the autopsy of people and animals in the veins there was blood, and the arteries were empty, without blood.

This belief was disproved as a result of the work of a Roman scholar and physician. Claudia Galen (130-200). He experimentally proved that blood moves in the heart through arteries and veins.

After Galen, up to the 17th century, it was believed that blood from the right atrium enters the left atrium through the septum somehow.

IN 1628 year English physiologist, anatomist and doctor William Harvey (1578 - 1657) published his work “Anatomical Study on the Movement of the Heart and Blood in Animals”, in which for the first time in the history of medicine experimentally showed that blood moves from the ventricles of the heart through arteries and returns to the atria through the veins. Undoubtedly, the circumstance that led more than others William Harvey to the realization that the blood circulates, there was the presence of valves in the veins, the functioning of which is a passive hydrodynamic process. He realized that this could only make sense if the blood in the veins flows to the heart, and not from him, as suggested Galen and as European medicine believed before Harvey. Harvey was also the first to quantify a person’s cardiac output, and mainly because of this, despite the huge underestimation (1020.6 g, i.e. about 1 l / min instead of 5 l / min), skeptics were convinced that arterial blood cannot be continuously created in liver, and, therefore, it must circulate. Thus, he built a modern circulatory system of humans and other mammals, including two circles (see below). The question of how blood flows from arteries to veins remained unclear.

It is interesting that it was in the year of publication of the revolutionary work of Harvey (1628) that Marcello Malpigi, which 50 years later opened the capillaries - the link of the blood vessels that connects the arteries and veins - and thus completed the description of the closed vascular system.

The very first quantitative measurements of mechanical phenomena in the blood circulation were made Stephen Hales (1677 - 1761), which measured arterial and venous blood pressure, the volume of individual heart chambers, and the rate of blood flow from several veins and arteries, thus demonstrating that most of the resistance to blood flow falls on the microcirculation area. He believed that due to the elasticity of the arteries, the blood flow in the veins was more or less established, and not pulsating, as in the arteries.

Later, in the XVIII and XIX centuries. a number of well-known hydromechanics became interested in blood circulation issues and made a significant contribution to understanding this process. Among them were Euler, Daniel Bernoulli (the former is actually a professor of anatomy) and Poiseuille (also a doctor; his example especially shows how an attempt to solve a particular applied problem can lead to the development of fundamental science). One of the largest universal scientists was Thomas Jung (1773 - 1829), also a doctor whose research in optics led to the adoption of the wave theory of light and an understanding of color perception. Another important area of \u200b\u200bresearch concerns the nature of elasticity, in particular the properties and functions of elastic arteries; his theory of wave propagation in elastic tubes is still considered the fundamental correct description of pulse pressure in arteries. It is in his lecture on this subject in the Royal Society in London that he explicitly states that “the question of how and to what extent the blood circulation depends on the muscular and elastic forces of the heart and arteries under the assumption that the nature of these forces is known should become just a matter of the most advanced sections of theoretical hydraulics. ”

In the XX century. it was shown that skeletal muscle contractions and the suction action of the chest also play a significant role for venous return (see below) .

Human circulatory system

Blood circulation through the heart. The pulmonary circulation passes through the right atrium, right ventricle, pulmonary artery, pulmonary vessels, pulmonary veins. The large circle passes through the left atrium and ventricle, the aorta, the vessels of the organs, the superior and inferior vena cava. The direction of blood flow is regulated by the valves of the heart.

Blood circulation occurs in two main ways, called circles: small and big blood circulation.

In a small circle, blood circulates through the lungs. The movement of blood in this circle begins with a reduction right atriumafter which the blood enters right ventricle heart whose contraction pushes blood into pulmonary trunk. Blood circulation in this direction is regulated ventricular septum and two valves: tricuspid (between the right atrium and the right ventricle), preventing the return of blood to the atrium, and pulmonary valvepreventing the return of blood from the pulmonary trunk to the right ventricle. The pulmonary trunk branches out to the network pulmonary capillarieswhere the blood is saturated oxygen due to lung ventilation. Then blood through pulmonary veins returns from the lungs to left atrium.

The large circle of blood circulation supplies organs and tissues with oxygenated blood. Left atrium contracts simultaneously with the right and pushes blood into left ventricle. From the left ventricle, blood enters the aorta. Aorta branching into arteries and arteriolesgoing to various parts of the body and ending with a capillary network in organs and tissues. Blood circulation in this direction is regulated by the atrioventricular septum, bivalve ( mitral) valve and aortic valve.

Thus, the blood moves in a large circle of blood circulation from the left ventricle to the right atrium, and then in the small circle of blood circulation from the right ventricle to the left atrium.

Blood circulation mechanism

The movement of blood through the vessels is carried out mainly due to the pressure difference between the arterial system and the venous. This statement is fully true for arteries and arterioles, auxiliary mechanisms appear in the capillaries and veins, which are described below. The pressure difference is created by the rhythmic work of the heart pumping blood from veins to arteries. Since the pressure in the veins is very close to zero, this difference can be taken, for practical purposes, equal to blood pressure.

Heart cycle

The right half of the heart and the left work synchronously. For convenience of presentation, the work of the left heart will be examined here.

The heart cycle includes total diastole (relaxation), systole (reduction) atria, ventricular systole. During total diastole the pressure in the cavities of the heart is close to zero, in the aorta it slowly decreases from systolic to diastolic, normally in humans equal 120 and 80, respectively mmHg Art. Since the pressure in the aorta is higher than in the ventricle, the aortic valve is closed. The pressure in the large veins (central venous pressure, CVP) is 2-3 mm Hg, i.e. slightly higher than in the cavities of the heart, so that blood enters the atria and, in transit, into the ventricles. The atrioventricular valves are open at this time.

During atrial systole the circular muscles of the atria squeeze the entrance from the veins into the atria, which prevents the reverse flow of blood, the pressure in the atria rises to 8-10 mm Hg, and the blood moves into the ventricles.

During subsequent ventricular systole the pressure in them becomes higher than the pressure in the atria (which begin to relax), which leads to the closure of the atrioventricular valves. The external manifestation of this event is the I heart tone. Then, the pressure in the ventricle exceeds the aortic pressure, as a result of which the aortic valve opens and the expulsion of blood from the ventricle to the arterial system begins. The relaxed atrium at this time is filled with blood. The physiological significance of the atria mainly consists in the role of an intermediate reservoir for blood coming from the venous system during ventricular systole.

At the beginning total diastole, the pressure in the ventricle drops below the aortic (closing of the aortic valve, II tone), then below the pressure in the atria and veins (opening of the atrioventricular valves), the ventricles again begin to fill with blood.

The volume of blood ejected by the ventricle of the heart for each systole is 50-70 ml. This value is called stroke volume. The duration of the heart cycle is 0.8 - 1 s., Which gives a heart rate (HR) of 60-70 per minute. Hence, the minute volume of blood flow, as you can easily calculate, 3-4 liters per minute (minute volume of the heart, MOS).

Arterial system

Arteries, which almost do not contain smooth muscles, but have a powerful elastic membrane, play mainly a “buffer” role, smoothing out pressure drops between systole and diastole. The walls of the arteries are elastically extensible, which allows them to take an additional volume of blood, “thrown” by the heart during systole, and only moderately, by 50-60 mm Hg. raise the pressure. During diastole, when the heart does not pump anything, it is the elastic stretching of the arterial walls that maintains pressure, preventing it from falling to zero, and thereby ensures the continuity of blood flow. It is the extension of the vessel wall that is perceived as a pulse beat. Arterioles have developed smooth muscles, thanks to which they are able to actively change their lumen and, thus, regulate blood flow resistance. It is arterioles that account for the largest drop in pressure, and they determine the ratio of the volume of blood flow and blood pressure. Accordingly, arterioles are called resistive vessels.

Capillaries

Capillaries are characterized by the fact that their vascular wall is represented by a single layer of cells, so that they are highly permeable to all low molecular weight substances dissolved in the blood plasma. Here there is a metabolism between tissue fluid and blood plasma.

Venous system

From organs, blood returns through postcapillaries to venules and veins in the right atrium along the superior and inferior vena cava, as well as coronary veins (veins that return blood from the heart muscle).

Venous return is carried out by several mechanisms. Firstly, due to the pressure drop at the end of the capillary (about 25 mmHg) and atria (about 0). Secondly, for skeletal muscle veins, it is important that when the muscle contracts, the pressure "outside" exceeds the pressure in the vein, so that the blood is "squeezed" from the veins of the contracted muscle. The presence of venous valves determines the direction of blood flow in this case - from the arterial end to the venous. This mechanism is especially important for the veins of the lower extremities, since here the blood rises through the veins, overcoming gravity. Thirdly, the suction role of the chest. During inspiration, the pressure in the chest falls below atmospheric (which we take for zero), which provides an additional mechanism for the return of blood. The size of the lumen of the veins, and accordingly their volume, significantly exceeds those of the arteries. Moreover, smooth muscles veins provide a change in their volume over a very wide range, adapting their capacity to the changing volume of circulating blood. therefore, the physiological role of veins is defined as "capacitive vessels."

Quantitative indicators and their relationship

Stroke volume of the heart (V contr) - The volume that the left ventricle ejects into the aorta

(and the right - into the pulmonary trunk) for one reduction. In humans, it is 50-70 ml.

Minute volume of blood flow (V minute) - the volume of blood passing through the cross section of the aorta (and pulmonary trunk) per minute.

Heart rate (Freq) is the number of heart contractions per minute.

Easy to see that

(1) V minute = V contr * Freq (1)

Arterial pressure - blood pressure in large arteries.

Systolic pressure - The highest pressure during the cardiac cycle, reached by the end of systole.

Diastolic pressure - the lowest pressure during the cardiac cycle, is achieved at the end of the diastole of the ventricles.

Pulse pressure - the difference between systolic and diastolic.

Mean arterial pressure (P mean) is most easily defined as a formula. So, if blood pressure during the heart cycle is a function of time, then

where t begin and t end are the time of the beginning and end of the cardiac cycle, respectively.

The physiological meaning of this quantity: it is such an equivalent pressure that, if it were constant, the minute volume of blood flow would not differ from that observed in reality.

Total peripheral resistance - resistance that the vascular system exerts to the bloodstream. It cannot be measured directly, but can be calculated based on the minute volume and mean arterial pressure.

(3)

The minute volume of blood flow is equal to the ratio of mean arterial pressure to peripheral resistance.

This statement is one of the central laws of hemodynamics.

The resistance of one vessel with rigid walls is determined by the Poiseuille law:

(4)

where η is the viscosity of the liquid, R is the radius, and L is the length of the vessel.

For series-connected vessels, resistances add up:

For parallel, add up conductivity:

(6)

Thus, the total peripheral resistance depends on the length of the vessels, the number of vessels connected in parallel, and the radius of the vessels. It is clear that there is no practical way to find out all these quantities, in addition, the walls of the vessels are not rigid, and the blood does not behave like a classical Newtonian fluid with constant viscosity. Because of this, as V. A. Lishchuk noted in the Mathematical Theory of Blood Circulation, "Poiseuille’s law has an illustrative rather than a constructive role for blood circulation." Nevertheless, it is clear that of all the factors determining peripheral resistance, the radius of the vessels is of the greatest importance (the length in the formula is in the 1st power, the radius in the 4th), and that this factor is the only one capable of physiological regulation. The number and length of the vessels are constant, but the radius can vary depending on the tone of the vessels, mainly arterioles.

Taking into account formulas (1), (3) and the nature of peripheral resistance, it becomes clear that the average arterial pressure depends on the volumetric blood flow, which is determined mainly by the heart (see (1)) and vascular tone, mainly arterioles.

Literature
2. Lishchuk V.A. Mathematical theory of blood circulation. - 1991.

3.R.D. Sinelnikov. Atlas of Human Anatomy T.3 –Moscow “Medicine” 1994.

4. Weight M.Ya. Human anatomy. - Moscow “Medicine” 1988.
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Question 1. What are the prerequisites for the development of the venous system?

With the complexity of the organization and the increase in body size, special structures become necessary that take on the functions of transferring substances necessary for life throughout the body. This is how the circulatory system develops, in which blood circulates, capable of binding and transporting oxygen and carbon dioxide, nutrients and cell excretion products.

Question 2. Prove that increasing the number of heart chambers increases the level of organization of the animal.

An increase in the number of heart chambers from three (amphibians, reptiles) to four (birds, mammals) contributes to the complete separation of arterial and venous blood. Due to this, the supply of oxygen to body tissues improves, the exchange rate of substances increases, which leads to warm-blooded birds and mammals, that is, the ability to maintain a constant body temperature and allows them to be less dependent on living conditions.

Question 3. How are the structure and function of the heart interconnected?

The main function of the heart is to ensure the continuous movement of blood through the vessels, in connection with which the heart is a powerful muscular organ that constantly rhythmically contracts, redirecting blood.

Question 4. What is the difference between a closed and non-closed circulatory system?

In a closed circulatory system, unlike open, the blood moves only through the vessels and does not spill out into the body cavity.

Question 5. What does the similarity of the blood composition with seawater in some animals testify to?

The similarity of the blood composition with seawater in some animals indicates the marine origin of life.

Question 6. What are the main functions of the blood?

The main functions of the blood: transport - the transfer of gases, nutrients and metabolic products; regulatory - maintaining body temperature, regulates the activity of all body systems through substances secreted by the endocrine glands, protective - the destruction of pathogens (with the help of white blood cells).

Question 7. What carries blood? Material from the site

Blood carries salts and nutrients from the digestive system to all cells of the body, due to which the body grows and develops, and removes waste products from tissues that are excreted through the excretory system. From the lungs to the tissues and organs, the blood carries oxygen and carries carbon dioxide. Blood also carries substances secreted by the endocrine glands, with the help of which the body's activity is regulated.
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Summary: The human circulatory system. General structure and significance of the circulatory system (heart, blood vessels)

The constituent parts of the circulatory system.

WORK OF THE BLOOD SYSTEM

Pulmonary circulation.

Systemic circulation.

Arteries.

The structure of the arteries.

Capillaries.

Veins.

Subsidiary organs.

Spleen.

Liver.

The kidneys.

BLOOD (ARTERIAL) PRESSURE

BLOOD VESSEL DISEASES

Aorta.

Atherosclerosis.

Syphilitic aortitis.

Arteriosclerosis

Pulmonary artery.

Arteries of medium caliber.

Arterioles.

Veins.

The constituent parts of the circulatory system.

WORK OF THE BLOOD SYSTEM

Pulmonary circulation.

Systemic circulation.

Arteries.

The structure of the arteries.

Capillaries.

Veins.

Subsidiary organs.

Spleen.

Liver.

The kidneys.

BLOOD (ARTERIAL) PRESSURE

BLOOD VESSEL DISEASES

Aorta.

Atherosclerosis.

Syphilitic aortitis.

Arteriosclerosis

Pulmonary artery.

Arteries of medium caliber.

Arterioles.

Veins.

Report on the circulatory system Grade 4

Circulatory System Report Grade 4

The value of the circulatory system grade 4 report

What is called blood circulation. structure of blood vessel function

Short report on the circulatory system

What are the organs and departments that make up the cardiovascular system.

Describe the biological functions of the cardiovascular system.

Schematically depict the direction of blood flow in the cardiovascular system.

What type of human circulatory system belongs to?

Name the benefits of a four-chamber heart.

Ministry of Education of the Russian Federation

State educational institution

higher professional education

ORDER OF LENINA AND KRAZNOGO KNOWLEDGE

Baltic State Technical University

“VOENMEH”

them. D.F. Ustinova, St. Petersburg

(branch in Bishkek)

Department “ “

abstract

According to the course .

On the topic " ’’

Student .

Groups: .

Teacher: .

Overall rating: .

Bishkek 2008

Circulatory system

Historical reference

Human circulatory system

Blood circulation mechanism

Heart cycle

Arterial system

Capillaries

Venous system