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Types, functions, structure of human blood vessels, vascular diseases. Vessels Names of blood vessels

Blood vessels in the human body perform the function of transferring blood from the heart to all tissues of the body and back. The pattern of interweaving of vessels in the bloodstream allows for the uninterrupted functioning of all important organs or systems. Total length blood vessels in humans it reaches 100,000 km.

Blood vessels are tubular structures different lengths and diameter, through the cavity of which blood moves. The heart functions as a pump, so blood circulates throughout the body under powerful pressure. The speed of blood circulation is quite high, since the blood circulation system itself is closed.
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Structure and classification

In simple terms, blood vessels are flexible, elastic tubes through which blood flow circulates. The vessels are quite durable and can even withstand chemical exposure. High strength is due to the structure of three main layers:

The entire vascular network (dispersal pattern), as well as types of blood vessels, includes millions of tiny nerve endings, called in medicine effectors, receptor compounds. They have a close, proportional relationship with nerve endings, reflexively providing nervous regulation blood flow in the vascular cavity.

What is the classification of blood vessels? Medicine divides vascular pathways according to the type of structure, characteristics, functionality into three types: arteries, veins, capillaries. Each type has great value in the structure of the vascular network. These main types of blood vessels are described below.

Arteries are blood vessels that originate from the heart and cardiac muscle and go to the vital important bodies. It is noteworthy that in ancient medicine these tubes were considered air-carrying, since they were empty when the corpse was opened. Movement of blood through arterial canals carried out under high pressure. The walls of the cavity are quite strong, elastic, reaching several millimeters in density in various anatomical departments. Arteries are divided into two groups:

Arteries of the elastic type (aorta, its largest branches) are located as close as possible to the heart. Such arteries conduct blood - this is their main function. Under the influence of powerful heart rhythms, blood rushes through the arteries under high pressure. The elastic walls of the artery are quite strong and perform mechanical functions.

Arteries of the muscular type are represented by many small and medium-sized arteries. In them, the pressure of the blood mass is no longer so high, so the walls of the vessels are constantly contracting to further move the blood. The walls of the arterial cavity consist of a smooth muscle fibrous structure, the walls are constantly changing towards narrowing or natural expansion to ensure uninterrupted flow of blood along their paths.

Capillaries

They belong to a variety of the smallest vessels in the entire vascular system. Localized between arterial vessels and vena cava. The diametric parameters of the capillaries vary in the range of 5-10 microns. Capillaries are involved in organizing the exchange of gaseous substances and special nutrients between tissues and the blood itself.

Oxygen-containing molecules penetrate into tissues and organs through the thin structure of capillary walls, carbon dioxide, metabolic products in the opposite direction.

Veins, on the contrary, have a different function - they provide blood supply to the heart muscle. The rapid movement of blood through the cavity of the veins is in the opposite direction from the flow of blood through the arteries or capillaries. Blood through the venous bed does not pass under strong pressure, so the walls of the vein contain less muscle structure.
The vascular system is a closed circle in which blood regularly circulates from the heart throughout the body, and then in the opposite direction through the veins to the heart. This results in a complete cycle that ensures adequate functioning of the body.

Functionality of vessels depending on type

Blood vascular system is not only a conductor of blood, but has a powerful functional effect on the body as a whole. In anatomy, there are six subspecies:

precardiac (vava, pulmonary veins, pulmonary arterial trunk, elastic type of arteries).
main (arteries and veins, large or medium vessels, arteries of the muscular type, enveloping the organ from the outside);
organ (veins, capillaries, intraorgan arteries, responsible for the full trophism of internal organs and systems).

Pathological conditions of the circulatory system

Vessels, like other organs, can be affected specific diseases, have pathological conditions, developmental anomalies that are a consequence of other serious diseases and their cause.

There are several serious vascular diseases that have severe course and implications for general condition patient's health:

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Blood vessels in the human body represent a unique system for transporting blood to important systems and organs, tissues and muscle structures.
The vascular system ensures the removal of decay products as a result of vital activity. The circulatory system must work correctly, so for any manifestations alarming symptoms you should immediately consult a doctor and start preventive measures to further strengthen the vascular branches and their walls.

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Blood vessels - elastic tubes through which blood is transported to all organs and tissues and then collected again to the heart. The study of blood vessels, along with lymphatic vessels, is a branch of medicine - angiology. Blood vessels form: a) the macrocirculatory bed - these are arteries and veins through which blood moves from the heart to the organs and returns to the heart; b) microcirculatory bed - includes capillaries, arterioles and venules located in organs that ensure the exchange of substances between blood and tissues.

Arteries - blood vessels through which blood moves from the heart to organs and tissues. The walls of the arteries have three layers:

outer layer built of loose connective tissue, it contains nerves that regulate the expansion and contraction of blood vessels;

middle layer consists of smooth muscle membrane And elastic fibers(due to muscle contraction or relaxation, the lumen of blood vessels can change, regulating the flow of blood, and elastic fibers give elasticity to the vessels)

inner layer - formed by a special connective tissue, the cells of which have very smooth membranes and do not interfere with the movement of blood.

Depending on the diameter of the arteries, the structure of the wall in them also changes, therefore three types of arteries are distinguished: elastic (for example, the aorta, pulmonary trunk), muscular (arteries of organs) and mixed, or muscle-elastic (for example, carotid artery) type.

Capillaries- the smallest blood vessels that connect arteries and veins and ensure the exchange of substances between blood and tissue fluid. Their diameter is about 1 micron, the total surface of all capillaries of the body is 6300 m2. The walls consist of one layer of flat epithelial cells- endothelium. The endothelium is the inner layer of flat, elongated cells with uneven wavy edges, which line the capillaries, as well as all other vessels and the heart. Endotheliocytes produce a number of physiologically active substances. Among them, nitric oxide causes relaxation of smooth muscle cells, thereby causing vasodilation. In organs, capillaries provide microcirculation of blood and form a mesh, but they can also form loops (for example, in the papillae of the skin), as well as glomeruli (for example, in the nephrons of the kidneys). Various organs have different levels development capillary mesh. For example, in the skin there are 40 capillaries per 1 mm2, and in muscles there are about 1000. The significant development of the capillary network has gray matter organs of the central nervous system, endocrine glands, skeletal muscles, heart, adipose tissue.

Vienna- blood vessels through which blood moves from organs and tissues to the heart. They have the same wall structure as arteries, but thin and less elastic. Medium and some large veins have semilunar valves that allow blood to flow in only one direction. The veins are muscular (hollow) and non-muscular (retina, bones). The movement of blood through the veins to the heart is facilitated by the suction action of the heart, the stretching of the vena cava in the chest cavity when air is inhaled, and the presence of a valve apparatus.

Comparative characteristics of vessels

signs	arteries	capillaries	veins
structure	Thick walls made of 3 layers. lack of valves	Walls of one layer of flat cells	Thin walls made of 3 layers Availability of valves
	Movement of blood away from the heart	Metabolism between blood and tissues	Movement of blood to the heart
blood speed	About 0.5 m/s	About 0.5mm/s	About 0.2 m/s
blood pressure	Up to 120 mm Hg. Art.	Up to 20 mm Hg. Art.	From 3-8 mm Hg. Art. and below

Vessels are tube-like formations that extend throughout the human body and through which blood moves. The pressure in the circulatory system is very high because the system is closed. Through this system, blood circulates quite quickly.

After many years, obstacles to the movement of blood - plaques - form on the vessels. These are formations with inside vessels. Thus, the heart must pump blood more intensively in order to overcome obstacles in the blood vessels, which disrupts the functioning of the heart. At this point, the heart can no longer deliver blood to the organs of the body and cannot cope with its work. But at this stage it is still possible to recover. The vessels are cleansed of salts and cholesterol deposits. (Read also: Cleansing the vessels)

When the blood vessels are cleansed, their elasticity and flexibility returns. Many diseases associated with blood vessels go away. These include sclerosis, headaches, a tendency to heart attack, and paralysis. Hearing and vision are restored, varicose veins are reduced. The condition of the nasopharynx returns to normal.

Blood circulates through the vessels that make up the systemic and pulmonary circulation.

All blood vessels consist of three layers:

Inner layer vascular wall They form endothelial cells; the surface of the vessels inside is smooth, which facilitates the movement of blood through them.

The middle layer of the walls provides the strength of blood vessels and consists of muscle fibers, elastin and collagen.

The upper layer of the vascular walls is made up of connective tissue; it separates the vessels from nearby tissues.

Arteries

The walls of arteries are stronger and thicker than those of veins, since blood moves through them with greater pressure. Arteries carry oxygenated blood from the heart to the internal organs. The arteries of the dead are empty, which is revealed at autopsy, so it was previously believed that the arteries were air tubes. This is reflected in the name: the word “artery” consists of two parts; translated from Latin, the first part aer means air, and tereo means to contain.

Depending on the structure of the walls, two groups of arteries are distinguished:

The elastic type of arteries are vessels located closer to the heart, these include the aorta and its large branches. The elastic framework of the arteries must be strong enough to withstand the pressure with which blood is thrown into the vessel from heart contractions. The elastin and collagen fibers that make up the frame of the middle wall of the vessel help resist mechanical stress and stretching.

Thanks to the elasticity and strength of the walls of the elastic arteries, blood continuously flows into the vessels and ensures constant circulation to nourish organs and tissues and supply them with oxygen. The left ventricle of the heart contracts and forcefully throws a large volume of blood into the aorta, its walls stretch to accommodate the contents of the ventricle. After relaxation of the left ventricle, blood does not flow into the aorta, the pressure is weakened, and blood from the aorta flows into other arteries into which it branches. The walls of the aorta regain their previous shape, since the elastin-collagen framework provides their elasticity and resistance to stretching. Blood moves through the vessels continuously, entering in small portions from the aorta after each heart rate.

The elastic properties of arteries also ensure the transmission of vibrations along the walls of blood vessels - this is a property of any elastic system with mechanical influences, which is the cardiac impulse. The blood hits the elastic walls of the aorta, and they transmit vibrations along the walls of all the vessels of the body. Where the vessels come close to the skin, these vibrations can be felt as a weak pulsation. Pulse measurement methods are based on this phenomenon.

Muscular-type arteries in the middle layer of the walls contain a large number of smooth muscle fibers. This is necessary to ensure blood circulation and continuity of its movement through the vessels. Muscular-type vessels are located further from the heart than elastic-type arteries, so the force of the cardiac impulse in them weakens; to ensure further movement of blood, contraction of muscle fibers is necessary. When the smooth muscles of the inner layer of the arteries contract, they narrow, and when they relax, they expand. As a result, blood moves through the vessels with constant speed and promptly enters organs and tissues, providing them with nutrition.

Another classification of arteries determines their location in relation to the organ to which they supply blood. Arteries that pass inside an organ, forming a branching network, are called intraorgan. The vessels located around the organ, before entering it, are called extraorgan. Lateral branches that arise from the same or different arterial trunks may reconnect or branch into capillaries. At the point of their connection before they begin to branch into capillaries, these vessels are called anastomosis or anastomosis.

Arteries that do not have an anastomosis with adjacent vascular trunks are called terminal. These, for example, include the arteries of the spleen. The arteries that form the anastomosis are called anastomizing; most arteries belong to this type. U terminal arteries there is a greater risk of blockage by a blood clot and a high predisposition to a heart attack, which may result in the death of part of the organ.

In the last branches, the arteries become very thin; such vessels are called arterioles, and the arterioles already pass directly into capillaries. Arterioles contain muscle fibers that perform contractile function and regulate the flow of blood into the capillaries. The layer of smooth muscle fibers in the walls of arterioles is very thin compared to an artery. The place where the arteriole branches into capillaries is called the precapillary; here the muscle fibers do not form a continuous layer, but are located diffusely. Another difference between a precapillary and an arteriole is the absence of a venule. The precapillary gives rise to numerous branches on the smallest vessels– capillaries.

Capillaries

Capillaries are the smallest vessels, the diameter of which varies from 5 to 10 microns; they are present in all tissues, being a continuation of the arteries. Capillaries provide tissue metabolism and nutrition, supplying all structures of the body with oxygen. In order to ensure the transfer of oxygen and nutrients from the blood to the tissues, the capillary wall is so thin that it consists of only one layer of endothelial cells. These cells are highly permeable, so through them substances dissolved in the liquid enter the tissues, and metabolic products return to the blood.

Number of working capillaries in different areas bodies differ - in large quantities they are concentrated in working muscles, which require constant blood supply. For example, in the myocardium (the muscular layer of the heart) up to two thousand open capillaries are found in one square millimeter, and in skeletal muscles there are several hundred capillaries in the same area. Not all capillaries function at the same time - many of them are in reserve, in a closed state, to start working when necessary (for example, during stress or increased physical activity).

The capillaries anastomize and, branching, form a complex network, the main links of which are:

Arterioles - branch into precapillaries;

Precapillaries are transitional vessels between arterioles and the capillaries themselves;

True capillaries;

Postcapillaries;

Venules are the transition points between capillaries and veins.

Each type of vessel that makes up this network has its own transmission mechanism nutrients and metabolites between the blood they contain and nearby tissues. The muscles of larger arteries and arterioles are responsible for the movement of blood and its flow into the smallest vessels. In addition, the regulation of blood flow is also carried out by the muscular sphincters of the pre- and post-capillaries. The function of these vessels is mainly distributive, while true capillaries perform a trophic (nutritional) function.

Veins are another group of vessels, the function of which, unlike arteries, is not to deliver blood to tissues and organs, but to ensure its flow to the heart. To do this, blood moves through the veins in the opposite direction - from tissues and organs to the heart muscle. Due to the difference in functions, the structure of veins is somewhat different from the structure of arteries. The factor of strong pressure that blood exerts on the walls of blood vessels is much less manifested in veins than in arteries, therefore the elastin-collagen framework in the walls of these vessels is weaker, and muscle fibers are also represented in smaller quantities. This is why veins that do not receive blood collapse.

Similar to arteries, veins branch widely to form networks. Many microscopic veins merge into single venous trunks, which lead to the largest vessels flowing into the heart.

The movement of blood through the veins is possible due to the action on it negative pressure in the chest cavity. Blood moves in the direction of the suction force into the heart and chest cavity, in addition, its timely outflow ensures smooth muscle layer in the walls of blood vessels. Movement of blood from lower limbs upward is difficult, therefore in the vessels of the lower part of the body the muscles of the walls are more developed.

In order for blood to move towards the heart, and not in the opposite direction, valves are located in the walls of the venous vessels, represented by a fold of endothelium with a connective tissue layer. The free end of the valve freely directs blood in the direction of the heart, and the outflow is blocked back.

Most veins run adjacent to one or more arteries: small arteries usually have two veins near them, and larger ones usually have one vein near them. Veins, which do not accompany any arteries, are found in the connective tissue under the skin.

Wall nutrition more large vessels provide arteries and veins of smaller sizes, arising from the same trunk or from neighboring vascular trunks. The entire complex is located in the connective tissue layer surrounding the vessel. This structure is called the vascular sheath.

Venous and arterial walls well innervated, contain a variety of receptors and effectors, well connected with guiding nerve centers, due to which the automatic regulation of blood circulation is carried out. Thanks to the work of the reflexogenic areas of the blood vessels, nervous and humoral regulation metabolism in tissues.

Functional groups of blood vessels

All circulatory system By functional load divided by six different groups vessels. Thus, in human anatomy one can distinguish shock-absorbing, exchange, resistive, capacitive, shunting and sphincteric vessels.

Shock absorbing vessels

This group mainly includes arteries in which the layer of elastin and collagen fibers is well represented. It includes the largest vessels - the aorta and pulmonary artery, as well as areas adjacent to these arteries. The elasticity and resilience of their walls provides the necessary shock-absorbing properties, due to which the systolic waves that occur during heart contractions are smoothed out.

The damping effect in question is also called the Windkessel effect, which German means "compression chamber effect".

To clearly demonstrate this effect, the following experiment is used. Two tubes are connected to a container filled with water, one made of elastic material (rubber) and the other made of glass. From solid glass tube water splashes out in sharp intermittent bursts, and from soft rubber it flows out evenly and constantly. This effect is explained physical properties tube materials. The walls of the elastic tube are stretched under the influence of liquid pressure, which leads to the generation of so-called elastic stress energy. Thus, the kinetic energy resulting from pressure is converted into potential energy, which increases voltage.

The kinetic energy of cardiac contraction acts on the walls of the aorta and large vessels that extend from it, causing them to stretch. These vessels form a compression chamber: the blood entering them under the pressure of heart systole stretches their walls, the kinetic energy is converted into elastic tension energy, which contributes to the uniform movement of blood through the vessels during diastole.

Arteries located further from the heart are of the muscular type, their elastic layer is less pronounced, and they have more muscle fibers. The transition from one type of vessel to another occurs gradually. Further blood flow is ensured by contraction of the smooth muscles of the muscular arteries. At the same time, the smooth muscle layer of large elastic arteries has virtually no effect on the diameter of the vessel, which ensures the stability of hydrodynamic properties.

Resistive vessels

Resistive properties are found in arterioles and terminal arteries. The same properties, but to a lesser extent, are characteristic of venules and capillaries. The resistance of blood vessels depends on their cross-sectional area, and the terminal arteries have a well-developed muscular layer that regulates the lumen of the vessels. Vessels with a small lumen and thick, strong walls provide mechanical resistance to blood flow. Developed smooth muscle resistive vessels provide regulation of blood volume velocity, controls blood supply to organs and systems due to cardiac output.

Sphincter vessels

Sphincters are located at the end sections of the precapillaries; when they narrow or expand, the number of working capillaries that provide tissue trophism changes. When the sphincter expands, the capillary enters a functioning state; in non-functioning capillaries, the sphincters are narrowed.

Exchange vessels

Capillaries are vessels that perform an exchange function, carrying out diffusion, filtration and trophism of tissues. Capillaries cannot independently regulate their diameter; changes in the lumen of blood vessels occur in response to changes in the sphincters of the precapillaries. The processes of diffusion and filtration occur not only in capillaries, but also in venules, so this group of vessels also belongs to the exchange vessels.

Capacitive vessels

Vessels that act as reservoirs for large volumes of blood. Most often, capacitive vessels include veins - their structural features allow them to hold more than 1000 ml of blood and eject it as needed, ensuring stability of blood circulation, uniform blood flow and complete blood supply to organs and tissues.

Humans, unlike most other warm-blooded animals, do not have special reservoirs for storing blood from which it could be released as needed (in dogs, for example, this function is performed by the spleen). Veins can accumulate blood to regulate the redistribution of its volume throughout the body, which is facilitated by their shape. Flattened veins accommodate large volumes of blood, without stretching, but acquiring an oval lumen shape.

Capacitive vessels include large veins in the abdominal area, veins in the subpapillary plexus of the skin, veins of the liver. The function of depositing large volumes of blood can also be performed by the pulmonary veins.

Shunt vessels

Shunt vessels are an anastomosis of arteries and veins; when they are open, blood circulation in the capillaries is significantly reduced. Shunt vessels are divided into several groups according to their function and structural features:

Pericardial vessels - these include elastic type arteries, vena cava, pulmonary arterial trunk and pulmonary vein. They begin and end the systemic and pulmonary circulation.

Great vessels are large and medium-sized vessels, veins and arteries of the muscular type, located outside the organs. With their help, blood is distributed to all parts of the body.

Organ vessels - intraorgan arteries, veins, capillaries, providing trophism to the tissues of internal organs.

Most dangerous diseases vessels that pose a threat to life: abdominal aneurysm and thoracic aorta, arterial hypertension, ischemic disease, stroke, renal vascular diseases, atherosclerosis of the carotid arteries.

Vascular diseases of the legs are a group of diseases that lead to impaired blood circulation in the vessels, pathologies of the vein valves, and blood clotting disorders.

Atherosclerosis of the lower extremities – pathological process affects large and medium vessels (aorta, iliac, popliteal, femoral arteries), causing them to narrow. As a result, the blood supply to the extremities is disrupted, and severe pain, the patient’s performance is impaired.

Varicose veins are a disease that results in dilation and lengthening of the veins of the upper and lower extremities, thinning of their walls, and the formation of varicose nodes. The changes that occur in the vessels are usually persistent and irreversible. Varicose veins are more common in women - in 30% of women after 40 and only 10% of men of the same age. (Read also: Varicose veins - causes, symptoms and complications)

Which doctor should I contact for blood vessels?

Vascular diseases, their conservative and surgical treatment and prevention is carried out by phlebologists and angiosurgeons. After all the necessary diagnostic procedures, the doctor draws up a course of treatment, which combines conservative methods and surgery. Drug therapy Vascular diseases is aimed at improving blood rheology, lipid metabolism in order to prevent atherosclerosis and other vascular diseases caused by elevated blood cholesterol levels. (Read also: High cholesterol in the blood - what does this mean? What are the reasons?) The doctor may prescribe vasodilators, medicines to combat concomitant diseases, such as hypertension. In addition, the patient is prescribed vitamin and mineral complexes and antioxidants.

The course of treatment may include physiotherapy procedures - barotherapy of the lower extremities, magnetic and ozone therapy.

An indispensable condition for the existence of the body is the circulation of fluids through the blood vessels that carry blood and the lymphatic vessels through which lymph moves.

Transports fluids and substances dissolved in them (nutrients, cell waste products, hormones, oxygen, etc.) The cardiovascular system is the most important integrating system of the body. The heart in this system acts as a pump, and the vessels serve as a kind of pipeline through which everything necessary is delivered to every cell of the body.

Blood vessels

Among the blood vessels, larger ones are distinguished - arteries and smaller ones - arterioles, through which blood flows from the heart to the organs, venules And veins, through which blood returns to the heart, and capillaries, through which blood passes from arterial vessels to venous vessels (Fig. 1). The most important metabolic processes between the blood and organs take place in the capillaries, where the blood gives the oxygen and nutrients it contains to the surrounding tissues, and takes metabolic products from them. Thanks to constant blood circulation, the optimal concentration of substances in tissues is maintained, which is necessary for the normal functioning of the body.

Blood vessels form the systemic and pulmonary circulations, which begin and end in the heart. The blood volume in a person weighing 70 kg is 5-5.5 liters (approximately 7% of body weight). Blood consists of a liquid part - plasma and cells - erythrocytes, leukocytes and platelets. Due to the high speed of circulation, 8000-9000 liters of blood flow through the blood vessels every day.

IN different vessels blood moves with at different speeds. In the aorta, emerging from the left ventricle of the heart, the blood speed is the highest - 0.5 m/s, in the capillaries - the lowest - about 0.5 mm/s, and in the veins - 0.25 m/s. Differences in the speed of blood flow are due to unequal width general cross section bloodstream in different areas. The total lumen of the capillaries is 600-800 times greater than the lumen of the aorta, and the width of the lumen of the venous vessels is approximately 2 times greater than that of the arterial vessels. According to the laws of physics, in a system of communicating vessels, the speed of fluid flow is higher in narrower places.

The wall of arteries is thicker than that of veins and consists of three layers of membranes (Fig. 2). The middle shell is built from bundles of smooth muscle tissue, between which elastic fibers are located. In the inner membrane, lined on the side of the lumen of the vessel with endothelium, and on the border between the middle and outer shells there are elastic membranes. Elastic membranes and fibers form a kind of frame of the vessel, giving its walls strength and elasticity.

There are relatively more elastic elements in the wall of the large arteries closest to the heart (the aorta and its branches). This is due to the need to counteract the stretching by the mass of blood that is ejected from the heart during its contraction. As they move away from the heart, the arteries divide into branches and become smaller. In medium and small arteries, in which the inertia of the cardiac impulse weakens and the own contraction of the vascular wall is required for further movement of blood, it is well developed muscle tissue. Under the influence of nervous stimulation, such arteries are able to change their lumen.

The walls of the veins are thinner, but consist of the same three membranes. Because they contain significantly less elastic and muscle tissue, the walls of the veins may collapse. A special feature of veins is the presence in many of them of valves that prevent the reverse flow of blood. Vein valves are pocket-like projections inner shell.

Lymphatic vessels

They also have a relatively thin wall lymphatic vessels . They also have many valves that allow lymph to flow in only one direction - towards the heart.

Lymphatic vessels and flow through them lymph also relate to the cardiovascular system. Lymphatic vessels together with veins ensure the absorption of water from tissues with substances dissolved in it: large protein molecules, fat droplets, cell breakdown products, foreign bacteria and others. The smallest lymphatic vessels are lymphatic capillaries- closed at one end and located in organs next to blood capillaries. The permeability of the wall of lymphatic capillaries is higher than that of blood capillaries, and their diameter is larger, so those substances that, due to their large size, cannot penetrate from the tissues into blood capillaries, enter the lymphatic capillaries. Lymph is similar in composition to blood plasma; of the cells it contains only leukocytes (lymphocytes).

Lymph formed in tissues through lymphatic capillaries, and then through larger lymphatic vessels, constantly flows into the circulatory system, into the veins great circle blood circulation 1200-1500 ml of lymph enters the blood per day. It is important that before the lymph flowing from the organs enters the circulatory system and mixes with the blood, it passes through a cascade lymph nodes, which are located along the lymphatic vessels. IN lymph nodes substances foreign to the body and pathogens are retained and neutralized, and the lymph is enriched with lymphocytes.

Location of vessels

Rice. 3. Venous system
Rice. 3a. Arterial system

The distribution of blood vessels in the human body follows certain patterns. Arteries and veins usually run together, with small and medium-sized arteries accompanied by two veins. Lymphatic vessels also pass through these vascular bundles. The course of the vessels corresponds to the general structure of the human body (Fig. 3 and 3a). Along spinal column The aorta and large veins pass through, and branches extending from them are located in the intercostal spaces. On the limbs, in those sections where the skeleton consists of one bone (shoulder, hip), there is one main artery, accompanied by veins. Where there are two bones in the skeleton (forearm, lower leg), there are two main arteries, and with a radial structure of the skeleton (hand, foot), the arteries are located corresponding to each digital ray. The vessels are sent to the organs by the shortest distance. Vascular bundles pass in sheltered places, in canals, formed by bones and muscles, and only on the flexor surfaces of the body.

In some places, the arteries are located superficially, and their pulsation can be felt (Fig. 4). Thus, the pulse can be examined on the radial artery in the lower part of the forearm or on carotid artery in the side of the neck. In addition, superficial arteries can be pressed against adjacent bone to stop bleeding.

Both the branches of the arteries and the tributaries of the veins are widely connected to each other, forming so-called anastomoses. When there are disturbances in the flow of blood or its outflow through the main vessels, anastomoses facilitate the movement of blood in different directions and its movement from one area to another, which leads to the restoration of blood supply. This is especially important in case sudden violation patency of the main vessel in atherosclerosis, trauma, injury.

The most numerous and thin vessels- blood capillaries. Their diameter is 7-8 µm, and the thickness of the wall formed by one layer of endothelial cells lying on the basement membrane is about 1 µm. The exchange of substances between blood and tissues occurs through the capillary wall. Blood capillaries are found in almost all organs and tissues (they are absent only in the outermost layer of the skin - the epidermis, cornea and lens of the eye, in hair, nails, and tooth enamel). Length of all capillaries human body is approximately 100,000 km. If you stretch them in one line, you can encircle the globe along the equator 2.5 times. Inside the organ, blood capillaries are connected to each other, forming capillary networks. Blood enters the capillary networks of organs through arterioles and flows out through venules.

Microcirculation

The movement of blood through capillaries, arterioles and venules, and lymph through lymphatic capillaries is called microcirculation, and the smallest vessels themselves (their diameter, as a rule, does not exceed 100 microns) - microvasculature . The structure of the last channel has its own characteristics in different organs, and delicate mechanisms microcirculation allows you to regulate the activity of the organ and adapt it to the specific conditions of the functioning of the body. At any moment, only part of the capillaries is working, that is, open and allowing blood to pass through, while others remain in reserve (closed). Thus, more than 75% of skeletal muscle capillaries can be closed at rest. At physical activity most of them open because the working muscle requires an intense flow of nutrients and oxygen.

The function of blood distribution in the microvasculature is performed by arterioles, which have a well-developed muscularis propria. This allows them to narrow or expand, changing the amount of blood entering the capillary networks. This feature of arterioles allowed the Russian physiologist I.M. Sechenov called them “taps of the circulatory system.”

Studying the microvasculature is possible only with the help of a microscope. That is why active research into microcirculation and the dependence of its intensity on the condition and needs of surrounding tissues became possible only in the twentieth century. Capillary researcher August Krogh was awarded Nobel Prize. In Russia, a significant contribution to the development of ideas about microcirculation in the 70-90s was made by the scientific schools of academicians V.V. Kupriyanov and A.M. Chernukha. Currently, thanks to modern technical advances, methods for studying microcirculation (including using computer and laser technologies) are widely used in clinical practice and experimental work.

Blood pressure

An important characteristic of the activity cardiovascular system is the value of blood pressure (BP). Due to the rhythmic work of the heart, it fluctuates, increasing during systole (contraction) of the ventricles of the heart and decreasing during diastole (relaxation). The highest blood pressure observed during systole is called maximum, or systolic. The lowest blood pressure is called minimum, or diastolic. Blood pressure is usually measured in brachial artery. In adults healthy people The maximum blood pressure is normally 110-120 mm Hg, and the minimum is 70-80 mm Hg. In children, due to the greater elasticity of the arterial wall, blood pressure is lower than in adults. With age, when the elasticity of the vascular walls decreases due to sclerotic changes, the blood pressure level increases. At muscle work systolic blood pressure increases, but diastolic blood pressure does not change or decreases. The latter is explained by the dilation of blood vessels in working muscles. Decrease in maximum blood pressure below 100 mm Hg. called hypotension, and an increase above 130 mmHg. - hypertension.

Blood pressure level is maintained complex mechanism, which involves the nervous system and various substances carried by the blood itself. Thus, there are vasoconstrictor and vasodilator nerves, the centers of which are located in the medulla oblongata and spinal cord. There is a significant amount chemicals, under the influence of which the lumen of blood vessels changes. Some of these substances are formed in the body itself (hormones, mediators, carbon dioxide), others come from external environment(medicinal and nutrients). During emotional stress(anger, fear, pain, joy) the hormone adrenaline enters the blood from the adrenal glands. It increases the activity of the heart and constricts blood vessels, which increases blood pressure. Hormone works the same way thyroid gland thyroxine.

Every person should know that his body has powerful self-regulation mechanisms, with the help of which it maintains normal condition blood vessels and blood pressure levels. This ensures the necessary blood supply to all tissues and organs. However, it is necessary to pay attention to failures in the functioning of these mechanisms and, with the help of specialists, to identify and eliminate their cause.

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Topic: Cardiovascular system. Blood vessels. General plan buildings. Varieties. Dependence of the structure of the vascular wall on hemodynamic conditions. Arteries. Vienna. Classification. Features of the structure. Functions. Age characteristics.

Cardiovascular system includes the heart, blood and lymphatic vessels. In this case, the heart, blood vessels and lymphatic vessels are called the circulatory system or circulatory system. Lymphatic vessels, together with lymph nodes, belong to the lymphatic system.

Circulatory system is a closed system of tubes of different calibers that performs transport, trophic, metabolic functions and the function of regulating blood microcirculation in organs and tissues.

Vascular development

The source of the development of blood vessels is mesenchyme. In the third week of embryonic development, clusters of mesenchymal cells—blood islands—are formed outside the body of the embryo in the wall of the yolk sac and in the chorion (in mammals). Peripheral islet cells form the walls of blood vessels, and centrally located mesenchymocytes differentiate into primary blood cells. Later, in the same way, vessels appear in the body of the embryo and communication is established between the primary blood vessels extraembryonic organs and the body of the embryo. Further development vascular wall and the acquisition of various structural features occurs under the influence of hemodynamic conditions, which include: blood pressure, the magnitude of its jumps, blood flow speed.

Classification of vessels

Blood vessels are divided into arteries, veins and microvasculature, which include arterioles, capillaries, venules and arteriole-venular anastomoses.

General plan of the structure of the wall of blood vessels

With the exception of capillaries and some veins, blood vessels have a general structural plan, they all consist of three membranes:

Inner membrane (intima) consists of two mandatory layers

Endothelium - a continuous layer of single-layer cells squamous epithelium lying on the basement membrane and lining the inner surface of the vessel;

Subendothelial layer (subendothelium), formed by loose fibrous connective tissue.

Middle shell which usually contains smooth myocytes and the intercellular substance formed by these cells, represented by proteoglycans, glycoproteins, collagen and elastic fibers.

Outer shell (adventitia) It is represented by loose fibrous connective tissue, with vascular vessels, lymphatic capillaries and nerves located in it.

Arteries– these are vessels that ensure the movement of blood from the heart to the microvasculature in organs and tissues. Arterial blood flows through the arteries, with the exception of the pulmonary and umbilical arteries.

Classification of arteries

According to the quantitative ratio of elastic and muscular elements in the vessel wall, arteries are divided into:

Arteries of elastic type.

Arteries mixed type(muscular-elastic) type.

Arteries of the muscular type.

The structure of elastic arteries

To the arteries of this type include the aorta and pulmonary artery. The wall of these vessels is subject to large pressure differences, so they require high elasticity.

1. Inner shell consists of three layers:

Endothelial layer

The subendothelial layer, which has a significant thickness, because it absorbs pressure surges. It is represented by loose fibrous connective tissue. In old age, cholesterol and fatty acids appear here.

The plexus of elastic fibers is a dense interweaving of longitudinally and circularly arranged elastic fibers

2. Middle shell It is represented by 50-70 fenestrated elastic membranes, which look like cylinders inserted into each other, between which there are individual smooth myocytes, elastic and collagen fibers.

3. Outer shell It is represented by loose fibrous connective tissue with blood vessels supplying the artery wall (vascular vessels) and nerves.

The structure of arteries of mixed (muscular-elastic) type

Arteries of this type include the subclavian, carotid and iliac arteries).

Three layers:

Endothelium

Subendothelial layer

Inner elastic membrane

2. The tunica media consists of approximately equal numbers of elastic elements (which include fibers and elastic membranes) and smooth myocytes.

3. The outer shell consists of loose connective tissue, where, along with vessels and nerves, there are longitudinally located bundles of smooth myocytes.

The structure of muscular arteries

These are all other arteries of medium and small caliber.

1. The inner shell consists of

Endothelium

Subendothelial layer

Inner elastic membrane

2. The middle shell has the greatest thickness and is represented mainly by spirally arranged bundles of smooth muscle cells, between which collagen and elastic fibers are located.

Between the middle and outer membranes of the artery there is a weakly defined outer elastic membrane.

3. The outer shell is represented by loose fibrous connective tissue with vessels and nerves; there are no smooth myocytes.

Vienna- These are vessels that carry blood to the heart. Venous blood flows through them, with the exception of the pulmonary and umbilical veins.

Due to the peculiarities of hemodynamics, which include lower blood pressure than in the arteries, the absence of sudden changes in pressure, slow blood movement and lower oxygen content in the blood, veins have a number of structural features with arteries:

Veins have a larger diameter.

Their wall is thinner and collapses easily.

The elastic component and subendothelial layer are poorly developed.

Weaker development of smooth muscle elements in the medial shell.

The outer shell is well defined.

The presence of valves, which are derivatives of the inner membrane, the outside of the valve leaflets are covered with endothelium, their thickness is formed by loose fibrous connective tissue, and at the base there are smooth myocytes.

Vascular vessels are contained in all membranes of the vessel.

Vein classification

Veins are of non-muscular type.

2. Veins of the muscular type, which in turn are divided into:

Veins with poor myocyte development

Veins with average myocyte development

Vienna with strong development myocytes

The degree of development of myocytes depends on the location of the vein: in the upper part of the body the muscle component is poorly developed, in the lower part it is stronger.

The structure of a muscleless vein

Veins of this type are located in the brain, its membranes, retina, placenta, spleen, and bone tissue.

The vessel wall is formed by endothelium, surrounded by loose fibrous connective tissue, tightly fused with the stroma of the organs and therefore does not collapse.

The structure of veins with poor myocyte development

These are the veins of the face, neck, upper body and superior vena cava.

1. The inner shell consists of

Endothelium

Poorly developed subendothelial layer

2. In the middle shell there are poorly developed circularly arranged bundles of smooth muscle cells, between which there is a significant thickness of layer of loose connective tissue.

3. The outer shell is composed of loose fibrous connective tissue.

Structure of veins with average myocyte development

These include the brachial vein and the small veins of the body.

1. The inner shell consists of:

Endothelium

Subendothelial layer

2. The tunica media includes several layers of circularly arranged myocytes.

3. The outer shell is thick and contains longitudinally arranged bundles of smooth myocytes in loose fibrous connective tissue.

Structure of veins with strong myocyte development

These veins are located in the lower part of the body and lower extremities. In addition to the good development of myocytes in all layers of the wall, they are characterized by the presence of valves that ensure the movement of blood towards the heart.

Regeneration of blood vessels

When the vessel wall is damaged, rapidly dividing endothelial cells close the defect. The formation of smooth myocytes occurs slowly due to their division and differentiation of myoblasts and pericytes. With a complete rupture of medium and large vessels, their restoration without surgical intervention is impossible, but distal to the rupture, the blood supply is restored due to collaterals and the formation of small vessels from protrusions of endothelial cells of the walls of arterioles and venules.

Age-related features of blood vessels

The ratio between the diameter of arteries and veins at the time of birth of a child is 1:1; in old people, these ratios change to 1:5. In a newborn, all blood vessels have thin walls, their muscle tissue and elastic fibers are poorly developed. In the first years of life in large vessels, the volume of the muscular membrane increases and the number of elastic and collagen fibers of the vascular wall increases. The intima and its subendothelial layer develop relatively quickly. The lumen of blood vessels increases slowly. Complete formation of the wall of all blood vessels is completed by 12 years. With the onset of 40 years of age, the reverse development of the arteries begins, while elastic fibers and smooth myocytes are destroyed in the arterial wall, collagen fibers grow, the subendothelium sharply thickens, the vascular wall thickens, salts are deposited in it, and sclerosis develops. Age-related changes in veins are similar, but appear earlier.