Circulation circles are short and clear. Movement of blood through the circulatory system diagram

After all, it’s a shame for future doctors not to know the basics - the blood circulation. Without having this information and an understanding of how blood moves through the body, it is impossible to understand the mechanism of development of vascular and heart diseases, or to explain the pathological processes that occur in the heart with a particular lesion. Without knowing the blood circulation it is impossible to work as a doctor. This information will not hurt the common man, because knowledge about one’s own body is never superfluous.

1 Big trip

To better understand how it works big circle blood circulation, let's imagine a little? Let's imagine that all the vessels of the body are rivers, and the heart is a bay, into the bay of which all the river channels flow. Let's go on a journey: our ship begins a long voyage. From the left ventricle we swim to the aorta - the main vessel human body. This is where the great circle of blood circulation begins.

Blood saturated with oxygen flows in the aorta, because aortic blood is distributed throughout the human body. The aorta gives off branches, like a river, tributaries that supply blood to the brain and all organs. Arteries branch to arterioles, which in turn give off capillaries. Bright, arterial blood gives oxygen and nutrients to cells, and takes away metabolic products of cellular life.

The capillaries are organized into venules, which carry dark, cherry-colored blood, because it has given oxygen to the cells. Venules collect into larger veins. Our ship completes its journey along the two largest “rivers” - the superior and inferior vena cava - and ends up in the right atrium. The journey is over. A large circle can be schematically represented as follows: the beginning is the left ventricle and the aorta, the end is the vena cava and the right atrium.

2 Small trip

What is the pulmonary circulation? Let's go on our second trip! Our ship originates from the right ventricle, from which the pulmonary trunk arises. Remember that when completing the systemic circulation, we moored in the right atrium? From it, venous blood flows into the right ventricle, and then, with cardiac contraction, is pushed into a vessel that extends from it - the pulmonary trunk. This vessel goes to the lungs, where it bifurcates into pulmonary arteries and then into capillaries.

Capillaries envelop the bronchi and alveoli of the lungs, give off carbon dioxide and metabolic products and are enriched with life-giving oxygen. Capillaries organize into venules as they exit the lungs and then into larger pulmonary veins. We are accustomed to the fact that venous blood flows in the veins. Just not in the lungs! These veins are rich in arterial, bright scarlet, O2-rich blood. Through the pulmonary veins, our ship sails into the bay, where its journey ends - in the left atrium.

So, the beginning of the small circle is the right ventricle and the pulmonary trunk, the end is the pulmonary veins and the left atrium. More detailed description the following: the pulmonary trunk is divided into two pulmonary arteries, which in turn branch into a network of capillaries, like a web, encircling the alveoli, where gas exchange occurs, then the capillaries collect into venules and pulmonary veins, which flow into the left upper cardiac chamber of the heart.

3 Historical facts

Having dealt with the sections of the blood circulation, it seems that there is nothing complicated in their structure. Everything is simple, logical, understandable. Blood leaves the heart, collects metabolic products and CO2 from the cells of the whole body, saturates them with oxygen, venous blood returns to the heart, which, passing through the natural “filters” of the body - the lungs, becomes arterial again. But it took many centuries to study and understand the movement of blood flow in the body. Galen mistakenly assumed that the arteries contained air rather than blood.

This position today can be explained by the fact that in those days they studied vessels only on corpses, and in a dead body the arteries are bloodless, and the veins, on the contrary, are full of blood. It was believed that blood was produced in the liver, and was consumed in the organs. Miguel Servet in the 16th century suggested that “the spirit of life originates in the left cardiac ventricle, this is facilitated by the lungs, where the mixing of air and blood coming from the right cardiac ventricle occurs,” thus, the scientist recognized and described for the first time the small circle.

But practically no attention was paid to Servetus' discovery. Harvey is considered the father of the circulatory system, who already in 1616 wrote in his writings that the blood “circles throughout the body.” For many years he studied the movement of blood, and in 1628 he published a work that became a classic, and crossed out all Galen’s ideas about blood circulation; in this work, blood circulation circles were outlined.

Harvey did not discover only capillaries, discovered later by the scientist Malpighi, who supplemented the knowledge about the “circles of life” with a connecting capillary link between arterioles and venules. The scientist was helped to open the capillaries by a microscope, which provided magnification up to 180 times. Harvey's discovery was met with criticism and challenge by the great minds of those times, many scientists did not agree with Harvey's discovery.

But even today, reading his works, you are surprised at how accurately and in detail for that time the scientist described the work of the heart and the movement of blood through the vessels: “The heart, while doing work, first moves, and then rests in all animals while they are still alive. At the moment of contraction, it squeezes blood out of itself, the heart empties at the moment of contraction.” The blood circulation was also described in detail, except that Harvey could not observe the capillaries, but he accurately described that blood collects from the organs and flows back to the heart?

But how does the transition from arteries to veins occur? This question haunted Harvey. Malpighi revealed this secret of the human body by discovering capillary blood circulation. It’s a shame that Harvey did not live several years to see this discovery, because the discovery of capillaries confirmed with 100% certainty the veracity of Harvey’s teachings. The great scientist did not have the opportunity to feel the fullness of the triumph of his discovery, but we remember him and his huge contribution in the development of anatomy and knowledge about nature human body.

4 From largest to smallest

I would like to dwell on the main elements of the circulatory circles, which are their framework through which the blood moves - the vessels. Arteries are vessels that carry blood from the heart. The aorta is the most important and important artery of the body, it is the largest - about 25 mm in diameter, it is through it that blood flows to other vessels extending from it and is delivered to organs, tissues, and cells.

Exception: the pulmonary arteries do not carry O2-rich blood, but CO2-rich blood to the lungs.

Veins are vessels that carry blood to the heart, their walls are easily stretchable, the diameter of the hollow veins is about 30 mm, and the small ones are 4-5 mm. Their blood is dark, the color of ripe cherry, rich in metabolic products.

Exception: the pulmonary veins are the only veins in the body through which arterial blood flows.

Capillaries are the thinnest vessels, consisting of only one layer of cells. The single-layer structure allows gas exchange, exchange of useful and harmful products between cells and directly capillaries.

The diameter of these vessels is only 0.006 mm on average, and the length is no more than 1 mm. That's how small they are! However, if we sum up the length of all the capillaries together, we get a very significant figure - 100 thousand km... Our body inside is shrouded in them like a cobweb. And it’s not surprising - after all, every cell of the body needs oxygen and nutrients, and capillaries can provide the supply of these substances. All vessels, both the largest and smallest capillaries, form a closed system, or rather two systems - the above-mentioned circulatory circles.

5 Important features

Why are blood circulation circles needed? Their role cannot be overestimated. Just as life on Earth is impossible without water resources, human life is impossible without the circulatory system. The main role of the large circle is:

1. Providing oxygen to every cell of the human body;
2. The flow of nutrients from the digestive system into the blood;
3. Filtration of waste products from the blood into the excretory organs.

The role of the small circle is no less important than those described above: removing CO2 from the body and metabolic products.

Knowledge about the structure own body are never superfluous, knowledge of how the sections of the blood circulation function leads to a better understanding of the work of the body, and also forms an idea of ​​the unity and integrity of organs and systems, the connecting link of which is undoubtedly the bloodstream, organized in circulatory circles.

The pattern of blood movement in circulatory circles was discovered by Harvey (1628). Subsequently, the doctrine of the physiology and anatomy of blood vessels was enriched with numerous data that revealed the mechanism of general and regional blood supply to organs.

In goblin animals and humans, which have a four-chambered heart, the greater, lesser, and cardiac circles of blood circulation are distinguished (Fig. 367). The heart occupies a central place in blood circulation.

367. Blood circulation diagram (according to Kishsh, Sentagotai).

1 - common carotid artery;
2 - aortic arch;
3 - pulmonary artery;
4 - pulmonary vein;
5 - left ventricle;
6 - right ventricle;
7 - celiac trunk;
8 - superior mesenteric artery;
9 - inferior mesenteric artery;
10 - inferior vena cava;
11 - aorta;
12 - common iliac artery;
13 - common iliac vein;
14 - femoral vein. 15 - portal vein;
16 - hepatic veins;
17 - subclavian vein;
18 - superior vena cava;
19 - internal jugular vein.

Pulmonary circulation (pulmonary)

Venous blood from the right atrium passes through the right atrioventricular orifice into the right ventricle, which contracts and pushes blood into the pulmonary trunk. It divides into the right and left pulmonary arteries, which enter the lungs. In the lung tissue, the pulmonary arteries are divided into capillaries surrounding each alveolus. After red blood cells release carbon dioxide and enrich them with oxygen, venous blood turns into arterial blood. Arterial blood flows through four pulmonary veins (there are two veins in each lung) into the left atrium, then passes through the left atrioventricular orifice into the left ventricle. The systemic circulation begins from the left ventricle.

Systemic circulation

Arterial blood from the left ventricle is ejected into the aorta during its contraction. The aorta splits into arteries that supply blood to the limbs and torso. all internal organs and ending with capillaries. Nutrients, water, salts and oxygen are released from the blood capillaries into the tissues, metabolic products and carbon dioxide are resorbed. The capillaries gather into venules, where the venous system of vessels begins, representing the roots of the superior and inferior vena cava. Venous blood through these veins enters the right atrium, where the systemic circulation ends.

Cardiac circulation

This circle of blood circulation begins from the aorta with two coronary cardiac arteries, through which blood enters all layers and parts of the heart, and then collects through small veins into the venous coronary sinus. This vessel opens with a wide mouth into the right atrium. Some of the small veins of the heart wall directly open into the cavity of the right atrium and ventricle of the heart.

Blood circulation is the continuous movement of blood along a closed cardiac circuit. vascular system, providing vital functions of the body. The cardiovascular system includes organs such as the heart and blood vessels.

Heart

Heart - central authority blood circulation, ensuring the movement of blood through the vessels.

The heart is a hollow four-chambered muscular organ, shaped like a cone, located in the chest cavity, in the mediastinum. It is divided into right and left halves by a continuous partition. Each half consists of two sections: the atrium and the ventricle, connected to each other by an opening that is closed by a leaflet valve. In the left half, the valve consists of two valves, in the right - of three. The valves open towards the ventricles. This is facilitated by tendon filaments, which at one end are attached to the valve leaflets, and the other to the papillary muscles located on the walls of the ventricles. During ventricular contraction, tendon threads prevent the valves from everting towards the atrium. Blood enters the right atrium from the superior and inferior vena cava and the coronary veins of the heart itself; four pulmonary veins flow into the left atrium.

The ventricles give rise to vessels: the right one - to the pulmonary trunk, which is divided into two branches and carries venous blood into the right and left lungs, that is, into the pulmonary circulation; The left ventricle gives rise to the left aortic arch, but through which arterial blood enters the systemic circulation. At the border of the left ventricle and the aorta, the right ventricle and the pulmonary trunk, there are semilunar valves (three cusps in each). They close the lumens of the aorta and pulmonary trunk and allow blood to pass from the ventricles into the vessels, but prevent the reverse flow of blood from the vessels to the ventricles.

The wall of the heart consists of three layers: the inner - endocardium, formed by epithelial cells, the middle - myocardium, muscle and outer - epicardium, consisting of connective tissue.

The heart lies freely in the pericardial sac of connective tissue, where fluid is constantly present, moisturizing the surface of the heart and ensuring its free contraction. The main part of the heart wall is muscular. The greater the force of muscle contraction, the more powerfully developed muscle layer the heart, for example, the greatest thickness of the walls is in the left ventricle (10–15 mm), the walls of the right ventricle are thinner (5–8 mm), and the walls of the atria are even thinner (23 mm).

The structure of the heart muscle is similar to the striated muscles, but differs from them in the ability to automatically contract rhythmically due to impulses arising in the heart itself, regardless of external conditions - cardiac automaticity. This is due to special nerve cells, located in the heart muscle, in which excitations arise rhythmically. The automatic contraction of the heart continues even when it is isolated from the body.

Normal metabolism in the body is ensured by the continuous movement of blood. Blood in the cardiovascular system flows in only one direction: from the left ventricle through the systemic circulation it enters the right atrium, then into the right ventricle and then through the pulmonary circulation it returns to the left atrium, and from there to the left ventricle. This movement of blood is determined by the work of the heart due to the sequential alternation of contractions and relaxations of the heart muscle.

There are three phases in the work of the heart: the first is contraction of the atria, the second is contraction of the ventricles (systole), the third is the simultaneous relaxation of the atria and ventricles, diastole, or pause. The heart beats rhythmically about 70–75 times per minute when the body is at rest, or 1 time every 0.8 seconds. Of this time, contraction of the atria accounts for 0.1 seconds, contraction of the ventricles accounts for 0.3 seconds, and the total pause of the heart lasts 0.4 seconds.

The period from one atrial contraction to another is called the cardiac cycle. The continuous activity of the heart consists of cycles, each of which consists of contraction (systole) and relaxation (diastole). The heart muscle, the size of a fist and weighing about 300 g, works continuously for decades, contracts about 100 thousand times a day and pumps more than 10 thousand liters of blood. Such high performance of the heart is due to its increased blood supply and high level metabolic processes occurring in it.

The nervous and humoral regulation of the activity of the heart coordinates its work with the needs of the body at any given moment, regardless of our will.

The heart as a working organ is regulated by the nervous system in accordance with the influences of external and internal environment. Innervation occurs with the participation of the autonomic nervous system. However, a pair of nerves (sympathetic fibers), when irritated, strengthen and speed up heart contractions. When another pair of nerves (parasympathetic, or vagus) is irritated, impulses entering the heart weaken its activity.

The activity of the heart is also influenced humoral regulation. Thus, adrenaline produced by the adrenal glands has the same effect on the heart as the sympathetic nerves, and an increase in potassium in the blood inhibits the heart, just like the parasympathetic (vagus) nerves.

Circulation

The movement of blood through vessels is called circulation. Only by being constantly in motion does the blood carry out its main functions: the delivery of nutrients and gases and the removal of final decay products from tissues and organs.

Blood moves through blood vessels - hollow tubes of various diameters, which, without interruption, pass into others, forming a closed circulatory system.

Three types of vessels of the circulatory system

There are three types of vessels: arteries, veins and capillaries. Arteries called the vessels through which blood flows from the heart to the organs. The largest of them is the aorta. In organs, arteries branch into vessels of smaller diameter - arterioles, which in turn break up into capillaries. Moving through the capillaries, arterial blood gradually turns into venous blood, which flows through veins.

Two circles of blood circulation

All arteries, veins and capillaries in the human body are combined into two circles of blood circulation: large and small. Systemic circulation begins in the left ventricle and ends in the right atrium. Pulmonary circulation begins in the right ventricle and ends in the left atrium.

Blood moves through the vessels due to the rhythmic work of the heart, as well as the difference in pressure in the vessels when blood leaves the heart and in the veins when it returns to the heart. Rhythmic fluctuations in the diameter of arterial vessels caused by the work of the heart are called pulse.

Using your pulse, you can easily determine the number of heartbeats per minute. Spread speed pulse wave about 10 m/s.

The speed of blood flow in the vessels is about 0.5 m/s in the aorta, and only 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 the fact that their number is huge (about 40 billion) and, despite their microscopic size, their total lumen is 800 times larger than the lumen of the aorta. In the veins, with their enlargement as they approach the heart, the total lumen of the bloodstream decreases, and the speed of blood flow increases.

Blood pressure

When the next portion of blood is ejected from the heart into the aorta and into the pulmonary artery, high blood pressure is created in them. Blood pressure rises when the heart pumps faster and harder, pumping more blood into the aorta, and when arterioles narrow.

If the arteries dilate, blood pressure drops. By the amount blood pressure The amount of circulating blood and its viscosity also affect. As you move away from the heart, blood pressure decreases and becomes lowest in the veins. Difference between high pressure blood in the aorta and pulmonary artery and low, even negative pressure in the vena cava and pulmonary veins ensures continuous blood flow throughout the entire circulation.

In healthy people, the maximum blood pressure in the brachial artery at rest is normally about 120 mmHg. Art., and the minimum is 70–80 mm Hg. Art.

A persistent increase in blood pressure at rest is called hypertension, and a decrease in blood pressure is called hypotension. In both cases, the blood supply to the organs is disrupted, and their working conditions worsen.

First aid for blood loss

First aid for blood loss is determined by the nature of the bleeding, which can be arterial, venous or capillary.

The most dangerous arterial bleeding, which occurs when arteries are injured, and the blood is bright scarlet in color and flows in a strong stream (spring). If an arm or leg is injured, it is necessary to raise the limb, keep it in a bent position, and press the damaged artery with a finger above the wound site (closer to the heart ); then you need to apply a tight bandage made of a bandage, towel, or piece of cloth above the wound site (also closer to the heart). A tight bandage should not be left in place for more than an hour and a half, so the victim must be taken to a medical facility as soon as possible.

With venous bleeding, the flowing blood is darker in color; to stop it, the damaged vein is pressed with a finger at the wound site, the arm or leg is bandaged below it (further from the heart).

With a small wound, capillary bleeding appears, to stop which it is enough to apply a tight sterile bandage. The bleeding will stop due to the formation of a blood clot.

Lymph circulation

It's called lymph circulation, moving lymph through the vessels. Lymphatic system promotes additional outflow of fluid from organs. Lymph movement is very slow (03 mm/min). It moves in one direction - from the organs to the heart. Lymphatic capillaries turn into larger vessels, which collect in the right and left thoracic ducts, flowing into large veins. Along the course of the lymphatic vessels there are The lymph nodes: in the groin, popliteal and armpits, under the lower jaw.

The lymph nodes contain cells (lymphocytes) that have a phagocytic function. They neutralize microbes and utilize foreign substances that have entered the lymph, causing the lymph nodes to swell and become painful. Tonsils are lymphoid accumulations in the pharynx area. Sometimes they are stored pathogens, metabolic products of which negatively affect the function internal organs. Often resort to surgical removal of the tonsils.

The large circle of blood circulation allows the blood to provide all human cells with oxygen, deliver to them the nutrients and hormones necessary for normal life, and remove carbon dioxide and other decay products. In addition, thanks to the blood flow in the body, a stable body temperature is maintained, the interconnection of all organs and systems.

Blood circulation is the continuous flow of blood (liquid tissue, which consists of plasma, leukocytes, platelets, red blood cells) through the cardiovascular system, which permeates all tissues of the body. This system is complex, it includes the heart, veins, arteries, capillaries, while the blood flow occurs in large and small circles.

The central organ in this system is the heart, which is a muscle that can contract rhythmically under the influence of impulses arising within it, regardless of external factors.

The heart muscle consists of four chambers:

• left and right atrium;
• two ventricles.

The main task of the heart is to ensure continuous flow of blood through the vessels. The movement of liquid tissue occurs according to a sequential pattern. Through the arteries, which belong to the large circle, blood rich in oxygen, hormones and nutrients is transported to the cells. The liquid substance flowing to the heart is saturated with carbon dioxide, decay products and other elements. In the small circle of blood flow, a different picture is observed: liquid tissue filled with carbon dioxide moves through the arteries, and saturated with oxygen through the veins.

All tissues of the human body are penetrated by the smallest vessels - capillaries, with the help of which arterioles are connected to venules (the so-called small arteries and veins). An exchange takes place in the capillaries of the systemic circulation: the blood gives oxygen and useful components to the cells, and they give it carbon dioxide and decay products.

Large and small circles

During the movement of liquid tissue in a small circle, it is saturated with oxygen, and here it gets rid of carbon dioxide. The path originates from the right ventricle, where blood moves from the right atrium when the heart muscle relaxes from the vein.

Then the liquid substance saturated with carbon dioxide ends up in the common pulmonary artery, which, dividing in two, sends it to the lungs. Here the arteries diverge into capillaries, which lead to the pulmonary vesicles (alveoli), where the blood gets rid of carbon dioxide and enriches it with oxygen. Thanks to oxygen, the liquid substance brightens and moves through the capillaries into the veins, then ends up in the left atrium, where it completes its journey according to the small circle pattern.

But the blood flow does not end there. Then the systemic circulation begins according to a sequential pattern. First, the liquid tissue enters the left ventricle, from there it moves to the aorta, which is largest artery in the human body.

The aorta diverges into arteries that reach out to all human cells, and reaching the desired organ, branch first into arterioles, then into capillaries. Through capillary walls, blood transfers oxygen and substances necessary for their life to cells and takes away metabolic products and carbon dioxide.

Accordingly, in this area the composition of the liquid tissue changes slightly, and it becomes darker in color. Then it moves through the capillaries to the venules, and then into the veins. At the final stage, the veins converge into two large trunks. Through them, the liquid substance moves into the right atrium. At this stage, the large circle of blood flow ends.

Blood distribution is regulated by the central nervous system a person by relaxing the smooth muscles of a particular organ: this causes the artery leading to it to dilate, and more blood flows to the organ. At the same time, because of this, it reaches other parts of the body in smaller quantities.

Thus, the organs that perform a specific task and are therefore in working condition receive more blood at the expense of the organs that are at rest. But if it happens that all the arteries dilate at once, then a sharp decline blood pressure and the speed of plasma movement through the vessels slows down.

What does blood flow depend on?

Since blood is a liquid substance, like any liquid, its path lies from an area with higher pressure towards a lower one. The greater the difference between pressures, the faster the plasma flows. The difference in pressure between the starting and ending points of the great circle path is created by the heart's rhythmic contractions.

According to research, if the heart beats seventy to eighty times per minute, blood passes through the systemic circulation in a little over twenty seconds.

In sections of the path where the liquid tissue is maximally saturated with oxygen (in the left ventricle and in the aorta), the pressure is much greater than in the right atrium and the veins flowing into it. This difference allows blood to move quickly throughout the body. Movement in a small circle is ensured by the difference between the pressures in the right ventricle (pressure higher) and in the left atrium (pressure lower).

During movement, the liquid substance rubs against the walls of the vessels, due to which the pressure gradually decreases. Especially low indicators it reaches the arterioles and capillaries. As blood enters the veins, the pressure continues to decrease, and when the liquid tissue reaches the vena cava, it becomes equal to atmospheric pressure, and may even be less than it.

Also, the speed of blood flow depends on the width of the vessel. In the aorta, which is the widest artery, the maximum speed is half a meter per second. When the plasma passes into narrower arteries, the speed slows down, and in the capillaries it is 0.5 mm/sec. Due to the low flow rate, as well as the fact that the capillaries together are capable of covering a huge area, the blood has time to transfer to the tissues all the nutrients and oxygen necessary for their functioning and absorb the products of their vital activity.

When the liquid substance ends up in venules, which gradually turn into larger veins, the speed of the current increases compared to the movement in the capillaries. It should be noted that about seventy percent of the blood is always in the veins. This is because they have thinner walls and therefore stretch more easily, allowing them to hold more fluid than arteries.

Another factor on which the movement of blood through the venous vessels depends is breathing, when when inhaling, the pressure in the chest decreases, which increases the difference between the end and the beginning venous system. In addition, the blood in the veins begins to move under the influence skeletal muscles, which, when contracted, compress the veins, promoting blood flow.

Taking care of your health

The human body is able to function normally only in the absence pathological processes in the cardiovascular system. It is the speed of blood flow that determines the degree of supply of cells with the substances they need and their timely disposal of decay products.

At physical work The human body's need for oxygen increases along with the acceleration of heart muscle contraction. Therefore, the stronger it is, the more resilient and healthy the person will be. To train the heart muscle, you need to play sports and exercise. This is especially important for people whose work is not related to physical activity. In order for a person’s blood to be maximally enriched with oxygen, it is better to do exercises at fresh air. It should be borne in mind that excessive stress can cause problems with the heart.

In order for the heart to function normally, it is necessary to give up alcoholic beverages, nicotine, and drugs that poison the body and can cause serious malfunctions. of cardio-vascular system. According to statistics, young people who smoke and drink excessively are much more likely to experience vascular spasms, which are accompanied by heart attacks and can be fatal.

The vascular system consists of two circles of blood circulation - large and small (Fig. 17).

Systemic circulation starts from the left ventricle of the heart, from where blood enters the aorta. From the aorta, the path of arterial blood continues through the arteries, which branch as they move away from the heart and the smallest of them break up into capillaries, which permeate the entire body in a dense network. Through the thin walls of the capillaries, the blood releases nutrients and oxygen into the tissue fluid, and the waste products of cells from the tissue fluid enter the blood. From the capillaries, blood flows into small veins, which, merging, form larger veins and flow into the superior and inferior vena cava. The superior and inferior vena cava bring venous blood to the right atrium, where the systemic circulation ends.

Rice. 17. Blood circulation diagram.

Pulmonary circulation starts from the right ventricle of the heart by the pulmonary artery. Venous blood is carried through the pulmonary artery to the capillaries of the lungs. In the lungs, gases are exchanged between the venous blood of the capillaries and the air in the alveoli of the lungs. From the lungs, arterial blood returns through four pulmonary veins to the left atrium. The pulmonary circulation ends in the left atrium. From the left atrium, blood enters the left ventricle, where the systemic circulation begins.

Closely related to the circulatory system lymphatic system. It serves to drain fluid from tissues, unlike circulatory system, creating both inflow and outflow of fluid. The lymphatic system begins with a network of closed capillaries, which turn into lymphatic vessels, which flow into the left and right lymphatic ducts, and from there into large veins. On the way to the veins, lymph flowing from different organs and tissues passes through the lymph nodes, which act as biological filters that protect the body from foreign bodies and infections. The formation of lymph is associated with the transition of a number of substances dissolved in the blood plasma from capillaries to tissues and from tissues to lymphatic capillaries. During the day, the human body produces 2-4 liters of lymph.

During normal functioning of the body, there is a balance between the rate of lymph formation and the rate of outflow of lymph, which returns through the veins to the bloodstream. Lymphatic vessels penetrate almost all organs and tissues, there are especially many of them in the liver and small intestine. In structure, lymphatic vessels are similar to veins, just like veins, they are equipped with valves that create conditions for the movement of lymph in only one direction.

The flow of lymph through the vessels is carried out due to the contraction of the walls of blood vessels and muscle contraction. The movement of lymph is also facilitated by negative pressure in the chest cavity, especially during inhalation. At the same time, the thoracic lymphatic duct, which lies on the way to the veins, expands, which facilitates the flow of lymph into the bloodstream.

10.4.3. The structure of the heart and its age-related features. The main pump of the circulatory system - the heart - is a muscular bag divided into 4 chambers: two atria and two ventricles (Fig. 18). The left atrium is connected to the left ventricle by an opening in the cusp of which there is mitral valve. The right atrium is connected to the right ventricle by an opening that closes tricuspid valve. The right and left halves are not connected to each other, therefore the “venous” half of the heart is always located in the right half of the heart, i.e. oxygen-poor blood, and in the left - “arterial”, saturated with oxygen. The exit from the right (pulmonary artery) and left (aorta) ventricles is closed with similar designs semilunar valves. They prevent blood from these large outgoing vessels from returning to the heart during the period of its relaxation.

Although the bulk of the heart walls is the muscle layer (myocardium), there are several additional layers of tissue that protect the heart from external influences and strengthening its walls, which experience enormous pressure during operation. These protective layers are called pericardium. The inner surface of the heart cavity is lined endocardium, the properties of which allow it not to harm blood cells during contractions. The heart is located on the left side chest(although in some cases there is a different location) “top” down.

The weight of the heart in an adult is 0.5% of body weight, i.e. 250-300 g for men and about 200 g for women. In children, the relative size of the heart is slightly larger - approximately 0.7% of body weight. The heart as a whole increases in proportion to the increase in body size. For the first 8 months. after birth, the weight of the heart doubles, by 3 years - three times, by 5 years - 4 times, and by 16 years - 11 times compared to the weight of the heart of a newborn. Boys usually have slightly larger hearts than girls; Only during puberty do girls who begin to mature earlier have larger hearts.

The atrial myocardium is much thinner than the ventricular myocardium. This is understandable: the work of the atria is to pump a portion of blood through the valves into the adjacent ventricle, while the ventricles need to give the blood such an acceleration that will force it to reach the most distant parts of the capillary network from the heart. For the same reason, the myocardium of the left ventricle is 2.5 times thicker than the myocardium of the right ventricle: pushing blood through the pulmonary circulation requires much less effort than through the systemic circulation.

The heart muscle consists of fibers similar to those of skeletal muscles. However, along with structures that have contractile activity, the heart also contains another - conductive - structure, which ensures rapid conduction of excitation to all parts of the myocardium and its synchronous periodic contraction. Each part of the heart is, in principle, capable of independent (spontaneous) periodic contractile activity, but normally heart contraction is controlled by a certain part of the cells, which is called pacemaker and is located in the upper part of the right atrium (sinus node). The impulse automatically generated here with a frequency of approximately 1 time per second (in adults; in children - much more often) spreads across conducting system heart, which includes atriumno-ventricular node, bundle of Hiss, splitting into right and left legs, branching in the mass of the ventricular myocardium (Fig. 19). Most cardiac arrhythmias are the result of certain damage to the fibers of the conduction systems

Rice. 18. Structure of the heart.

10.4.4. Properties of the heart muscle. The bulk of the heart wall is made up of a powerful muscle - the myocardium, consisting of a special kind of striated muscle tissue. The thickness of the myocardium varies in different parts of the heart. It is thinnest in the atria (2-3 mm), the left ventricle has the most powerful muscular wall, it is 2.5 times thicker than in the right ventricle.

The bulk of the cardiac muscle is represented by fibers typical of the heart, which ensure contraction of the heart’s parts. Their main function is contractility. This is the working muscle of the heart. In addition, there are atypical fibers in the heart muscle. The activity of atypical fibers is associated with the occurrence of excitation in the heart and its conduction from the atria to the ventricles.

These fibers form conduction system of the heart. The conduction system consists of the sinoatrial node, atriogastric node, atrioventricular bundle and its branches (Fig. 19). The sinoatrial node is located in the right atrium and is the pacemaker of the heart; automatic excitation impulses that determine the contraction of the heart are generated here. The atrioventricular node is located between the right atrium and the ventricles. In this area, excitation from the atria spreads to the ventricles. Under normal conditions, the atrioventricular node is excited by impulses coming from the sinoatrial node, but it is also capable of automatic excitation and in some pathological cases provokes excitation in the ventricles and their contraction, which does not follow the rhythm created by the sinoatrial node. A so-called extrasystole occurs. From the atrioventricular node, excitation is transmitted through the atrioventricular bundle (bundle of His), which, passing along the interventricular septum, branches into the left and right legs. The legs pass into a network of conducting myocytes (atypical muscle fibers), which cover the working myocardium and transmit excitation to it.

Cardiac cycle. The heart contracts rhythmically: contractions of the heart parts alternate with their relaxation. Contraction of the heart is called systole, and relaxation is called diastole.

Rice. 19. Schematic representation of the conduction system of the heart.

1- sinus node; 2 - atrioventricular node;

3-bundle of Hiss; 4 and 5 - right and left legs of the Hiss bundle; 6 - terminal branches of the conductive system. The period covering one contraction and relaxation of the heart is called the cardiac cycle. In a state of relative rest cardiac cycle

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