It is a rather complex structure. At first glance, it is associated with an extensive network of roads that allows vehicles to run. However, the structure of blood vessels at the microscopic level is quite complex. The functions of this system include not only the transport function, the complex regulation of the tone of blood vessels and the properties of the inner membrane allows it to participate in many complex processes of adaptation of the body. The vascular system is richly innervated and is under the constant influence of blood components and instructions coming from the nervous system. Therefore, in order to have a correct idea of ​​how our body functions, it is necessary to consider this system in more detail.

Some interesting facts about the circulatory system

Did you know that the length of the vessels of the circulatory system is 100 thousand kilometers? That 175,000,000 liters of blood pass through the aorta during a lifetime?
An interesting fact is the data on the speed with which blood moves through the main vessels - 40 km / h.

Structure of blood vessels

Three main membranes can be distinguished in blood vessels:
1. Inner shell- represented by a single layer of cells and is called endothelium. The endothelium has many functions - it prevents thrombosis in the absence of damage to the vessel, ensures blood flow in the parietal layers. It is through this layer at the level of the smallest vessels ( capillaries) there is an exchange in the tissues of the body of liquids, substances, gases.

2. Middle shell- Represented by muscle and connective tissue. In different vessels, the ratio of muscle and connective tissue varies widely. For larger vessels, the predominance of connective and elastic tissue is characteristic - this allows you to withstand the high pressure created in them after each heartbeat. At the same time, the ability to passively slightly change their own volume allows these vessels to overcome the wave-like blood flow and make its movement smoother and more uniform.

In smaller vessels, there is a gradual predominance of muscle tissue. The fact is that these vessels are actively involved in the regulation of blood pressure, carry out the redistribution of blood flow, depending on external and internal conditions. Muscle tissue envelops the vessel and regulates the diameter of its lumen.

3. outer shell vessel ( adventitia) - provides a connection between the vessels and the surrounding tissues, due to which the mechanical fixation of the vessel to the surrounding tissues occurs.

What are the blood vessels?

There are many classifications of vessels. In order not to get tired of reading these classifications and to gather the necessary information, let us dwell on some of them.

According to the nature of the blood Vessels are divided into veins and arteries. Through the arteries, blood flows from the heart to the periphery, through the veins it flows back - from tissues and organs to the heart.
arteries have a more massive vascular wall, have a pronounced muscle layer, which allows you to regulate the flow of blood to certain tissues and organs, depending on the needs of the body.
Vienna have a fairly thin vascular wall, as a rule, in the lumen of large-caliber veins there are valves that prevent the reverse flow of blood.

According to the caliber of the artery can be divided into large, medium caliber and small
1. Large arteries- aorta and vessels of the second, third order. These vessels are characterized by a thick vascular wall - this prevents their deformation when the heart pumps blood under high pressure, at the same time, some compliance and elasticity of the walls can reduce pulsating blood flow, reduce turbulence and ensure continuous blood flow.

2. Vessels of medium caliber- take an active part in the distribution of blood flow. In the structure of these vessels there is a fairly massive muscle layer, which, under the influence of many factors ( chemical composition of blood, hormonal effects, immune reactions of the body, effects of the autonomic nervous system), changes the diameter of the lumen of the vessel during contraction.

3. smallest vessels These vessels are called capillaries. Capillaries are the most branched and long vascular network. The lumen of the vessel barely passes one erythrocyte - it is so small. However, this lumen diameter provides the maximum area and duration of contact of the erythrocyte with the surrounding tissues. When blood passes through the capillaries, erythrocytes line up one at a time and move slowly, simultaneously exchanging gases with surrounding tissues. Gas exchange and exchange of organic substances, the flow of liquid and the movement of electrolytes occur through the thin wall of the capillary. Therefore, this type of vessel is very important from a functional point of view.
So, gas exchange, metabolism occurs precisely at the level of capillaries - therefore, this type of vessel does not have an average ( muscular) shell.

What are small and large circles of blood circulation?

Small circle of blood circulation- this is, in fact, the circulatory system of the lung. The small circle begins with the largest vessel - the pulmonary trunk. Through this vessel, blood flows from the right ventricle to the circulatory system of the lung tissue. Then there is a branching of the vessels - first into the right and left pulmonary arteries, and then into smaller ones. The arterial vascular system ends with alveolar capillaries, which, like a mesh, envelop the air-filled alveoli of the lung. It is at the level of these capillaries that carbon dioxide is removed from the blood and attached to the hemoglobin molecule ( hemoglobin is found inside red blood cells) oxygen.
After enrichment with oxygen and removal of carbon dioxide, the blood returns through the pulmonary veins to the heart - to the left atrium.

Systemic circulation- this is the whole set of blood vessels that are not included in the circulatory system of the lung. According to these vessels, blood moves from the heart to peripheral tissues and organs, as well as the reverse flow of blood to the right heart.

The beginning of a large circle of blood circulation takes from the aorta, then the blood moves through the vessels of the next order. The branches of the main vessels direct blood to the internal organs, to the brain, limbs. It does not make sense to list the names of these vessels, however, it is important to regulate the distribution of blood flow pumped by the heart to all tissues and organs of the body. Upon reaching the blood-supplying organ, there is a strong branching of the vessels and the formation of a circulatory network from the smallest vessels - microvasculature. At the level of capillaries, metabolic processes take place and the blood, which has lost oxygen and part of the organic substances necessary for the functioning of organs, is enriched with substances formed as a result of the work of the cells of the organ and carbon dioxide.

As a result of such continuous work of the heart, small and large circles of blood circulation, continuous metabolic processes occur throughout the body - the integration of all organs and systems into a single organism is carried out. Thanks to the circulatory system, it is possible to supply oxygen to organs distant from the lung, remove and neutralize ( liver, kidneys) decay products and carbon dioxide. The circulatory system allows hormones to be distributed throughout the body in the shortest possible time, to reach any organ and tissue with immune cells. In medicine, the circulatory system is used as the main drug-distributing element.

Distribution of blood flow in tissues and organs

The intensity of the blood supply to the internal organs is not uniform. This largely depends on the intensity and energy intensity of their work. For example, the greatest intensity of blood supply is observed in the brain, retina, heart muscle and kidneys. Organs with an average level of blood supply are represented by the liver, digestive tract, and most endocrine organs. Low intensity of blood flow is inherent in skeletal tissues, connective tissue, subcutaneous fatty retina. However, under certain conditions, the blood supply to a particular organ can repeatedly increase or decrease. For example, muscle tissue with regular physical exertion can be supplied with blood more intensively, with a sharp massive blood loss, as a rule, blood supply is maintained only in vital organs - the central nervous system, lungs, heart ( to other organs, the blood flow is partially limited).

Therefore, it is clear that the circulatory system is not only a system of vascular highways - it is a highly integrated system that actively participates in the regulation of the body's work, simultaneously performing many functions - transport, immune, thermoregulatory, regulating the rate of blood flow of various organs.
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What is a "shell of the heart"?How many red blood cells are in a drop of blood?

How many kilometers of blood vessels are in my body?

This is a classic SWOT. The circulatory system consists of veins, arteries and capillaries. Its length is approximately 100,000 kilometers, and the area is more than half a hectare, and all this is in the body of one adult. According to Dave Williams, most of the length of the circulatory system is in "capillary miles." " Each capillary is very short, but we have an extremely large number of them.» 7 .

If you are in relatively good health, you will survive even if you lose about a third of your blood.

People living above sea level have a relatively large volume of blood compared to those living at sea level. Thus, the body adapts to an environment with a lack of oxygen.

If your kidneys are healthy, they filter about 95 milliliters of blood per minute.

If you stretch all your arteries, veins and blood vessels in length, you can wrap them around the Earth twice.

Blood travels throughout your body, starting from one side of the heart and returning to the other at the end of a full circle. Your blood travels 270,370 kilometers per day.

All useful substances circulate through the cardiovascular system, which, like a kind of transport system, needs a trigger mechanism. The main motor impulse enters the human circulatory system from the heart. As soon as we overwork or experience a spiritual experience, our heartbeat quickens.

The heart is connected to the brain, and it is no coincidence that the ancient philosophers believed that all our spiritual experiences are hidden in the heart. The main function of the heart is to pump blood throughout the body, nourish every tissue and cell, and remove waste products from them. Having made the first beat, this occurs in the fourth week after the conception of the fetus, the heart then beats at a frequency of 120,000 beats per day, which means that our brain works, the lungs breathe, and the muscles act. A person's life depends on the heart.

The human heart is the size of a fist and weighs 300 grams. The heart is located in the chest, it is surrounded by the lungs, and the ribs, sternum and spine protect it. This is a fairly active and durable muscular organ. The heart has strong walls and is made up of intertwined muscle fibers that are not at all like other muscle tissues in the body. In general, our heart is a hollow muscle made up of a pair of pumps and four cavities. The two upper cavities are called the atria, and the two lower cavities are called the ventricles. Each atrium is connected directly to the lower ventricle by thin but very strong valves, they ensure the correct direction of blood flow.

The right heart pump, in other words, the right atrium with the ventricle, sends blood through the veins to the lungs, where it is enriched with oxygen, and the left pump, as strong as the right one, pumps the blood to the most distant organs of the body. With each heartbeat, both pumps work in a two-stroke mode - relaxation and concentration. Throughout our lives, this mode is repeated 3 billion times. Blood enters the heart through the atria and ventricles when the heart is in a relaxed state.

As soon as it is completely filled with blood, an electrical impulse passes through the atrium, it causes a sharp contraction of atrial systole, as a result, blood enters through the open valves into the relaxed ventricles. In turn, as soon as the ventricles fill with blood, they contract and push the blood out of the heart through the external valves. All this takes about 0.8 seconds. Blood flows through the arteries in time with the heartbeat. With each beat of the heart, blood flow presses on the walls of the arteries, giving the heart a characteristic sound - this is how the pulse sounds. In a healthy person, the pulse rate is usually 60-80 beats per minute, but the heart rate depends not only on our physical activity at the moment, but also on the state of mind.

Some heart cells are capable of self-irritation. In the right atrium there is a natural focus of automatism of the heart, it produces approximately one electrical impulse per second when we rest, then this impulse travels throughout the heart. Although the heart is able to work completely on its own, the heart rate depends on signals received from nerve stimuli and commands from the brain.

Circulatory system

The human circulatory system is a closed circuit through which blood is supplied to all organs. Upon exiting the left ventricle, the blood passes through the aorta and begins its circulation throughout the body. First of all, it flows through the smallest arteries, and enters a network of thin blood vessels - capillaries. There, the blood exchanges oxygen and nutrients with the tissue. From the capillaries, blood flows into the vein, and from there into the paired wide veins. The upper and lower cavities of the vein are connected directly to the right atrium.

Further, the blood enters the right ventricle, and then into the pulmonary arteries and lungs. The pulmonary arteries gradually expand, and form microscopic cells - alveoli, covered with a membrane only one cell thick. Under the pressure of gases on the membrane, on both sides, the process of interchange takes place in the blood, as a result, the blood is cleared of carbon dioxide and saturated with oxygen. Enriched with oxygen, the blood passes through the four pulmonary veins and enters the left atrium - this is how a new circulation cycle begins.

Blood makes one complete revolution in about 20 seconds. Following, thus, through the body, the blood enters the heart twice. All this time, it moves along a complex tubular system, the total length of which is approximately twice the circumference of the Earth. There are many more veins in our circulatory system than arteries, although the muscle tissue of the veins is less developed, but the veins are more elastic than the arteries, and about 60% of the blood flow passes through them. The veins are surrounded by muscles. As the muscles contract, they push blood towards the heart. Veins, especially those located on the legs and arms, are equipped with a system of self-regulating valves.

After passing through the next portion of the blood flow, they close, preventing the backflow of blood. In a complex, our circulatory system is more reliable than any modern high-precision technical device; it not only enriches the body with blood, but also removes waste from it. Due to continuous blood flow, we maintain a constant body temperature. Evenly distributed through the blood vessels of the skin, the blood protects the body from overheating. Through the blood vessels, blood is equally distributed throughout the body. Normally, the heart pumps 15% of the blood flow to the bone muscles, because they account for the lion's share of physical activity.

In the circulatory system, the intensity of blood flow entering the muscle tissue increases by 20 times, or even more. To produce vital energy for the body, the heart needs a lot of blood, even more than the brain. It is estimated that the heart receives 5% of the blood it pumps, and absorbs 80% of the blood it receives. Through a very complex circulatory system, the heart also receives oxygen.

human heart

Human health, as well as the normal functioning of the whole organism, depends mainly on the state of the heart and circulatory system, on their clear and well-coordinated interaction. However, a violation in the activity of the cardiovascular system, and related diseases, thrombosis, heart attack, atherosclerosis, are quite frequent phenomena. Arteriosclerosis, or atherosclerosis, occurs due to hardening and blockage of blood vessels, which impedes blood flow. If some vessels are completely clogged, blood stops flowing to the brain or heart, and this can cause a heart attack, in fact, complete paralysis of the heart muscle.

Fortunately, in the past decade, cardiovascular disease has been curable. Armed with modern technology, surgeons can restore the affected focus of cardiac automatism. They can, and replace a damaged blood vessel, and even transplant the heart of one person to another. Worldly troubles, smoking, fatty foods adversely affect the cardiovascular system. But playing sports, quitting smoking and a calm lifestyle provide the heart with a healthy working rhythm.

The structure of the cardiovascular system and its functions- these are the key knowledge that a personal trainer needs to build a competent training process for wards, based on loads adequate to their level of training. Before starting to build training programs, it is necessary to understand the principle of this system, how blood is pumped through the body, in what ways it happens and what affects the throughput of its vessels.

The cardiovascular system is needed by the body for the transfer of nutrients and components, as well as for the elimination of metabolic products from tissues, maintaining the constancy of the internal environment of the body, optimal for its functioning. The heart is its main component, which acts as a pump that pumps blood around the body. At the same time, the heart is only a part of the whole circulatory system of the body, which first drives blood from the heart to the organs, and then from them back to the heart. We will also consider separately the arterial and separately venous circulatory systems of a person.

The structure and functions of the human heart

The heart is a kind of pump, consisting of two ventricles, which are interconnected and at the same time independent of each other. The right ventricle drives blood through the lungs, the left ventricle drives it through the rest of the body. Each half of the heart has two chambers: an atrium and a ventricle. You can see them in the image below. The right and left atria act as reservoirs from which blood enters directly into the ventricles. Both ventricles at the moment of contraction of the heart push out blood and drive it through the system of pulmonary and peripheral vessels.

The structure of the human heart: 1-pulmonary trunk; 2-valve of the pulmonary artery; 3-superior vena cava; 4-right pulmonary artery; 5-right pulmonary vein; 6-right atrium; 7-tricuspid valve; 8-right ventricle; 9-inferior vena cava; 10-descending aorta; 11-arch of the aorta; 12-left pulmonary artery; 13-left pulmonary vein; 14-left atrium; 15-aortic valve; 16 mitral valve; 17-left ventricle; 18-interventricular septum.

The structure and functions of the circulatory system

The blood circulation of the whole body, both central (heart and lungs) and peripheral (the rest of the body) forms an integral closed system, divided into two circuits. The first circuit drives blood away from the heart and is called the arterial circulatory system, the second circuit returns blood to the heart and is called the venous circulatory system. Blood returning from the periphery to the heart initially enters the right atrium through the superior and inferior vena cava. Blood flows from the right atrium into the right ventricle and through the pulmonary artery to the lungs. After the exchange of oxygen with carbon dioxide occurs in the lungs, the blood returns to the heart through the pulmonary veins, entering first into the left atrium, then into the left ventricle, and then only again into the arterial blood supply system.

The structure of the human circulatory system: 1-superior vena cava; 2-vessels going to the lungs; 3-aorta; 4-inferior vena cava; 5-hepatic vein; 6-portal vein; 7-pulmonary vein; 8-superior vena cava; 9-inferior vena cava; 10-vessels of internal organs; 11-vessels of the limbs; 12-vessels of the head; 13-pulmonary artery; 14-heart.

I-small circle of blood circulation; II-large circle of blood circulation; III-vessels going to the head and hands; IV-vessels going to the internal organs; V-vessels leading to the legs

The structure and functions of the human arterial system

The function of the arteries is to transport blood, which is ejected by the heart during its contraction. Since this release occurs under fairly high pressure, nature has provided the arteries with strong and elastic muscle walls. Smaller arteries, called arterioles, are designed to control the volume of blood circulation and serve as vessels through which blood enters directly into the tissues. Arterioles play a key role in the regulation of blood flow in the capillaries. They are also protected by elastic muscular walls, which enable the vessels to either close their lumen as needed, or significantly expand it. This makes it possible to change and control blood circulation within the capillary system, depending on the needs of specific tissues.

The structure of the human arterial system: 1-shoulder head trunk; 2-subclavian artery; 3-arch of the aorta; 4-axillary artery; 5-internal thoracic artery; 6-descending aorta; 7-internal thoracic artery; 8-deep brachial artery; 9-beam recurrent artery; 10-upper epigastric artery; 11-descending aorta; 12-lower epigastric artery; 13-interosseous arteries; 14-beam artery; 15-ulnar artery; 16 palmar carpal arch; 17-dorsal carpal arch; 18 palm arches; 19-finger arteries; 20-descending branch of the circumflex artery; 21-descending knee artery; 22-upper knee arteries; 23-lower knee arteries; 24-peroneal artery; 25-posterior tibial artery; 26-large tibial artery; 27-peroneal artery; 28-arterial arch of the foot; 29-metatarsal artery; 30-anterior cerebral artery; 31-middle cerebral artery; 32-posterior cerebral artery; 33-basilar artery; 34-external carotid artery; 35-internal carotid artery; 36-vertebral arteries; 37-common carotid arteries; 38-pulmonary vein; 39-heart; 40-intercostal arteries; 41-celiac trunk; 42-gastric arteries; 43-splenic artery; 44-common hepatic artery; 45-superior mesenteric artery; 46-renal artery; 47-inferior mesenteric artery; 48-internal seminal artery; 49-common iliac artery; 50-internal iliac artery; 51-external iliac artery; 52 circumflex arteries; 53-common femoral artery; 54-piercing branches; 55-deep femoral artery; 56-superficial femoral artery; 57-popliteal artery; 58-dorsal metatarsal arteries; 59-dorsal digital arteries.

The structure and functions of the human venous system

The purpose of venules and veins is to return blood through them back to the heart. From tiny capillaries, blood flows into small venules, and from there into larger veins. Since the pressure in the venous system is much lower than in the arterial system, the walls of the vessels are much thinner here. However, the walls of the veins are also surrounded by elastic muscle tissue, which, by analogy with the arteries, allows them to either strongly narrow, completely blocking the lumen, or expand greatly, acting in this case as a reservoir for blood. A feature of some veins, for example in the lower extremities, is the presence of one-way valves, the task of which is to ensure the normal return of blood to the heart, thereby preventing its outflow under the influence of gravity when the body is in an upright position.

The structure of the human venous system: 1-subclavian vein; 2-internal thoracic vein; 3-axillary vein; 4-lateral vein of the arm; 5-brachial veins; 6 intercostal veins; 7-medial vein of the arm; 8-median cubital vein; 9-sternal epigastric vein; 10-lateral vein of the arm; 11-ulnar vein; 12-medial vein of the forearm; 13 epigastric inferior vein; 14-deep palmar arch; 15-surface palmar arch; 16 palmar digital veins; 17-sigmoid sinus; 18-external jugular vein; 19-internal jugular vein; 20-inferior thyroid vein; 21-pulmonary arteries; 22-heart; 23-inferior vena cava; 24-hepatic veins; 25-renal veins; 26-abdominal vena cava; 27 seed vein; 28-common iliac vein; 29-piercing branches; 30-external iliac vein; 31-internal iliac vein; 32-external pudendal vein; 33-deep vein of the thigh; 34-large leg vein; 35-femoral vein; 36-accessory leg vein; 37-upper knee veins; 38-popliteal vein; 39-lower knee veins; 40-large leg vein; 41-small vein of the leg; 42-anterior/posterior tibial vein; 43-deep plantar vein; 44-dorsal venous arch; 45-dorsal metacarpal veins.

The structure and functions of the system of small capillaries

The functions of capillaries are to carry out the exchange of oxygen, fluids, various nutrients, electrolytes, hormones and other vital components between the blood and body tissues. The supply of nutrients to the tissues occurs due to the fact that the walls of these vessels have a very small thickness. Thin walls allow nutrients to penetrate to the tissues and provide them with all the necessary components.

The structure of microcirculation vessels: 1-arteries; 2-arterioles; 3-veins; 4-venules; 5-capillaries; 6-cell tissue

The work of the circulatory system

The movement of blood throughout the body depends on the capacity of the vessels, more precisely on their resistance. The lower this resistance, the stronger the increase in blood flow, at the same time, the higher the resistance, the weaker the blood flow. In itself, the resistance depends on the size of the lumen of the vessels of the arterial circulatory system. The total resistance of all vessels in the circulatory system is called the total peripheral resistance. If in the body in a short period of time there is a reduction in the lumen of the vessels, the total peripheral resistance increases, and when the lumen of the vessels expands, it decreases.

Both expansion and contraction of the vessels of the entire circulatory system occur under the influence of many different factors, such as the intensity of training, the level of stimulation of the nervous system, the activity of metabolic processes in specific muscle groups, the course of heat exchange processes with the external environment, and not only. During training, the excitation of the nervous system leads to vasodilation and increased blood flow. At the same time, the most significant increase in blood circulation in the muscles is primarily the result of metabolic and electrolytic reactions in muscle tissues under the influence of both aerobic and anaerobic physical activity. This includes an increase in body temperature and an increase in the concentration of carbon dioxide. All these factors contribute to vasodilation.

At the same time, the blood flow in other organs and parts of the body that are not involved in the performance of physical activity decreases due to the reduction of arterioles. This factor, along with the narrowing of the large vessels of the venous circulatory system, contributes to an increase in the volume of blood, which is involved in the blood supply to the muscles involved in the work. The same effect is observed during the performance of power loads with small weights, but with a large number of repetitions. The reaction of the body in this case can be equated to aerobic exercise. At the same time, when performing strength work with large weights, the resistance to blood flow in the working muscles increases.

Conclusion

We examined the structure and functions of the human circulatory system. As it has now become clear to us, it is needed to pump blood through the body with the help of the heart. The arterial system drives blood away from the heart, the venous system returns blood back to it. In terms of physical activity, it can be summed up as follows. The blood flow in the circulatory system depends on the degree of resistance of the blood vessels. When vascular resistance decreases, blood flow increases, and when resistance increases, it decreases. The contraction or expansion of blood vessels, which determine the degree of resistance, depends on factors such as the type of exercise, the reaction of the nervous system and the course of metabolic processes.

The distribution of blood throughout the human body is carried out due to the work of the cardiovascular system. Its main organ is the heart. Each of his blows contributes to the fact that the blood moves and nourishes all organs and tissues.

System Structure

There are different types of blood vessels in the body. Each of them has its own purpose. So, the system includes arteries, veins and lymphatic vessels. The first of them are designed to ensure that blood enriched with nutrients enters the tissues and organs. It is saturated with carbon dioxide and various products released during the life of cells, and returns through the veins back to the heart. But before entering this muscular organ, the blood is filtered in the lymphatic vessels.

The total length of the system, consisting of blood and lymphatic vessels, in the body of an adult is about 100 thousand km. And the heart is responsible for its normal functioning. It is it that pumps about 9.5 thousand liters of blood every day.

Principle of operation

The circulatory system is designed to support the entire body. If there are no problems, then it functions as follows. Oxygenated blood exits the left side of the heart through the largest arteries. It spreads throughout the body to all cells through wide vessels and the smallest capillaries, which can only be seen under a microscope. It is the blood that enters the tissues and organs.

The place where the arterial and venous systems connect is called the capillary bed. The walls of the blood vessels in it are thin, and they themselves are very small. This allows you to fully release oxygen and various nutrients through them. The waste blood enters the veins and returns through them to the right side of the heart. From there, it enters the lungs, where it is enriched again with oxygen. Passing through the lymphatic system, the blood is cleansed.

Veins are divided into superficial and deep. The first are close to the surface of the skin. Through them, blood enters the deep veins, which return it to the heart.

The regulation of blood vessels, heart function and general blood flow is carried out by the central nervous system and local chemicals released in the tissues. This helps control the flow of blood through the arteries and veins, increasing or decreasing its intensity depending on the processes taking place in the body. For example, it increases with physical exertion and decreases with injuries.

How does blood flow

The spent "depleted" blood through the veins enters the right atrium, from where it flows into the right ventricle of the heart. With powerful movements, this muscle pushes the incoming fluid into the pulmonary trunk. It is divided into two parts. The blood vessels of the lungs are designed to enrich the blood with oxygen and return them to the left ventricle of the heart. Each person has this part of him more developed. After all, it is the left ventricle that is responsible for how the entire body will be supplied with blood. It is estimated that the load that falls on it is 6 times greater than that to which the right ventricle is subjected.

The circulatory system includes two circles: small and large. The first of them is designed to saturate the blood with oxygen, and the second - for its transportation throughout the orgasm, delivery to every cell.

Requirements for the circulatory system

In order for the human body to function normally, a number of conditions must be met. First of all, attention is paid to the state of the heart muscle. After all, it is she who is the pump that drives the necessary biological fluid through the arteries. If the work of the heart and blood vessels is impaired, the muscle is weakened, then this can cause peripheral edema.

It is important that the difference between the areas of low and high pressure is observed. It is necessary for normal blood flow. So, for example, in the region of the heart, the pressure is lower than at the level of the capillary bed. This allows you to comply with the laws of physics. Blood moves from an area of ​​higher pressure to an area where it is lower. If a number of diseases occur, due to which the established balance is disturbed, then this is fraught with congestion in the veins, swelling.

The ejection of blood from the lower extremities is carried out thanks to the so-called musculo-venous pumps. This is what the calf muscles are called. With each step, they contract and push the blood against the natural force of gravity towards the right atrium. If this function is disturbed, for example, as a result of injury and temporary immobilization of the legs, then edema occurs due to a decrease in venous return.

Another important link responsible for ensuring that the human blood vessels function normally are venous valves. They are designed to support the fluid flowing through them until it enters the right atrium. If this mechanism is disturbed, and this is possible as a result of injuries or due to valve wear, abnormal blood collection will be observed. As a result, this leads to an increase in pressure in the veins and squeezing out the liquid part of the blood into the surrounding tissues. A striking example of a violation of this function is varicose veins in the legs.

Vessel classification

To understand how the circulatory system works, it is necessary to understand how each of its components functions. So, the pulmonary and hollow veins, the pulmonary trunk and the aorta are the main ways of moving the necessary biological fluid. And all the rest are able to regulate the intensity of the inflow and outflow of blood to the tissues due to the ability to change their lumen.

All vessels in the body are divided into arteries, arterioles, capillaries, venules, veins. All of them form a closed connecting system and serve a single purpose. Moreover, each blood vessel has its own purpose.

arteries

The areas through which blood moves are divided depending on the direction in which it moves in them. So, all arteries are designed to carry blood from the heart throughout the body. They are elastic, muscular and muscular-elastic type.

The first type includes those vessels that are directly connected with the heart and exit from its ventricles. This is the pulmonary trunk, pulmonary and carotid arteries, aorta.

All of these vessels of the circulatory system consist of elastic fibers that are stretched. This happens with every heartbeat. As soon as the contraction of the ventricle has passed, the walls return to their original form. Due to this, normal pressure is maintained for a period until the heart fills with blood again.

Blood enters all tissues of the body through the arteries that depart from the aorta and pulmonary trunk. At the same time, different organs need different amounts of blood. This means that the arteries must be able to narrow or expand their lumen so that the fluid passes through them only in the required doses. This is achieved due to the fact that smooth muscle cells work in them. Such human blood vessels are called distributive. Their lumen is regulated by the sympathetic nervous system. The muscular arteries include the artery of the brain, radial, brachial, popliteal, vertebral and others.

Other types of blood vessels are also isolated. These include muscular-elastic or mixed arteries. They can contract very well, but at the same time they have high elasticity. This type includes the subclavian, femoral, iliac, mesenteric arteries, celiac trunk. They contain both elastic fibers and muscle cells.

Arterioles and capillaries

As blood moves along the arteries, their lumen decreases and the walls become thinner. Gradually they pass into the smallest capillaries. The area where arteries end is called arterioles. Their walls consist of three layers, but they are weakly expressed.

The thinnest vessels are the capillaries. Together, they represent the longest part of the entire circulatory system. It is they who connect the venous and arterial channels.

A true capillary is a blood vessel that is formed as a result of branching of arterioles. They can form loops, networks that are located in the skin or synovial bags, or vascular glomeruli that are located in the kidneys. The size of their lumen, the speed of blood flow in them and the shape of the networks formed depend on the tissues and organs in which they are located. So, for example, the thinnest vessels are located in skeletal muscles, lungs and nerve sheaths - their thickness does not exceed 6 microns. They form only flat networks. In mucous membranes and skin, they can reach 11 microns. In them, the vessels form a three-dimensional network. The widest capillaries are found in the hematopoietic organs, endocrine glands. Their diameter in them reaches 30 microns.

The density of their placement is also not the same. The highest concentration of capillaries is noted in the myocardium and brain, for every 1 mm 3 there are up to 3,000 of them. At the same time, there are only up to 1000 of them in the skeletal muscle, and even less in the bone tissue. It is also important to know that in an active state, under normal conditions, blood does not circulate in all capillaries. About 50% of them are in an inactive state, their lumen is compressed to a minimum, only plasma passes through them.

Venules and veins

Capillaries, which receive blood from arterioles, unite and form larger vessels. They are called postcapillary venules. The diameter of each such vessel does not exceed 30 µm. Folds form at the transition points, which perform the same functions as the valves in the veins. Elements of blood and plasma can pass through their walls. Postcapillary venules unite and flow into collecting venules. Their thickness is up to 50 microns. Smooth muscle cells begin to appear in their walls, but often they do not even surround the lumen of the vessel, but their outer shell is already clearly defined. The collecting venules become muscle venules. The diameter of the latter often reaches 100 microns. They already have up to 2 layers of muscle cells.

The circulatory system is designed in such a way that the number of vessels that drain blood is usually twice the number of those through which it enters the capillary bed. In this case, the liquid is distributed as follows. Up to 15% of the total amount of blood in the body is in the arteries, up to 12% in the capillaries, and 70-80% in the venous system.

By the way, fluid can flow from arterioles to venules without entering the capillary bed through special anastomoses, the walls of which include muscle cells. They are found in almost all organs and are designed to ensure that blood can be discharged into the venous bed. With their help, pressure is controlled, the transition of tissue fluid and blood flow through the organ is regulated.

Veins are formed after the confluence of venules. Their structure directly depends on the location and diameter. The number of muscle cells is affected by the place of their localization and the factors under the influence of which fluid moves in them. Veins are divided into muscular and fibrous. The latter include the vessels of the retina, spleen, bones, placenta, soft and hard membranes of the brain. The blood circulating in the upper part of the body moves mainly under the force of gravity, as well as under the influence of the suction action during inhalation of the chest cavity.

The veins of the lower extremities are different. Each blood vessel in the legs must resist the pressure that is created by the fluid column. And if the deep veins are able to maintain their structure due to the pressure of the surrounding muscles, then the superficial ones have a harder time. They have a well-developed muscle layer, and their walls are much thicker.

Also, a characteristic difference between the veins is the presence of valves that prevent the backflow of blood under the influence of gravity. True, they are not in those vessels that are in the head, brain, neck and internal organs. They are also absent in the hollow and small veins.

The functions of blood vessels differ depending on their purpose. So, veins, for example, serve not only to move fluid to the region of the heart. They are also designed to reserve it in separate areas. The veins are activated when the body is working hard and needs to increase the volume of circulating blood.

The structure of the walls of the arteries

Each blood vessel is made up of several layers. Their thickness and density depend solely on what type of veins or arteries they belong to. It also affects their composition.

So, for example, elastic arteries contain a large number of fibers that provide stretching and elasticity of the walls. The inner shell of each such blood vessel, which is called the intima, is about 20% of the total thickness. It is lined with endothelium, and under it is loose connective tissue, intercellular substance, macrophages, muscle cells. The outer layer of the intima is limited by an internal elastic membrane.

The middle layer of such arteries consists of elastic membranes, with age they thicken, their number increases. Between them are smooth muscle cells that produce intercellular substance, collagen, elastin.

The outer shell of the elastic arteries is formed by fibrous and loose connective tissue, elastic and collagen fibers are located longitudinally in it. It also contains small vessels and nerve trunks. They are responsible for the nutrition of the outer and middle shells. It is the outer part that protects the arteries from ruptures and overstretching.

The structure of blood vessels, which are called muscular arteries, is not much different. They also have three layers. The inner shell is lined with endothelium, it contains the inner membrane and loose connective tissue. In small arteries, this layer is poorly developed. The connective tissue contains elastic and collagen fibers, they are located longitudinally in it.

The middle layer is formed by smooth muscle cells. They are responsible for the contraction of the entire vessel and for pushing blood into the capillaries. Smooth muscle cells are connected to the intercellular substance and elastic fibers. The layer is surrounded by a kind of elastic membrane. The fibers located in the muscle layer are connected to the outer and inner shells of the layer. They seem to form an elastic frame that prevents the artery from sticking together. And muscle cells are responsible for regulating the thickness of the lumen of the vessel.

The outer layer consists of loose connective tissue, in which collagen and elastic fibers are located, they are located obliquely and longitudinally in it. Nerves, lymphatic and blood vessels pass through it.

The structure of mixed-type blood vessels is an intermediate link between muscular and elastic arteries.

Arterioles also consist of three layers. But they are rather weakly expressed. The inner shell is the endothelium, a layer of connective tissue and an elastic membrane. The middle layer consists of 1 or 2 layers of muscle cells that are arranged in a spiral.

The structure of the veins

In order for the heart and blood vessels called arteries to function, it is necessary that blood can rise back up, bypassing the force of gravity. For these purposes, venules and veins, which have a special structure, are intended. These vessels consist of three layers, as well as arteries, although they are much thinner.

The inner shell of the veins contains endothelium, it also has a poorly developed elastic membrane and connective tissue. The middle layer is muscular, it is poorly developed, there are practically no elastic fibers in it. By the way, precisely because of this, the cut vein always subsides. The outer shell is the thickest. It consists of connective tissue, it contains a large number of collagen cells. It also contains smooth muscle cells in some veins. They help push blood towards the heart and prevent its reverse flow. The outer layer also contains lymph capillaries.