Characteristics of blood vessels table. Blood vessel

Topic: Cardiovascular system. Blood vessels. General plan of the building. Varieties. Dependence of the vessel wall structure on hemodynamic conditions. arteries. Vienna. Classification. Structural features. Functions. Age features.

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

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

Vascular development

The source of the development of blood vessels is the mesenchyme. In the third week of embryonic development outside the body of the embryo in the wall of the yolk sac and in the chorion (in mammals), clusters of mesenchymal cells - blood islands - are formed. The peripheral cells of the islets form the walls of the vessels, and the centrally located mesenchymocytes differentiate into primary blood cells. Later, in the same way, the vessels appear in the body of the embryo and communication is established between the primary blood vessels of the extra-embryonic organs and the body of the embryo. Further development of the 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, and blood flow velocity.

Vessel classification

Blood vessels are subdivided into arteries, veins, and vessels of the microvasculature, which include arterioles, capillaries, venules, and arteriolovenular 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 shells:

Inner shell (intima) consists of two obligatory layers

Endothelium - a continuous layer of single-layer squamous epithelium cells 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 sheath (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 microcirculatory bed 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, the arteries are divided into:

Elastic arteries.

Arteries of mixed type (muscular-elastic) type.

Muscular arteries.

The structure of the elastic type arteries

These types of arteries include the aorta and the pulmonary artery. The wall of these vessels is subject to large pressure drops, 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. Represented by loose fibrous connective tissue. In old age, cholesterol and fatty acids appear here.

The plexus of elastic fibers is a dense interlacing 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 separate smooth myocytes, elastic and collagen fibers.

3. outer shell It is represented by loose fibrous connective tissue with blood vessels that feed the wall of the artery (vascular vessels) and nerves.

The structure of the arteries of the mixed (muscle-elastic) type

This type of artery includes the subclavian, carotid, and iliac arteries.

Three layers:

Endothelium

subendothelial layer

Internal elastic membrane

2. The middle shell consists of an approximately equal number 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 arranged bundles of smooth myocytes.

The structure of the arteries of the muscular type

These are all other arteries of medium and small caliber.

1. The inner shell consists of

endothelium

subendothelial layer

Internal elastic membrane

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

Between the middle and outer shells of the artery is a weakly expressed outer elastic membrane.

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

Vienna are the 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 pressure drops, slow blood movement and lower oxygen content in the blood, veins have a number of structural features in their structure with arteries:

The veins are larger.

Their wall is thinner, easily collapses.

The elastic component and the subendothelial layer are poorly developed.

Weaker development of smooth muscle elements in the middle shell.

The outer shell is well defined.

The presence of valves, which are derivatives of the inner shell, 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.

Vessels of vessels are contained in all shells of the vessel.

Vein classification

Muscleless veins.

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

Veins with poor myocyte development

Veins with medium myocyte development

Veins with strong myocyte development

The degree of development of myocytes depends on the localization of the vein: in the upper part of the body, the muscular 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 the endothelium, surrounded by loose fibrous connective tissue, tightly fuses with the stroma of the organs and therefore does not collapse.

The structure of veins with poor development of myocytes

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

1. The inner shell consists of

endothelium

Weakly developed subendothelial layer

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

3. The outer shell is represented by loose fibrous connective tissue.

The structure of the veins with the average development of myocytes

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

1. The inner shell consists of:

endothelium

subendothelial layer

2. The middle shell includes several layers of circularly arranged myocytes.

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

The structure of the veins with a strong development of myocytes

Such veins are located in the lower body and lower extremities. In addition to the good development of myocytes in all layers, the walls 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 endotheliocytes 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, blood supply is restored due to collaterals and the formation of small vessels from protrusions of endotheliocytes in the walls of arterioles and venules.

Age features of blood vessels

The ratio between the diameter of arteries and veins at the time of the birth of a child is 1:1; in the elderly, 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 the vessels grows slowly. The complete formation of the wall of all blood vessels is completed by the age of 12. At the onset of the age of 40, the reverse development of the arteries begins, while elastic fibers and smooth myocytes are destroyed in the arterial wall, collagen fibers grow, the subendothelium thickens sharply, the vessel wall thickens, salts are deposited in it, and sclerosis develops. Age-related changes in veins are similar, but appear earlier.

Classification of blood vessels

Among the vessels of the circulatory system, there are arteries, arterioles, hemocapillaries, venules, veins and arteriolovenous anastomoses; vessels of the microcirculatory system carry out the relationship between arteries and veins. Vessels of different types differ not only in their thickness, but also in tissue composition and functional features.

Arteries are vessels that carry blood away from the heart. Arteries have thick walls that contain muscle fibers as well as collagen and elastic fibers. They are very elastic and can narrow or expand, depending on the amount of blood pumped by the heart.
Arterioles are small arteries that immediately precede the capillaries in blood flow. Smooth muscle fibers predominate in their vascular wall, thanks to which arterioles can change the size of their lumen and, thus, resistance.
Capillaries are the smallest blood vessels, so thin that substances can freely penetrate through their wall. Through the wall of the capillaries, nutrients and oxygen are transferred from the blood to the cells and carbon dioxide and other waste products are transferred from the cells to the blood.
Venules are small blood vessels that provide in a large circle the outflow of oxygen-depleted and saturated blood from the capillaries into the veins.
Veins are the vessels that carry blood to the heart. The walls of the veins are less thick than the walls of the arteries and contain correspondingly fewer muscle fibers and elastic elements.

The structure of blood vessels (for example, the aorta)

The structure of the aorta: 1. elastic membrane (outer membrane or Tunica externa, 2. muscular membrane (Tunica media), 3. inner membrane (Tunica intima)

This example describes the structure of an arterial vessel. The structure of other types of vessels may differ from that described below. See related articles for details.

- the most important physiological mechanism responsible for nourishing body cells and removing harmful substances from the body. The main structural component is the vessels. There are several types of vessels that differ in structure and function. Vascular diseases lead to serious consequences that negatively affect the entire body.

General information

A blood vessel is a hollow, tube-shaped formation that permeates body tissues. Blood is transported through the vessels. In humans, the circulatory system is closed, as a result of which the movement of blood in the vessels occurs under high pressure. Transportation through the vessels is carried out due to the work of the heart, which performs a pumping function.

Blood vessels can change under the influence of certain factors. Depending on the external influence, they expand or narrow. The process is regulated by the nervous system. The ability to expand and contract provides a specific structure of human blood vessels.

Vessels are made up of three layers:

External. The outer surface of the vessel is covered with connective tissue. Its function is to protect against mechanical stress. Also, the task of the outer layer is to separate the vessel from nearby tissues.
Average. Contains muscle fibers characterized by mobility and elasticity. They provide the ability of the vessel to expand or contract. In addition, the function of the muscle fibers of the middle layer is to maintain the shape of the vessel, due to which there is a full-fledged unhindered blood flow.
Interior. The layer is represented by flat single-layer cells - endothelium. The tissue makes the vessels smooth inside, thereby reducing the resistance to blood flow.

It should be noted that the walls of venous vessels are much thinner than arteries. This is due to a small amount of muscle fibers. The movement of venous blood occurs under the action of skeletal blood, while arterial blood moves due to the work of the heart.

In general, a blood vessel is the main structural component of the cardiovascular system, through which blood moves to tissues and organs.

Types of vessels

Previously, the classification of human blood vessels included only 2 types - arteries and veins. At the moment, 5 types of vessels are distinguished, differing in structure, size, and functional tasks.

Types of blood vessels:

. Vessels provide the movement of blood from the heart to the tissues. They are distinguished by thick walls with a high content of muscle fibers. Arteries are constantly narrowing and expanding, depending on the level of pressure, preventing excess blood flow to some organs and deficiency in others.
Arterioles. Small vessels that are the terminal branches of arteries. Composed primarily of muscle tissue. They are a transitional link between arteries and capillaries.
capillaries. The smallest vessels penetrating organs and tissues. A feature is very thin walls through which blood is able to penetrate outside the vessels. The capillaries supply the cells with oxygen. At the same time, the blood is saturated with carbon dioxide, which is subsequently excreted from the body through the venous pathways.

Venules. They are small vessels that connect capillaries and veins. They transport oxygen used by cells, residual waste products, and dying blood particles.
Vienna. They ensure the movement of blood from the organs to the heart. Contain fewer muscle fibers, which is associated with low resistance. Because of this, the veins are less thick and more likely to be damaged.

Thus, several types of vessels are distinguished, the totality of which forms the circulatory system.

Functional groups

Depending on the location, the vessels perform different functions. In accordance with the functional load, the structure of the vessels differs. Currently, there are 6 main functional groups.

The functional groups of vessels include:

Shock-absorbing. The vessels belonging to this group have the largest number of muscle fibers. They are the largest in the human body and are located in close proximity to the heart (aorta, pulmonary artery). These vessels are the most elastic and resilient, which is necessary to smooth out the systolic waves that form during cardiac contraction. The amount of muscle tissue in the walls of blood vessels decreases depending on the degree of remoteness from the heart.
Resistive. These include the final, thinnest blood vessels. Due to the smallest lumen, these vessels provide the greatest resistance to blood flow. The resistive vessels contain many muscle fibers that control the lumen. Due to this, the volume of blood entering the body is regulated.
Capacitive. They perform a reservoir function, keeping large volumes of blood. This group includes large venous vessels that can hold up to 1 liter of blood. Capacitive vessels regulate the movement of blood to, controlling its volume in order to reduce the workload on the hearts.
Sphincters. They are located in the terminal branches of small capillaries. By constriction and expansion, the sphincter vessels control the amount of incoming blood. With the narrowing of the sphincters, the blood does not flow, as a result of which the trophic process is disturbed.
Exchange. Represented by the terminal branches of capillaries. The exchange of substances takes place in the vessels, providing nutrition to the tissues and removal of harmful substances. Similar functional tasks are performed by venules.
Shunting. Vessels provide communication between veins and arteries. This does not affect the capillaries. These include atrial, main and organ vessels.

In general, there are several functional groups of vessels that provide a full flow of blood and nutrition of all body cells.

Regulation of vascular activity

The cardiovascular system instantly reacts to external changes or the impact of negative factors inside the body. For example, when stressful situations occur, heart palpitations are noted. The vessels narrow, due to which it increases, and the muscle tissues are supplied with a large amount of blood. Being at rest, more blood flows to the brain tissues and digestive organs.

The nerve centers located in the cerebral cortex and hypothalamus are responsible for the regulation of the cardiovascular system. The signal arising from the reaction to the stimulus affects the center that controls vascular tone. In the future, through the nerve fibers, the impulse moves to the vascular walls.

In the walls of blood vessels there are receptors that perceive pressure surges or changes in the composition of the blood. Vessels are also able to transmit nerve signals to the appropriate centers, notifying of a possible danger. This makes it possible to adapt to changing environmental conditions, such as changes in temperature.

The work of the heart and blood vessels is affected. This process is called humoral regulation. Adrenaline, vasopressin, acetylcholine have the greatest effect on the vessels.

Thus, the activity of the cardiovascular system is regulated by the nerve centers of the brain and endocrine glands responsible for the production of hormones.

Diseases

Like any organ, the vessel can be affected by diseases. The causes of the development of vascular pathologies are often associated with the wrong way of life of a person. Less often, diseases develop due to congenital abnormalities, acquired infections, or against the background of concomitant pathologies.

Common vascular diseases:

. It is considered one of the most dangerous pathologies of the cardiovascular system. With this pathology, blood flow through the vessels that feed the myocardium, the heart muscle, is disrupted. Gradually, due to atrophy, the muscle weakens. As a complication are a heart attack, as well as heart failure, in which sudden cardiac arrest is possible.
Cardiopsychoneurosis. A disease in which the arteries are affected due to malfunctions of the nerve centers. Spasm develops in the vessels due to excessive sympathetic influence on muscle fibers. Pathology often manifests itself in the vessels of the brain, also affects the arteries located in other organs. The patient has intense pain, interruptions in the work of the heart, dizziness, changes in pressure.
Atherosclerosis. A disease in which the walls of blood vessels narrow. This leads to a number of negative consequences, including atrophy of the supply tissues, as well as a decrease in the elasticity and strength of the vessels located behind the constriction. is a provoking factor in many cardiovascular diseases, and leads to the formation of blood clots, heart attack, stroke.
aortic aneurysm. With such a pathology, saccular bulges form on the walls of the aorta. In the future, scar tissue is formed, and the tissues gradually atrophy. As a rule, the pathology develops against the background of a chronic form of hypertension, infectious lesions, including syphilis, as well as anomalies in the development of the vessel. If left untreated, the disease provokes rupture of the vessel and death of the patient.
. Pathology in which the veins of the lower extremities are affected. They greatly expand due to increased load, while the outflow of blood to the heart slows down greatly. This leads to swelling and pain. Pathological changes in the affected veins of the legs are irreversible, the disease in the later stages is treated only surgically.

. A disease in which varicose veins develop in the hemorrhoidal veins that feed the lower intestines. Late stages of the disease are accompanied by prolapse of hemorrhoids, severe bleeding, and impaired stool. Infectious lesions, including blood poisoning, act as a complication.
Thrombophlebitis. Pathology affects the venous vessels. The danger of the disease is explained by the potential for a blood clot to break off, which blocks the lumen of the pulmonary arteries. However, large veins are rarely affected. Thrombophlebitis affects small veins, the defeat of which does not pose a significant danger to life.

There is a wide range of vascular pathologies that have a negative impact on the functioning of the whole organism.

While watching the video, you will learn about the cardiovascular system.

Blood vessels are an important element of the human body responsible for the movement of blood. There are several types of vessels that differ in structure, functionality, size, location.

The wall of a blood vessel consists of several layers: internal (tunica intima), containing endothelium, subendothelial layer and internal elastic membrane; middle (tunica media), formed by smooth muscle cells and elastic fibers; external (tunica externa), represented by loose connective tissue, in which there are nerve plexuses and vasa vasorum. The wall of the blood vessel receives its nourishment from the branches extending from the main trunk of the same artery or another adjacent artery. These branches penetrate the wall of an artery or vein through the outer shell, forming a plexus of arteries in it, which is why they are called "vascular vessels" (vasa vasorum).

The blood vessels leading to the heart are called veins, and those leaving the heart are called arteries, regardless of the composition of the blood that flows through them. Arteries and veins differ in the features of the external and internal structure.
1. The following types of arterial structure are distinguished: elastic, elastic-muscular and muscular-elastic.

The elastic arteries include the aorta, the brachiocephalic trunk, the subclavian, common and internal carotid arteries, and the common iliac artery. In the middle layer of the wall, elastic fibers predominate over collagen fibers, which lie in the form of a complex network that forms the membrane. The inner shell of the vessel of the elastic type is thicker than that of the artery of the muscular-elastic type. The vessel wall of the elastic type consists of endothelium, fibroblasts, collagen, elastic, argyrophilic and muscle fibers. In the outer shell, there are many collagen connective tissue fibers.

For arteries of the elastic-muscular and muscular-elastic types (upper and lower limbs, extraorgan arteries), the presence of elastic and muscle fibers in their middle layer is characteristic. Muscle and elastic fibers are intertwined in the form of spirals along the entire length of the vessel.

2. Muscular type of structure have intraorgan arteries, arterioles and venules. Their middle shell is formed by muscle fibers (Fig. 362). At the border of each layer of the vascular wall there are elastic membranes. The inner shell in the area of arterial branching thickens in the form of pads that resist the vortex impacts of the blood flow. With the contraction of the muscular layer of the vessels, the regulation of blood flow occurs, which leads to an increase in resistance and an increase in blood pressure. In this case, conditions arise when the blood is directed to another channel, where the pressure is lower due to the relaxation of the vascular wall, or the blood flow is discharged through arteriovenular anastomoses into the venous system. The body is constantly redistributing blood, and first of all it goes to more needy organs. For example, during contraction, i.e., work, of striated muscles, their blood supply increases 30 times. But in other organs, a compensatory slowdown in blood flow and a decrease in blood supply occur.

362. Histological section of an artery of the elastic-muscular type and a vein.
1 - the inner layer of the vein; 2 - the middle layer of the vein; 3 - outer layer of the vein; 4 - outer (adventitial) layer of the artery; 5 - middle layer of the artery; 6 - inner layer of the artery.

363. Valves in the femoral vein. The arrow shows the direction of blood flow (according to Sthor).
1 - vein wall; 2 - valve leaf; 3 - valve sinus.

3. Veins differ in structure from arteries, which depends on low blood pressure. The wall of the veins (inferior and superior vena cava, all extraorganic veins) consists of three layers (Fig. 362). The inner layer is well developed and contains, in addition to the endothelium, muscle and elastic fibers. In many veins there are valves (Fig. 363), which have a connective tissue flap and at the base of the valve there is a roller-like thickening of muscle fibers. The middle layer of the veins is thicker and consists of spiral muscle, elastic and collagen fibers. The veins lack an outer elastic membrane. At the confluence of the veins and distal to the valves, which act as sphincters, muscle bundles form circular thickenings. The outer shell consists of loose connective and adipose tissue, contains a denser network of perivascular vessels (vasa vasorum) than the arterial wall. Many veins have a paravenous bed due to a well-developed perivascular plexus (Fig. 364).

364. Schematic representation of a vascular bundle representing a closed system, where a pulse wave promotes the movement of venous blood.

In the wall of the venules, muscle cells are detected that act as sphincters, functioning under the control of humoral factors (serotonin, catecholamine, histamine, etc.). Intraorganic veins are surrounded by a connective tissue case located between the wall of the vein and the parenchyma of the organ. Often in this connective tissue layer there are networks of lymphatic capillaries, for example, in the liver, kidneys, testicles and other organs. In the abdominal organs (heart, uterus, bladder, stomach, etc.), the smooth muscles of their walls are woven into the wall of the vein. The veins that are not filled with blood collapse due to the absence of an elastic elastic frame in their wall.

4. Blood capillaries have a diameter of 5-13 microns, but there are organs with wide capillaries (30-70 microns), for example, in the liver, anterior pituitary gland; even wider capillaries in the spleen, clitoris and penis. The capillary wall is thin and consists of a layer of endothelial cells and a basement membrane. From the outside, the blood capillary is surrounded by pericytes (connective tissue cells). There are no muscle and nerve elements in the capillary wall, therefore, the regulation of blood flow through the capillaries is completely under the control of the muscle sphincters of arterioles and venules (this distinguishes them from capillaries), and the activity is regulated by the sympathetic nervous system and humoral factors.

In the capillaries, blood flows in a constant stream without pulsating shocks at a speed of 0.04 cm / s under a pressure of 15-30 mm Hg. Art.

Capillaries in organs, anastomosing with each other, form networks. The shape of the networks depends on the design of the organs. In flat organs - fascia, peritoneum, mucous membranes, conjunctiva of the eye - flat networks are formed (Fig. 365), in three-dimensional ones - the liver and other glands, lungs - there are three-dimensional networks (Fig. 366).

365. Single-layer network of blood capillaries of the mucous membrane of the bladder.

366. Network of blood capillaries of the alveoli of the lung.

The number of capillaries in the body is enormous and their total lumen exceeds the diameter of the aorta by 600-800 times. 1 ml of blood is poured over a capillary area of 0.5 m 2 .

Vessels are tubular 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. According to this system, the blood circulates quite quickly.

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

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

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

All blood vessels are made up of three layers:

The inner layer of the vascular wall is formed by 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 strength to blood vessels, consists of muscle fibers, elastin and collagen.

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

arteries

The walls of the arteries are stronger and thicker than those of the veins, as the blood moves through them with greater pressure. Arteries carry oxygenated blood from the heart to the internal organs. In the dead, the arteries are empty, which is found at autopsy, so it was previously believed that the arteries are air tubes. This was 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 is the 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 ejected into the vessel from heart contractions. The fibers of elastin and collagen, which make up the frame of the middle wall of the vessel, help to resist mechanical stress and stretching.

Due to the elasticity and strength of the walls of the elastic arteries, blood continuously enters the vessels and its constant circulation is ensured to nourish organs and tissues, supplying them with oxygen. The left ventricle of the heart contracts and forcefully ejects a large volume of blood into the aorta, its walls stretch, containing the contents of the ventricle. After relaxation of the left ventricle, blood does not enter the aorta, the pressure is weakened, and blood from the aorta enters other arteries, into which it branches. The walls of the aorta regain their former shape, as the elastin-collagen framework provides them with elasticity and resistance to stretching. Blood moves continuously through the vessels, coming in small portions from the aorta after each heartbeat.

The elastic properties of the arteries also ensure the transmission of vibrations along the walls of the vessels - this is a property of any elastic system under mechanical influences, which is played by a 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. Based on this phenomenon, methods for measuring the pulse are based.

Muscular arteries in the middle layer of the walls contain a large number of smooth muscle fibers. This is necessary to ensure blood circulation and the continuity of its movement through the vessels. The vessels of the muscular type are located farther from the heart than the arteries of the elastic type, therefore, the force of the cardiac impulse in them weakens, in order to ensure further movement of the blood, it is necessary to contract the muscle fibers. 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 at a constant speed and enters the organs and tissues in a timely manner, providing them with nutrition.

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

Arteries that do not anastomose with neighboring vascular trunks are called terminal. These include, for example, the arteries of the spleen. The arteries that form fistulas are called anastomizing, most of the arteries belong to this type. The terminal arteries have a greater risk of blockage by a thrombus and a high susceptibility to a heart attack, as a result of which part of the organ may die.

In the last branches, the arteries become very thin, such vessels are called arterioles, and the arterioles already pass directly into the capillaries. Arterioles contain muscle fibers that perform a 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 the artery. The branching point of the arteriole 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 into 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 body structures 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 the substances dissolved in the liquid enter the tissues, and the metabolic products return to the blood.

The number of working capillaries in different parts of the body varies - in large numbers they are concentrated in the working muscles, which need a constant blood supply. For example, in the myocardium (the muscular layer of the heart), up to two thousand open capillaries are found per square millimeter, and in skeletal muscles there are several hundred capillaries per square millimeter. 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).

Capillaries anastomize and, branching out, make up a complex network, the main links of which are:

Arterioles - branch into precapillaries;

Precapillaries - transitional vessels between arterioles and capillaries proper;

True capillaries;

Postcapillaries;

Venules are places where capillaries pass into veins.

Each type of vessel that makes up this network has its own mechanism for the transfer of nutrients and metabolites between the blood they contain and nearby tissues. The musculature of larger arteries and arterioles is responsible for the promotion of blood and its entry into the smallest vessels. In addition, the regulation of blood flow is also carried out by the muscular sphincters of 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 entry into the heart. To do this, the movement of blood through the veins occurs in the opposite direction - from tissues and organs to the heart muscle. Due to the difference in functions, the structure of the veins is somewhat different from the structure of the 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 a smaller amount. That is why veins that do not receive blood collapse.

Like arteries, veins branch widely to form networks. Many microscopic veins merge into single venous trunks that lead to the largest vessels that flow into the heart.

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

In order for the 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 the endothelium with a connective tissue layer. The free end of the valve freely directs blood towards the heart, and the outflow is blocked back.

Most veins run next to one or more arteries: small arteries usually have two veins, and larger ones have one. Veins that do not accompany any arteries occur in the connective tissue under the skin.

The walls of larger vessels are nourished by smaller arteries and veins that originate 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.

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

Functional groups of vessels

According to the functional load, the entire circulatory system is divided into six different groups of vessels. Thus, in the human anatomy, shock-absorbing, exchange, resistive, capacitive, shunting and sphincter vessels can be distinguished.

Cushioning Vessels

This group mainly includes arteries in which a layer of elastin and collagen fibers is well represented. It includes the largest vessels - the aorta and the pulmonary artery, as well as the 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 cushioning effect in question is also called the Windkessel effect, which in German means "compression chamber effect".

To demonstrate this effect, the following experiment is used. Two tubes are attached to a container filled with water, one of an elastic material (rubber) and the other of glass. From a hard glass tube, water splashes out in sharp intermittent shocks, and from a soft rubber one it flows evenly and constantly. This effect is explained by the physical properties of the tube materials. The walls of an elastic tube are stretched under the action of fluid pressure, which leads to the emergence of the so-called elastic stress energy. Thus, the kinetic energy that appears due to pressure is converted into potential energy, which increases the voltage.

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

The arteries located farther from the heart are of the muscular type, their elastic layer is less pronounced, they have more muscle fibers. The transition from one type of vessel to another occurs gradually. Further blood flow is provided by the contraction of the smooth muscles of the muscular arteries. At the same time, the smooth muscle layer of large elastic type arteries practically does not affect 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 the vessels depends on their cross-sectional area, and the terminal arteries have a well-developed muscle layer that regulates the lumen of the vessels. Vessels with a small lumen and thick, strong walls provide mechanical resistance to blood flow. The developed smooth muscles of resistive vessels provide regulation of the volumetric blood velocity, controls the blood supply to organs and systems due to cardiac output.

Vessels-sphincters

Sphincters are located in the terminal sections of the precapillaries; when they narrow or expand, the number of working capillaries that provide tissue trophism changes. With the expansion of the sphincter, the capillary goes into a functioning state, in non-working capillaries, the sphincters are narrowed.

exchange vessels

Capillaries are vessels that perform an exchange function, carry out diffusion, filtration and trophism of tissues. Capillaries cannot independently regulate their diameter, changes in the lumen of the 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 ones.

capacitive vessels

Vessels that act as reservoirs for large volumes of blood. Most often, capacitive vessels include veins - the peculiarities of their structure allow them to hold more than 1000 ml of blood and throw it out as needed, ensuring the stability of blood circulation, uniform blood flow and full blood supply to organs and tissues.

In humans, unlike most other warm-blooded animals, there are no special reservoirs for depositing blood from which it could be ejected as needed (in dogs, for example, this function is performed by the spleen). Veins can accumulate blood to regulate the redistribution of its volumes throughout the body, which is facilitated by their shape. Flattened veins contain large volumes of blood, while not stretching, but acquiring an oval lumen shape.

Capacitive vessels include large veins in the womb, veins in the subpapillary plexus of the skin, and liver veins. 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:

Cardiac vessels - these include the elastic type arteries, vena cava, pulmonary arterial trunk and pulmonary vein. They begin and end with a large and small circle of blood circulation.

The main 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 that provide trophism to the tissues of internal organs.

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

Diseases of the vessels of the legs - a group of diseases that lead to impaired blood circulation through the vessels, pathologies of the valves of the veins, impaired blood clotting.

Atherosclerosis of the lower extremities - the pathological process affects large and medium-sized vessels (aorta, iliac, popliteal, femoral arteries), causing their narrowing. As a result, the blood supply to the limbs is disturbed, severe pain appears, and the patient's performance is impaired.

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

Which doctor should I contact with vessels?

Vascular diseases, their conservative and surgical treatment and prevention are dealt with 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 of 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. (See also: High blood cholesterol - what does it mean? What are the causes?) The doctor may prescribe vasodilators, medicines to combat associated diseases, such as hypertension. In addition, the patient is prescribed vitamin and mineral complexes, antioxidants.

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