Blood vessels are a type of tissue. Structure of the vascular wall

The human body is completely riddled with blood vessels. These peculiar highways ensure continuous delivery of blood from the heart to the most distant parts of the body. Thanks to the unique structure of the circulatory system, each organ receives a sufficient amount of oxygen and nutrients. The total length of blood vessels is about 100 thousand km. This is really so, although it is hard to believe. The movement of blood through the vessels is ensured by the heart, which acts as a powerful pump.

To understand the answer to the question: how the human circulatory system works, you need, first of all, to carefully study the structure of blood vessels. In simple terms, these are strong elastic tubes through which blood moves.

Blood vessels branch throughout the body, but ultimately form a closed circuit. For normal blood flow, there must always be excess pressure in the vessel.

The walls of blood vessels consist of 3 layers, namely:

The first layer is epithelial cells. The fabric is very thin and smooth, providing protection against blood elements.
The second layer is the densest and thickest. Consists of muscle, collagen and elastic fibers. Thanks to this layer, blood vessels have strength and elasticity.
The outer layer consists of connective fibers with a loose structure. Thanks to this fabric, the vessel can be securely fixed to different parts of the body.

Blood vessels additionally contain nerve receptors that connect them to the central nervous system. Thanks to this structure, nervous regulation of blood flow is ensured. In anatomy, there are three main types of vessels, each of which has its own functions and structure.

Arteries

The main vessels that transport blood directly from the heart to the internal organs are called aortas. Very high pressure is constantly maintained inside these elements, so they must be as dense and elastic as possible. Doctors distinguish two types of arteries.

Elastic. The largest blood vessels that are located in the human body closest to the heart muscle. The walls of such arteries and the aorta are made of dense elastic fibers that can withstand continuous heartbeats and sudden surges of blood. The aorta can expand, filling with blood, and then gradually return to its original size. It is thanks to this element that the continuity of blood circulation is ensured.

Muscular. Such arteries are smaller in size compared to the elastic type of blood vessels. Such elements are removed from the heart muscle and are located near peripheral internal organs and systems. The walls of muscle arteries can contract strongly, allowing blood to flow even at low pressure.

The main arteries supply all internal organs with a sufficient amount of blood. Some circulatory elements are located around the organs, while others go directly into the liver, kidneys, lungs, etc. The arterial system is very branched, it can smoothly turn into capillaries or veins. Small arteries are called arterioles. Such elements can directly participate in the self-regulation system, since they consist of only one layer of muscle fibers.

Capillaries

Capillaries are the smallest peripheral vessels. They can freely penetrate any tissue, as a rule, they are located between larger veins and arteries.

The main function of microscopic capillaries is to transport oxygen and nutrients from the blood to the tissues. Blood vessels of this type are very thin, so they consist of only one layer of epithelium. Thanks to this feature, useful elements can easily penetrate through their walls.

There are two types of capillaries:

Open – constantly involved in the blood circulation process;
Closed ones are, as it were, in reserve.

1 mm of muscle tissue can accommodate from 150 to 300 capillaries. When muscles are under stress, they need more oxygen and nutrients. In this case, reserve closed blood vessels are additionally used.

Vienna

The third type of blood vessel is veins. Their structure is the same as arteries. However, their function is completely different. After the blood has given up all its oxygen and nutrients, it rushes back to the heart. At the same time, it is transported precisely through the veins. The pressure in these blood vessels is reduced, so their walls are less dense and thick, and their middle layer is less thin than in the arteries.

The venous system is also very branched. In the area of the upper and lower extremities there are small veins, which gradually increase in size and volume towards the heart. The outflow of blood is ensured by back pressure in these elements, which is formed during contraction of muscle fibers and exhalation.

Diseases

In medicine, there are many pathologies of blood vessels. Such diseases can be congenital or acquired throughout life. Each type of vessel may have one or another pathology.

Vitamin therapy is the best prevention of diseases of the circulatory system. Saturating the blood with useful microelements allows you to make the walls of arteries, veins and capillaries stronger and more elastic. People at risk of developing vascular pathologies must additionally include the following vitamins in their diet:

C and R. These microelements strengthen the walls of blood vessels and prevent capillary fragility. Contained in citrus fruits, rose hips, and fresh herbs. You can also additionally use Troxevasin medicinal gel.
Vitamin B. To enrich your body with these microelements, include legumes, liver, cereal porridge, and meat in your menu.
AT 5. Chicken meat, eggs, and broccoli are rich in this vitamin.

Eat oatmeal with fresh raspberries for breakfast, and your blood vessels will always be healthy. Dress salads with olive oil, and for drinks, give preference to green tea, rosehip infusion or fresh fruit compote.

The circulatory system performs the most important functions in the body - it delivers blood to all tissues and organs. Always take care of the health of your blood vessels, undergo regular medical examinations, and take all necessary tests.

Blood circulation (video)

Structure of blood vessels

Blood vessels develop from mesenchyme. First, the primary wall is formed, which subsequently turns into the inner lining of the vessels. Mesenchyme cells, connecting, form the cavity of future vessels. The wall of the primary vessel consists of flat mesenchymal cells that form the inner layer of future vessels. This layer of flat cells belongs to the endothelium. Later, the final, more complex vessel wall is formed from the surrounding mesenchyme. It is characteristic that all vessels in the embryonic period are laid down and built as capillaries, and only in the process of their further development is the simple capillary wall gradually surrounded by various structural elements, and the capillary vessel turns into either an artery, a vein, or a lymphatic vessel.

The final formed walls of the vessels of both arteries and veins are not the same along their entire length, but both of them consist of three main layers (Fig. 231). Common to all vessels is a thin inner membrane, or intima (tunica intima), lined on the side of the vascular cavity with the thinnest, very elastic and flat polygonal endothelial cells. The intima is a direct continuation of the endothelium and endocardium. This inner lining with a smooth and even surface protects the blood from clotting. If the endothelium of a vessel is damaged by injury, infection, inflammatory or degenerative process, etc., then small blood clots (blood clots) form at the site of damage, which can increase in size and cause blockage of the vessel. Sometimes they break away from the site of formation, are carried away by the blood stream and, as so-called emboli, clog a vessel in some other place. The effect of such a thrombus or embolus depends on where the vessel is blocked. Thus, blockage of a vessel in the brain can cause paralysis; A blockage in the coronary artery of the heart deprives the heart muscle of blood flow, resulting in a severe heart attack and often leading to death. Blockage of a vessel leading to any part of the body or internal organ deprives it of nutrition and can lead to necrosis (gangrene) of the supplied part of the organ.

Outside the inner layer is the middle shell (media), consisting of circular smooth muscle fibers with an admixture of elastic connective tissue.

The outer shell of the vessels (adventitia) covers the middle one. In all vessels it is built of fibrous fibrous connective tissue, containing predominantly longitudinally located elastic fibers and connective tissue cells.

At the border of the middle and inner, middle and outer shells of blood vessels, elastic fibers form a kind of thin plate (membrana elastica interna, membrana elastica externa).

In the outer and middle membranes of blood vessels, the vessels that feed their wall (vasa vasorum) branch.

The walls of capillary vessels are extremely thin (about 2 μ) and consist mainly of a layer of endothelial cells that form the capillary tube. This endothelial tube is braided on the outside with a thin network of fibers on which it is suspended, thanks to which it moves very easily and without damage. The fibers extend from a thin, main film, with which special cells are also associated - pericytes, covering the capillaries. The capillary wall is easily permeable to leukocytes and blood; It is at the level of capillaries through their wall that exchange takes place between blood and tissue fluids, as well as between blood and the external environment (in the excretory organs).

Arteries and veins are usually divided into large, medium and small. The smallest arteries and veins that turn into capillaries are called arterioles and venules. The arteriole wall consists of all three membranes. The innermost is endothelial, and the next middle one is built from circularly arranged smooth muscle cells. When an arteriole passes into a capillary, only single smooth muscle cells are observed in its wall. With the enlargement of the arteries, the number of muscle cells gradually increases to a continuous annular layer - a muscle-type artery.

The structure of small and medium arteries differs in some other feature. Under the inner endothelial membrane there is a layer of elongated and stellate cells, which in larger arteries form a layer that plays the role of cambium (germ layer) for blood vessels. This layer is involved in the processes of regeneration of the vessel wall, i.e. it has the property of restoring the muscular and endothelial layers of the vessel. In arteries of medium caliber or mixed type, the cambial (germ) layer is more developed.

Large-caliber arteries (aorta and its large branches) are called elastic arteries. Elastic elements predominate in their walls; in the middle shell, strong elastic membranes are concentrically laid, between which lies a significantly smaller number of smooth muscle cells. The cambial layer of cells, well defined in small and medium-sized arteries, in large arteries turns into a layer of subendothelial loose connective tissue rich in cells.

Due to the elasticity of the walls of the arteries, like rubber tubes, they can easily stretch under the pressure of blood and do not collapse, even if the blood is released from them. All the elastic elements of the vessels together form a single elastic frame, which works like a spring, each time returning the vessel wall to its original state as soon as the smooth muscle fibers relax. Since arteries, especially large ones, have to withstand fairly high blood pressure, their walls are very strong. Observations and experiments show that arterial walls can withstand even such strong pressure as occurs in the steam boiler of a conventional locomotive (15 atm.).

The walls of veins are usually thinner than the walls of arteries, especially their tunica media. There is also significantly less elastic tissue in the venous wall, so the veins collapse very easily. The outer shell is made of fibrous connective tissue, which is dominated by collagen fibers.

A feature of the veins is the presence of valves in them in the form of semilunar pockets (Fig. 232), formed from doubling the inner membrane (intima). However, not all veins in our body have valves; The veins of the brain and its membranes, the veins of the bones, as well as a significant part of the veins of the viscera, lack them. Valves are more often found in the veins of the limbs and neck; they are open towards the heart, i.e. in the direction of blood flow. By blocking the backflow that can occur due to low blood pressure and the law of gravity (hydrostatic pressure), the valves facilitate blood flow.

If there were no valves in the veins, the entire weight of a column of blood more than 1 m high would put pressure on the blood entering the lower limb and thereby greatly impede blood circulation. Further, if the veins were inflexible tubes, the valves alone could not ensure blood circulation, since the entire column of liquid would still press on the underlying sections. Veins are located among large skeletal muscles, which, contracting and relaxing, periodically compress the venous vessels. When a contracting muscle compresses a vein, the valves located below the clamping point close, and those located above open; when the muscle relaxes and the vein is again free from compression, the upper valves in it close and retain the upper column of blood, while the lower ones open and allow the vessel to refill with blood coming from below. This pumping action of the muscles (or "muscle pump") greatly aids blood circulation; standing for many hours in one place, in which the muscles help little to move the blood, is more tiring than walking.

Blood vessels are the most important part of the body, part of the circulatory system and penetrating almost the entire human body. They are absent only in the skin, hair, nails, cartilage and cornea of the eyes. And if you collect them and stretch them into one even line, then the total length will be about 100 thousand km.

These tubular elastic formations continuously function, transferring blood from the constantly contracting heart to all corners of the human body, saturating them with oxygen and nourishing them, and then returning it back. By the way, the heart pushes more than 150 million liters of blood through the vessels throughout a human life.

There are the following main types of blood vessels: capillaries, arteries and veins. Each type performs its own specific functions. It is necessary to dwell on each of them in more detail.

Division into types and their characteristics

The classification of blood vessels varies. One of them involves division:

on arteries and arterioles;
precapillaries, capillaries, postcapillaries;
veins and venules;
arteriovenous anastomoses.

They represent a complex network, differing from each other in structure, size and their specific function, and form two closed systems connected to the heart - circulatory circles.

What is common in the device is the following: the walls of both arteries and veins have a three-layer structure:

an inner layer that provides smoothness, built from endothelium;
medium, which is a guarantee of strength, consisting of muscle fibers, elastin and collagen;
the top layer of connective tissue.

The differences in the structure of their walls are only in the width of the middle layer and the predominance of either muscle fibers or elastic ones. Another thing is that venous ones contain valves.

Arteries

They deliver blood rich in nutrients and oxygen from the heart to all cells of the body. The structure of human arterial vessels is stronger than veins. This device (a denser and stronger middle layer) allows them to withstand the load of strong internal blood pressure.

The names of arteries, as well as veins, depend on:

Once upon a time it was believed that arteries carry air and therefore the name is translated from Latin as “containing air.”

Feedback from our reader - Alina Mezentseva

I recently read an article that talks about the natural cream “Bee Spas Kashtan” for treating varicose veins and cleaning blood vessels from blood clots. With this cream you can cure VARICOSIS FOREVER, eliminate pain, improve blood circulation, increase the tone of veins, quickly restore the walls of blood vessels, clean and restore varicose veins at home.

I’m not used to trusting any information, but I decided to check and ordered one package. I noticed changes within a week: the pain went away, my legs stopped “humming” and swelling, and after 2 weeks the venous lumps began to decrease. Try it too, and if anyone is interested, below is the link to the article.

The following types are distinguished:

The arteries, leaving the heart, thin out into small arterioles. This is the name given to the thin branches of the arteries that pass into the precapillaries, which form capillaries.

These are the finest vessels, with a diameter much thinner than a human hair. This is the longest part of the circulatory system, and their total number in the human body ranges from 100 to 160 billion.

The density of their accumulation varies everywhere, but is greatest in the brain and myocardium. They consist only of endothelial cells. They carry out a very important activity: chemical exchange between the bloodstream and tissues.

For the treatment of VARICOSE and cleaning blood vessels from THROMBUS, Elena Malysheva recommends a new method based on Cream of Varicose Veins. It contains 8 useful medicinal plants that are extremely effective in the treatment of VARICOSE. Only natural ingredients are used, no chemicals or hormones!

The capillaries subsequently connect with postcapillaries, which become venules - small and thin venous vessels that flow into the veins.

Vienna

These are blood vessels that carry oxygen-depleted blood back to the heart.

The walls of veins are thinner than the walls of arteries because there is no strong pressure. The most developed layer of smooth muscle is in the middle wall of the vessels of the legs, because moving upward is not easy work for the blood under the influence of gravity.

The venous vessels (all except the superior and inferior vena cava, pulmonary, nuchal, renal, and cephalic veins) contain special valves that allow blood to move toward the heart. The valves block its reverse outflow. Without them, the blood would flow to the feet.

Arteriovenous anastomoses are branches of arteries and veins connected to each other by anastomoses.

Division by functional load

There is another classification that blood vessels undergo. It is based on the difference in the functions they perform.

There are six groups:

There is another very interesting fact regarding this unique system of the human body. If you are overweight, more than 10 km (per 1 kg of fat) of additional blood-carrying vessels are created in the body. All this creates a very large load on the heart muscle.

Heart disease and excess weight, and even worse, obesity, are always very closely related. But the good thing is that the human body is also capable of the reverse process - removing unnecessary blood vessels when getting rid of excess fat (namely, from it, and not just from extra pounds).

What role do blood vessels play in human life? Overall, they do very serious and important work. They are transport that ensures the delivery of necessary substances and oxygen to every cell of the human body. They also remove carbon dioxide and waste from organs and tissues. Their importance cannot be overestimated.

DO YOU STILL THINK THAT IT IS IMPOSSIBLE TO GET RID OF VARICOSE VARICOSIS!?

Have you ever tried to get rid of VARICOSE? Judging by the fact that you are reading this article, victory was not on your side. And of course you know firsthand what it is:

feeling of heaviness in the legs, tingling...
swelling of the legs, worsening in the evening, swollen veins...
lumps on the veins of the arms and legs...

Now answer the question: are you satisfied with this? Can ALL THESE SYMPTOMS be tolerated? How much effort, money and time have you already wasted on ineffective treatment? After all, sooner or later the SITUATION WILL GET WORSE and the only way out will be surgical intervention!

That's right - it's time to start putting an end to this problem! Do you agree? That is why we decided to publish an exclusive interview with the head of the Institute of Phlebology of the Ministry of Health of the Russian Federation - V. M. Semenov, in which he revealed the secret of a cheap method of treating varicose veins and complete restoration of blood vessels. Read the interview...

Blood vessels in vertebrates form a dense closed network. The wall of the vessel consists of three layers:

The inner layer is very thin, it is formed by one row of endothelial cells, which give the smoothness of the inner surface of the vessels.
The middle layer is the thickest, containing many muscle, elastic and collagen fibers. This layer ensures the strength of the blood vessels.
The outer layer is connective tissue; it separates the vessels from the surrounding tissues.

According to the circles of blood circulation, blood vessels can be divided into:

Arteries of the systemic circulation [show]
- The largest arterial vessel in the human body is the aorta, which emerges from the left ventricle and gives rise to all the arteries that form the systemic circulation. The aorta is divided into the ascending aorta, aortic arch and descending aorta. The aortic arch is in turn divided into the thoracic aorta and the abdominal aorta.
- Arteries of the neck and head
  The common carotid artery (right and left), which at the level of the upper edge of the thyroid cartilage is divided into the external carotid artery and the internal carotid artery.
  - The external carotid artery gives off a number of branches, which, according to their topographical characteristics, are divided into four groups - anterior, posterior, medial and a group of terminal branches supplying the thyroid gland, the muscles of the hyoid bone, the sternocleidomastoid muscle, the muscles of the laryngeal mucosa, the epiglottis, the tongue, palate, tonsils, face, lips, ear (external and internal), nose, back of the head, dura mater.
  - The internal carotid artery in its course is a continuation of both carotid arteries. It distinguishes between the cervical and intracranial (head) parts. In the cervical part, the internal carotid artery usually does not give branches. In the cranial cavity, branches to the cerebrum and the orbital artery depart from the internal carotid artery, supplying blood to the brain and eye.
  The subclavian artery is a pair, starting in the anterior mediastinum: the right one - from the brachiocephalic trunk, the left one - directly from the aortic arch (therefore, the left artery is longer than the right). In the subclavian artery, three sections are topographically distinguished, each of which gives its branches:
  - The branches of the first section are the vertebral artery, the internal thoracic artery, the thyroid-cervical trunk, each of which gives its own branches that supply blood to the brain, cerebellum, neck muscles, thyroid gland, etc.
  - Branches of the second section - here only one branch departs from the subclavian artery - the costocervical trunk, which gives rise to arteries supplying blood to the deep muscles of the back of the head, spinal cord, back muscles, intercostal spaces
  - Branches of the third section - one branch also departs here - the transverse artery of the neck, which supplies blood to the back muscles
- Arteries of the upper limb, forearm and hand
- Arteries of the trunk
- Pelvic arteries
- Arteries of the lower limb
Veins of the systemic circulation [show]
- Superior vena cava system
  - Veins of the trunk
  - Veins of the head and neck
  - Veins of the upper limb
- Inferior vena cava system
  - Veins of the trunk
- Veins of the pelvis
  - Veins of the lower extremities
Vessels of the pulmonary circulation [show]
The vessels of the pulmonary, pulmonary, circulation include:
- pulmonary trunk
- pulmonary veins in two pairs, right and left
Pulmonary trunk is divided into two branches: the right pulmonary artery and the left pulmonary artery, each of which is directed to the gate of the corresponding lung, bringing venous blood from the right ventricle to it.
The right artery is slightly longer and wider than the left. Having entered the root of the lung, it is divided into three main branches, each of which enters the gate of the corresponding lobe of the right lung.
The left artery at the root of the lung is divided into two main branches that enter the gate of the corresponding lobe of the left lung.
A fibromuscular cord (arterial ligament) runs from the pulmonary trunk to the aortic arch. During fetal development, this ligament is the ductus arteriosus, through which most of the blood from the pulmonary trunk of the fetus passes into the aorta. After birth, this duct is obliterated and turns into the indicated ligament.
Pulmonary veins, right and left, - remove arterial blood from the lungs. They leave the hilum of the lungs, usually two from each lung (although the number of pulmonary veins can reach 3-5 or even more), the right veins are longer than the left ones, and flow into the left atrium.

According to their structural features and functions, blood vessels can be divided into:

Groups of vessels according to the structural features of the wall

Arteries

Blood vessels going from the heart to the organs and carrying blood to them are called arteries (aer - air, tereo - contain; on corpses the arteries are empty, which is why in the old days they were considered air tubes). Blood from the heart flows through the arteries under high pressure, which is why the arteries have thick elastic walls.

According to the structure of the walls, arteries are divided into two groups:

Elastic arteries - the arteries closest to the heart (aorta and its large branches) primarily perform the function of conducting blood. In them, counteraction to stretching by the mass of blood, which is ejected by the heart impulse, comes to the fore. Therefore, structures of a mechanical nature are relatively more developed in their walls, i.e. elastic fibers and membranes. The elastic elements of the arterial wall form a single elastic frame that works like a spring and determines the elasticity of the arteries.
Elastic fibers give arteries elastic properties, which ensure continuous blood flow throughout the vascular system. During contraction, the left ventricle pushes out more blood under high pressure than flows out of the aorta into the arteries. In this case, the walls of the aorta stretch, and it accommodates all the blood ejected by the ventricle. When the ventricle relaxes, the pressure in the aorta drops, and its walls, due to their elastic properties, collapse slightly. Excess blood contained in the distended aorta is pushed out of the aorta into the arteries, although no blood flows from the heart at this time. Thus, the periodic expulsion of blood by the ventricle, due to the elasticity of the arteries, turns into a continuous movement of blood through the vessels.
The elasticity of the arteries provides another physiological phenomenon. It is known that in any elastic system a mechanical shock causes vibrations that propagate throughout the system. In the circulatory system, this impulse is the impact of the blood ejected by the heart against the walls of the aorta. The resulting vibrations propagate along the walls of the aorta and arteries at a speed of 5-10 m/s, which significantly exceeds the speed of blood movement in the vessels. In areas of the body where large arteries come close to the skin - on the wrist, temples, neck - you can feel the vibrations of the artery walls with your fingers. This is the arterial pulse.
Arteries of the muscular type are medium and small arteries in which the inertia of the cardiac impulse weakens and the own contraction of the vascular wall is required for further movement of blood, which is ensured by the relatively greater development of smooth muscle tissue in the vascular wall. Smooth muscle fibers, contracting and relaxing, narrow and dilate arteries and thus regulate blood flow in them.

Individual arteries supply blood to entire organs or parts thereof. In relation to an organ, there are arteries that go outside the organ before entering it - extraorgan arteries - and their continuations that branch inside it - intraorgan or intraorgan arteries. Lateral branches of the same trunk or branches of different trunks can connect to each other. This connection of vessels before they break up into capillaries is called anastomosis or anastomosis. The arteries that form anastomoses are called anastomosing (they are the majority). Arteries that do not have anastomoses with neighboring trunks before they become capillaries (see below) are called terminal arteries (for example, in the spleen). Terminal, or terminal, arteries are more easily blocked by a blood plug (thrombus) and predispose to the formation of a heart attack (local death of an organ).

The last branches of the arteries become thin and small and are therefore called arterioles. They directly pass into the capillaries, and due to the presence of contractile elements in them, they perform a regulatory function.

An arteriole differs from an artery in that its wall has only one layer of smooth muscle, thanks to which it carries out a regulatory function. The arteriole continues directly into the precapillary, in which the muscle cells are scattered and do not form a continuous layer. The precapillary differs from the arteriole in that it is not accompanied by a venule, as is observed with the arteriole. Numerous capillaries extend from the precapillary.

Capillaries - the smallest blood vessels located in all tissues between arteries and veins; their diameter is 5-10 microns. The main function of capillaries is to ensure the exchange of gases and nutrients between blood and tissues. In this regard, the capillary wall is formed by only one layer of flat endothelial cells, permeable to substances and gases dissolved in the liquid. Through it, oxygen and nutrients easily penetrate from the blood to the tissues, and carbon dioxide and waste products in the opposite direction.

At any given moment, only part of the capillaries is functioning (open capillaries), while the other remains in reserve (closed capillaries). On an area of 1 mm 2 of cross-section of skeletal muscle at rest, there are 100-300 open capillaries. In a working muscle, where the need for oxygen and nutrients increases, the number of open capillaries reaches 2 thousand per 1 mm 2.

Widely anastomosing among themselves, the capillaries form networks (capillary networks), which include 5 links:

arterioles as the most distal parts of the arterial system;
precapillaries, which are an intermediate link between arterioles and true capillaries;
capillaries;
postcapillaries
venules, which are the roots of veins and pass into veins

All these links are equipped with mechanisms that ensure the permeability of the vascular wall and the regulation of blood flow at the microscopic level. Blood microcirculation is regulated by the work of the muscles of the arteries and arterioles, as well as special muscle sphincters, which are located in the pre- and post-capillaries. Some vessels of the microvasculature (arterioles) perform primarily a distributive function, while others (precapillaries, capillaries, postcapillaries and venules) perform a predominantly trophic (metabolic) function.

Vienna

Unlike arteries, veins (Latin vena, Greek phlebs; hence phlebitis - inflammation of the veins) do not carry, but collect blood from the organs and carry it in the opposite direction to the arteries: from the organs to the heart. The walls of veins have the same structure as the walls of arteries, but the blood pressure in the veins is very low, so the vein walls are thin and have less elastic and muscle tissue, causing empty veins to collapse. The veins widely anastomose with each other, forming venous plexuses. Merging with each other, small veins form large venous trunks - veins that flow into the heart.

The movement of blood through the veins is carried out due to the suction action of the heart and the chest cavity, in which negative pressure is created during inhalation due to the pressure difference in the cavities, the contraction of striated and smooth muscles of the organs and other factors. The contraction of the muscular lining of the veins is also important, which in the veins of the lower half of the body, where conditions for venous outflow are more difficult, is more developed 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. Venous valves consist 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 run 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 exceptions are mainly the superficial veins, running in the subcutaneous tissue and almost never accompanying the arteries.

The walls of blood vessels have their own thin arteries and veins, vasa vasorum, serving them. They arise either from the same trunk, the wall of which is supplied with blood, or from a neighboring one and pass in the connective tissue layer surrounding the blood vessels and more or less closely connected with their adventitia; this layer is called the vascular vagina, vagina vasorum.

The walls of arteries and veins contain numerous nerve endings (receptors and effectors) connected to the central nervous system, due to which the nervous regulation of blood circulation is carried out through the mechanism of reflexes. Blood vessels represent extensive reflexogenic zones that play an important role in the neurohumoral regulation of metabolism.

Functional groups of blood vessels

All vessels, depending on the function they perform, can be divided into six groups:

shock-absorbing vessels (elastic type vessels)
resistance vessels
sphincter vessels
exchange vessels
capacitive vessels
shunt vessels

Shock-absorbing vessels. These vessels include elastic-type arteries with a relatively high content of elastic fibers, such as the aorta, pulmonary artery and adjacent sections of large arteries. The pronounced elastic properties of such vessels, in particular the aorta, cause a shock-absorbing effect, or the so-called Windkessel effect (Windkessel in German means “compression chamber”). This effect is to dampen (smooth) the periodic systolic waves of blood flow.

The Windkessel effect for smoothing the movement of liquid can be explained by the following experiment: water is released from the tank in an intermittent stream simultaneously through two tubes - rubber and glass, which end in thin capillaries. In this case, water flows out of a glass tube in spurts, while from a rubber tube it flows evenly and in greater quantities than from a glass tube. The ability of an elastic tube to equalize and increase the flow of liquid depends on the fact that at the moment when its walls are stretched by a portion of liquid, elastic tension energy of the tube arises, i.e., a portion of the kinetic energy of liquid pressure is converted into potential energy of elastic tension.

In the cardiovascular system, part of the kinetic energy developed by the heart during systole is spent on stretching the aorta and the large arteries extending from it. The latter form an elastic, or compression, chamber into which a significant volume of blood enters, stretching it; in this case, the kinetic energy developed by the heart is converted into the energy of elastic tension of the arterial walls. When systole ends, this elastic tension of the vascular walls created by the heart maintains blood flow during diastole.

More distally located arteries have more smooth muscle fibers, so they are classified as muscular-type arteries. Arteries of one type smoothly pass into vessels of another type. Obviously, in large arteries, smooth muscles influence mainly the elastic properties of the vessel, without actually changing its lumen and, consequently, hydrodynamic resistance.

Resistive vessels. Resistive vessels include terminal arteries, arterioles and, to a lesser extent, capillaries and venules. It is the terminal arteries and arterioles, i.e., precapillary vessels that have a relatively small lumen and thick walls with developed smooth muscles, that provide the greatest resistance to blood flow. Changes in the degree of contraction of the muscle fibers of these vessels lead to distinct changes in their diameter and, therefore, in the total cross-sectional area (especially when it comes to multiple arterioles). Considering that hydrodynamic resistance largely depends on the cross-sectional area, it is not surprising that it is the contractions of the smooth muscles of the precapillary vessels that serve as the main mechanism for regulating the volumetric velocity of blood flow in various vascular areas, as well as the distribution of cardiac output (systemic blood flow) among different organs .

The resistance of the postcapillary bed depends on the condition of the venules and veins. The relationship between precapillary and postcapillary resistance is of great importance for the hydrostatic pressure in the capillaries and, therefore, for filtration and reabsorption.

Sphincter vessels. The number of functioning capillaries, i.e., the exchange surface area of the capillaries (see Fig.), depends on the narrowing or expansion of the sphincters - the last sections of the precapillary arterioles.

Exchange vessels. These vessels include capillaries. It is in them that such important processes as diffusion and filtration occur. Capillaries are not capable of contraction; their diameter changes passively following pressure fluctuations in pre- and post-capillary resistive vessels and sphincter vessels. Diffusion and filtration also occur in venules, which should therefore be classified as exchange vessels.

Capacitive vessels. Capacitive vessels are mainly veins. Due to their high distensibility, veins are able to accommodate or eject large volumes of blood without significantly affecting other parameters of blood flow. In this regard, they can play the role of blood reservoirs.

Some veins at low intravascular pressure are flattened (i.e., have an oval lumen) and therefore can accommodate some additional volume without stretching, but only acquiring a more cylindrical shape.

Some veins have a particularly high capacity as blood reservoirs, which is due to their anatomical structure. These veins include primarily 1) the veins of the liver; 2) large veins of the celiac region; 3) veins of the subpapillary plexus of the skin. Together, these veins can hold more than 1000 ml of blood, which is released when needed. Short-term deposition and release of sufficiently large quantities of blood can also be carried out by the pulmonary veins connected to the systemic circulation in parallel. This changes the venous return to the right heart and/or the output of the left heart [show]

Intrathoracic vessels as a blood depot

Due to the great distensibility of the pulmonary vessels, the volume of blood circulating in them can temporarily increase or decrease, and these fluctuations can reach 50% of the average total volume of 440 ml (arteries - 130 ml, veins - 200 ml, capillaries - 110 ml). Transmural pressure in the vessels of the lungs and their distensibility change slightly.

The volume of blood in the pulmonary circulation, together with the end-diastolic volume of the left ventricle of the heart, constitutes the so-called central blood reserve (600-650 ml) - a quickly mobilized depot.

So, if it is necessary to increase the output of the left ventricle within a short time, then about 300 ml of blood can come from this depot. As a result, the balance between the output of the left and right ventricles will be maintained until another mechanism for maintaining this balance is activated - an increase in venous return.

Humans, unlike animals, do not have a true depot in which blood could be retained in special formations and released as necessary (an example of such a depot is the spleen of a dog).

In a closed vascular system, changes in the capacity of any department are necessarily accompanied by a redistribution of blood volume. Therefore, changes in the capacity of the veins that occur during contractions of smooth muscles affect the distribution of blood throughout the entire circulatory system and thereby directly or indirectly on the overall circulatory function.

Shunt vessels - These are arteriovenous anastomoses present in some tissues. When these vessels are open, blood flow through the capillaries is either reduced or stopped completely (see figure above).

According to the functions and structure of various sections and the characteristics of innervation, all blood vessels have recently begun to be divided into 3 groups:

pericardial vessels that begin and end both circles of blood circulation - the aorta and pulmonary trunk (i.e., elastic arteries), hollow and pulmonary veins;
main vessels that serve to distribute blood throughout the body. These are large and medium-sized extraorgan arteries of the muscular type and extraorgan veins;
organ vessels that provide exchange reactions between blood and organ parenchyma. These are intraorgan arteries and veins, as well as capillaries

/ 12.11.2017

What is the middle layer of the vessel wall called? Vessels, types. The structure of the walls of blood vessels.

Anatomy of the heart.

2. Types of blood vessels, features of their structure and function.

3. Structure of the heart.

4. Topography of the heart.

1. General characteristics of the cardiovascular system and its significance.

The cardiovascular system includes two systems: circulatory (circulatory system) and lymphatic (lymph circulation system). The circulatory system connects the heart and blood vessels. The lymphatic system includes lymphatic capillaries, lymphatic vessels, lymphatic trunks and lymphatic ducts branched in organs and tissues, through which lymph flows towards large venous vessels. The doctrine of SSS is called angiocardiology.

The circulatory system is one of the main systems of the body. It ensures the delivery of nutrients, regulatory, protective substances, oxygen to tissues, removal of metabolic products, and heat exchange. It is a closed vascular network that penetrates all organs and tissues, and has a centrally located pumping device - the heart.

Types of blood vessels, features of their structure and function.

Anatomically, blood vessels are divided into arteries, arterioles, precapillaries, capillaries, postcapillaries, venules And veins.

Arteries – these are blood vessels that carry blood from the heart, regardless of what type of blood is in them: arterial or venous. They are cylindrical tubes, the walls of which consist of 3 shells: outer, middle and inner. Outdoor(adventitia) membrane is composed of connective tissue, average– smooth muscle, internal– endothelial (intima). In addition to the endothelial lining, the inner lining of most arteries also has an internal elastic membrane. The outer elastic membrane is located between the outer and middle membranes. Elastic membranes give the artery walls additional strength and elasticity. The thinnest arterial vessels are called arterioles. They go to precapillaries, and the latter - in capillaries, the walls of which are highly permeable, allowing the exchange of substances between blood and tissues.

Capillaries – these are microscopic vessels that are found in tissues and connect arterioles to venules through precapillaries and postcapillaries. Postcapillaries are formed from the fusion of two or more capillaries. As postcapillaries merge, they form venules- the smallest venous vessels. They flow into the veins.

Vienna These are blood vessels that carry blood to the heart. The walls of veins are much thinner and weaker than arterial ones, but consist of the same three membranes. However, the elastic and muscular elements in the veins are less developed, so the vein walls are more pliable and can collapse. Unlike arteries, many veins have valves. The valves are semilunar folds of the inner membrane that prevent blood from flowing back into them. There are especially many valves in the veins of the lower extremities, in which the movement of blood occurs against gravity and creates the possibility of stagnation and reverse blood flow. There are many valves in the veins of the upper extremities, and fewer in the veins of the torso and neck. Only both vena cavae, the veins of the head, the renal veins, the portal and pulmonary veins do not have valves.

The branches of the arteries are connected to each other, forming arterial anastomosis - anastomoses. The same anastomoses connect veins. When the inflow or outflow of blood through the main vessels is disrupted, anastomoses promote the movement of blood in different directions. Vessels that provide blood flow bypassing the main path are called collateral (roundabout).

The blood vessels of the body are united into big And pulmonary circulation. In addition, there is an additional coronary circulation.

Systemic circulation (bodily) starts from the left ventricle of the heart, from which blood enters the aorta. From the aorta, through the system of arteries, blood is carried into the capillaries of organs and tissues throughout the body. Through the walls of the body's capillaries, the exchange of substances between blood and tissues occurs. Arterial blood gives oxygen to tissues and, saturated with carbon dioxide, turns into venous blood. The systemic circulation ends with two vena cavae flowing into the right atrium.

Pulmonary circulation (pulmonary) begins with the pulmonary trunk, which arises from the right ventricle. It delivers blood to the pulmonary capillary system. In the capillaries of the lungs, venous blood, enriched with oxygen and freed from carbon dioxide, turns into arterial blood. Arterial blood flows from the lungs through 4 pulmonary veins into the left atrium. The pulmonary circulation ends here.

Thus, blood moves through a closed circulatory system. The speed of blood circulation in a large circle is 22 seconds, in a small circle – 5 seconds.

Coronary circulation (cardiac) includes the vessels of the heart itself to supply blood to the heart muscle. It begins with the left and right coronary arteries, which arise from the initial part of the aorta - the aortic bulb. Flowing through the capillaries, the blood delivers oxygen and nutrients to the heart muscle, receives breakdown products, and turns into venous blood. Almost all the veins of the heart flow into a common venous vessel - the coronary sinus, which opens into the right atrium.

Structure of the heart.

Heart(cor; Greek cardia) is a hollow muscular organ shaped like a cone, the apex of which faces down, left and forward, and the base faces up, right and back. The heart is located in the chest cavity between the lungs, behind the sternum, in the anterior mediastinum. Approximately 2/3 of the heart is in the left half of the chest and 1/3 is in the right.

The heart has 3 surfaces. Front surface the heart is adjacent to the sternum and costal cartilages, back– to the esophagus and thoracic aorta, lower- to the diaphragm.

The heart also has edges (right and left) and grooves: coronary and 2 interventricular (anterior and posterior). The coronary groove separates the atria from the ventricles, and the interventricular grooves separate the ventricles. Vessels and nerves are located in the grooves.

The size of the heart varies individually. Usually the size of the heart is compared with the size of a given person’s fist (length 10-15 cm, transverse size - 9-11 cm, anteroposterior size - 6-8 cm). The average weight of an adult human heart is 250-350 g.

The wall of the heart consists of 3 layers:

- inner layer (endocardium) lines the cavities of the heart from the inside, its outgrowths form the heart valves. It consists of a layer of flattened, thin, smooth endothelial cells. The endocardium forms the atrioventricular valves, valves of the aorta, pulmonary trunk, as well as the valves of the inferior vena cava and coronary sinus;

- middle layer (myocardium) is the contractile apparatus of the heart. The myocardium is formed by striated cardiac muscle tissue and is the thickest and functionally powerful part of the heart wall. The thickness of the myocardium is not the same: the greatest is in the left ventricle, the smallest in the atria.

The ventricular myocardium consists of three muscle layers - outer, middle and inner; the atrial myocardium is made up of two layers of muscles - superficial and deep. The muscle fibers of the atria and ventricles originate from the fibrous rings that separate the atria from the ventricles. fibrous rings are located around the right and left atrioventricular openings and form a kind of skeleton of the heart, which includes thin rings of connective tissue around the openings of the aorta, pulmonary trunk and the adjacent right and left fibrous triangles.

- outer layer (epicardium) covers the outer surface of the heart and the areas of the aorta, pulmonary trunk and vena cava closest to the heart. It is formed by a layer of cells of the epithelial type and represents the inner layer of the pericardial serous membrane - pericardium. The pericardium insulates the heart from surrounding organs, protects the heart from excessive stretching, and the fluid between its plates reduces friction during cardiac contractions.

The human heart is divided by a longitudinal septum into two halves that do not communicate with each other (right and left). At the top of each half is located atrium(atrium) right and left, in the lower part – ventricle(ventriculus) right and left. Thus, the human heart has 4 chambers: 2 atria and 2 ventricles.

The right atrium receives blood from all parts of the body through the superior and inferior vena cava. Four pulmonary veins flow into the left atrium, carrying arterial blood from the lungs. The pulmonary trunk emerges from the right ventricle, through which venous blood enters the lungs. The aorta emerges from the left ventricle, carrying arterial blood to the vessels of the systemic circulation.

Each atrium communicates with the corresponding ventricle through atrioventricular orifice, stocked flap valve. The valve between the left atrium and ventricle is bicuspid (mitral), between the right atrium and ventricle – tricuspid. The valves open towards the ventricles and allow blood to flow only in that direction.

The pulmonary trunk and aorta at their origin have semilunar valves, consisting of three semilunar valves and opening in the direction of blood flow in these vessels. Special protrusions of the atria form right And left atrial appendage. On the inner surface of the right and left ventricles there are papillary muscles- these are outgrowths of the myocardium.

Topography of the heart.

Upper limit corresponds to the upper edge of the cartilages of the third pair of ribs.

Left border runs along an arcuate line from the cartilage of the third rib to the projection of the apex of the heart.

Top the heart is determined in the left 5th intercostal space 1–2 cm medial to the left midclavicular line.

Right border passes 2 cm to the right of the right edge of the sternum

Bottom line– from the upper edge of the cartilage of the fifth right rib to the projection of the apex of the heart.

There are age-related and constitutional features of the location (in newborn children, the heart lies entirely horizontally in the left half of the chest).

Main hemodynamic parameters is volumetric blood flow velocity, pressure in various parts of the vascular bed.

Volume velocity- this is the amount of blood flowing through the cross-section of a vessel per unit of time and depends on the pressure difference at the beginning and end of the vascular system and on resistance.

Arterial pressure depends on the work of the heart. Blood pressure fluctuates in the vessels with each systole and diastole. During systole, blood pressure increases - systolic pressure. At the end of diastole it decreases - diastolic. The difference between systolic and diastolic characterizes pulse pressure.

Vessels are tube-like structures that run throughout the human body. Blood moves through them. The pressure in the circulatory system is quite high, since the system is closed. Blood circulates through such a system very quickly.

After a long period of time, plaques form on the vessels, which obstruct the movement of blood. They form on the inside of blood vessels. To overcome obstacles in the vessels, the heart must pump blood with greater intensity, as a result of which the working process of the heart is disrupted. The heart is currently no longer capable of delivering blood to the organs of the body. It doesn't do the job. At this stage there is still a possibility of recovery. The vessels are cleansed of cholesterol deposits and salts.

After cleansing the blood vessels, their flexibility and elasticity are restored. Most vascular diseases disappear, for example, headaches, paralysis, sclerosis, and a tendency to heart attack. Vision and hearing are restored, decreased, and the condition of the nasopharynx is normalized.

Types of Blood Vessels

There are three types of blood vessels in the human body: arteries, veins and blood capillaries. Arteries perform the function of delivering blood to various tissues and organs from the heart. They strongly form arterioles and branch. Veins, on the contrary, return blood from tissues and organs to the heart. Blood capillaries are the thinnest vessels. When they merge, the smallest veins are formed - venules.

Arteries

Blood moves through arteries from the heart to various human organs. At the distance furthest from the heart, the arteries divide into fairly small branches. Such branches are called arterioles.

The artery consists of an inner, outer and middle membrane. The inner shell is a flat epithelium with smooth

The inner shell consists of squamous epithelium, the surface of which is very smooth, it is adjacent to, and also rests on the basal elastic membrane. The middle shell consists of smooth muscle tissue and elastic developed tissues. Thanks to muscle fibers, the arterial lumen changes. Elastic fibers provide strength, elasticity and elasticity to the arteries' walls.

Thanks to the fibrous loose connective tissue present in the outer shell, the arteries are in the necessary fixed state, while they are perfectly protected.

The middle arterial layer does not have muscle tissue; it consists of elastic tissues, which make it possible for them to exist at a sufficiently high blood pressure. Such arteries include the aorta and pulmonary trunk. The small arteries located in the middle layer have practically no elastic fibers, but they are equipped with a muscle layer that is very developed.

Blood capillaries

Capillaries are located in the intercellular space. Of all the vessels they are the thinnest. They are located close to the arterioles - in places of strong branching of small arteries, and they are also further from the other vessels from the heart. The length of the capillaries is in the range of 0.1 - 0.5 mm, the clearance is 4-8 microns. A huge number of capillaries in the heart muscle. On the contrary, in muscles there are very few skeletal capillaries. There are more capillaries in the human head in gray matter than in white matter. This is because the number of capillaries increases in tissues that have a high metabolic rate. When capillaries merge, they form venules - veins of the smallest size.

Vienna

These vessels are designed to return blood back to the heart from human organs. The venous wall also consists of an inner, outer and middle layer. But since the middle layer is quite thin in comparison with the arterial middle layer, the venous wall is much thinner.

Since veins do not need to withstand high blood pressures, there are much fewer muscle and elastic fibers in these vessels than in arteries. Veins also have significantly more venous valves on the inner wall. Such valves are absent in the superior vena cava, veins of the brain of the head and heart, and in the pulmonary veins. Venous valves prevent the reverse movement of blood in the veins during the working process of skeletal muscles.

VIDEO

Traditional methods of treating vascular diseases

Treatment with garlic

You need to crush one head of garlic using a garlic press. Then the chopped garlic is placed in a jar and filled with a glass of unrefined sunflower oil. If possible, it is better to use fresh linseed oil. Let the mixture sit for one day in a cold place.

After this, you need to add one squeezed lemon in a juicer along with the peel to this tincture. The resulting mixture is intensively mixed and taken 30 minutes before meals, a teaspoon three times throughout the day.

The course of treatment must be continued for one to three months. A month later, the treatment is repeated.

Tincture for heart attack and stroke

In folk medicine, there is a huge variety of remedies designed to treat blood vessels, prevent the formation of blood clots, as well as for the prevention of heart attacks. Datura tincture is one such remedy.

The fruit of Datura resembles a chestnut. It also has spines. Datura has five-centimeter white pipes. The plant can reach a height of up to one meter. The fruit cracks after ripening. During this period, its seeds ripen. Datura is sown in spring or autumn. In autumn, the plant is attacked by the Colorado potato beetle. To get rid of beetles, it is recommended to lubricate the plant trunk two centimeters from the ground with Vaseline or fat. After drying, the seeds are stored for three years.

Recipe: 85 g of dry (100 g of ordinary seeds) is filled with moonshine in an amount of 0.5 l (moonshine can be replaced with medical alcohol diluted with water in a ratio of 1:1). The product must be allowed to brew for fifteen days, and it must be shaken every day. There is no need to strain the tincture. It should be stored in a dark bottle at room temperature, protected from direct sunlight.

Directions for use: daily in the morning, 30 minutes before meals, 25 drops, always on an empty stomach. The tincture is diluted in 50-100 ml of cool but boiled water. The treatment course is one month. The treatment process must be constantly monitored; it is recommended to draw up a schedule. Repeated course of treatment after six months, and then after two. After taking the tincture I feel very thirsty. Therefore, you need to drink a lot of water.

Blue iodine for the treatment of blood vessels

People talk a lot about blue iodine. In addition to its use for the treatment of vascular diseases, it is used in a number of other diseases.

Cooking method: you need to dilute one teaspoon of potato starch in 50 ml of warm water, stir, add one teaspoon of sugar, citric acid on the tip of a knife. Then this solution is poured into 150 ml of boiled water. The mixture should be allowed to cool completely, and then pour 5% iodine tincture into it in the amount of one teaspoon.

Recommendations for use: The mixture can be stored in a closed jar at room temperature for several months. You need to take 6 teaspoons after meals once a day for five days. Then a five-day break is taken. The medicine can be taken every other day. If allergies occur, you need to drink two tablets of activated charcoal on an empty stomach.

It must be remembered that if citric acid and sugar are not added to the solution, then its shelf life is reduced to ten days. It is also not recommended to abuse blue iodine, because when it is consumed in excess, the amount of mucus increases, and signs of a cold or cold appear. In such cases, you need to stop consuming blue iodine.

Special balm for blood vessels

People have two methods of treating blood vessels using balms that can help with deep atherosclerosis, hypertension, coronary heart disease, cerebral vascular spasms, and stroke.

Cooking recipe 1: 100 ml of alcohol tinctures of blue cyanosis root, prickly hawthorn flowers, white mistletoe leaves, medicinal lemon balm herb, dog nettle, large plantain leaves, peppermint herb.

Cooking recipe 2: Mix 100 ml of alcohol-based tinctures of Baikal skullcap root, hop cones, medicinal valerian root, dog nettle, and lily of the valley herb.

How to use the balm: 3 tablespoons per day, 15 minutes before meals.

MOST INTERESTING NEWS

Outside the inner layer is the middle shell (media), consisting of circular smooth muscle fibers with an admixture of elastic connective tissue.

At the border of the middle and inner, middle and outer shells of blood vessels, elastic fibers form a kind of thin plate (membrana elastica interna, membrana elastica externa).

In the outer and middle membranes of blood vessels, the vessels that feed their wall (vasa vasorum) branch.

The distribution of blood throughout the human body is carried out due to the work of the cardiovascular system. Its main organ is the heart. Each blow helps the blood move and nourish all organs and tissues.

System structure

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

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

Principle of operation

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

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

Veins are divided into superficial and deep. The first ones are close to the surface of the skin. They carry blood into the deep veins, which return it to the heart.

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

How does blood flow

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

The circulatory system includes two circles: small and large. The first of them is designed to saturate the blood with oxygen, and the second is to transport it throughout the orgasm, delivering it to every cell.

Requirements for the circulatory system

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

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

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

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

Classification of vessels

To understand how the circulatory system works, you need to understand how each of its components functions. Thus, the pulmonary and vena cava, pulmonary trunk and aorta are the main routes for the movement of the necessary biological fluid. And everyone else is able to regulate the intensity of blood inflow and outflow to tissues due to the ability to change their lumen.

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

Arteries

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

The first type includes those vessels that are directly connected to the heart and emerge from its ventricles. These are the pulmonary trunk, pulmonary and carotid arteries, and aorta.

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

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

Other types of blood vessels are also distinguished. These include muscular-elastic or mixed arteries. They can contract very well, but are also highly elastic. This type includes the subclavian, femoral, iliac, mesenteric arteries, and celiac trunk. They contain both elastic fibers and muscle cells.

Arterioles and capillaries

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

The thinnest vessels are capillaries. Together they represent the longest part of the entire circulatory system. They are the ones that connect the venous and arterial beds.

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

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

Venules and veins

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

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

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

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

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

Another characteristic feature of veins is the presence of valves that prevent the reverse flow of blood under the influence of gravity. True, they are not in those vessels that are located in the head, brain, neck and internal organs. They are also absent in the hollow and small veins.

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

Structure of arterial walls

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

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

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

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

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

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

The outer layer consists of loose connective tissue, which contains collagen and elastic fibers; they are located obliquely and longitudinally in it. It also contains nerves, lymphatic and blood vessels.

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

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

Vein structure

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

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

Blood vessels in vertebrates form a dense closed network. The wall of the vessel consists of three layers:

The inner layer is very thin, it is formed by one row of endothelial cells, which give the smoothness of the inner surface of the vessels.
The middle layer is the thickest, containing many muscle, elastic and collagen fibers. This layer ensures the strength of the blood vessels.
The outer layer is connective tissue; it separates the vessels from the surrounding tissues.

According to the circles of blood circulation, blood vessels can be divided into:

Arteries of the systemic circulation [show]
- The largest arterial vessel in the human body is the aorta, which emerges from the left ventricle and gives rise to all the arteries that form the systemic circulation. The aorta is divided into the ascending aorta, aortic arch and descending aorta. The aortic arch is in turn divided into the thoracic aorta and the abdominal aorta.
- Arteries of the neck and head
  The common carotid artery (right and left), which at the level of the upper edge of the thyroid cartilage is divided into the external carotid artery and the internal carotid artery.
  - The external carotid artery gives a number of branches, which, according to their topographical characteristics, are divided into four groups - anterior, posterior, medial and a group of terminal branches supplying the thyroid gland, muscles of the hyoid bone, sternocleidomastoid muscle, muscles of the mucous larynx, epiglottis, tongue, palate, tonsils, face, lips, ear (external and internal), nose, back of the head, dura mater.
  - The internal carotid artery in its course is a continuation of both carotid arteries. It distinguishes between the cervical and intracranial (head) parts. In the cervical part, the internal carotid artery usually does not give branches. In the cranial cavity, branches to the cerebrum and the orbital artery depart from the internal carotid artery, supplying blood to the brain and eye.
  The subclavian artery is a pair, starting in the anterior mediastinum: the right one - from the brachiocephalic trunk, the left one - directly from the aortic arch (therefore, the left artery is longer than the right). In the subclavian artery, three sections are topographically distinguished, each of which gives its branches:
  - The branches of the first section are the vertebral artery, the internal thoracic artery, the thyroid-cervical trunk, each of which gives its own branches that supply blood to the brain, cerebellum, neck muscles, thyroid gland, etc.
  - Branches of the second section - here only one branch departs from the subclavian artery - the costocervical trunk, which gives rise to arteries supplying blood to the deep muscles of the back of the head, spinal cord, back muscles, intercostal spaces
  - Branches of the third section - one branch also departs here - the transverse artery of the neck, which supplies blood to the back muscles
- Arteries of the upper limb, forearm and hand
- Arteries of the trunk
- Pelvic arteries
- Arteries of the lower limb
Veins of the systemic circulation [show]
- Superior vena cava system
  - Veins of the trunk
  - Veins of the head and neck
  - Veins of the upper limb
- Inferior vena cava system
  - Veins of the trunk
- Veins of the pelvis
  - Veins of the lower extremities
Vessels of the pulmonary circulation [show]
The vessels of the pulmonary, pulmonary, circulation include:
- pulmonary trunk
- pulmonary veins in two pairs, right and left
Pulmonary trunk is divided into two branches: the right pulmonary artery and the left pulmonary artery, each of which is directed to the gate of the corresponding lung, bringing venous blood from the right ventricle to it.
The right artery is slightly longer and wider than the left. Having entered the root of the lung, it is divided into three main branches, each of which enters the gate of the corresponding lobe of the right lung.
The left artery at the root of the lung is divided into two main branches that enter the gate of the corresponding lobe of the left lung.
A fibromuscular cord (arterial ligament) runs from the pulmonary trunk to the aortic arch. During fetal development, this ligament is the ductus arteriosus, through which most of the blood from the pulmonary trunk of the fetus passes into the aorta. After birth, this duct is obliterated and turns into the indicated ligament.
Pulmonary veins, right and left, - remove arterial blood from the lungs. They leave the hilum of the lungs, usually two from each lung (although the number of pulmonary veins can reach 3-5 or even more), the right veins are longer than the left ones, and flow into the left atrium.

According to their structural features and functions, blood vessels can be divided into:

Groups of vessels according to the structural features of the wall

Arteries

Blood vessels going from the heart to the organs and carrying blood to them are called arteries (aer - air, tereo - contain; on corpses the arteries are empty, which is why in the old days they were considered air tubes). Through the arteries, blood from the heart flows under, so the arteries have thick elastic walls.

According to the structure of the walls, arteries are divided into two groups:

Elastic arteries - the arteries closest to the heart (aorta and its large branches) primarily perform the function of conducting blood. In them, counteraction to stretching by the mass of blood, which is ejected by the heart impulse, comes to the fore. Therefore, structures of a mechanical nature are relatively more developed in their walls, i.e. elastic fibers and membranes. The elastic elements of the arterial wall form a single elastic frame that works like a spring and determines the elasticity of the arteries.
Elastic fibers give arteries elastic properties, which ensure continuous blood flow throughout the vascular system. During contraction, the left ventricle pushes out more blood under high pressure than flows out of the aorta into the arteries. In this case, the walls of the aorta stretch, and it accommodates all the blood ejected by the ventricle. When the ventricle relaxes, the pressure in the aorta drops, and its walls, due to their elastic properties, collapse slightly. Excess blood contained in the distended aorta is pushed out of the aorta into the arteries, although no blood flows from the heart at this time. Thus, the periodic expulsion of blood by the ventricle, due to the elasticity of the arteries, turns into a continuous movement of blood through the vessels.
The elasticity of the arteries provides another physiological phenomenon. It is known that in any elastic system a mechanical shock causes vibrations that propagate throughout the system. In the circulatory system, this impulse is the impact of the blood ejected by the heart against the walls of the aorta. The resulting vibrations propagate along the walls of the aorta and arteries at a speed of 5-10 m/s, which significantly exceeds the speed of blood movement in the vessels. In areas of the body where large arteries come close to the skin - on the wrist, temples, neck - you can feel the vibrations of the artery walls with your fingers. This is the arterial pulse.
Arteries of the muscular type are medium and small arteries in which the inertia of the cardiac impulse weakens and the own contraction of the vascular wall is required for further movement of blood, which is ensured by the relatively greater development of smooth muscle tissue in the vascular wall. Smooth muscle fibers, contracting and relaxing, narrow and dilate arteries and thus regulate blood flow in them.

Widely anastomosing among themselves, the capillaries form networks (capillary networks), which include 5 links:

arterioles as the most distal parts of the arterial system;
precapillaries, which are an intermediate link between arterioles and true capillaries;
capillaries;
postcapillaries
venules, which are the roots of veins and pass into veins

Vienna

Functional groups of blood vessels

All vessels, depending on the function they perform, can be divided into six groups:

shock-absorbing vessels (elastic type vessels)
resistance vessels
sphincter vessels
exchange vessels
capacitive vessels
shunt vessels

Some veins at low intravascular pressure are flattened (i.e., have an oval lumen) and therefore can accommodate some additional volume without stretching, but only acquiring a more cylindrical shape.

Intrathoracic vessels as a blood depot

Humans, unlike animals, do not have a true depot in which blood could be retained in special formations and released as necessary (an example of such a depot is the spleen of a dog).

According to the functions and structure of various sections and the characteristics of innervation, all blood vessels have recently begun to be divided into 3 groups:

pericardial vessels that begin and end both circles of blood circulation - the aorta and pulmonary trunk (i.e., elastic arteries), hollow and pulmonary veins;
main vessels that serve to distribute blood throughout the body. These are large and medium-sized extraorgan arteries of the muscular type and extraorgan veins;
organ vessels that provide exchange reactions between blood and organ parenchyma. These are intraorgan arteries and veins, as well as capillaries