The structure of the wall of the veins. All about blood vessels: types, classifications, characteristics, meaning. Functions of the venous system

Veins are blood vessels that carry blood from capillaries back to the heart. Blood, having given oxygen and nutrients to the tissues through the capillaries and filled with carbon dioxide and decay products, returns to the heart through the veins. It is worth noting that the heart has its own blood supply system - the coronary circle, which consists of coronary veins, arteries and capillaries. Coronary vessels are identical to other similar vessels of the body.

FEATURES OF THE STRUCTURE OF VEINS The walls of the veins consist of three layers, which, in turn, include various tissues:
The inner layer is very thin, consists of simple cells located on the elastic membrane of the connective tissue.
;The middle layer is more durable, consists of elastic and muscle tissue.
The outer layer consists of a thin layer of loose and mobile connective tissue, through which the lower layers of the venous membrane are fed and thanks to which the veins are attached to the surrounding tissues.

Through the veins, the so-called reverse circulation is carried out - the blood from the tissues of the body flows back to the heart. For veins located in the upper part of the body, this is possible because the walls of the veins are extensible and the pressure in them is less than in the right atrium, which performs the task of "suction". The situation is different with the veins located in the lower part of the body, especially in the legs, because in order for the blood from them to flow back to the heart, it needs to overcome the force of gravity. To fulfill this vein functions, located in the lower part of the body, are equipped with a system of internal valves that make the blood move in only one direction - up - and prevent the blood from flowing back. Besides, in lower limbs there is a “muscle pump” mechanism that contracts the muscles, between which the veins are located in such a way that blood flows upward through them.

AT peripheral system distinguish two vein type: superficial veins, located very close to the surface of the body, which are visible through the skin, especially on the limbs, and deep veins located between the muscles, usually following the path of the main arteries. In addition, especially in the lower extremities, there are perforating and communicating veins, which connect both parts of the venous system and promote the flow of blood from the superficial veins to the thicker deep veins, and then to the heart.

The valves, which allow blood flow in only one direction, from the superficial to the deep veins and from the deep to the heart, consist of two folds on the inner walls of the veins, or hemispherical valves: when blood is pushed up, the walls of the valves rise and allow a certain amount of blood to pass up; when the impulse dries up, the valves close under the weight of the blood. Thus, the blood cannot go down and on the next impulse it rises another flight, always in the direction of the heart.

The venous system is an important part of the circulation of the human body. Thanks to it, toxins and toxins are removed, the fluid balance in the cells is regulated. Here, the movement of blood goes to the heart and lungs to enrich the lean mixture with oxygen.

General definitions

The arterial and venous systems provide the body with oxygen, minerals, and useful substances. There are protective cells in the blood that allow to destroy foreign inclusions: bacteria, viruses, decomposition results. It also releases carbon dioxide.

The venous system is the reverse branch of the blood flow. Through it there is a movement to the heart. Here, the pressure in the vessels is minimal, fluid accumulates, and as a result, the venous walls are stretched.

The systems have check valves that exclude the reverse movement of blood. Veins contain great amount bacteria in inflammation. Therefore, congestion in the vessels is the cause inflammatory processes In most cases.

Small veins drain blood from the skin, joints, and muscles. They merge into larger vessels passing through the whole body - this is the upper and the First collects small veins from the head, cervical region, upper limbs. The second connects to the leg area, the internal digestive organs, and the hip area.

After passing through the heart, the blood returns to the pulmonary artery, where it is again saturated with oxygen and carbon dioxide is released here. In this area, oxygen particles are completely absent. This is the only depleted part of the circulatory system.

Principle of blood circulation

There is less pressure in the veins. If blood pumps the heart in the arteries, then the outflow venous blood occurs due to muscle contraction. If this does not happen, the veins are stretched. Accumulated blood contains carbon dioxide, and it poses a threat to the health of the whole organism.

Veins have valves. To overcome them, the blood requires an effort from the outside, and the heart often cannot cope with this. The photo clearly shows how this happens. Due to this, the blood cannot flow back.

Orthopedic stockings help compress the veins. But this is only useful when the person is moving. With a sedentary lifestyle, stockings speed up the work of the heart. He needs more effort to push the blood through the artificially created additional pressure.

It is better to wear orthopedic stockings for walking, running, physical education until the muscles themselves can put pressure on the vessels. Another negative factor that impedes the movement of blood through the vessels is gravity. When a person is standing, the load is maximum due to body weight and hydrostatic pressure. In the supine position, tissue tension is reduced. Therefore, before putting on orthopedic stockings, it is recommended to raise your legs up for a few minutes, allowing the veins to free up as much as possible.

Blood flows through the arteries easier and faster, without stretching the walls of the vessels. Therefore, they are less visible under the tissues of the skin. Diseases of the venous system are manifested externally due to the dark color of the blood. This becomes especially noticeable when the vessels are on the surface of the skin.

Purpose

The venous system serves to store blood and return depleted volumes to the heart and lungs. However, its functions do not end there. Vessels carry nutrients to the tissues, perform the functions of blood circulation, a lot importance has tissue saturation with carbon dioxide.

The outflow of blood through the veins of each person is different and depends on the conditions of existence, as well as the individual characteristics of the body: gender, lifestyle, nutrition, hereditary diseases venous system. Also, chronic inflammatory processes in the internal organs, infections, deviations in immune system. The reverse vessels remove decay products from the following cells:

• tumor;
• inflammatory;
• fatty;
• leukocyte.

The venous system of the lower extremities is more often affected. If there is a predisposition to vascular disease, then such people should take precautions. Otherwise, by adulthood, even athletes swell the veins on their legs.

The venous system transports blood from the organs: stomach, kidneys, intestines. Stagnation in the vessels affects the digestibility of food. Useful substances should be carried to all parts of the body. With a saturated-fat diet, thrombosis is formed, which we observe on the surface of the skin.

Structure

The venous-vascular system experiences tissue pressure from blood circulation, it has several layers:

1. Collagen: Tissues resist the internal pressure of blood flow.
2. Muscle protection tissues: muscle contraction and stretching helps blood flow and at the same time protects blood vessels from external influences (temperature, pressure, mechanical damage).
3. Longitudinal fibers have elasticity, they work constantly when the body moves: flexion and extension of the torso, arms or legs, with head tilts.

When the veins are stretched, the outflow is difficult, but when the muscles contract, there is additional force to push the blood. The speed of movement through the vessels is higher due to a set of the following factors: heartbeat, movement of the chest during breathing, flexion of the limbs, changes in body position in space, blood thinning due to digestion or the action of drugs. Also, blood flow increases due to an increase in the temperature surrounding the body: in a bath, a hot bath.

The main veins have a significant diameter. The movement of fluid inside the vessels occurs in a certain direction due to the presence of numerous valves. They consist of fabrics of increased elasticity and strength. Withstand a huge number of compression cycles throughout a person's life.

The venous system cannot function effectively without valves. During their weakening, they may form pathological conditions called varicose veins. The most common place of its occurrence is the lower limbs.

Deviations in the state of health

The venous system of the lower extremities is vulnerable due to high loads while walking, running, and even in a normal position - a standing position. Diseases of the venous system appear for many reasons, not only physical. This refers to, for example, malnutrition. Excessive consumption of fried, salty, sweet leads to the formation of plaques in the blood, sticking into huge clots. Thrombosis is dangerous for any person.

First, blockages occur in small veins. But growing, clots can get into the leading to the heart. Severe cases of illness lead to its stop. Blood clots should be removed in a timely manner - this is how a dangerous complication is prevented.

The most common is varicose veins. More than half of the female population suffers from this disease. With age, the elasticity of the veins decreases, but the load remains the same. Often excess weight leads to the formation of stretched walls of blood vessels. The size of the heart does not change, and the volume of blood transfer increases with the acquisition of additional kilograms.

An additional negative factor is a fixed lifestyle. Stagnation of blood provokes not only the appearance of vascular diseases, but also complications in other parts of the body. Oxygen starvation affects appearance skin face, hands, neck.

Types of complications

And thrombosis of the legs becomes a disturbed venous system. The anatomy of the body is arranged in such a way that with a passive lifestyle, the weakening of the walls of blood vessels is inevitable. Similar deviations in health occur with inadequate and malnutrition, the presence of bad habits, professional stress.

Among the many diseases of the circulatory system are:

• Thrombophlebitis is an inflammatory process on the walls of the veins, which subsequently closes the entire vessel. Thrombi are dangerous during the period when they break away from the vessel and begin to wander through the circulatory system. A blood clot can get into almost any part of the body, causing a serious condition. This is possible when small lumps move to the region of the heart or head.
• Varicose veins are an outwardly unpleasant change in the venous channels. This is due to the thinning of the walls of the veins, the loss of their plasticity. The vessel increases its capacity, where dark blood accumulates. It is easy to see through the skin of a sick person. The affected areas take chaotic forms. The degree of pathology depends on the characteristics of the organism.
• Atherosclerosis of the veins - occurs due to a violation of lipid metabolism. Atherosclerotic plaques form in the lumen of the veins, making it difficult for the normal outflow of blood. Advanced stages of the disease in the main veins may result in the loss of part of the limb. Signs of complications are leg fatigue when walking, lameness.
• Telangiectasia - describes the condition of the expansion of small veins, due to this, stars appear on the skin. This process is lengthy: health deviations often take several years to form.

Disease provocateurs

For women, high heels and a passive lifestyle have always been negative factors in the formation of problems with blood vessels. Stagnation in the legs appeared due to swelling that appears as a result of a long position in a standing position. Compressed veins restrict blood flow and reduce the ability to exchange oxygen and nutrients.

Almost all pathologies arise due to the appearance of provoking factors:

• Blood clots and weakening of vascular tissues occur due to smoking. Smoke deprives the blood of oxygen and saturates with toxins.
• Elevated blood cholesterol is more often formed as a result of malnutrition of saturated fat foods.
• Hypertension, diabetes mellitus contribute to the expansion of veins.
• Overweight.
• Addiction to alcoholic beverages.
• The hereditary factor is the main source of problems with the vessels of the legs. The presence of hemorrhoids in parents indicates the risk of varicose veins in children.
• A sedentary lifestyle, combined with the above factors, accelerates the formation of diseases.
• Excessive physical activity or performance of the same type of work.

To exclude problems with blood vessels, it is required to conduct a periodic examination of the circulatory system and engage in health: a full and balanced diet, moderate physical exercise, respect for the feet.

Diagnostic methods

The venous system of the legs can be checked by the following methods:

• Doppler study - recommended for hidden symptoms, problems with the veins. It is carried out at the initial suspicion of pathology. If there is no doubt that varicose veins or thrombosis has formed, then this method becomes optional.
• Ultrasound duplex examination - combines the capabilities of ultrasound and Doppler scanning methods. The resulting indicators allow you to evaluate the speed of their geometry, the quality of the walls and the overall operation of the venous system.
• Angiography is an X-ray examination using contrast. The condition of the vessels is assessed.

Problems with the lower sections can be detected by the primary symptoms:

• Detection of a network of vessels on the legs, a blood clot or external defects in the veins.
• Fatigue and pain in the legs in the muscular or vascular part. Periodic swelling, inflammation.
• External defects formed asymptomatically.
• Expansion of the veins, distortion of the shape of the vessels, swelling of the ducts.
• Pain with fatigue in the popliteal area or other part in the region of the venous ducts.
• Cramps, aches, pinching.

Based on the results of the examination, an effective course of individual treatment is prescribed, and measures are taken to prevent pathologies. Pathological venous lymphatic system may not bother a person throughout life. But the disease will definitely manifest itself at an older age.

Development of pathologies

The weakened venous system of the extremities goes through several stages of varicose veins. Scientists divide the disease into 6 stages according to the degree of danger: from unfavorable to resuscitation. Severe stages are already treated surgically.

Let's determine the well-being of a person at each stage of the disease:

• Zero passes imperceptibly outwardly, but the state of the legs is already beginning to bother. There is a burning sensation of the upper layers of the skin of the muscles. Puffiness is often formed, fatigue from walking is evident.
• First stage. A grid of small vessels, asterisks and the conditions listed above are visible.
• Second. Swollen veins and dark-colored nodules are palpable. The size of the pathology area changes during the day. With a fixed lifestyle, the affected areas hurt and ache.
• Third. To the listed conditions are added evening and night puffiness.
• Fourth. The top layer of the skin is damaged. There are dimples, tubercles of impressive size. Often formed trophic ulcers.
• Fifth stage. Residual effects after trophic ulcers are visible to the naked eye.
• Sixth. Trophic ulcers are intractable and practically do not heal.

Based on the established stage of the disease, doctors decide on the choice of treatment method. The last, 6th (complicated) form of varicose veins ends on the operating table. There may be external defects that require intervention plastic surgery. Disability, deprivation of a limb becomes a severe outcome.

How are vascular problems treated?

The venous circulatory system affects all areas of the body. Vascular diseases should be treated immediately. To exclude the formation of complicated stages of varicose veins or thrombosis, preventive measures are used. Dilated veins try to remove partially or completely. Thrombi are often excised to prevent accidental entry into the blood stream.

Common methods of treating veins help to exclude further growth of the vessel, remove pathological areas, and reduce the risk of complications. Sclerotherapy is used in beauty salons and clinics. The procedure is safe and takes only a few minutes. A substance is injected into the affected vessel that glues the walls together.

The body gets rid of the glued vein on its own. It dissolves, in its place clarified tissues form. There are no external defects. The procedure can be performed without anesthesia. This method is tried to be applied on small veins. Abundant bluish areas appear on large vessels.

The laser coagulation method is chosen when the affected veins are large. The procedure is painful and requires local anesthesia. After that, a light guide is introduced into the affected vessel, the radiation of which brews the liquid contents of the vein. Subject to the recommendations of the doctor after the operation, the resulting area resolves.

(Latin vena, Greek phlebs; hence phlebitis - inflammation of the veins) carry blood in the opposite direction to the arteries, from the organs to the heart. Their walls are arranged according to the same plan as the walls of the arteries, but they are much thinner and have less elastic and muscle tissue, due to which the empty veins collapse, while the lumen of the arteries gapes in the cross section; veins, merging with each other, form large venous trunks - veins that flow into the heart. The veins anastomose widely with each other, forming venous plexuses.

The movement of blood through the veins is carried out due to the activity and suction action of the heart and chest cavity, in which negative pressure is created during inspiration due to the pressure difference in the cavities, as well as due to the contraction of the skeletal and visceral muscles of the organs and other factors. The contraction of the muscular membrane of the veins is also important, which is more developed in the veins of the lower half of the body, where the conditions for venous outflow are more difficult, than in the veins of the upper body.

The reverse flow of venous blood is prevented by special devices of the veins - valves, which make up the features of the venous wall. The venous valves are composed of a fold of endothelium containing a layer of connective tissue. They face the free edge towards the heart and therefore do not interfere with the flow of blood in this direction, but keep it from returning back. Arteries and veins usually go together, with small and medium-sized arteries accompanied by two veins, and large ones by one. From this rule, except for some deep veins, the main exception is the superficial veins, which run in the subcutaneous tissue and almost never accompany the arteries.

The walls of blood vessels have their own racing arteries and veins, vasa vasorum. They depart either from the same trunk, the wall of which is supplied with blood, or from the neighboring one and pass in the connective tissue layer surrounding the blood vessels and more or less closely associated with their outer shell; this layer is called the vascular vagina, vagina vasorum. Numerous nerve endings (receptors and effectors) associated with the central nervous system are laid in the wall of arteries and veins, due to which the nervous regulation of blood circulation is carried out by the mechanism of reflexes. Blood vessels are extensive reflexogenic zones that play an important role in the neurohumoral regulation of metabolism.

According to function and structure various departments and features of innervation, all blood vessels have recently been divided into 3 groups:

1. cardiac vessels that begin and end both circles of blood circulation - the aorta and pulmonary trunk (i.e., elastic-type arteries), hollow and pulmonary veins;
2. main vessels that serve to distribute blood throughout the body. These are large and medium extraorganic arteries of the muscular type and extraorganic veins;
3. organ vessels that provide exchange reactions between the blood and the parenchyma of organs. These are intraorgan arteries and veins, as well as links of the microcirculatory bed.

Vein development. At the beginning of placental circulation, when the heart is located in the cervical region and is not yet divided by partitions into venous and arterial halves, the venous system has a relatively simple device. Large veins run along the body of the embryo: in the head and neck area - the anterior cardinal veins (right and left) and in the rest of the body - the right and left posterior cardinal veins. Approaching the venous sinus of the heart, the anterior and posterior cardinal veins on each side merge, forming the common cardinal veins (right and left), which, having at first a strictly transverse course, flow into the venous sinus of the heart. Along with the paired cardinal veins, there is another unpaired venous trunk - the primary vena cava inferior, which also flows into the venous sinus in the form of an insignificant vessel.

Thus, at this stage of development, three venous trunks flow into the heart: the paired common cardinal veins and the unpaired primary inferior vena cava. Further changes in the location of the venous trunks are associated with the displacement of the heart from the cervical region down and the division of its venous part into the right and left atria. Due to the fact that after the division of the heart, both common cardinal veins turn out to flow into the right atrium, the blood flow in the right common cardinal vein is in more favorable conditions. In this regard, an anastomosis appears between the right and left anterior cardinal veins, through which blood flows from the head into the right common cardinal vein. As a result, the left common cardinal vein ceases to function, its walls collapse and it is obliterated, with the exception of a small part, which becomes the coronary sinus of the heart, sinus coronarius cordis. The anastomosis between the anterior cardinal veins gradually increases, turning into the vena brachiocephalica sinistra, and the left anterior cardinal vein below the anastomotic outlet is obliterated. Two vessels form from the right anterior cardinal vein: the part of the vein above the confluence of the anastomosis turns into vena brachiocephalica dextra, and the part below it, together with the right common cardinal vein, turns into the superior vena cava, thus collecting blood from the entire cranial half of the body. With underdevelopment of the described anastomosis, an anomaly of development in the form of two superior vena cava is possible.

The formation of the inferior vena cava is associated with the appearance of anastomoses between the posterior cardinal veins. One anastomosis, located in the iliac region, diverts blood from the left lower limb to the right posterior cardinal vein; as a result, the segment of the left posterior cardinal vein, located above the anastomosis, is reduced, and the anastomosis itself turns into the left common iliac vein. The right posterior cardinal vein in the area before the confluence of the anastomosis (which has become the left common iliac vein) is transformed into the right common iliac vein, and from the confluence of both iliac veins to the confluence of the renal veins, it develops into the secondary inferior vena cava. The rest of the secondary inferior vena cava is formed from the unpaired primary inferior vena cava that flows into the heart, which connects to the right inferior cardinal vein at the confluence of the renal veins (there is a 2nd anastomosis between the cardinal veins, which drains blood from the left kidney).

Thus, the finally formed inferior vena cava is composed of 2 parts: from the right posterior cardinal vein (before the confluence of the renal veins) and from the primary inferior vena cava (after its confluence). Since blood is drained to the heart from the entire caudal half of the body through the inferior vena cava, the value of the posterior cardinal veins weakens, they lag behind in development and turn into v. azygos (right posterior cardinal vein) and in v. hemiazygos and v. hemiazygos accessoria (left posterior cardinal vein). v. hemiazygos flows into v. azygos through the 3rd anastomosis developing in the thoracic region between the former posterior cardinal veins.

The portal vein is formed in connection with the transformation of the yolk veins, through which blood from the yolk sac comes to the liver. vv. omphalomesentericae in the space from the confluence of the mesenteric vein into them to the gates of the liver turn into the portal vein. With the formation of placental circulation, the emerging umbilical veins enter into direct communication with the portal vein, namely: the left umbilical vein opens into the left branch of the portal vein and thus carries blood from the placenta to the liver, and the right umbilical vein is obliterated. Part of the blood, however, goes, in addition to the liver, through the anastomosis between the left branch of the portal vein and the final segment of the right hepatic vein. This previously formed anastomosis, along with the growth of the embryo, and consequently, the increase in blood passing through the umbilical vein, expands significantly and turns into a ductus venosus. After birth, it is obliterated in lig. venosum.

Which doctors to contact for a vein examination:

Phlebologist

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.

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 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 .

The structure of the veins

Features of the structure of the veins, their difference from the arteries due to the difference in their functions.

Conditions for the movement of blood through the venous system are completely different than in the arteries. In the capillary network, the pressure drops to 10 mm Hg. Art., exhausting almost completely the force of the cardiac impulse in the arterial system. Movement through the veins is due to two factors: the suction action of the heart and the pressure of more and more portions of blood entering the venous system. Hence, the pressure and speed of blood flow in the venous vessels is immeasurably lower than the arterial one. A much smaller volume of blood passes through the veins per unit time, which requires a much larger capacity from the entire venous system, thus causing a morphological difference in the structure of the veins. The venous system is also distinguished by the fact that the blood in it moves against gravity in parts of the body located below the level of the heart. Therefore, for the implementation of normal blood circulation, the walls of the veins must be adapted to hydrostatic pressure, which affects histological structure veins.

The increased capacity of the venous bed is provided by a significantly larger diameter of the venous branches and trunks - usually one artery on the limbs is accompanied by two to three veins. The capacity of the veins of the great circle is twice the capacity of its arteries. The conditions of the function of the venous system create the possibility of stagnation of blood and even its reverse flow. The possibility of centripetal movement of blood through the venous vessels is ensured by the presence of numerous valves of collaterals and anastomoses. In addition, the suction action of the chest and the movement of the diaphragm contribute to the movement of blood; muscle contractions favorably affect the emptying of the deep veins of the extremities.

The unloading function in the venous system is also possessed by numerous communications, extensive venous plexuses, especially strongly developed in the small pelvis, on the back of the hand. These collaterals allow blood to flow from one system to another.

The number of communications between the superficial and deep veins on the upper limb is calculated from 31 to 169, on the lower - from 53 to 112 with a diameter of 0.01 to 2 mm. There are direct anastomoses, directly connecting two venous trunks, and indirect, connecting separate branches of different trunks.

Venous valves

An exceptional role in the structure of the veins is played by valves, which are parietal folds of the intima of the veins. The basis of the valves is collagen tissue lined with endothelium. At the base of the valves are networks of elastic fibers. The pocket valves are always open towards the heart, so they do not interfere with blood flow. The wall of the vein involved in the formation of the pocket, at its location, forms a bulge - a sinus. Valves are available in one, two or three sails. The smallest caliber of venous vessels with valves is 0.5 mm. The localization of the valves is due to hemodynamic and hydrostatic conditions; valves withstand a pressure of 2-3 atm., the higher the pressure, the tighter they close. The valves are mainly located in those veins that are subject to maximum external influence - the veins of the subcutaneous tissue and muscles - and where the flow of blood is hindered by hydrostatic pressure, which is observed in the venous vessels located below the level of the heart, in which blood moves against gravity. Valves are also located in large numbers in those veins where the flow of blood is easily blocked mechanically. This is observed especially often in the veins of the extremities, and there are more valves in the deep veins than in the superficial ones.

The valve system, in their normal state, contributes to the forward movement of blood towards the heart. In addition, the valve system protects the capillaries from hydrostatic pressure. Valves also exist in venous anastomoses. Of exceptionally great practical importance are the valves located between the superficial and deep veins of the lower extremities, open towards the deep venous vessels. However, a number of valveless communications allow reverse blood flow: from deep veins to superficial ones. On the upper limbs, less than half of the communications are equipped with valves, therefore, during intense muscular work, part of the blood can pass from deep venous vessels to superficial ones.

The structure of the walls of the venous vessels reflects the features of the function of the venous system; the walls of venous vessels are thinner and more elastic than arterial ones. Extremely filled veins do not take a rounded shape, which also depends on low pressure blood, which in the peripheral parts of the system is not more than 10 mm Hg. Art., at the level of the heart - 3-6 mm Hg. Art. In the large central veins, the pressure becomes negative due to the suction action of the chest. The veins are deprived of the active hemodynamic function that the powerful muscular walls of the arteries possess; the weaker musculature of the veins only counteracts the influence of hydrostatic pressure. In the venous vessels located above the heart, the muscular system is much less developed than in the venous vessels below this level. In addition to the pressure factor, their histological structure, determine the caliber and location of the veins.

The wall of the venous vessels has three layers. The structure of the veins has a powerful collagen skeleton, which is especially well developed in the adventitia and consists of longitudinal collagen bundles. The muscles of the veins rarely form a continuous layer, located in all elements of the wall in the form of bundles. The latter have a longitudinal direction in the intima and adventitia; the middle layer is characterized by their circular or spiral direction.

Of the large veins, the superior vena cava is completely devoid of muscles; the lower hollow has a powerful layer of muscles in the outer shell, but does not contain them in the middle one. The popliteal, femoral, and iliac veins contain muscles in all three layers. V. saphena magna has longitudinal and spiral muscle bundles. The collagen base laid in the structure of the veins is penetrated by elastic tissue, which also forms a single skeleton for all three layers of the wall. However, the elastic skeleton, which is also associated with the muscular one, is less developed in the veins than the collagen one, especially in the adventitia. Membrana elastica interna is also weakly expressed. Elastic fibers, like muscle fibers, have a longitudinal direction in the adventitia and intima, and a circular direction in the middle layer. The structure of the vein is stronger than the arteries for breaking, which is associated with the special strength of their collagen skeleton.

The intima in all veins contains the subendothelial cambial layer. Venules differ from arterioles in the annular direction of elastic fibers. Postcapillary venules differ from precapillaries in their large diameter and the presence of circular elastic elements.

The blood supply to the walls of the veins is carried out due to the arterial vessels located in their immediate vicinity. The arteries feeding the walls form numerous transverse anastomoses between themselves in the periadventitial tissue. From this arterial network, branches extend into the wall and at the same time supply the subcutaneous tissue and nerves. Arterial paravenous tracts can play the role of roundabout ways of blood circulation.

The innervation of the veins of the extremities is carried out similarly to the arterial branches of the adjacent nerves. In the structure of the veins, a rich nervous apparatus was found, consisting of receptor and motor nerve fibers.

The structure of arteries, veins and capillaries;

general characteristics vascular system

BIG AND SMALL CIRCULATIONS. A HEART.

THE CARDIOVASCULAR SYSTEM. ARTERIES. VIENNA. CAPILLARIES.

1. Offer type (BSP).

2. Number of predicative parts.

3. According to the purpose of the statement.

4. By emotional coloring.

5. The main means of communication of predicative parts.

6. Grammatical meaning.

7. Homogeneous or heterogeneous composition, open or closed structure.

8. Additional means of connecting predicative parts and expressions

a) order of parts (fixed/unfixed);

b) structural parallelism of parts;

c) the ratio of aspectual-temporal forms of verbs-predicates;

d) lexical indicators of connection (synonyms, antonyms, words of one lexico-semantic or thematic group);

e) incompleteness of one of the parts;

f) anaphoric or cataphoric words;

g) a common minor member or a common subordinate clause.

1. Transport- all the necessary substances (proteins, carbohydrates, oxygen, vitamins, mineral salts) are delivered to the tissues and organs through the blood vessels, and metabolic products and carbon dioxide are removed.

2. Regulatory - with the blood flow through the vessels, hormonal substances, which are specific regulators of metabolic processes, are carried to the organs and tissues produced by the endocrine glands.

3. Protective - antibodies are carried with the blood stream, which are necessary for the body's defense reactions against infectious diseases.

In collaboration with the nervous and humoral systems, the vascular system plays an important role in ensuring the integrity of the body.

Vascular system divided by circulatory and lymphatic. These systems are anatomically and functionally closely related, complement each other, but there are certain differences between them.

A branch of systemic anatomy that studies the structure of the blood and lymphatic vessels, is called angiology.

Arteries are vessels that carry blood from the heart to organs and tissues.

Veins are blood vessels that carry blood from organs to the heart .

The arterial and venous parts of the vascular system are interconnected capillaries, through the walls of which there is an exchange of substances between blood and tissues.

- parietal (parietal) - nourish the walls of the body;

- visceral (intraorgan)- arteries internal organs.

There are connections between the branches of the arteries - arterial anastomoses.

Arteries that provide roundabout blood flow, bypassing the main path, are called collateral. Allocate intersystem and intrasystemic anastomoses. Intersystem form connections between branches of different arteries, intrasystem between branches of the same artery. Of particular importance is the presence of such a compensatory mechanism of blood circulation in case of occlusion of the main vessel, for example, by a thrombus or progressively increasing in size atherosclerotic plaque.

Intraorganic vessels are successively divided into arteries of the 1st-5th order, forming microvasculature. It is formed from arterioles, precapillary arteriole(precapillaries), capillaries, postcapillary venules(postcapillaries) and venule. From the intraorgan vessels, blood enters the arterioles, which form rich circulatory networks in the tissues of the organs. Then the arterioles pass into thinner vessels - precapillaries, the diameter of which is 40-50 microns, and the latter - into smaller - capillaries with a diameter of 6 to 30-40 microns and a wall thickness of 1 microns. The narrowest capillaries are located in the lungs, brain, and smooth muscles, while the wide ones are located in the glands. The widest capillaries (sinuses) are observed in the liver, spleen, bone marrow and lacunae of the cavernous bodies of the lobar organs.

AT capillaries blood flows at a low speed (0.5-1.0 mm/s), has low pressure (up to 10-15 mm Hg). This is due to the fact that the most intensive exchange of substances between blood and tissues occurs in the walls of capillaries. Capillaries are found in all organs, except for the epithelium of the skin and serous membranes, tooth enamel and dentin, cartilage tissue, cornea, heart valves, etc. Connecting with each other, the capillaries form capillary networks, the features of which depend on the structure and function of the organ.

After passing through the capillaries, the blood enters the postcapillary venules, and then into the venules, the diameter of which is 30-40 microns. From the venules, the formation of intraorganic veins of the 1st-5th order begins, which then flow into the extraorganic veins.

In the circulatory system, there is also a direct transition of blood from arterioles to venules - arteriolo-venular anastomoses. The total capacity of venous vessels is 3-4 times greater than that of arteries. This is due to pressure and low blood velocity in the veins, compensated by the volume of the venous bed.

Veins are the depot for venous blood. The venous system contains about 2/3 of the body's blood. Extraorganic venous vessels, connecting with each other, form the largest venous vessels of the human body - the superior and inferior vena cava, which enter the right atrium.

Arteries differ in structure and function from veins. Thus, the walls of the arteries resist blood pressure, are more elastic and extensible, and pulsate. Thanks to these qualities, the rhythmic flow of blood becomes continuous. Depending on the diameter of the artery are divided into large, medium and small. The arteries are filled with scarlet blood, which spurts when an artery is damaged.

The wall of the arteries has 3 shells: .

Inner shell - intima formed by the endothelium, basement membrane and subendothelial layer. Middle shell - media It consists mainly of smooth muscle cells of a circular (spiral) direction, as well as of collagen and elastic fibers. outer shell - adventitia It is built from loose connective tissue, which contains collagen and elastic fibers and performs protective, insulating and fixing functions, has blood vessels and nerves. The inner shell does not have its own vessels, it receives nutrients directly from the blood.

Depending on the ratio of tissue elements in the wall of the artery, they are divided into elastic, muscular and mixed types. to elastic type include the aorta and pulmonary trunk. These vessels can be greatly stretched during the contraction of the heart. Muscular type arteries are located in organs that change their volume (intestines, bladder, uterus, arteries of the extremities). To mixed type(muscular-elastic) include carotid, subclavian, femoral and other arteries. As the distance from the heart in the arteries decreases, the number of elastic elements and the number of muscle increases, the ability to change the lumen increases. Therefore, small arteries and arterioles are the main regulators of blood flow in organs.

The wall of the capillaries is thin, the inner layer is endothelium consists of a single layer of endothelial cells located on the basement membrane. Capillaries have a porous structure, due to which they are capable of all types of exchange.

The wall of the veins has 3 shells: internal (intima), middle (media) and external (adventitia). The wall of the veins is thinner than the arteries, and they are filled with dark red blood, which, if the vessel is damaged, flows smoothly, without jerks.

The lumen of the veins is slightly larger than that of the arteries. The inner layer is lined with a layer of endothelial cells, the middle layer is relatively thin and contains few muscle and elastic elements, so the veins collapse on the cut. The outer layer is represented by a well-developed connective tissue membrane. Along the entire length of the veins are valves in pairs that prevent the reverse flow of blood. valves- these are the semilunar folds of the inner lining of the venous vessel, which are usually located in pairs, they pass blood towards the heart and prevent its reverse flow. There are more valves in the superficial veins than in the deep ones, in the veins of the lower extremities than in the veins of the upper extremities. The blood pressure in the veins is low, there is no pulsation.

Depending on the topography and position in the body and organs, the veins are divided into superficial and deep. On the extremities, deep veins accompany the arteries of the same name in pairs. The name of the deep veins is similar to the name of the arteries to which they adjoin (brachial artery - brachial vein, etc.). Superficial veins connected to deep penetrating veins that act as anastomoses. Often adjacent veins, having joined together by numerous anastomoses, form venous plexuses on the surface or in the walls of a number of internal organs (bladder, rectum).

The movement of blood through the veins is facilitated by:

Contraction of the muscles adjacent to the neurovascular bundle (the so-called peripheral venous hearts);

Suction action of the chest and chambers of the heart;

Pulsation of an artery adjacent to a vein.

In the walls of the vessels there are nerve fibers associated with receptors that perceive changes in the composition of the blood and the vessel wall. There are especially many receptors in the aorta, carotid sinus, and pulmonary trunk.

The regulation of blood circulation both in the body as a whole and in individual organs, depending on their functional state, is carried out by the nervous and endocrine systems.

How are veins different from arteries

Human arteries and veins perform different jobs in the body. In this regard, significant differences in the morphology and conditions of blood passage can be observed, although general structure, with rare exceptions, all vessels have the same. Their walls have three layers: inner, middle, outer.

The inner shell, called intima, without fail has 2 layers:

• the endothelium lining the inner surface is a layer of squamous epithelial cells;
• subendothelium - located under the endothelium, consists of connective tissue with a loose structure.

The middle shell is made up of myocytes, elastic and collagen fibers.

The outer shell, called "adventitia", is a fibrous connective tissue with a loose structure, equipped with vascular vessels, nerves, and lymphatic vessels.

arteries

These are blood vessels that carry blood from the heart to all organs and tissues. There are arterioles and arteries (small, medium, large). Their walls have three layers: intima, media and adventitia. Arteries are classified according to several criteria.

According to the structure of the middle layer, three types of arteries are distinguished:

• Elastic. Their middle layer of the wall consists of elastic fibers that can withstand the high blood pressure that develops when it is ejected. This species includes the pulmonary trunk and aorta.
• Mixed (muscular-elastic). The middle layer consists of a variable number of myocytes and elastic fibers. These include carotid, subclavian, iliac.
• Muscular. Their middle layer is represented by individual myocytes located circularly.

By location relative to the organs of the artery are divided into three types:

• Trunk - supply blood to parts of the body.
• Organ - carry blood to the organs.
• Intraorganic - have branches inside the organs.

They are non-muscular and muscular.

The walls of non-muscular veins consist of endothelium and loose connective tissue. Such vessels are in bone tissue, placenta, brain, retina, spleen.

Muscular veins, in turn, are divided into three types, depending on how myocytes are developed:

• poorly developed (neck, face, upper body);
• medium (brachial and small veins);
• strongly (lower body and legs).

The structure and its features:

• Larger in diameter than arteries.
• Poorly developed subendothelial layer and elastic component.
• The walls are thin and fall off easily.
• The smooth muscle elements of the middle layer are rather poorly developed.
• Pronounced outer layer.
• The presence of a valvular apparatus, which is formed by the inner layer of the vein wall. The base of the valves consists of smooth myocytes, inside the valves - fibrous connective tissue, outside they are covered with a layer of endothelium.
• All shells of the wall are endowed with vascular vessels.

The balance between venous and arterial blood is ensured by several factors:

• a large number of veins;
• their larger caliber;
• dense network of veins;
• formation of venous plexuses.

Differences

How are arteries different from veins? These blood vessels have significant differences in many ways.

Arteries and veins, first of all, differ in the structure of the wall

According to the structure of the wall

Arteries have thick walls and are full of elastic fibers. smooth muscle well developed, they do not fall off unless filled with blood. Due to the contractility of the tissues that make up their walls, oxygenated blood is quickly delivered to all organs. The cells that make up the layers of the walls ensure the unhindered passage of blood through the arteries. Their inner surface is corrugated. The arteries must withstand the high pressure that is created by the powerful ejections of blood.

The pressure in the veins is low, so the walls are thinner. They fall off in the absence of blood in them. Them muscle layer unable to contract like the arteries. The surface inside the vessel is smooth. Blood moves slowly through them.

In veins, the thickest shell is considered to be the outer, in the arteries - the middle one. Veins do not have elastic membranes; arteries have internal and external.

By shape

Arteries have a fairly regular cylindrical shape, they are round in cross section.

Due to the pressure of other organs, the veins are flattened, their shape is tortuous, they either narrow or expand, which is associated with the location of the valves.

In count

There are more veins in the human body, fewer arteries. Most medium arteries are accompanied by a pair of veins.

By the presence of valves

Most veins have valves that prevent blood from flowing backwards. They are located in pairs opposite each other throughout the vessel. They are not found in the portal caval, brachiocephalic, iliac veins, as well as in the veins of the heart, brain and red bone marrow.

In the arteries, valves are located at the exit of the vessels from the heart.

By blood volume

The veins circulate about twice as much blood as the arteries.

By location

Arteries lie deep in the tissues and approach the skin only in a few places where the pulse is heard: on the temples, neck, wrist, and instep. Their location is about the same for all people.

The veins are mostly located close to the surface of the skin.

The location of the veins may vary from person to person.

To ensure the movement of blood

In the arteries, blood flows under the pressure of the force of the heart, which pushes it out. At first, the speed is about 40 m/s, then it gradually decreases.

Blood flow in the veins occurs due to several factors:

• pressure force, depending on the impulse of blood from the heart muscle and arteries;
• the suction force of the heart during relaxation between contractions, that is, the creation of negative pressure in the veins due to the expansion of the atria;
• suction action on the chest veins of respiratory movements;
• contraction of the muscles of the legs and arms.

In addition, about a third of the blood is in the venous depots (in the portal vein, spleen, skin, walls of the stomach and intestines). It is pushed out from there if it is necessary to increase the volume of circulating blood, for example, with massive bleeding, with high physical exertion.

By color and composition of blood

Arteries carry blood from the heart to the organs. It is enriched with oxygen and has a scarlet color.

Arterial and venous bleeding have different symptoms. In the first case, the blood is ejected in a fountain, in the second, it flows in a jet. Arterial - more intense and dangerous for humans.

Thus, the main differences can be identified:

• Arteries transport blood from the heart to the organs, veins carry it back to the heart. Arterial blood carries oxygen, venous blood returns carbon dioxide.
• Arterial walls are more elastic and thicker than venous ones. In the arteries, blood is pushed out with force and moves under pressure, in the veins it flows calmly, while valves do not allow it to move in the opposite direction.
• There are 2 times less arteries than veins, and they are deep. Veins are located in most cases superficially, their network is wider.

Veins, unlike arteries, are used in medicine to obtain material for analysis and for administration. medicines and other fluids directly into the bloodstream.

43. Arteries and veins. The principle of the structure and tissue composition of the walls of blood vessels. Classification. The structure of venous valves.

Elastic type arteries due to the large number of elastic fibers and membranes, they are able to stretch during systole of the heart and return to their original position during diastole. In such arteries, blood flows under high pressure (mm Hg) and at high speed (0.5-1.3 m/s). As an example of an elastic artery, consider the structure of the aorta.

Rice. 1. Elastic type artery - rabbit aorta. Stained with orcein. Lens 4.

Internal the aortic membrane consists of the following elements:

2) subendothelial layer,

3) plexus of elastic fibers.

The endothelium consists of large (sometimes up to 500 microns in length and 150 microns in width) flat, single-nuclear, less often multi-nuclear, polygonal cells located on the basement membrane. In endothelial cells, the endoplasmic reticulum is poorly developed, but there are many mitochondria, microfilaments, and pinocytic vesicles.

The subendothelial layer is well developed (15-20% of the wall thickness). It is formed by loose fibrous unformed connective tissue, which contains thin collagen and elastic fibers, a lot of amorphous substance and poorly differentiated cells such as smooth muscle fibroblasts, macrophages. The main amorphous substance of the subendothelial layer, rich in glycosaminoglycans and phospholipids, plays an important role in the trophism of the vessel wall. The physicochemical state of this substance determines the degree of permeability of the vascular wall. With age, it accumulates cholesterol and fatty acids. This layer lacks its own vessels (vasa vasorum).

The plexus of elastic fibers consists of two layers:

Medium the aortic membrane consists of elastic fenestrated membranes, which are interconnected by elastic fibers and form, together with the elastic elements of other membranes, a single elastic frame. Between the membranes are smooth myocytes, fibroblasts, vascular vessels, and nerve elements. A large number of elastic elements in the aortic wall softens the tremors of blood ejected into the vessel during contraction of the left ventricle of the heart, and maintains the tone of the vascular wall during diastole.

outdoor the aortic membrane is formed by loose fibrous connective tissue with a large number of thick collagen and elastic fibers, located mainly in the longitudinal direction. This shell also contains feeding vessels, nerve elements and fat cells.

Muscular type arteries

Inner shell contains

1) endothelium with basement membrane,

2) subendothelial layer, consisting of thin elastic and collagen fibers and unspecialized cells,

3) the internal elastic membrane, which is aggregated elastic fibers. Sometimes the membrane can be double.

Middle shell consists predominantly of smooth myocytes arranged in a gentle spiral. Between them are connective tissue cells such as fibroblasts, collagen and elastic fibers. The spiral arrangement of smooth myocytes during their contraction ensures a decrease in the volume of the vessel and the pushing of blood into the distal sections. Elastic fibers at the border with the inner and outer shells merge with their elastic elements. Due to this, a single elastic frame of the vessel is created, providing elasticity in tension and elasticity in compression, and prevents arteries from falling off.

At the border of the middle and outer shells, an outer elastic membrane can form.

outer shell It is formed by loose fibrous unformed connective tissue, in which the fibers are arranged obliquely and longitudinally. It should be noted that as the diameter of the arteries decreases, the thickness of all membranes decreases. The subendothelial layer and the inner elastic membrane of the inner shell become thinner, the number of smooth myocytes and elastic fibers in the middle decreases, and the outer elastic membrane disappears.

Mixed type arteries by structure and functional features occupy an intermediate position between the vessels of the elastic and muscular types.

Inner shell consists of endotheliocytes, sometimes binuclear, located on the basement membrane, subendothelial layer and internal elastic membrane.

Middle shell formed by an approximately equal number of spirally oriented smooth myocytes, elastic fibers and fenestrated membranes, a small number of fibroblasts and collagen fibers.

outer shell consists of two layers:

1) internal - contains bundles of smooth myocytes, connective tissue and microvessels;

2) external - formed by longitudinal and oblique bundles of collagen and elastic fibers, connective tissue cells, amorphous substance, vascular vessels, nerves and nerve plexuses.

The structure of the wall of the artery and vein

ARTERIES AND VEINS. MICROCIRCULATOR BED. LYMPHATIC VESSELS. A HEART.

Using lectures (presentations and the text of lectures are posted on the web-page of the department), textbooks, additional literature and other sources, students should prepare the following theoretical questions:

1. General plan of the structure of the wall of blood vessels.

2. Features of the structure of blood vessels depending on the hemodynamic conditions of functioning. The value of the structural elements of the vessel wall.

3. Classification and functional significance of different types of arteries.

4. The structure of arteries of muscular and mixed types. Examples.

5. The structure of the arteries of the elastic type. Aorta. Features of its middle shell.

6. Veins. General structural differences compared to arteries.

7. Characteristics of veins with weak development of muscle elements. valve structure.

8. Morphofunctional characteristics and significance of the microvasculature.

9. The structure of the wall of the blood capillary. Endothelium, its submicroscopic features, regeneration.

10. Types of hemocapillaries according to the structure of the endothelium and basement membrane, their localization.

11. Microscopic structure of the wall of arterioles and venules.

12. Classification and structure of arteriolo-venular anastomoses, their functions.

13. Lymphatic system and its significance. Features of the structure of lymphatic capillaries.

14. Sources of development of the heart.

15. General characteristics of the structure of the heart wall.

16. Micro- and submicroscopic structure of the endocardium and heart valves.

17. Genetic and structural unity of the endocardium and blood vessels.

18. Myocardium, micro- and ultrastructure of typical cardiomyocytes. Features of the structure and function of the heart muscle.

19. Conducting system of the heart. Morphofunctional characteristics of atypical myocytes.

20. The structure of the epicardium. Innervation, blood supply and age-related changes in the heart.

21. Modern ideas about the regeneration and transplantation of the heart.

The vascular system is a complex of branched tubes of different diameters that provide blood transport to all organs, regulation of the blood supply to organs, metabolism between blood and adjacent tissues, and also conduction of lymph from tissues to the venous bed. Approximately 20% of all liquid medium organism. Closely connected to the vascular system is the heart, which is the pump that sets the blood in motion.

Blood vessels are subdivided into arteries, arterioles, hemocapillaries, venules, veins, as well as arteriolovenular anastomoses. Blood flows from the heart through the arteries, it is saturated with oxygen (with the exception of the pulmonary artery). Through the veins, blood flows to the heart, it contains little oxygen (with the exception of the pulmonary veins). Capillaries are located between arteries and veins. In addition, there are so-called miraculous capillary networks: in the kidney - arterial, in the adenohypophysis, in the liver - venous miraculous capillary networks.

Arterio-venular anastomoses provide a discharge of blood without passing it through the capillary bed.

The hemomicrocirculatory bed is a system of small vessels, which include arterioles, hemocapillaries, venules, as well as arteriolovenular anastomoses. This functional complex of blood vessels, surrounded by lymphatic capillaries and vessels, together with the surrounding connective tissue, performs such important functions as the regulation of blood supply to organs, transcapillary exchange, drainage, and blood deposition. In each organ, according to its function, there are specific features of the structure and location of the vessels of the microvasculature. Vessels of the microvasculature are very plastic and respond to changes in blood flow. They can deposit blood cells or be spasmodic and pass only plasma, change permeability to tissue fluid, and the like.

Rice. 1. Light microscopy of vessels of the microvasculature. Staining with hematoxylin, eosin. Triangular arrows show capillary endotheliocytes.

Hemocapillaries (vasa haemocapillary aria) perform the main function of the circulatory system regarding the metabolism between blood and tissues, play the role of a histohematic barrier, and also provide microcirculation.

basement membrane

Fenestra endothelium

Rice. 2. Scheme of the structure of the hemocapillary

Hemodynamic conditions in the capillaries are characterized by low pressure (25.30 mm Hg at the arterial end and 8.12 at the venous end) and low blood flow velocity (0.5 mm/s). These are the thinnest vessels. The Latin word "caril l aris" means "hairy"; this term has stuck to the thinnest blood vessels, since most of them are thinner than a human hair.

The lumen of capillaries is sometimes smaller than the diameter of erythrocytes (3.5 microns), but there are also large capillaries with a diameter of over 20.30 microns, the so-called sinusoidal capillaries and lacunae. The average length of the capillary is 750 µm, the cross-sectional area is 30 µm 3 . Capillaries are the most numerous vessels in the human body.

In most cases, capillaries form a network, but they can also form loops (eg, in skin papillae and synovial villi of joints) as well as glomeruli (vascular glomeruli in the kidney). Various organs have different levels of development of the capillary network. For example, in the skin there are 40 capillaries per 1 mm 2, and about 1000 in the muscles. High level development of the capillary network is observed in the gray matter of the organs of the central nervous system, in endocrine glands, skeletal muscle, heart, adipose tissue.

The capillary wall is very thin, containing endothelium, basement membrane and pericytes. The endothelium is the inner layer of cells that line the capillaries, as well as all other vessels and the heart. This is a layer of flat polygonal cells, elongated in length, with unequal wavy edges, which are clearly visible upon silver impregnation. Cell width 8.19 microns, length from 10.22 to 75.175 microns and more (up to 500 microns in the aorta). The thickness of the cell is not the same in its different parts.

The lumenal (facing to the blood flow) surface of endotheliocytes is covered with a layer of glycoproteins. Pinocytic vesicles and caveolae are located along the inner and outer surface of the cells, which indicates active transendothelial transfer. different substances. Endotheliocytes may have individual microvilli as well as form valve-like structures.

Rice. 3. Electron micrograph of a fragment of the hemocapillary wall. One can see numerous pinocytic vesicles in the cytoplasm of the endotheliocyte, as well as microvilli on the lumenal surface of endothelial cells. The arrows show the basement membrane surrounding the endothelium from the outside.

The basal membrane of hemocapillaries with a thickness of 35.50 nm has a fine fibrillar structure, contains collagen, glycosaminoglycans, and lipids. It plays an important role in the transport of substances through the capillary wall, its condition predetermines the permeability of the capillaries: At the same time, it facilitates the fixation of endothelial cells and creates an external support for their cytoskeleton. The basement membrane can be solid or contain holes - pores.

Pericytes are connective tissue cells with processes, with which they cover the capillaries from the outside. Pericytes may lie in basement membrane clefts. In areas where the basement membrane contains pores, pericytes form endotheliopericytic tight contacts with the endothelium and, thus, form an integral system with them. Around the capillaries there are always poorly differentiated connective tissue cells, which are called adventitious. They are located externally from the pericytes and are surrounded by an intercellular substance with thin collagen fibers. These cells are not part of the capillary wall proper.

Depending on the structure of the endothelium, the basement membrane, and also on the diameter, capillaries are classified into the following three types:

1) somatic - up to 10 microns in diameter, have unfenestrated endothelium and a continuous basement membrane, they are localized in the skin, muscle tissue, heart, brain;

2) visceral - have a fenestrated endothelium and a continuous basement membrane, are localized in the renal glomeruli, villi of the small intestine, endocrine glands;

3) capillaries of the sinusoidal type - have fenestra in the endothelium and pores in the basement membrane, located in the hematopoietic organs, liver.

Rice. 4. Types of capillaries (schematic representation): A – somatic type capillary, B – visceral type capillary, C – sinusoidal type capillary.

Rice. 5. Electron micrograph of a somatic capillary. A continuous basement membrane and unfenestrated endothelium are seen. Long arrows point to endothelial microvilli. Triangular small arrows point to the place of contact between endotheliocytes. Arrows of medium length indicate numerous caveolae in the cytoplasm of the endotheliocyte.

Rice. 6. Electron micrograph of a visceral type capillary. A continuous basement membrane and fenestrated endothelium are seen. Long arrows point to numerous fenestrae - areas of the endotheliocyte, where there is no cytoplasm between the two plasmolemms (lumenal and basal), and the plasmolemms merge to form the so-called membrane window. Protein molecules, such as hormones, easily penetrate through such fenestrae.

The wall of a blood vessel reacts very subtly to changes in hemodynamics and chemical composition of the blood. A peculiar sensitive element that captures these changes is the endothelial cell, which on the one hand is washed by the blood, and on the other hand is turned to the structures of the vascular wall.

Endothelium- a thin layer of flat cells that forms the inner lining of all blood vessels and chambers of the heart. The wall of small blood vessels and capillaries is represented only by this cell type. The total number of endothelial cells in the body reaches 61013 and is 1 kg by weight. Endothelial cells contain Weibel-Palade bodies, elongated structures 0.1 µm wide and 3 µm long surrounded by a membrane. The bodies contain von Willebrand factor and P-selectin. Endothelial cells not only form a selective permeability barrier that controls the transport of substances from the blood to the tissue and vice versa, but also participate in many other functions. The endothelium produces extracellular matrix molecules, participates in the transition of leukocytes from blood to tissue (Fig. 10-6 and 10-7), is associated with the processes of vasoconstriction and vasodilation, blood clotting (clot formation and fibrinolysis), the formation of new blood vessels (angiogenesis), immune response and inflammation. In the glomeruli of the kidney and the blood-brain barrier, the endothelium is specialized to perform the function of a cellular filter. The most significant intracellular signaling pathways for endothelial adhesion and survival are shown in Figure 10-8.

Functions of the endothelium violated at vascular diseases and with the most common of them - atherosclerosis. One of the key mechanisms of endothelial dysfunction is associated with a decrease in the level of nitric oxide, often due to an increase in the content of dimethylarginine, which inhibits the formation of nitric oxide from L-arginine.

Rice. 7. Interaction of blood cells with endothelial cells of small blood vessels. The leukocyte forms temporary adhesive contacts with the endothelial cell. Proteins of the selectin family participate in the formation of contacts: E-selectin on the surface of the endothelial cell, P-selectin on the surface of the endothelial cell and platelet, L-selectin on the surface of many leukocytes.

Rice. 8. Adhesion of blood cells and endothelium and subsequent transmigration of blood cells through the endothelium. Representatives of the Ig superfamily of the ICAM-1 and VCAM-1 molecules participate in adhesion on the part of endothelial cells, and integrins VLA-4, LFA-1 on the part of leukocytes. The PECAM-1 (CD31) molecule, which also belongs to the Ig superfamily, is involved in the diapedesis of leukocytes through the wall of venules.

Blood clotting. The endothelial cell is an important component of the hemocoagulation process. On the surface of endothelial cells, prothrombin can be activated by clotting factors. On the other hand, the endothelial cell exhibits anticoagulant properties. The direct participation of the endothelium in blood coagulation consists in the secretion by endothelial cells of certain plasma coagulation factors (for example, factor VIII, or von Willebrand factor). Under normal conditions, the endothelium interacts weakly with shaped elements blood, as with clotting factors. The endothelial cell produces prostacyclin PGI2, which inhibits platelet adhesion.

Restoration of blood flow in thrombosis. The effect of ligands (ADP and serotonin, thrombin) on the endothelial cell stimulates the secretion of NO. His targets are located nearby the MMC. As a result of relaxation of the SMC, the lumen of the vessel in the area of ​​the thrombus increases, and the blood flow can be restored. Activation of other endothelial cell receptors leads to a similar effect: histamine, m-cholinergic receptors, α2-adrenergic receptors.

growth factors and cytokines. Endothelial cells synthesize and secrete growth factors and cytokines that influence the behavior of other cells in the vascular wall. This aspect is important in the mechanism of atherosclerosis development, when, in response to pathological effects from platelets, macrophages, and SMCs, endothelial cells produce platelet-derived growth factor (PDGF), alkaline fibroblast growth factor (bFGF), and insulin-like growth factor 1 (IGF-1). ), IL1, TGF. On the other hand, endothelial cells are targets for growth factors and cytokines. For example, endothelial cell mitosis is induced by alkaline fibroblast growth factor (bFGF), while endothelial cell proliferation is stimulated by platelet-derived endothelial cell growth factor. Cytokines from macrophages and B-lymphocytes - TGF, IL1 and -IFN - inhibit the proliferation of endothelial cells.

hormone processing. The endothelium is involved in the modification of hormones circulating in the blood and other biologically active substances. So, in the endothelium of the vessels of the lungs, angiotensin I is converted to angiotensin II.

Inactivation of biologically active substances. Endothelial cells metabolize norepinephrine, serotonin, bradykinin, prostaglandins.

Breakdown of lipoproteins. In endothelial cells, lipoproteins are broken down to form triglycerides and cholesterol. In the endothelial membrane of the capillaries of adipose tissue and skeletal muscles, there is lipoprotein lipase, which breaks down triglycerides with the formation of fatty acids and glycerol.

Homing of lymphocytes. Venules in the paracortical zone lymph nodes, tonsils, Peyer's patches of the ileum, containing clusters of lymphocytes, have a high endothelium, expressing on its surface the so-called. a vascular addressin recognized by the CD44 molecule of circulating lymphocytes. In these areas, lymphocytes attach to the endothelium and leave the bloodstream (homing).

barrier function. The endothelium controls the permeability of the vascular wall. This function is most clearly manifested in the blood-brain and hematothymic barriers.

Maintenance of hematopoiesis. The endothelium of the sinusoids of the bone marrow and umbilical cord vessels supports the proliferation and differentiation of hematopoietic stem cells. Endothelial cells from these vessels with built-in genes for thrombopoietin, erythropoietin, GM-CSF and some other active molecules (c-kit, flt 3/flk-2) stably stimulate hematopoiesis and are considered as a promising tool for stem cell activation when used to correct hematopoietic defects.

Genesis and maintenance of endothelial cell populations. The endothelium is derived from the mesodermal cells of the splanchnopleura. In the adult organism, the existence of a circulating endothelial stem cell of bone marrow origin is assumed. Its early committed descendants (angioblasts) make up less than 1% of the population of all CD34+ cells from the bone marrow, express vascular endothelial growth factor receptor 2 (VEGFR-2) and hematopoietic stem cell antigen AC133. Vascular endothelial growth factor (VEGF) is a key factor supporting the differentiation of endothelial cells from early progenitor cells.

The totality of arterioles, capillaries and venules constitutes the structural and functional unit of the cardiovascular system - the microcirculatory (terminal) bed (Fig. 9). Terminal channel organized in the following way: at a right angle from the terminal arteriole, the metarteriole departs, crossing the entire capillary bed and opening into the venule. From the arterioles, anastomosing true capillaries originate, forming a network; the venous part of the capillaries opens into postcapillary venules. At the point where the capillary leaves the arterioles, there are precapillary sphincters - an accumulation of circularly oriented smooth muscle cells (SMCs). The sphincters control the local volume of blood passing through the true capillaries; the volume of blood that passes through the terminal vascular bed as a whole is determined by the tone of the SMC arterioles. In the microvasculature, there are arteriolo-venular anastomoses that connect arterioles directly with venules or small arteries with small veins. The wall from the vessels of the anastomosis contains many SMCs. Arteriovenous anastomoses are present in large numbers in some areas of the skin, where they play an important role in thermoregulation (earlobe, fingers).

Rice. 9. Diagram of the microvasculature. Arteriola ® metarteriol ® capillary network with two sections - arterial and venous ® venule. Arteriole-venular anastomoses unite arterioles with venules.

The terminal arteriole contains longitudinally oriented endothelial cells and a continuous layer of circularly oriented SMCs. Fibroblasts are located around the SMC (see Fig. 10).

Blood from the capillaries of the terminal bed sequentially enters the postcapillary, prefabricated, muscle venules and enters the veins.

Postcapillary venules (8 to 30 µm in diameter) serve as the usual site for leukocytes to leave the circulation. As the diameter of postcapillary venules increases, the number of pericytes increases, SMCs are absent. Histamine (through histamine receptors) causes a sharp increase in the penetration of the endothelium of postcapillary venules, which leads to swelling of the surrounding tissues.

Rice. 10. Light microscopy of arterioles and venules. Stained with iron hematoxylin. The triangular arrow points to the pericyte in the venule wall.

Arteriovenular anastomoses (ABA). This part of the microvasculature provides a direct transition of arterial blood to the veins, bypassing the capillaries. ABA exist in almost all organs, their diameter ranges from 30 to 500 microns, and their length reaches 4 mm. There are two groups of anastomoses: 1) real ABA, or shunts, where pure arterial blood is thrown off, distinguish real simple anastomoses and real anastomoses, equipped with contractile structures; 2) atypical ABA, or semi-shunts, where mixed blood flows.

True simple anastomoses have an arteriole-venule border that corresponds to the site where the medial sheath of the arteriole ends. The regulation of blood flow is carried out by the muscle cells of the middle shell of the arteriole itself without special contractile apparatus. Real anastomoses of the second subgroup have special contractile devices in the form of rollers or pillows in the subendothelial layer, which are formed by longitudinally located muscle cells. The contraction of the muscle pads protruding into the lumen of the anastomosis stops the blood flow.

This subgroup also includes ABAs of the epithelioid type, which are divided into simple and complex. Simple in the middle shell have an inner longitudinal and outer circular layers of smooth muscle cells, which, when approaching the venous end, are gradually replaced by short, oval, light cells similar to epithelial cells. In the venous segment, the wall of such an arteriolo-venular anastomosis is sharply thinned and contains a small number of muscle cells in the middle shell, arranged circularly. The outer shell is built from loose connective tissue. In complex, glomerular, anastomoses of the epithelioid type, in contrast to simple ones, the afferent arteriole splits into two to four branches.

The second group of anastomoses - atypical (or semi-shunts) - is the connection of arterioles and venules through a short capillary-type vessel, so the blood that enters the venous bed is not completely arterial.

The connection of the arterial and venous systems directly, bypassing the capillaries, is of great importance for the regulation of blood pressure, blood supply to organs, arterialization of venous blood, mobilization of deposited blood, and regulation of the passage of tissue fluid into the venous bed.

Rice. 11. Diagram of the microvasculature. 1 - a typical network of capillaries between an arteriole and a venule. 2 - atypical anastomosis (semi-shunt). 3 - arterial capillary glomerulus of the kidney (a wonderful arterial network of capillaries). 4 - a wonderful venous capillary network (characteristic of the adenohypophysis).

Hemodynamic conditions in the arteries are characterized by high blood flow velocity and high blood pressure (in the aorta, respectively, 0.5.1 m/s and 120 mm Hg). According to the diameter and structural features of the artery, they are divided into three types: 1) arteries of the muscular type (medium and small caliber); 2) mixed, muscular-elastic type (medium caliber); 3) elastic type (large caliber).

Mixed type arteries. Using the example of the structure of the wall of an artery of the muscular-elastic type, let us consider the general plan of the structure of the vascular wall in general. Consequently, the wall of a mixed-type artery, as well as other arteries and veins, is built from three shells: internal (tunica interne, seu intima), middle (tunica media), external (tunica externa, seu adventitia).

Rice. 12. Scheme of the structure of a blood vessel: the inner shell - intima; middle shell - media; outer shell - adventitia.

The inner shell is formed by the endothelium, the subendothelial layer and the inner elastic membrane. The endothelium was discussed above when characterizing the structure of capillaries. The subendothelial layer is a layer of loose, unformed connective tissue, which contains thin elastic and collagen fibers that have a predominantly longitudinal orientation, as well as poorly differentiated connective tissue cells of irregular stellate shape. The amorphous substance contains sulfated glycosaminoglycans. The internal elastic membrane is located externally from the subendothelial layer and lies on the border with the middle shell. This is a fenestrated elastic lamina, on histological preparations it looks like a wavy shiny ribbon (due to the post-mortem contraction of the muscle cells of the middle shell, the membrane acquires a wavy appearance).

The middle shell consists of two main elements: smooth myocytes, arranged circularly, or rather in the form of a gentle spiral, and elastic fibers, also arranged mainly spirally, but, in addition, also radial and arcuate. The ratio of smooth myocytes and elastic fibers in the media of a mixed type artery is approximately 1:1. The same shell also contains a small amount of collagen fibers, fibroblasts, and an amorphous substance rich in acidic glycosaminoglycans. On the border of the middle and outer shells lies the outer elastic membrane, similar in structure, but somewhat thinner than the inner elastic membrane. All elastic elements are interconnected and form a single elastic skeleton of the artery, which provides the vessel with elasticity during stretching and elasticity during compression, prevents collapse and, thus, predetermines the continuity of blood flow.

The outer sheath (adventitia) consists of loose, fibrous, irregular connective tissue, the fibers of which are mostly oriented longitudinally. In the inner layer of this membrane, there may also be smooth myocytes. The outer shell contains small feeding vessels and nerves of the vessels.

Muscular arteries. With a decrease in the caliber of the arteries, the structure of their walls changes. The main changes relate to the middle shell - the relative content of elastic fibers decreases and, accordingly, the content of smooth myocytes increases. This is due to changes in hemodynamic conditions; Muscular-type arteries are located far from the heart, blood pressure decreases here, and additional work is needed to maintain it, which is achieved by contracting the muscular elements of vessels of this type. In addition to these changes, in the middle shell, with a decrease in the caliber of the arteries, the thickness of all shells decreases, the subendothelial layer and the inner elastic membrane become thinner, and the outer elastic membrane disappears.

The total diameter of muscular arteries (wall thickness + lumen diameter) reaches 1 cm, the lumen diameter varies from 0.3 to 10 mm. Such vessels belong to distribution vessels (Fig. 13).

Rice. 13. Muscular artery and accompanying vein. The artery and has a rounded lumen (1), the lumen of the vein is slit-like (2). On the border of the inner and middle shells of the artery, a wavy light line is visible - the inner elastic membrane (3). The middle sheath (4), thick in the artery and thin in the vein, is formed by circularly oriented smooth muscle cells. The connective tissue fibrous outer sheath (5) is more pronounced in the vein. A thrombus is seen in the lumen of the artery (6). Stained with hematoxylin and eosin.

The internal elastic membrane is not equally well developed in all muscular arteries. It is relatively weakly expressed in the arteries of the brain and its membranes, in the branches of the pulmonary artery, and is completely absent in the umbilical arteries.

The smallest arterial vessels of the muscular type (arterioles) belong to microvasculature and pass into the capillaries, their diameter does not exceed 50. 100 microns. All three shells are preserved in these vessels, but they are very poorly developed. The middle shell is formed by one or two layers of smooth muscle cells. In the precapillary arterioles, the muscle elements are located singly.

Rice. 14. Artery and vein of small caliber in the subcutaneous adipose tissue. Arrows indicate capillaries. Stained with hematoxylin.

To elastic type arteries belong to the aorta and pulmonary artery. The composition of their walls in large quantities includes elastic membranes and elastic fibers. The thickness of the wall of arteries of the elastic type a c leaves approximately 15% of the diameter and their lumen. The middle shell is dominated by elastic elements that form 40–50 elastic fenestrated membranes. There are fewer muscle cells, they are located obliquely relative to the elastic fibers. The indicated specificity of the structure is due high pressure and high speed of blood in the arteries of the elastic type, provides a high elasticity of the latter - to soften the shocks of the blood.

Other structural features of the aortic wall are: large endothelial cells (500x150 microns); the presence in the subendothelial layer of a large number of poorly differentiated stellate cells; the presence in the inner shell of longitudinally oriented smooth myocytes; the absence of an internal elastic membrane, in place of which there is a dense plexus of elastic fibers, in which the inner circular and outer longitudinal layers can be distinguished.

Rice. 15. Light micrograph of the elastic type artery - the aorta. Stained with orcein. Numerous elastic fenestrated membranes are visible in the thick middle shell. In the adventitia, the arrows show the vessels of the vessels.

Rice. 16. Schematic representation of the structure of the wall of the muscular type artery (left) and the elastic type artery (right).

VIENNA ( Venae) provide blood return to the heart, blood storage and drainage. The general plan of the structure of the wall of the veins is the same as in the arteries. But their structure also has significant differences as a result of other hemodynamic conditions, which are low blood pressure and low blood flow.

These factors predetermine such general differences in the structure of veins compared to arteries: 1) the wall of the vein is thinner than that of the corresponding artery; 2) among the structural elements of the vein, collagen fibers predominate, and the elastic ones are poorly developed; 3) absence of an external elastic membrane and weak development (or complete absence) of an internal elastic membrane; 4) the lumen of the vein on the preparation is often irregular in shape, while in the artery it is round; 5) the outer shell has the greatest thickness in the veins, and the middle shell is the most developed in the arteries; 6) the presence of valves in some veins (see Fig. 13, 17).

Rice. 17. Schematic representation of the structure of the wall of an artery of a muscular type (left) and a vein of the corresponding caliber (right)

Table 1. Comparative morphological characteristics of a muscular artery and an accompanying vein

The human venous system is a collection of various veins that provide full blood circulation in the body. Thanks to this system, all organs and tissues are nourished, as well as the regulation of the water balance in the cells and the removal of toxic substances from the body. According to the anatomical structure, it is similar to the arterial system, however, there are some differences that are responsible for certain functions. What is the functional purpose of the veins and what diseases can occur if the patency of blood vessels is impaired?

general characteristics

Veins are the vessels of the circulatory system that carry blood to the heart. They are formed from branched venules of small diameter, which are formed from a capillary network. The set of venules is transformed into larger vessels, from which the main veins are formed. Their walls are somewhat thinner and less elastic than those of arteries, since they are subjected to less stress and pressure.

The blood flow through the vessels is provided by the work of the heart and chest, when the diaphragm contracts during inspiration, forming a negative pressure. Valves are located in the vascular walls that prevent the reverse movement of blood. A factor contributing to the work of the venous system is the rhythmic contraction of the muscle fibers of the vessel, pushing the blood up, creating a venous pulsation.

The blood vessels that drain blood away from the tissues of the neck and head contain fewer valves because gravity makes circulation above the heart easier.

How is blood circulation carried out?

The human venous system is conditionally divided into a small and a large circle of blood circulation. The small circle is designed for thermoregulation and gas exchange in the pulmonary system. It originates from the cavity of the right ventricle, then the blood enters the pulmonary trunk, which consists of small vessels and ends in the alveoli. Oxygenated blood from the alveoli forms the venous system, which flows into left atrium, thereby completing the pulmonary circulation. A complete circulation of blood is less than five seconds.

The task of the systemic circulation is to provide all tissues of the body with blood enriched with oxygen. The circle originates in the cavity of the left ventricle, where high oxygen saturation occurs, after which the blood enters the aorta. The biological fluid saturates the peripheral tissues with oxygen, then returns to the heart through the vascular system. From most parts of the digestive tract, blood is initially filtered in the liver rather than moving directly to the heart.

Functional purpose

The full functioning of blood circulation depends on many factors, such as:

• individual features of the structure and location of the veins;
• gender;
• age category;
• lifestyle;
• genetic predisposition to chronic diseases;
• the presence of inflammatory processes in the body;
• violations of metabolic processes;
• actions of infectious agents.

If a person has risk factors that affect the functioning of the system, he should observe preventive measures, since with age there is a risk of developing venous pathologies.

Vessels contribute to the saturation of tissues with carbon dioxide

The main functions of venous vessels:

• Blood circulation. Continuous movement of blood from the heart to organs and tissues.
• Transportation nutrients. They ensure the transfer of nutrients from the digestive tract to the bloodstream.
• distribution of hormones. Regulation of active substances that carry out humoral regulation of the body.
• excretion of toxins. Conclusion harmful substances and end products of metabolism from all tissues to the organs of the excretory system.
• Protective. The blood contains immunoglobulins, antibodies, leukocytes and platelets, which protect the body from pathogenic factors.

Veins carry out general and local regulation of blood circulation

The venous system takes an active part in the spread of the pathological process, since it serves as the main route for the spread of purulent and inflammatory phenomena, tumor cells, fat and air embolism.

Structural features

Anatomical features The vascular system lies in its important functional significance in the body and in terms of blood circulation. The arterial system, unlike the venous system, functions under the influence of the contractile activity of the myocardium and does not depend on the impact external factors.

The anatomy of the venous system implies the presence of superficial and deep veins. Superficial veins are located under the skin, they start from the superficial vascular plexus or venous arch of the head, trunk, lower and upper extremities. Deeply located veins, as a rule, are paired, originate in separate parts of the body, accompany the arteries in parallel, from which they got the name "satellites".

The structure of the venous network consists in the presence of a large number of vascular plexuses and messages that provide blood circulation from one system to another. Veins of small and medium caliber, as well as some large vessels on the inner shell contain valves. The blood vessels of the lower extremities have a small number of valves, therefore, when they are weakened, pathological processes begin to form. The veins of the cervical, head and vena cava do not contain valves.

The venous wall consists of several layers:

• Collagen (resist the internal movement of blood).
• Smooth muscle (contraction and stretching of the venous walls facilitates the process of blood circulation).
• Connective tissue (provides elasticity during body movement).

The venous walls have insufficient elasticity, since the pressure in the vessels is low, and the blood flow velocity is negligible. When the vein is stretched, outflow is difficult, but muscle contractions help the movement of fluid. An increase in blood flow velocity occurs when exposed to additional temperatures.

Risk factors in the development of vascular pathologies

The vascular system of the lower extremities is subjected to high stress during walking, running and prolonged standing. There are many reasons that provoke the development of venous pathologies. So, non-compliance with the principles of rational nutrition, when fried, salty and sweet foods predominate in the patient's diet, leads to the formation of blood clots.

Primarily, thrombus formation is observed in veins of small diameter, however, with the growth of a clot, its parts enter the main vessels, which are directed to the heart. In severe pathology, blood clots in the heart lead to its stop.

Hypodynamia contributes to stagnant processes in the vessels

Causes of venous disorders:

• Hereditary predisposition (inheritance of a mutated gene responsible for the structure of blood vessels).
• Change hormonal background(during pregnancy and menopause, an imbalance of hormones occurs that affects the condition of the veins).
• Diabetes mellitus (permanently elevated level glucose in the bloodstream leads to damage to the venous walls).
• Abuse of alcoholic beverages (alcohol dehydrates the body, resulting in a thickening of blood flow with further formation of clots).
• Chronic constipation (increased intra-abdominal pressure, making it difficult for fluid to drain from the legs).

Varicose veins of the lower extremities is a fairly common pathology among the female population. This disease develops due to a decrease in the elasticity of the vascular wall, when the body is subject to intense stress. An additional provoking factor is excess body weight, which leads to stretching of the venous network. An increase in the volume of circulating fluid contributes to an additional load on the heart, since its parameters remain unchanged.

Vascular pathologies

Violation in the functioning of the venous-vascular system leads to thrombosis and varicose veins. The following diseases are most often observed in people:

• Varicose veins. It is manifested by an increase in the diameter of the vascular lumen, but its thickness decreases, forming nodes. In most cases, the pathological process is localized on the lower extremities, but cases of damage to the veins of the esophagus are possible.
• Atherosclerosis. The disorder of fat metabolism is characterized by the deposition of cholesterol formations in the vascular lumen. There is a high risk of complications if coronary vessels myocardial infarction occurs, and damage to the sinuses of the brain leads to the development of a stroke.
• Thrombophlebitis. Inflammatory damage to the blood vessels, as a result of which there is a complete blockage of its lumen by a thrombus. The greatest danger lies in the migration of a thrombus throughout the body, as it can provoke severe complications in any organ.

Pathological dilation of veins of small diameter is called telangiectasia, which is manifested by a long pathological process with the formation of asterisks on the skin.

The first signs of damage to the venous system

The severity of symptoms depends on the stage of the pathological process. With the progression of damage to the venous system, the severity of manifestations increases, accompanied by the appearance of skin defects. In most cases, violation of the venous outflow occurs in the lower extremities, since they bear the greatest load.

Early signs of impaired circulation of the lower extremities:

• strengthening of the venous pattern;
• increased fatigue when walking;
• painful sensations, accompanied by a feeling of squeezing;
• severe swelling;
• inflammation on the skin;
• vascular deformity;
• convulsive pain.

In the later stages, there is increased dryness and pallor of the skin, which in the future may be complicated by the appearance of trophic ulcers.

How to diagnose pathology?

Diagnosis of diseases associated with venous circulation disorders consists in the following studies:

• Functional tests (allow to assess the degree of vascular patency and the condition of their valves).
• Duplex angioscanning (assessment of blood flow in real time).
• Dopplerography (local determination of blood flow).
• Phlebography (carried out by introducing a contrast agent).
• Phleboscintiography (the introduction of a special radionuclide substance allows you to identify all possible vascular abnormalities).

Method of duplex scanning of venous circulation in the lower extremities

Studies of the state of superficial veins are carried out by visual inspection and palpation, as well as the first three methods from the list. For the diagnosis of deep vessels, the last two methods are used.

The venous system has a fairly high strength and elasticity, but the impact of negative factors leads to disruption of its activity and the development of diseases. To reduce the risk of pathologies, a person needs to follow the recommendations for a healthy lifestyle, normalize the load and undergo a timely examination by a specialist.