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 an 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 the blood vessels called arteries to function, it is necessary that the 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.

This is the CIRCULATION SYSTEM. It consists of two complex systems - circulatory and lymphatic, which work together to form the body's transport system.

The structure of the circulatory system

Blood

Blood is a specific connective tissue containing cells that are in a liquid - plasma. It is a transport system that connects the internal world of the organism with the external world.

Blood is made up of two parts - plasma and cells. Plasma is a straw-colored liquid that makes up about 55% of blood. It consists of 10% proteins, including: albumin, fibrinogen and prothrombin, and 90% of water, in which chemicals are dissolved or suspended: decay products, nutrients, hormones, oxygen, mineral salts, enzymes, antibodies and antitoxins.

Cells make up the remaining 45% of blood. They are produced in the red bone marrow, which is found in the cancellous bone.

There are three main types of blood cells:

1. Erythrocytes are concave, elastic disks. They do not have a nucleus, as it disappears as the cell is formed. Removed from the body by the liver or spleen; they are constantly being replaced by new cells. Millions of new cells replace old ones every day! Red blood cells contain hemoglobin (hemo=iron, globin=protein).
2. Leukocytes are colorless, of different shapes, have a nucleus. They are larger than red blood cells, but inferior to them quantitatively. Leukocytes live from several hours to several years, depending on their activity.

There are two types of leukocytes:

1. Granulocytes, or granular white blood cells, make up 75% of white blood cells and protect the body from viruses and bacteria. They can change their shape and penetrate from the blood into adjacent tissues.
2. Non-granular leukocytes (lymphocytes and monocytes). Lymphocytes are part of the lymphatic system, are produced by lymph nodes and are responsible for the formation of antibodies, which play a leading role in the body's resistance to infections. Monocytes are able to absorb harmful bacteria. This process is called phagocytosis. It effectively eliminates the danger to the body.
3. Platelets, or platelets, are much smaller than red blood cells. They are fragile, do not have a nucleus, are involved in the formation of blood clots at the site of injury. Platelets are formed in the red bone marrow and live for 5-9 days.

A heart

The heart is located in the chest between the lungs and is slightly shifted to the left. In size, it corresponds to the fist of its owner.

The heart works like a pump. It is the center of the circulatory system and is involved in the transport of blood to all parts of the body.

• The systemic circulation includes the circulation of blood between the heart and all parts of the body through the blood vessels.
• The pulmonary circulation refers to the circulation of blood between the heart and lungs through the vessels of the pulmonary circulation.

The heart is made up of three layers of tissue:

• Endocardium - the inner lining of the heart.
• Myocardium is the heart muscle. It carries out involuntary contractions - heartbeat.
• The pericardium is a pericardial sac that has two layers. The cavity between the layers is filled with a fluid that prevents friction and allows the layers to move more freely when the heart beats.

The heart has four compartments, or cavities:

• The upper cavities of the heart are the left and right atria.
• The lower cavities are the left and right ventricles.

The muscular wall - the septum - separates the left and right parts of the heart, preventing the blood from the left and right sides of the body from mixing. The blood in the right side of the heart is poor in oxygen, in the left side it is enriched with oxygen.

The atria are connected to the ventricles by valves:

• The tricuspid valve connects the right atrium to the right ventricle.
• The bicuspid valve connects the left atrium to the left ventricle.

Blood vessels

Blood circulates throughout the body through a network of vessels called arteries and veins.

Capillaries form the ends of arteries and veins and provide a link between the circulatory system and cells throughout the body.

Arteries are hollow, thick-walled tubes made up of three layers of cells. They have a fibrous outer shell, a middle layer of smooth, elastic muscle tissue, and an inner layer of squamous epithelial tissue. The arteries are largest near the heart. As they move away from it, they become thinner. The middle layer of elastic tissue in large arteries is larger than in small ones. Larger arteries allow more blood to pass through, and the elastic tissue allows them to stretch. It helps to withstand the pressure of the blood coming from the heart and allows it to continue its movement throughout the body. The cavity of the arteries can become clogged, blocking the flow of blood. Arteries end in artepioles, which are similar in structure to arteries, but have more muscle tissue, which allows them to relax or contract, depending on the need. For example, when the stomach needs extra blood flow to start digestion, the arterioles relax. After the end of the digestion process, arterioles contract, directing blood to other organs.

Veins are tubes, also consisting of three layers, but thinner than arteries, and have a large percentage of elastic muscle tissue. Veins rely heavily on the voluntary movement of skeletal muscles to keep blood flowing back to the heart. The cavity of the veins is wider than that of the arteries. Just as arteries branch into arterioles at the end, veins divide into venules. Veins have valves that prevent blood from flowing backwards. Valve problems lead to poor flow to the heart, which can cause varicose veins. It especially occurs in the legs, where blood is trapped in the veins causing them to dilate and hurt. Sometimes a clot, or thrombus, forms in the blood and travels through the circulatory system and can cause a blockage that is very dangerous.

Capillaries create a network in tissues, providing oxygen and carbon dioxide gas exchange and metabolism. The walls of capillaries are thin and permeable, allowing substances to move in and out of them. Capillaries are the end of the blood path from the heart, where oxygen and nutrients from them enter the cells, and the beginning of its path from the cells, where carbon dioxide enters the blood, which it carries to the heart.

The structure of the lymphatic system

Lymph

Lymph is a straw-colored liquid, similar to blood plasma, which is formed as a result of the ingress of substances into the fluid that bathes the cells. It is called tissue, or interstitial. fluid and is derived from blood plasma. Lymph binds blood and cells, allowing oxygen and nutrients to flow from the blood into the cells, and waste products and carbon dioxide back. Some plasma proteins leak into adjacent tissues and must be collected back to prevent edema from forming. About 10 percent of tissue fluid enters the lymphatic capillaries, which easily pass plasma proteins, decay products, bacteria and viruses. The remaining substances leaving the cells are picked up by the blood of the capillaries and carried away through the venules and veins back to the heart.

Lymphatic vessels

Lymphatic vessels begin with lymphatic capillaries, which take excess tissue fluid from the tissues. They pass into larger tubes and run along those in parallel with the veins. Lymphatic vessels are similar to veins, as they also have valves that prevent the flow of lymph in the opposite direction. Lymph flow is stimulated by skeletal muscles, similar to the flow of venous blood.

Lymph nodes, tissues and ducts

Lymphatic vessels pass through lymph nodes, tissues, and ducts before joining veins and reaching the heart, after which the whole process begins anew.

lymph nodes

Also known as glands, they are located at strategic points in the body. They are formed by fibrous tissue containing different cells from white blood cells:

1. Macrophages - cells that destroy unwanted and harmful substances (antigens), filter the lymph passing through the lymph nodes.
2. Lymphocytes are cells that produce protective antibodies against antigens collected by macrophages.

Lymph enters the lymph nodes through afferent vessels, and leaves them through efferent vessels.

lymphatic tissue

In addition to the lymph nodes, there are lymphatic tissue in other areas of the body.

The lymphatic ducts take the purified lymph leaving the lymph nodes and direct it to the veins.

There are two lymphatic ducts:

• The thoracic duct is the main duct that runs from the lumbar vertebrae to the base of the neck. It is about 40 cm long and collects lymph from the left side of the head, neck and chest, left arm, both legs, abdominal and pelvic areas and releases it into the left subclavian vein.
• The right lymphatic duct is only 1 cm long and is located at the base of the neck. Collects lymph and releases it into the right subclavian vein.

After that, the lymph is included in the blood circulation, and the whole process is repeated again.

Functions of the circulatory system

Each cell relies on the circulatory system to carry out its individual functions. The circulatory system performs four main functions: circulation, transportation, protection and regulation.

Circulation

The movement of blood from the heart to the cells is controlled by the heartbeat - you can feel and hear how the cavities of the heart contract and relax.

• The atria relax and fill with venous blood, and a first heart sound can be heard as the valves close for blood passing from the atria into the ventricles.
• The ventricles contract, pushing blood into the arteries; when the valves close to prevent backflow of blood, a second heart sound is heard.
• Relaxation is called diastole, and contraction is called systole.
• The heart beats faster when the body needs more oxygen.

The heartbeat is controlled by the autonomic nervous system. The nerves respond to the needs of the body, and the nervous system puts the heart and lungs on alert. Breathing quickens, the rate at which the heart pushes incoming oxygen increases.

The pressure is measured with a sphygmomanometer.

• Maximum pressure associated with ventricular contraction = systolic pressure.
• Minimum pressure associated with ventricular relaxation = diastolic pressure.
• High blood pressure (hypertension) occurs when the heart is not working hard enough to push blood out of the left ventricle and into the aorta, the main artery. As a result, the load on the heart increases, the blood vessels of the brain can burst, causing a stroke. Common causes of high blood pressure are stress, poor diet, alcohol and smoking; another possible cause is kidney disease, hardening or narrowing of the arteries; sometimes the cause is heredity.
• Low blood pressure (hypotension) occurs due to the inability of the heart to pump enough blood force as it exits, resulting in poor blood supply to the brain and causing dizziness and weakness. The causes of low blood pressure can be hormonal and hereditary; shock can also be the cause.

The contraction and relaxation of the ventricles can be felt - this is the pulse - the pressure of the blood passing through the arteries, arterioles and capillaries to the cells. The pulse can be felt by pressing the artery against the bone.

The pulse rate corresponds to the heart rate, and its strength corresponds to the pressure of the blood leaving the heart. The pulse behaves in much the same way as blood pressure, ie. increases during activity and decreases at rest. The normal pulse of an adult at rest is 70-80 beats per minute, during periods of maximum activity it reaches 180-200 beats.

The flow of blood and lymph to the heart is controlled by:

• Bone muscle movements. Contracting and relaxing, the muscles direct blood through the veins, and lymph through the lymphatic vessels.
• Valves in the veins and lymphatic vessels that prevent the flow in the opposite direction.

The circulation of blood and lymph is a continuous process, but it can be divided into two parts: pulmonary and systemic with portal (related to the digestive system) and coronary (related to the heart) parts of the systemic circulation.

Pulmonary circulation refers to the circulation of blood between the lungs and the heart:

• Four pulmonary veins (two from each lung) carry oxygenated blood to the left atrium. It passes through the bicuspid valve into the left ventricle, from where it diverges throughout the body.
• The right and left pulmonary arteries carry oxygen-deprived blood from the right ventricle to the lungs, where carbon dioxide is removed and replaced with oxygen.

The systemic circulation includes the main flow of blood from the heart and the return of blood and lymph from the cells.

• Oxygenated blood passes through the bicuspid valve from the left atrium to the left ventricle and exits the heart through the aorta (main artery), after which it is carried to the cells of the whole body. From there, blood flows to the brain via the carotid artery, to the arms via the clavicular, axillary, bronchiogenic, radial, and ulnar arteries, and to the legs via the iliac, femoral, popliteal, and anterior tibial arteries.
• The main veins carry oxygen-deprived blood to the right atrium. These include: the anterior tibial, popliteal, femoral, and iliac veins from the legs; the ulnar, radial, bronchial, axillary, and clavicular veins from the arms; and the jugular veins from the head. From all of them, blood enters the upper and lower veins, into the right atrium, through the tricuspid valve into the right ventricle.
• Lymph flows through the lymphatic vessels parallel to the veins and is filtered in the lymph nodes: popliteal, inguinal, supratrochlear under the elbows, ear and occipital on the head and neck, before it is collected in the right lymphatic and thoracic ducts and enters from them into the subclavian veins, and then into the heart.
• The portal circulation refers to the flow of blood from the digestive system to the liver through the portal vein, which controls and regulates the supply of nutrients to all parts of the body.
• Coronary circulation refers to the flow of blood to and from the heart through the coronary arteries and veins, ensuring the supply of the required amount of nutrients.

A change in blood volume in different areas of the body leads to a discharge of blood. Blood is directed to those areas where it is needed according to the physical needs of a particular organ, for example, after eating, there is more blood in the digestive system than in the muscles, since blood is needed to stimulate digestion. After a heavy meal, procedures should not be performed, since in this case the blood will leave the digestive system to the muscles that are being worked on, which will cause digestive problems.

Transportation

Substances are carried throughout the body by blood.

• Red blood cells carry oxygen and carbon dioxide between the lungs and all body cells with the help of hemoglobin. When inhaled, oxygen mixes with hemoglobin to form oxyhemoglobin. It is bright red in color and carries oxygen dissolved in the blood to the cells through the arteries. Carbon dioxide, replacing oxygen, forms deoxyhemoglobin with hemoglobin. Dark red blood returns to the lungs through the veins, and carbon dioxide is removed with exhalation.
• In addition to oxygen and carbon dioxide, other substances dissolved in the blood are also transported through the body.
• Degradation products from cells, such as urea, are transported to the excretory organs: liver, kidneys, sweat glands, and are removed from the body in the form of sweat and urine.
• Hormones secreted by the glands send signals to all organs. The blood transports them as needed to the body's systems. For example,
  if necessary, to avoid danger, adrenaline secreted by the adrenal glands is transported to the muscles.
• Nutrients and water from the digestive system enter the cells, ensuring their division. This process nourishes the cells, allowing them to reproduce and repair themselves.
• Minerals that come from food and are produced in the body are necessary for cells to maintain pH levels and to perform their vital functions. Minerals include soda chloride, soda carbonate, potassium:, magnesium, phosphorus, calcium, iodine and copper.
• Enzymes, or proteins, produced by cells have the ability to make or speed up chemical changes without changing themselves. These chemical catalysts are also transported in the blood. Thus, pancreatic enzymes are used by the small intestine for digestion.
• Antibodies and antitoxins are transported from the lymph nodes, where they are produced when bacterial or viral toxins enter the body. The blood carries antibodies and antitoxins to the site of infection.

Lymph transports:

• Decay products and tissue fluid from cells to lymph nodes for filtration.
• Fluid from the lymph nodes to the lymphatic ducts to return it to the blood.
• Fats from the digestive system into the blood stream.

Protection

The circulatory system plays an important role in protecting the body.

• Leukocytes (white blood cells) contribute to the destruction of damaged and old cells. To protect the body from viruses and bacteria, some white blood cells are able to multiply by mitosis to cope with infection.
• Lymph nodes clean the lymph: macrophages and lymphocytes absorb antigens and produce protective antibodies.
• The cleansing of the blood in the spleen is in many ways similar to the cleansing of the lymph in the lymph nodes and contributes to the protection of the body.
• On the surface of the wound, the blood thickens to prevent excessive loss of blood/fluid. Platelets (platelets) perform this vital function by releasing enzymes that alter plasma proteins to form a protective structure on the surface of the wound. The blood clot dries out to form a crust that protects the wound until the tissues heal. After that, the crust is replaced by new cells.
• With an allergic reaction or damage to the skin, blood flow to this area increases. The reddening of the skin associated with this phenomenon is called erythema.

Regulation

The circulatory system is involved in maintaining homeostasis in the following ways:

• Blood-borne hormones regulate many processes in the body.
• The buffer system of the blood maintains the level of its acidity between 7.35 and 7.45. A significant increase (alkalosis) or decrease (acidosis) in this figure can be fatal.
• The structure of the blood maintains fluid balance.
• Normal blood temperature - 36.8 ° C - is maintained by transporting heat. Heat is produced by muscles and organs such as the liver. Blood is able to distribute heat to different areas of the body by contracting and relaxing blood vessels.

The circulatory system is the force that connects all the systems of the body, and the blood contains all the components necessary for life.

Possible violations

Possible disorders of the circulatory system from A to Z:

• ACROCYANOSIS - insufficient blood supply to the hands and/or feet.
• ANEURYSM - Local inflammation of an artery that can develop as a result of disease or damage to this blood vessel, especially with high blood pressure.
• ANEMIA - a decrease in hemoglobin levels.
• ARTERIAL THROMBOSIS - The formation of a blood clot in an artery that interferes with normal blood flow.
• Arteritis is an inflammation of an artery often associated with rheumatoid arthritis.
• ARTERIOSCLEROSIS is a condition where the walls of the arteries lose their elasticity and harden. Because of this, blood pressure rises.
• ATHEROSCLEROSIS - narrowing of the arteries caused by the buildup of fats, including cholesterol.
• Hodkins disease - cancer of the lymphatic tissue.
• GANGRENE - lack of blood supply to the fingers, as a result of which they rot and eventually die.
• HEMOPHILIA - incoagulability of blood, which leads to its excessive loss.
• HEPATITIS B and C - inflammation of the liver caused by viruses that are carried by infected blood.
• HYPERTENSION - high blood pressure.
• DIABETES is a condition in which the body is unable to absorb sugar and carbohydrates from food. The hormone insulin produced by the adrenal glands.
• CORONARY THROMBOSIS is a typical cause of heart attacks when there is an obstruction of the arteries supplying the heart with blood.
• LEUKEMIA - Excessive production of white blood cells leading to blood cancer.
• LYMPHEDEMA - inflammation of the limb, affecting the circulation of the lymph.
• Edema is the result of the accumulation of excess fluid in the tissues from the circulatory system.
• RHEUMATIC ATTACK - inflammation of the heart, often a complication of tonsillitis.
• SEPSIS is a blood poisoning caused by the accumulation of toxic substances in the blood.
• RAYNAUD'S SYNDROME - contraction of the arteries supplying the hands and feet, leading to numbness.
• BLUE (CYANOTIC) CHILD - a congenital heart disease, as a result of which not all blood passes through the lungs to receive oxygen.
• AIDS is the acquired immunodeficiency syndrome caused by HIV, the human immunodeficiency virus. T-lymphocytes are affected, which makes it impossible for the immune system to function normally.
• ANGINA - Decreased blood flow to the heart, usually as a result of physical exertion.
• STRESS is a condition that causes the heart to beat faster, increasing heart rate and blood pressure. Severe stress can cause heart problems.
• A thrombus is a blood clot in a blood vessel or heart.
• ATRIAL FIBRILLATION - an irregular heartbeat.
• Phlebitis - inflammation of the veins, usually on the legs.
• HIGH LEVEL CHOLESTEROL - overgrowth of blood vessels with fatty substance cholesterol, which causes ATHEROSCLEROSIS and HYPERTENSION.
• pulmonary embolism - blockage of blood vessels in the lungs.

Harmony

The circulatory and lymphatic systems interconnect all parts of the body and provide each cell with vital components: oxygen, nutrients and water. The circulatory system also cleanses the body of waste products and transports hormones that determine the actions of cells. To perform all these tasks effectively, the circulatory system needs some care to maintain homeostasis.

Liquid

Like all other systems, the circulatory system depends on the fluid balance in the body.

• The volume of blood in the body depends on the amount of fluid received. If the body does not receive enough fluid, dehydration occurs, and blood volume also decreases. As a result, blood pressure drops and fainting may occur.
• The volume of lymph in the body also depends on the intake of fluid. Dehydration leads to a thickening of the lymph, as a result of which its flow is difficult and edema occurs.
• The lack of water affects the composition of the plasma, and as a result, the blood becomes more viscous. Because of this, blood flow becomes difficult and blood pressure rises.

Nutrition

The circulatory system, which supplies nutrients to all other body systems, is itself very dependent on nutrition. She, like other systems, needs a balanced diet, high in antioxidants, especially vitamin C, which also maintains vascular flexibility. Other required substances:

• Iron - for the formation of hemoglobin in the red bone marrow. Found in pumpkin seeds, parsley, almonds, cashews and raisins.
• Folic acid - for the development of red blood cells. The foods richest in folic acid are wheat grains, spinach, peanuts and green shoots.
• Vitamin B6 - promotes the transport of oxygen in the blood; found in oysters, sardines and tuna.

Rest

During rest, the circulatory system relaxes. The heart beats slower, the frequency and strength of the pulse decreases. The flow of blood and lymph slows down, the supply of oxygen decreases. It is important to remember that venous blood and lymph returning to the heart experience resistance, and when we lie down, this resistance is much lower! Their current improves even more when we lie with our legs slightly elevated, which activates the reverse flow of blood and lymph. Rest must necessarily replace activity, but in excess it can be harmful. Bedridden people are more prone to circulatory problems than active people. The risk increases with age, malnutrition, lack of fresh air and stress.

Activity

The circulatory system needs activity that stimulates the flow of venous blood to the heart and the flow of lymph to the lymph nodes, ducts and vessels. The system responds much better to regular, consistent loads than to sudden ones. To stimulate the heart rate, oxygen consumption and body cleansing, 20-minute sessions three times a week are recommended. If the system is suddenly overloaded, heart problems can occur. For exercise to benefit the body, the heart rate should not exceed 85% of the “theoretical maximum”.

Jumping, such as trampoline sports, is especially good for blood and lymph circulation, and exercises that work the chest are especially good for the heart and thoracic duct. In addition, it is important not to underestimate the benefits of walking, climbing and descending stairs, and even housework, which keeps the whole body active.

Air

Certain gases, when ingested, affect the hemoglobin in erythrocytes (red blood cells), making it difficult to transport oxygen. These include carbon monoxide. A small amount of carbon monoxide is found in cigarette smoke - another point about the dangers of smoking. In an attempt to correct the situation, defective hemoglobin stimulates the formation of more red blood cells. Thus, the body can cope with the harm caused by a single cigarette, but long-term smoking has an effect that the body cannot resist. As a result, blood pressure rises, which can lead to disease. When climbing to a great height, the same stimulation of red blood cells occurs. The rarefied air has a low oxygen content, which causes the red bone marrow to produce more red blood cells. With an increase in the number of cells containing hemoglobin, the supply of oxygen increases, and its content in the blood returns to normal. When oxygen supply is increased, red blood cell production is reduced and thus homeostasis is maintained. This is why the body takes some time to adjust to new environmental conditions, such as high altitude or depth. The act of breathing itself stimulates the flow of lymph through the lymphatic vessels. The movements of the lungs massage the thoracic duct, stimulating the flow of lymph. Deep breathing increases this effect: fluctuations in pressure in the chest stimulate further lymph flow, which helps to cleanse the body. This prevents the accumulation of toxins in the body and avoids many problems, including swelling.

Age

Aging has the following effects on the circulatory system:

• Due to malnutrition, alcohol consumption, stress, etc. blood pressure may rise, which can lead to heart problems.
• Less oxygen enters the lungs and, accordingly, the cells, as a result of which breathing becomes more difficult with age.
• A decrease in oxygen supply affects cellular respiration, which worsens skin condition and muscle tone.
• With a decrease in overall activity, the activity of the circulatory system decreases, and protective mechanisms lose their effectiveness.

Color

Red is associated with oxygenated arterial blood, while blue is associated with oxygen-deprived venous blood. Red is stimulating, blue is calming. Red is said to be good for anemia and low blood pressure, while blue is good for hemorrhoids and high blood pressure. Green - the color of the fourth chakra - is associated with the heart and goiter. The heart is most associated with blood circulation, and the thymus is associated with the production of lymphocytes for the lymphatic system. Speaking of our innermost feelings, we often touch the area of ​​​​the heart - the area associated with green. Green, located in the middle of the rainbow, symbolizes harmony. The lack of green color (especially in cities where there is little vegetation) is considered a factor that violates internal harmony. An excess of green often leads to a feeling of overflowing with energy (for example, during a trip to the country or a walk in the park).

Knowledge

Good general health of the body is essential for the efficient operation of the circulatory system. A person who is taken care of will feel great both mentally and physically. Consider how much a good therapist, a caring boss, or a loving partner improves our lives. Therapy improves skin color, praise from the boss improves self-esteem, and a sign of attention warms from the inside. All this stimulates the circulatory system, on which our health depends. Stress, on the other hand, increases blood pressure and heart rate, which can overload this system. Therefore, it is necessary to try to avoid excessive stress: then the body systems will be able to work better and longer.

special care

Blood is often associated with personality. They say that a person has “good” or “bad” blood, and strong emotions are expressed with such phrases: “the blood boils from one thought” or “the blood runs cold from this sound.” This shows the connection between the heart and the brain, which work as a whole. If you want to achieve harmony between mind and heart, the needs of the circulatory system cannot be ignored. Special care in this case consists in understanding its structure and functions, which will allow us to rationally and maximally use our body and teach our patients this.

CIRCULATORY SYSTEM

The circulatory system is the system of blood vessels and cavities

which the blood circulates. Through the circulatory system of the cell

and tissues of the body are supplied with nutrients and oxygen and

released from metabolic products. Therefore, the circulatory system

sometimes referred to as a transport or distribution system.

The heart and blood vessels form a closed system through which

blood moves due to contractions of the heart muscle and myocytes of the walls

vessels. The blood vessels are the arteries that carry blood from

heart, veins through which blood flows to the heart, and microcirculatory

a channel consisting of arterioles, capillaries, postcopillary venules and

arteriovenular anastomoses.

As you move away from the heart, the caliber of the arteries gradually decreases.

down to the smallest arterioles, which in the thickness of the organs pass into the network

capillaries. The latter, in turn, continue into small, gradually

enlarge

veins that carry blood to the heart. Circulatory system

divided into two circles of blood circulation large and small. The first one starts at

left ventricle and ends in the right atrium, the second begins in

right ventricle and ends in the left atrium. Blood vessels

are absent only in the epithelial cover of the skin and mucous membranes, in

hair, nails, cornea and articular cartilage.

Blood vessels get their name from the organs they

blood supply (renal artery, splenic vein), places of their discharge from

larger vessel (superior mesenteric artery, inferior mesenteric

artery), the bone to which they are attached (ulnar artery), directions

(medial artery surrounding the thigh), depth of occurrence (superficial

or deep artery). Many small arteries are called branches, and veins are

tributaries.

Depending on the area of ​​branching, the arteries are divided into parietal

(parietal), blood-supplying walls of the body, and visceral

(visceral), blood supply to internal organs. Before artery entry

into an organ it is called organ, having entered an organ it is called intraorgan. Last

branches within and supplies its individual structural elements.

Each artery splits into smaller vessels. At the main

type of branching from the main trunk - the main artery, the diameter of which

side branches gradually decrease. With tree type

branching artery immediately after its discharge is divided into two or

several terminal branches, while resembling the crown of a tree.

Blood, tissue fluid and lymph form the internal environment. It retains the relative constancy of its composition - physical and chemical properties (homeostasis), which ensures the stability of all body functions. Preservation of homeostasis is the result of neuro-humoral self-regulation. Each cell needs a constant supply of oxygen and nutrients, and the removal of metabolic products. Both of these things happen through the blood. The cells of the body do not directly come into contact with blood, since the blood moves through the vessels of a closed circulatory system. Each cell is washed by a liquid that contains the substances necessary for it. It is intercellular or tissue fluid.

Between the tissue fluid and the liquid part of the blood - plasma, through the walls of the capillaries, the exchange of substances is carried out by diffusion. Lymph is formed from tissue fluid that enters the lymphatic capillaries, which originate between tissue cells and pass into the lymphatic vessels that flow into the large veins of the chest. Blood is a liquid connective tissue. It consists of a liquid part - plasma and individual shaped elements: red blood cells - erythrocytes, white blood cells - leukocytes and platelets - platelets. Formed elements of blood are formed in the hematopoietic organs: in the red bone marrow, liver, spleen, lymph nodes. 1 mm cube blood contains 4.5-5 million erythrocytes, 5-8 thousand leukocytes, 200-400 thousand platelets. The cellular composition of the blood of a healthy person is fairly constant. Therefore, its various changes occurring in diseases can be of great diagnostic value. Under certain physiological conditions of the body, the qualitative and quantitative composition of the blood often changes (pregnancy, menstruation). However, slight fluctuations occur throughout the day, influenced by food intake, work, and the like. To eliminate the influence of these factors, blood for repeated analyzes should be taken at the same time and under the same conditions.

The human body contains 4.5-6 liters of blood (1/13 of its body weight).

Plasma makes up 55% of the blood volume, and formed elements - 45%. The red color of blood is given by red blood cells containing a red respiratory pigment - hemoglobin, which attaches oxygen in the lungs and gives it to the tissues. Plasma is a colorless transparent liquid consisting of inorganic and organic substances (90% water, 0.9% various mineral salts). Plasma organic matter includes proteins - 7%, fats - 0.7%, 0.1% - glucose, hormones, amino acids, metabolic products. Homeostasis is maintained by the activity of the organs of respiration, excretion, digestion, etc., the influence of the nervous system and hormones. In response to influences from the external environment, responses automatically arise in the body that prevent strong changes in the internal environment.

The vital activity of body cells depends on the salt composition of the blood. And the constancy of the salt composition of the plasma ensures the normal structure and function of blood cells. Blood plasma performs the following functions:

1) transport;

2) excretory;

3) protective;

4) humoral.

Blood, continuously circulating in a closed system of blood vessels, performs various functions in the body:

1) respiratory - carries oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs;

2) nutritional (transport) - delivers nutrients to cells;

3) excretory - takes out unnecessary metabolic products;

4) thermoregulatory - regulates body temperature;

5) protective - produces substances necessary to fight microorganisms

6) humoral - connects various organs and systems, transferring substances that are formed in them.

Hemoglobin, the main component of erythrocytes (red blood cells), is a complex protein consisting of heme (the iron-containing part of Hb) and globin (the protein part of Hb). The main function of hemoglobin is to carry oxygen from the lungs to the tissues, as well as to remove carbon dioxide (CO2) from the body and regulate the acid-base state (ACS)

Erythrocytes - (red blood cells) - the most numerous formed elements of blood containing hemoglobin, transporting oxygen and carbon dioxide. Formed from reticulocytes after their release from the bone marrow. Mature erythrocytes do not contain a nucleus, have the shape of a biconcave disc. The average life span of erythrocytes is 120 days.

Leukocytes are white blood cells that differ from erythrocytes in the presence of a nucleus, large size and the ability to amoeboid movement. The latter makes possible the penetration of leukocytes through the vascular wall into the surrounding tissues, where they perform their functions. The number of leukocytes in 1 mm3 of the peripheral blood of an adult is 6-9 thousand and is subject to significant fluctuations depending on the time of day, the state of the body, and the conditions in which it resides. The sizes of various forms of leukocytes range from 7 to 15 microns. The duration of stay of leukocytes in the vascular bed is from 3 to 8 days, after which they leave it, passing into the surrounding tissues. Moreover, leukocytes are only transported by blood, and their main functions - protective and trophic - are performed in tissues. The trophic function of leukocytes consists in their ability to synthesize a number of proteins, including enzyme proteins, which are used by tissue cells for building (plastic) purposes. In addition, some proteins released as a result of the death of leukocytes can also serve to carry out synthetic processes in other cells of the body.

The protective function of leukocytes lies in their ability to free the body from genetically alien substances (viruses, bacteria, their toxins, mutant cells of one's own body, etc.), while maintaining and maintaining the genetic constancy of the internal environment of the body. The protective function of white blood cells can be carried out either

By phagocytosis ("devouring" genetically alien structures),

By damaging the membranes of genetically foreign cells (which is provided by T-lymphocytes and leads to the death of foreign cells),

The production of antibodies (substances of a protein nature that are produced by B-lymphocytes and their descendants - plasma cells and are able to specifically interact with foreign substances (antigens) and lead to their elimination (death))

The production of a number of substances (for example, interferon, lysozyme, components of the complement system), which are capable of exerting a nonspecific antiviral or antibacterial effect.

Platelets (platelets) are fragments of large cells of the red bone marrow - megakaryocytes. They are nuclear-free, oval-round in shape (in the inactive state they are disc-shaped, and in the active state they are spherical) and differ from other blood cells in the smallest sizes (from 0.5 to 4 microns). The number of platelets in 1 mm3 of blood is 250-450 thousand. The central part of platelets is granular (granulomere), and the peripheral part does not contain granules (hyalomer). They perform two functions: trophic in relation to the cells of the vascular walls (angiotrophic function: as a result of the destruction of platelets, substances are released that are used by cells for their own needs) and participate in blood clotting. The latter is their main function and is determined by the ability of platelets to cluster and stick together into a single mass at the site of damage to the vascular wall, forming a platelet plug (thrombus), which temporarily clogs the gap in the vessel wall. In addition, according to some researchers, platelets are able to phagocytize foreign bodies from the blood and, like other uniform elements, fix antibodies on their surface.

Blood clotting is a protective reaction of the body, aimed at preventing the loss of blood from damaged vessels. The mechanism of blood clotting is very complex. It involves 13 plasma factors, designated by Roman numerals in the order of their chronological discovery. In the absence of damage to the blood vessels, all blood clotting factors are in an inactive state.

The essence of the enzymatic process of blood coagulation is the transition of the soluble plasma protein fibrinogen into insoluble fibrous fibrin, which forms the basis of a blood clot - a thrombus. The chain reaction of blood coagulation is started by the enzyme thromboplastin, which is released when tissues, vascular walls, or platelets are damaged (stage 1). Together with certain plasma factors and in the presence of Ca2 "ions, it converts the inactive enzyme prothrombin, formed by liver cells in the presence of vitamin K, into the active thrombin enzyme (stage 2). At the 3rd stage, fibrinogen is converted to fibrin with the participation of thrombin and Ca2+ ions

According to the generality of some antigenic properties of erythrocytes, all people are divided into several groups, called blood groups. Belonging to a certain blood group is congenital and does not change throughout life. The most important is the division of blood into four groups according to the "AB0" system and into two groups - according to the "Rhesus" system. Compliance with blood compatibility for these groups is of particular importance for safe blood transfusion. However, there are other, less significant, blood types. You can determine the probability of a child having a particular blood type, knowing the blood types of his parents.

Each individual person has one of four possible blood types. Each blood group differs in the content of specific proteins in plasma and red blood cells. In our country, the population is distributed according to blood types approximately as follows: group 1 - 35%, 11 - 36%, III - 22%, group IV - 7%.

The Rh factor is a special protein found in the red blood cells of most people. They are classified as Rh-positive. If such people are transfused with human blood with the absence of this protein (Rh-negative group), then serious complications are possible. To prevent them, gamma globulin, a special protein, is additionally administered. Each person needs to know their Rh factor and blood type and remember that they do not change throughout life, this is a hereditary trait.

The heart is the central organ of the circulatory system, which is a hollow muscular organ that functions as a pump and ensures the movement of blood in the circulatory system. The heart is a muscular hollow cone-shaped organ. In relation to the midline of a person (the line dividing the human body into left and right halves), the human heart is located asymmetrically - about 2/3 - to the left of the middle line of the body, about 1/3 of the heart - to the right of the midline of the human body. The heart is located in the chest, enclosed in a pericardial sac - the pericardium, located between the right and left pleural cavities containing the lungs. The longitudinal axis of the heart goes obliquely from top to bottom, from right to left and from back to front. The position of the heart is different: transverse, oblique or vertical. The vertical position of the heart most often occurs in people with a narrow and long chest, the transverse position - in people with a wide and short chest. Distinguish the base of the heart, directed anteriorly, downwards and to the left. At the base of the heart are the atria. From the base of the heart exit: the aorta and the pulmonary trunk, into the base of the heart enter: the superior and inferior vena cava, right and left pulmonary veins. Thus, the heart is fixed on the large vessels listed above. With its posterior surface, the heart is adjacent to the diaphragm (a bridge between the chest and abdominal cavities), and with its sternocostal surface, it faces the sternum and costal cartilages. Three grooves are distinguished on the surface of the heart - one coronal; between the atria and ventricles and two longitudinal (anterior and posterior) between the ventricles. The length of the heart of an adult varies from 100 to 150 mm, the width at the base is 80–110 mm, and the anteroposterior distance is 60–85 mm. The weight of the heart on average in men is 332 g, in women - 253 g. In newborns, the weight of the heart is 18-20 g. The heart consists of four chambers: right atrium, right ventricle, left atrium, left ventricle. The atria are located above the ventricles. The atrial cavities are separated from each other by the interatrial septum, and the ventricles are separated by the interventricular septum. The atria communicate with the ventricles through openings. The right atrium has a capacity of 100–140 ml in an adult, and a wall thickness of 2–3 mm. The right atrium communicates with the right ventricle through the right atrioventricular orifice, which has a tricuspid valve. Behind, the superior vena cava flows into the right atrium above, below - the inferior vena cava. The mouth of the inferior vena cava is limited by a flap. The coronary sinus of the heart, which has a valve, flows into the posterior-lower part of the right atrium. The coronary sinus of the heart collects venous blood from the heart's own veins. The right ventricle of the heart has the shape of a trihedral pyramid, with its base facing up. The capacity of the right ventricle in adults is 150-240 ml, the wall thickness is 5-7 mm. The weight of the right ventricle is 64-74 g. Two parts are distinguished in the right ventricle: the ventricle itself and the arterial cone located in the upper part of the left half of the ventricle. The arterial cone passes into the pulmonary trunk - a large venous vessel that carries blood to the lungs. Blood from the right ventricle enters the pulmonary trunk through the tricuspid valve. The left atrium has a capacity of 90-135 ml, a wall thickness of 2-3 mm. On the back wall of the atrium are the mouths of the pulmonary veins (vessels carrying oxygen-enriched blood from the lungs), two on the right and two on the left. the left ventricle has a conical shape; its capacity is from 130 to 220 ml; wall thickness 11 - 14 mm. The weight of the left ventricle is 130-150 g. There are two openings in the cavity of the left ventricle: the atrioventricular (left and front), equipped with a bicuspid valve, and the opening of the aorta (the main artery of the body), equipped with a tricuspid valve. In the right and left ventricles there are numerous muscular protrusions in the form of crossbars - trabeculae. The valves are controlled by the papillary muscles. The wall of the heart consists of three layers: the outer one - the epicardium, the middle one - the myocardium (muscular layer), and the inner one - the endocardium. Both the right and left atrium have small protruding parts on the sides - ears. The source of innervation of the heart is the cardiac plexus - part of the general thoracic vegetative plexus. In the heart itself there are many nerve plexuses and ganglions that regulate the frequency and strength of heart contractions, the work of heart valves. The blood supply to the heart is carried out by two arteries: the right coronary and the left coronary, which are the first branches of the aorta. The coronary arteries divide into smaller branches that enclose the heart. The diameter of the mouths of the right coronary artery ranges from 3.5 to 4.6 mm, the left - from 3.5 to 4.8 mm. Sometimes, instead of two coronary arteries, there may be one. The outflow of blood from the veins of the walls of the heart mainly occurs in the coronary sinus, which flows into the right atrium. Lymphatic fluid flows through the lymphatic capillaries from the endocardium and myocardium to the lymph nodes located under the epicardium, and from there the lymph enters the lymphatic vessels and nodes of the chest. The work of the heart as a pump is the main source of mechanical energy for the movement of blood in the vessels, which maintains the continuity of metabolism and energy in the body. The activity of the heart occurs due to the conversion of chemical energy into mechanical energy of myocardial contraction. In addition, the myocardium has the property of excitability. Excitation impulses arise in the heart under the influence of the processes occurring in it. This phenomenon is called automation. There are centers in the heart that generate impulses leading to excitation of the myocardium with its subsequent contraction (i.e., the process of automation is carried out with subsequent excitation of the myocardium). Such centers (nodes) provide rhythmic contraction in the required order of the atria and ventricles of the heart. The contractions of both atria, and then both ventricles, are carried out almost simultaneously. Inside the heart, due to the presence of valves, the blood moves in one direction. In the diastole phase (expansion of the cavities of the heart associated with relaxation of the myocardium), blood flows from the atria into the ventricles. In the systole phase (consecutive contractions of the atrial myocardium, and then the ventricles), blood flows from the right ventricle to the pulmonary trunk, from the left ventricle to the aorta. In the diastolic phase of the heart, the pressure in its chambers is close to zero; 2/3 of the volume of blood entering in the diastolic phase flows due to positive pressure in the veins outside the heart and 1/3 is pumped into the ventricles in the atrial systole phase. The atria are a reservoir for incoming blood; atrial volume may increase due to the presence of atrial lugs. A change in pressure in the chambers of the heart and the vessels departing from it causes the movement of the heart valves, the movement of blood. During contraction, the right and left ventricles expel 60-70 ml of blood each. Compared to other organs (with the exception of the cerebral cortex), the heart absorbs oxygen most intensively. In men, the size of the heart is 10-15% larger than in women, and the heart rate is 10-15% lower. Physical activity causes an increase in blood flow to the heart due to its displacement from the veins of the extremities during muscle contraction and from the veins of the abdominal cavity. This factor acts mainly under dynamic loads; static loads insignificantly change venous blood flow. An increase in the flow of venous blood to the heart leads to an increase in the work of the heart. With maximum physical activity, the value of the energy costs of the heart can increase by 120 times compared to the state of rest. Prolonged exposure to physical activity causes an increase in the reserve capacity of the heart. Negative emotions cause the mobilization of energy resources and increase the release of adrenaline (hormone of the adrenal cortex) into the blood - this leads to an increase in heart rate (normal heart rate is 68-72 per minute), which is an adaptive reaction of the heart. The heart is also affected by environmental factors. So, in conditions of high mountains, with a low oxygen content in the air, oxygen starvation of the heart muscle develops with a simultaneous reflex increase in blood circulation as a response to this oxygen starvation. Sharp fluctuations in temperature, noise, ionizing radiation, magnetic fields, electromagnetic waves, infrasound, many chemicals (nicotine, alcohol, carbon disulfide, organometallic compounds, benzene, lead) have a negative effect on the activity of the heart.

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 efficient blood circulation as 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, the blood must bathe a number of special organs, such as the liver and kidneys, which neutralize or excrete the end products of metabolism. The accumulation of these products can lead to chronic ill health and even death.

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

Components of the circulatory system.

In its most general form, this transport system consists of a muscular four-chamber pump (heart) and many channels (vessels), the function of which 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 the cardiovascular, or cardiovascular.

Blood vessels are divided into three main types: arteries, capillaries, and veins. Arteries carry blood away from the heart. They branch into vessels of ever smaller diameter, through which blood enters all parts of the body. Closer to the heart, the arteries have the largest diameter (about the size of a thumb), in the extremities they are the size of a pencil. In the parts of the body farthest from the heart, the blood vessels are so small that they can only be seen 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 released from the load of carbon dioxide and saturated with oxygen.

In the process of passing through the body and its organs, some part of the liquid seeps through the walls of the capillaries into the tissues. This opalescent, plasma-like fluid is called lymph. The return of lymph to the general circulatory system is carried out 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, see the article LYMPHATIC SYSTEM.)

WORK OF THE CIRCULATION SYSTEM

Pulmonary circulation.

It is convenient to begin describing the normal movement of blood through 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, the inferior vena cava, from the bottom. Blood from both veins enters the collecting section of the right side of the heart, the right atrium, where it mixes with the blood brought by the coronary veins, which open 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 contracts to force blood through the pulmonary arteries into the lungs. The constant flow of blood in this direction is maintained by the operation of two important valves. One of them, tricuspid, located between the ventricle and the atrium, prevents the return of blood to the atrium, and the second, the pulmonary valve, closes at the moment of relaxation of the ventricle and thereby prevents the return of blood from the pulmonary arteries. In the lungs, blood passes through the ramifications of the vessels, falling into a network of thin capillaries that are in direct contact with the smallest air sacs - the alveoli. An exchange of gases takes place between the capillary blood and the alveoli, which completes the pulmonary phase of blood circulation, i.e. phase of blood entering the lungs see also RESPIRATORY ORGANS).

Systemic circulation.

From this moment, the systemic phase of blood circulation begins, i.e. phase of blood transfer to all tissues of the body. The carbon dioxide-free and oxygenated (oxygenated) blood returns to the heart through the four pulmonary veins (two from each lung) and enters the left atrium at low pressure. The path of blood flow from the right ventricle of the heart to the lungs and return from them to the left atrium is the so-called. small circle of blood circulation. The blood-filled left atrium contracts simultaneously with the right and pushes it into the massive left ventricle. The latter, when filled, contracts, sending blood under high pressure into the artery of the largest diameter - the aorta. All arterial branches that supply the tissues of the body depart from the aorta. As on the right side of the heart, there are two valves on the left side. The bicuspid (mitral) valve directs blood flow to the aorta and prevents blood from returning to the ventricle. The entire path of blood from the left ventricle up to its return (through the superior and inferior vena cava) to the right atrium is referred to as the systemic circulation.

arteries.

In a healthy person, the aorta is approximately 2.5 cm in diameter. This large vessel extends upward from the heart, forms an arc, and then descends through the chest into the abdominal cavity. Along the aorta, all the major arteries that enter the systemic 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 tissue of the heart. In addition to them, the ascending aorta (the first part of the arch) does not give branches. However, at the top of the arc, three important vessels depart from it. The first - the innominate 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 to the right hand. The second branch from the aortic arch is the left carotid artery, the third is the left subclavian artery; these branches carry blood to the head, neck, and left arm.

From the aortic arch, the descending aorta begins, which supplies blood to the organs of the chest, and then penetrates into the abdominal cavity through a hole in the diaphragm. Two renal arteries supplying the kidneys are separated from the abdominal aorta, as well as the abdominal trunk with the superior and inferior mesenteric arteries extending to the intestines, spleen and liver. The aorta then divides into two iliac arteries, which supply blood to the pelvic organs. In the groin area, the iliac arteries pass into the femoral; the latter, going down the thighs, 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 peroneal arteries, which feed the tissues of the legs and feet.

Throughout the course of the bloodstream, the arteries become smaller and smaller as they branch, and finally acquire a caliber that is only a few times the size of the blood cells they contain. 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 an erythrocyte (7 microns).

The structure of the arteries.

Although large and small arteries differ somewhat in their structure, the walls of both 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) pass through it, feeding the vascular wall, as well as branches of the autonomic nervous system that regulate the lumen of the vessel. The middle layer (media) consists of elastic tissue and smooth muscles that provide elasticity and contractility of the vascular wall. These properties are essential for regulating blood flow and maintaining normal blood pressure under changing physiological conditions. As a rule, the walls of large vessels, such as the aorta, contain more elastic tissue than the walls of smaller arteries, which are dominated by muscle tissue. According to this tissue feature, the arteries are divided into elastic and muscular. 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 a smoothness that facilitates blood flow. Through it, nutrients enter the deep layers of the media.

As the diameter of arteries decreases, their walls become thinner and the three layers become less and less distinct, until - at the arteriolar level - they remain mostly coiled muscle fibers, some elastic tissue, and an inner lining of endothelial cells.

capillaries.

Finally, the arterioles imperceptibly pass into the capillaries, the walls of which are expelled only by the endothelium. Although these tiny tubes contain less than 5% of the volume of circulating blood, they are extremely important. The 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 punctured without piercing a huge number of them. It is in these networks that, under the action of osmotic forces, oxygen and nutrients pass into individual cells of the body, and in return, the products of cellular metabolism enter the bloodstream.

In addition, this network (the so-called capillary bed) plays an important role in the regulation and maintenance of body temperature. The constancy of the internal environment (homeostasis) of the human body depends on maintaining body temperature within the narrow limits of the norm (36.8–37 °). Usually, blood from arterioles enters the venules through the capillary bed, but in cold conditions capillaries close and blood flow decreases, primarily in the skin; at the same time, blood from the arterioles enters the venules, bypassing the many branches of the capillary bed (shunting). On the contrary, if heat transfer is necessary, for example, in the tropics, all capillaries open, and skin blood flow increases, which contributes to heat loss and maintaining normal body temperature. This mechanism exists in all warm-blooded animals.

Vienna.

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 to form larger veins that carry blood from all parts of the body back to the heart. Constant blood flow in this direction is facilitated by a system of valves found in most veins. Venous pressure, unlike pressure in the arteries, does not directly depend on the tension of the muscles of the vascular wall, so that the blood flow in the right direction is determined mainly by other factors: the pushing force created by the arterial pressure of the systemic circulation; "Sucking" effect of negative pressure that occurs in the chest during inspiration; pumping action of the muscles of the limbs, which during normal contractions push venous blood to the heart.

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

On the way to the heart, the 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 extremities through the subclavian veins. Near the heart, two hollow veins are formed, through which blood enters the right atrium.

The vessels of the pulmonary circulation (pulmonary) resemble the vessels of the systemic circulation, with the only exception that they lack valves, and the walls of both arteries and veins are much thinner. In contrast to the systemic circulation, venous, non-oxygenated blood flows through the pulmonary arteries into the lungs, 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 bodies.

A number of organs perform functions that complement the work of the circulatory system. The spleen, liver and kidneys are most closely associated with it.

Spleen.

With repeated passage through the circulatory system, red blood cells (erythrocytes) are damaged. Such "waste" cells are removed from the blood in many ways, but the main role here belongs to the spleen. 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 reservoir of erythrocytes, but in humans this function is poorly expressed. see also SPLEEN.

Liver.

To carry out its more than 500 functions, the liver needs a 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. A number of liver functions are directly related to the blood, such as removing waste red blood cells from it, producing blood clotting factors, and regulating blood sugar levels by storing excess sugar in the form of glycogen. see also LIVER .

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 ventricular systole, and the relaxation phase of the ventricles is called diastole. During diastole, however, the elastic forces of large blood vessels come into play, maintaining blood pressure and not allowing interruption of the blood flow to various parts of the body. The change of systoles (contractions) and diastole (relaxations) gives the blood flow in the arteries a pulsating character. The pulse can be found in any major artery, but is usually felt at 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 when an artery is cut, bright red blood flows out in jerks, and when a vein is cut, bluish (due to a lower oxygen content) blood flows evenly, without visible shocks.

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 varies considerably 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 mm Hg. Another indicator - mean arterial pressure - can be approximately calculated by averaging systolic and diastolic pressure or adding half the pulse pressure to diastolic.

Normal blood pressure is determined, maintained and regulated by many factors, the main of which are the strength of heart contractions, the elastic "recoil" of the walls of the arteries, the volume of blood in the arteries and the resistance of small arteries (muscular type) and arterioles to blood flow. All these factors together determine the lateral pressure on the elastic walls of the arteries. It can be measured very accurately by using a special electronic probe 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).

The 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. Usually the cuff is wrapped tightly around the arm above the elbow and inflated until the pulse at the wrist disappears. The brachial artery is found at the level of the elbow bend and a stethoscope is placed over it, after which air is slowly released from the cuff. When the pressure in the cuff is reduced to a level that allows blood to flow through the artery, a sound is heard with 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 further release of air from the cuff, the nature 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 in the fine balance existing in the norm, which is maintained both by nerve impulses coming from the centers of the brain through the sympathetic nervous system, and by changes in the chemical composition of the blood, which have a direct or indirect regulatory effect on the blood vessels. With strong emotional stress, sympathetic nerves cause narrowing of small muscle-type arteries, which leads to an increase in blood pressure and pulse rate. Even more important is the chemical balance, the influence of which is mediated not only by the brain centers, but also by individual nerve plexuses associated with the aorta and carotid arteries. The sensitivity of this chemical regulation is illustrated, for example, by the effect of accumulation of carbon dioxide in the blood. With an increase in its level, the acidity of the blood increases; this both directly and indirectly causes the contraction of 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 paradoxically expand. The combination of these physiological reactions ensures a stable 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 a vertical position without significant movement of blood into 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 oxygenated blood is directed mainly to the vital organs. Vasomotor (vasomotor) mechanisms are even more important for animals such as the giraffe, whose brain, when it raises its head after drinking, moves up 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 in moments of stress, emotional distress, shock and trauma, allowing the brain, heart and muscles to receive more oxygen and nutrients.

Such fluctuations in blood pressure are normal, but changes in it are also observed in a number of pathological conditions. In heart failure, the force of contraction of the heart muscle can drop so much that blood pressure is too low (hypotension). Similarly, loss of blood or other fluids due to severe burns or bleeding can cause both systolic and diastolic blood pressure to drop to dangerous levels. With some congenital heart defects (for example, patent 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 may remain normal, but diastolic pressure drops significantly, 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 best allow us to understand the enormous complexity of the organization and operation of the circulatory system. This truly wonderful transport system is a real "lifeline" of the body, since the lack of blood supply to any vital organ, primarily the brain, for at least a few minutes leads to its irreversible damage and even death.

DISEASES OF THE BLOOD VESSELS

Diseases of the blood vessels (vascular diseases) are conveniently considered according to the type of vessels in which pathological changes develop. Stretching of 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. Aortic or ventricular aneurysm 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 to smaller arteries. Infectious (most often syphilitic) and arteriosclerotic processes can develop in the aorta; rupture of the aorta due to trauma or congenital weakness of its walls is also possible. High blood pressure often leads to chronic enlargement of the aorta. However, aortic disease is 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 and under this layer. One of the severe complications of this disease of the aorta and its main branches (innominate, iliac, carotid and renal arteries) is the formation of blood clots on the inner layer, which can interfere with blood flow in these vessels and lead to catastrophic disruption of the blood supply to the brain, legs and kidneys. This kind of obstructive (obstructing blood flow) lesions of some large vessels can be removed surgically (vascular surgery).

Syphilitic aortitis.

The decrease in the prevalence of syphilis itself makes the inflammation of the aorta 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. Narrowing of the mouth of the coronary arteries is also possible. Any of these conditions can lead to death, sometimes very quickly. The age at which aortitis and its complications appear ranges from 40 to 55 years; the disease is more common in men.

Arteriosclerosis

of the aorta, accompanied by a loss of elasticity of its walls, is characterized by damage not only to the intima (as in atherosclerosis), but also to the muscular layer of the vessel. This is a disease of the elderly, and with increasing life expectancy of the population, it is becoming more common. Loss of elasticity reduces the efficiency of blood flow, which in itself can lead to aneurysm-like expansion of the aorta and even to its rupture, especially in the abdominal region. Currently, sometimes it is possible to cope with this condition surgically ( see also ANEURYSM).

Pulmonary artery.

Lesions of the pulmonary artery and its two main branches are not numerous. In these arteries, arteriosclerotic changes sometimes occur, and congenital malformations also occur. The two most important changes are: 1) expansion of the pulmonary artery due to an increase in pressure in it due to any obstruction to blood flow in the lungs or on the way of blood to the left atrium and 2) blockage (embolism) of one of its main branches due to the passage of a blood clot from 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, either balloon angioplasty or coronary bypass surgery is performed. In balloon angioplasty, a catheter with a balloon at the end is inserted into the affected artery; inflation of the balloon leads to flattening of the deposits along the arterial wall and expansion of the lumen of the vessel. During bypass surgery, a section 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.

When the arteries of the legs and arms are affected, the middle, muscular layer of the vessels (media) thickens, which leads to their thickening and curvature. The defeat of these arteries has relatively less severe consequences.

Arterioles.

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

Vienna.

Vein diseases are very common. The most common varicose veins of the lower extremities; this condition develops under the influence of gravity during obesity or pregnancy, and sometimes due to inflammation. In this case, the function of the venous valves is disturbed, 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 training the muscles of the lower leg and reducing body weight. Another pathological process - inflammation of the veins (phlebitis) - is also most often observed in the legs. In this case, there are obstructions to blood flow with a violation of local circulation, but the main danger of phlebitis is the separation of small blood clots (emboli), which can pass through the heart and cause circulatory arrest in the lungs. This condition, called pulmonary embolism, is very serious and often fatal. The defeat of large veins is much less dangerous and is much less common.



Blood- a liquid tissue that circulates in the human circulatory system and is an opaque red liquid consisting of pale yellow plasma and cells suspended in it - red blood cells (erythrocytes), white blood cells (leukocytes) and red platelets (platelets). The share of suspended cells (shaped elements) accounts for 42–46% of the total blood volume.

The main function of blood is the transport of various substances within the body. It carries respiratory gases (oxygen and carbon dioxide) in both physically dissolved and chemically bound form. Blood has this ability due to hemoglobin, a protein contained in red blood cells. In addition, the blood carries nutrients from the organs where they are absorbed or stored to where they are consumed; the metabolites formed here (metabolic products) are transported to the excretory organs or to those structures where their further use can take place. Purposefully, hormones, vitamins and enzymes are also transferred to target organs by blood. Due to the high heat capacity of its main component - water (1 liter of plasma contains 900–910 g of water), blood ensures the distribution of heat generated during metabolism and its release into the external environment through the lungs, respiratory tract and skin surface.

The proportion of blood in an adult is approximately 6-8% of the total body weight, which corresponds to 4-6 liters. A person's blood volume can undergo significant and long-term fluctuations depending on the degree of fitness, climatic and hormonal factors. So, in some athletes, the volume of blood as a result of training can exceed 7 liters. And after a long period of bed rest, it can become below normal. Short-term changes in blood volume are observed during the transition from a horizontal to a vertical position of the body and during muscle exercise.

Blood can perform its functions only when it is in constant motion. This movement is carried out through the system of vessels (elastic tubules) and is provided by the heart. Thanks to the vascular system of the body, blood is available to all corners of the human body, every cell. The heart and blood vessels (arteries, capillaries, veins) form cardiovascular system (Fig. 2.1).

The movement of blood through the vessels of the lungs from the right heart to the left heart is called pulmonary circulation (small circle). It begins with the right ventricle, which ejects blood into the pulmonary trunk. Then the blood enters the vascular system of the lungs, which in general terms has the same structure as the systemic circulation. Further, through four large pulmonary veins, it enters the left atrium (Fig. 2.2).

It should be noted that arteries and veins differ not in the composition of the blood moving in them, but in the direction of movement. So, through the veins, blood flows to the heart, and through the arteries, it flows away from it. In the systemic circulation, oxygenated (oxygenated) blood flows through the arteries, and in the pulmonary circulation, through the veins. Therefore, when blood saturated with oxygen is called arterial, only the systemic circulation is meant.

A heart is a hollow muscular organ divided into two parts - the so-called "left" and "right" heart, each of which includes an atrium and a ventricle. Partially deoxygenated blood from the organs and tissues of the body enters the right heart, pushing it to the lungs. In the lungs, the blood is saturated with oxygen, partially deprived of carbon dioxide, then returns to the left heart and again enters the organs.

The pumping function of the heart is based on the alternation of contraction (systole) and relaxation (diastole) of the ventricles, which is possible due to the physiological characteristics of the myocardium (the muscle tissue of the heart, which makes up the bulk of its mass) - automaticity, excitability, conduction, contractility and refractoriness. During diastole the ventricles fill with blood, and during systole they throw it into large arteries (aorta and pulmonary trunk). At the outlet of the ventricles, valves are located that prevent the return of blood from the arteries to the heart. Before filling the ventricles, blood flows through large veins (caval and pulmonary) into the atria.

Rice. 2.1. Human cardiovascular system

Atrial systole precedes ventricular systole; thus, the atria serve as an auxiliary pump, contributing to the filling of the ventricles.

Rice. 2.2. The structure of the heart, small (pulmonary) and large circles of blood circulation

The blood supply to all organs (except the lungs) and the outflow of blood from them is called the systemic circulation (large circle). It begins with the left ventricle, which ejects blood into the aorta during systole. Numerous arteries depart from the aorta, through which the blood flow is distributed to several parallel regional vascular networks that supply blood to individual organs and tissues - the heart, brain, liver, kidneys, muscles, skin, etc. The arteries divide, and as their number grows the diameter of each of them decreases. As a result of the branching of the smallest arteries (arterioles), a capillary network is formed - a dense interlacing of small vessels with very thin walls. It is here that the main two-way exchange of various substances between blood and cells occurs. When the capillaries merge, venules are formed, which are then combined into veins. Ultimately, only two veins enter the right atrium - the superior vena cava and the inferior vena cava.

Of course, in fact, both circles of blood circulation constitute a single bloodstream, in two parts of which (the right and left heart) the blood is supplied with kinetic energy. Although there is a fundamental functional difference between them. The volume of blood ejected into a large circle should be distributed over all organs and tissues, the need for blood supply to which is different and depends on their condition and activity. Any changes are instantly registered by the central nervous system (CNS), and the blood supply to the organs is regulated by a number of control mechanisms. As for the vessels of the lungs, through which a constant amount of blood passes, they make relatively constant demands on the right heart and perform mainly the functions of gas exchange and heat transfer. Therefore, the system of regulation of pulmonary blood flow is less complex.

In an adult, approximately 84% of all blood is contained in the systemic circulation, 9% in the pulmonary circulation, and the remaining 7% directly in the heart. The largest volume of blood is contained in the veins (approximately 64% of the total blood volume in the body), i.e., the veins play the role of blood reservoirs. At rest, blood circulates in only about 25-35% of all capillaries. The main hematopoietic organ is the bone marrow.

The requirements imposed by the body on the circulatory system vary significantly, so its activity varies widely. So, at rest in an adult, 60-70 ml of blood (systolic volume) is ejected into the vascular system with each contraction of the heart, which corresponds to 4-5 liters of cardiac output (the amount of blood ejected by the ventricle in 1 min). And with heavy physical exertion, the minute volume increases to 35 liters and above, while the systolic blood volume can exceed 170 ml, and the systolic blood pressure reaches 200–250 mm Hg. Art.

In addition to blood vessels in the body, there is another type of vessel - lymphatic.

Lymph- a colorless liquid formed from blood plasma by filtering it into the interstitial spaces and from there into the lymphatic system. Lymph contains water, proteins, fats and metabolic products. Thus, the lymphatic system forms an additional drainage system, through which tissue fluid flows into the bloodstream. All tissues, with the exception of the superficial layers of the skin, central nervous system and bone tissue, are penetrated by many lymphatic capillaries. These capillaries, unlike blood capillaries, are closed at one end. Lymphatic capillaries are collected in larger lymphatic vessels, which flow into the venous bed in several places. Therefore, the lymphatic system is part of the cardiovascular system.