Blood vessels are a type of tissue. The structure of the vascular wall

The human body is all permeated with blood vessels. These peculiar highways provide continuous delivery of blood from the heart to the most remote parts of the body. Due 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 true, though hard to believe. The movement of blood through the vessels is provided by the heart, which acts as a powerful pump.

To deal with the answer to the question: how does the human circulatory system work, 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 eventually 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 having a loose structure. Thanks to this tissue, the vessel can be securely fixed on different parts of the body.

Blood vessels additionally contain nerve receptors that connect them to the CNS. Due to this structure, the 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 the aorta. Very high pressure is constantly maintained inside these elements, so they must be as dense and elastic as possible. Physicians 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 up of dense, elastic fibers that can withstand continuous heartbeats and 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 than the elastic type of blood vessels. Such elements are removed from the heart muscle, and are located near the peripheral internal organs and systems. The walls of the muscular arteries can contract strongly, which ensures blood flow even at reduced pressure.

The main arteries provide all the internal organs with a sufficient amount of blood. Some blood 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 pass into capillaries or veins. Small arteries are called arterioles. Such elements can directly take part 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, as they consist of only one layer of epithelium. Thanks to this feature, useful elements can easily penetrate their walls.

Capillaries are of two types:

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

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

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The third type of blood vessels are veins. They are similar in structure to arteries. However, their function is completely different. After the blood has given up all the 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, their middle layer is less thin than in the arteries.

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

Diseases

In medicine, many pathologies of blood vessels are distinguished. Such diseases can be congenital or acquired throughout life. Each type of vessel can have a particular pathology.

Vitamin therapy is the best prevention of diseases of the circulatory system. Saturation of blood with useful trace elements allows you to make the walls of arteries, veins and capillaries stronger and more elastic. People who are at risk of developing vascular pathologies should definitely include the following vitamins in their diet:

C and R. These trace elements strengthen the walls of blood vessels, prevent capillary fragility. Contained in citrus fruits, rose hips, fresh herbs. You can also additionally use the therapeutic gel Troxevasin.
Vitamin B. To enrich your body with these trace elements, include legumes, liver, cereals, meat in the menu.
AT 5. This vitamin is rich in chicken meat, eggs, broccoli.

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 broth 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 blood vessels, regularly undergo a medical examination, and take all the necessary tests.

Circulation (video)

The structure of blood vessels

Blood vessels develop from the mesenchyme. First, the primary wall is laid, which later turns into the inner shell of the vessels. Mesenchyme cells, when combined, form a 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, a simple capillary wall is gradually surrounded by various structural elements, and the capillary vessel turns either into an artery, or into a vein, or into a lymphatic vessel.

The finally formed vessel walls of both arteries and veins are not the same throughout their entire length, but both of them consist of three main layers (Fig. 231). Common to all vessels is a thin inner shell, or intima (tunica intima), lined from the side of the vessel cavity with the thinnest, very elastic and flat polygonal endothelial cells. The intima is a direct continuation of the endothelium of the endocardium. This inner shell with a smooth and even surface prevents blood from clotting. If the endothelium of the vessel is damaged by a wound, infection, inflammatory or dystrophic process, etc., then small blood clots (clots - thrombi) form at the site of damage, which can increase in size and cause blockage of the vessel. Sometimes they break away from the place of formation, are carried away by the blood flow and, as so-called emboli, clog the vessel in some other place. The effect of such a thrombus or embolus depends on where the vessel is blocked. So, blockage of a vessel in the brain can cause paralysis; blockage of the coronary artery of the heart deprives the heart muscle of blood flow, which is expressed in a severe heart attack and often leads to death. Blockage of a vessel, suitable for 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 of 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) envelops the middle one. It is built in all vessels from 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 the vessels, the elastic fibers form, as it were, a thin plate (membrana elastica interna, membrana elastica externa).

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

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 externally braided with the thinnest network of fibers on which it is suspended, due to which it is very easy and without damage to be displaced. The fibers depart from a thin, main film, which is also associated with special cells - 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 an 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 pass into the capillaries are called arterioles and venules. The wall of the arteriole consists of all three membranes. The innermost endothelial, and the middle one following it, is built from circularly arranged smooth muscle cells. When an arteriole passes into a capillary, only single smooth muscle cells are noted in its wall. With the enlargement of the same arteries, the number of muscle cells gradually increases to a continuous annular layer - arteries of the muscular type.

The structure of small and medium-sized arteries differs in some other feature. Directly under the inner endothelial membrane is a layer of elongated and stellate cells, which in larger arteries form a layer that plays the role of a cambium (growth layer) for the vessels. This layer is involved in the processes of regeneration of the vessel wall, i.e., it has the ability to restore the muscular and endothelial layers of the vessel. In arteries of medium caliber or mixed type, the cambial (growth) layer is more developed.

Arteries of large caliber (aorta, its large branches) are called arteries of the elastic type. 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 expressed 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 artery, like rubber tubes, under the pressure of blood, they can easily stretch and do not collapse, even if the blood is released from them. All the elastic elements of the vessels together form a single elastic skeleton, working like a spring, each time returning the vessel wall to its original state, as soon as 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 the arterial walls can withstand even such strong pressure as occurs in the steam boiler of an ordinary steam locomotive (15 atm.).

The walls of veins are usually thinner than the walls of arteries, especially their medial sheath. There is also much less elastic tissue in the venous wall, so the veins collapse very easily. The outer shell is built of fibrous connective tissue, in which collagen fibers predominate.

A feature of the veins is the presence of valves in them in the form of semi-lunar pockets (Fig. 232), formed from the doubling of the inner shell (intima). However, valves are not found in all veins in our body; they are deprived of 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. Valves are more common 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 due to the law of gravity (hydrostatic pressure), the valves facilitate the flow of blood.

If there were no valves in the veins, the entire weight of a column of blood more than 1 m high would press on the blood entering the lower limb and this would greatly impede blood circulation. Further, if the veins were rigid tubes, the valves alone would not be able to circulate the blood, since the entire column of fluid would still press on the underlying sections. The veins are located among the large skeletal muscles, which, contracting and relaxing, periodically compress the venous vessels. When the contracting muscle compresses the vein, the valves below the pinch close and those above open; when the muscle relaxes and the vein is again free from compression, the upper valves in it close and retain the upstream 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 the circulation of the blood; standing for many hours in one place, in which the muscles help little in the movement of blood, is more tiring than walking.

Blood vessels are the most important part of the body, which is part of the circulatory system and permeates almost the entire human body. They are absent only in the skin, hair, nails, cartilage and cornea of the eyes. And if they are assembled and stretched into one straight line, then the total length will be about 100 thousand km.

These tubular elastic formations function continuously, 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 in a lifetime.

The main types of blood vessels are: capillaries, arteries, and veins. Each type performs its 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 is different. 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 - circles of blood circulation.

The following can be distinguished in the device: the walls of both arteries and veins have a three-layer structure:

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

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. And also in the fact that venous - contain valves.

arteries

They deliver blood saturated with useful substances and oxygen from the heart to all cells of the body. By structure, human arterial vessels are more durable than veins. Such a device (a denser and more durable 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 the arteries carry air and therefore the name is translated from Latin as “containing air”.

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There are such types:

Arteries, leaving the heart, become thinner to small arterioles. This is the name of the thin branches of the arteries, passing into the precapillaries, which form the capillaries.

These are the thinnest 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 is different everywhere, but the highest in the brain and myocardium. They consist only of endothelial cells. They carry out a very important activity: the chemical exchange between the bloodstream and tissues.

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The capillaries are further connected to the post-capillaries, which become venules - small and thin venous vessels that flow into the veins.

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

The walls of the veins are thinner than the walls of the arteries, because there is no strong pressure. The layer of smooth muscles in the middle wall of the vessels of the legs is most developed, because moving up is not an easy job for the blood under the action of gravity.

Venous vessels (all but the superior and inferior vena cava, pulmonary, collar, renal veins and veins of the head) contain special valves that ensure the movement of blood to the heart. The valves block the return flow. Without them, the blood would drain to the feet.

Arteriovenous anastomoses are branches of arteries and veins connected by fistulas.

Separation 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. In the presence of excess weight in the body, more than 10 km (per 1 kg of fat) of additional blood vessels are created. All this creates a very large load on the heart muscle.

Heart disease and overweight, and even worse, obesity, are always very tightly linked. But the good thing is that the human body is also capable of the reverse process - the removal of unnecessary vessels while getting rid of excess fat (precisely from it, and not just from extra pounds).

What role do blood vessels play in human life? In general, they do a very serious and important job. They are a transport that provides 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.

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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 smoothness to the inner surface of the vessels.
The middle layer is the thickest, it has a lot of muscle, elastic and collagen fibers. This layer provides strength to the 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, the aortic arch and the descending aorta. The aortic arch, in turn, divides 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, divides into the external carotid artery and the internal carotid artery.
  - The external carotid artery gives a number of branches, which, according to their topographic features, are divided into four groups - anterior, posterior, medial and a group of terminal branches that supply blood to the thyroid gland, muscles of the hyoid bone, sternocleidomastoid muscle, muscles of the mucous membrane of the larynx, epiglottis, tongue, palate, tonsils, face, lips, ear (external and internal), nose, occiput, 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 large brain and the ophthalmic artery depart from the internal carotid artery, supplying the brain and eye.
  The subclavian artery is a steam room, 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 one). In the subclavian artery, three departments are topographically distinguished, each of which gives its own branches:
  - The branches of the first section - the vertebral artery, the internal thoracic artery, the thyroid-cervical trunk - each of which gives its own branches that supply the brain, cerebellum, neck muscles, thyroid gland, etc.
  - Branches of the second section - here only one branch departs from the subclavian artery - the costal-cervical trunk, which gives rise to arteries that supply blood to the deep muscles of the neck, spinal cord, back muscles, intercostal spaces
  - Branches of the third section - one branch also departs here - the transverse artery of the neck, the blood supplying part of the back muscles
- Arteries of the upper limb, forearm and hand
- Trunk arteries
- Pelvic arteries
- Arteries of the lower limb
Veins of the systemic circulation [show]
- Superior vena cava system
  - Trunk veins
  - Veins of the head and neck
  - Veins of the upper limb
- Inferior vena cava system
  - Trunk veins
- Veins of the pelvis
  - Veins of the lower extremities
Vessels of the pulmonary circulation [show]
The vessels of the small, pulmonary, circle of blood circulation include:
- pulmonary trunk
- pulmonary veins in the amount of 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 sent to the gate of the corresponding lung, bringing venous blood to it from the right ventricle.
The right artery is somewhat longer and wider than the left. Entering 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 divides into two main branches that enter the gate of the corresponding lobe of the left lung.
From the pulmonary trunk to the aortic arch is a fibromuscular cord (arterial ligament). In the period of intrauterine development, this ligament is an arterial duct, 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 specified ligament.
Pulmonary veins, right and left, - carry arterial blood from the lungs. They leave the gates 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, and flow into the left atrium.

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

Groups of vessels according to the structural features of the wall

arteries

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

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

Arteries of the elastic type - the arteries closest to the heart (the aorta and its large branches) perform mainly the function of conducting blood. In them, counteraction to stretching by a mass of blood, which is ejected by a cardiac impulse, comes to the fore. Therefore, mechanical structures are relatively more developed in their wall; 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 the arteries elastic properties that cause a continuous flow of blood throughout the vascular system. The left ventricle pumps out more blood at high pressure during contraction than flows from the aorta into the arteries. In this case, the walls of the aorta are stretched, and it contains all the blood ejected by the ventricle. When the ventricle relaxes, the pressure in the aorta drops, and its walls, due to the elastic properties, subside slightly. Excess blood contained in the distended aorta is pushed from the aorta into the arteries, although no blood is flowing from the heart at this time. Thus, the periodic ejection 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 push causes vibrations that propagate throughout the system. In the circulatory system, such an impetus is the impact of blood ejected by the heart against the walls of the aorta. The oscillations arising from this propagate along the walls of the aorta and arteries at a speed of 5-10 m/s, which significantly exceeds the speed of blood in the vessels. In areas of the body where large arteries come close to the skin - on the wrists, temples, neck - you can feel the vibrations of the walls of the arteries with your fingers. This is the arterial pulse.
Muscular-type arteries are medium and small arteries in which the inertia of the cardiac impulse weakens and its own contraction of the vascular wall is required to further move the blood, which is ensured by the relatively large development of smooth muscle tissue in the vascular wall. Smooth muscle fibers, contracting and relaxing, narrow and expand the arteries and thus regulate the blood flow in them.

Individual arteries supply blood to whole organs or parts of them. In relation to the organ, there are arteries that go outside the organ, before entering it - extraorganic arteries - and their continuations, branching inside it - intraorganic or intraorganic arteries. Lateral branches of the same trunk or branches of different trunks can be connected to each other. Such a connection of vessels before they break up into capillaries is called anastomosis or fistula. Arteries that form anastomoses are called anastomoses (they are the majority). Arteries that do not have anastomoses with neighboring trunks before they pass into capillaries (see below) are called terminal arteries (for example, in the spleen). The terminal, or terminal, arteries are more easily clogged with a blood plug (thrombus) and predispose to the formation of a heart attack (local necrosis of the organ).

The last branches of the arteries become thin and small and therefore stand out under the name 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 performs 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 also in that it is not accompanied by a venule, as is observed in relation to the arteriole. Numerous capillaries arise 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 (open capillaries) is functioning, while the other remains in reserve (closed capillaries). On an area of 1 mm 2 of the cross section of a 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 with each other, 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 pre- and post-capillaries. Some vessels of the microcirculatory bed (arterioles) perform a predominantly distributive function, while the rest (precapillaries, capillaries, postcapillaries and venules) perform a predominantly trophic (exchange) function.

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Unlike arteries, veins (lat. vena, Greek phlebs; hence phlebitis - inflammation of the veins) do not spread, 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 the veins are arranged according to the same plan as the walls of the arteries, however, the blood pressure in the veins is very low, so the walls of the veins are thin, they have less elastic and muscle tissue, due to which the empty veins collapse. The veins anastomose widely 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, during inhalation, negative pressure is created due to the pressure difference in the cavities, contraction of the striated and smooth 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 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 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 thin arteries and veins serving them, 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 adventitia; 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.

Functional groups of vessels

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

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

Cushioning vessels. These vessels include arteries of the elastic type with a relatively high content of elastic fibers, such as the aorta, the pulmonary artery, and adjacent portions of large arteries. The pronounced elastic properties of such vessels, in particular the aorta, determine the shock-absorbing effect, or the so-called Windkessel effect (Windkessel in German means "compression chamber"). This effect consists in amortization (smoothing) of periodic systolic waves of blood flow.

The windkessel effect for equalizing the movement of liquid can be explained by the following experiment: water is let out of the tank in an intermittent stream simultaneously through two tubes - rubber and glass, which end in thin capillaries. At the same time, water flows out of the glass tube in jerks, while it flows evenly and in greater quantities from the rubber tube than from the glass tube. The ability of an elastic tube to equalize and increase the flow of a liquid depends on the fact that at the moment when its walls are stretched by a portion of the liquid, the energy of the elastic stress of the tube arises, i.e., a part of the kinetic energy of the liquid pressure is transferred into the potential energy of the elastic stress.

In the cardiovascular system, part of the kinetic energy developed by the heart during systole is spent on stretching the aorta and large arteries extending from it. The latter form an elastic, or compression, chamber, into which a significant volume of blood enters, stretching it; at the same time, the kinetic energy developed by the heart is converted into the energy of the 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.

The more distally located arteries have more smooth muscle fibers, so they are referred to as muscular-type arteries. Arteries of one type smoothly pass into vessels of another type. Obviously, in large arteries, smooth muscles mainly affect 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, that is, the precapillary vessels, which 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, consequently, in the total cross-sectional area (especially when it comes to numerous arterioles). Considering that the 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 blood flow velocity in various vascular areas, as well as the distribution of cardiac output (systemic blood flow) in different organs. .

The resistance of the postcapillary bed depends on the condition of the venules and veins. The relationship between pre-capillary and post-capillary resistance is of great importance for the hydrostatic pressure in the capillaries and hence for filtration and reabsorption.

Vessels-sphincters. The number of functioning capillaries, that is, the area of the exchange surface of the capillaries, depends on the narrowing or expansion of the sphincters - the last sections of the precapillary arterioles (see Fig.).

exchange vessels. These vessels include capillaries. It is in them that such important processes as diffusion and filtration take place. Capillaries are not capable of contractions; 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 referred to as metabolic vessels.

capacitive vessels. Capacitive vessels are mainly veins. Due to their high extensibility, veins are able to contain or eject large volumes of blood without significantly affecting other blood flow parameters. 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, due to their anatomical structure. These veins include primarily 1) veins of the liver; 2) large veins of the celiac region; 3) veins of the papillary plexus of the skin. Together, these veins can hold more than 1000 ml of blood, which is expelled when needed. Short-term deposition and ejection of sufficiently large amounts of blood can also be carried out by 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 high extensibility 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 extensibility at the same time 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 rapidly mobilized depot.

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

In humans, unlike animals, there is no true depot in which blood could linger in special formations and be thrown out 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 circulatory system and thus directly or indirectly on the overall function of blood circulation.

Shunt vessels are arteriovenous anastomoses present in some tissues. When these vessels are open, blood flow through the capillaries either decreases or stops completely (see figure above).

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

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;
main vessels that serve to distribute blood throughout the body. These are large and medium extraorganic arteries of the muscular type and extraorganic veins;
organ vessels that provide exchange reactions between the blood and the parenchyma of organs. 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. The 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: the circulatory (circulatory system) and the lymphatic (lymphatic circulation system). The circulatory system combines the heart and blood vessels. The lymphatic system includes lymphatic capillaries branched in organs and tissues, lymphatic vessels, lymphatic trunks and lymphatic ducts, through which lymph flows towards large venous vessels. The doctrine of the 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, the removal of metabolic products, and heat transfer. It is a closed vascular network penetrating all organs and tissues, and having 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 whether they contain arterial or venous blood. They are a cylindrical tube, the walls of which consist of 3 shells: outer, middle and inner. outdoor(adventitial) membrane is represented by 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 shells. Elastic membranes give the walls of the arteries additional strength and elasticity. The thinnest arteries are called arterioles. They move into precapillaries, and the latter in capillaries, the walls of which are highly permeable, due to which there is an 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 formed from the fusion of two or more capillaries. As postcapillaries coalesce, they form venules are the smallest veins. They flow into the veins.

Vienna are blood vessels that carry blood to the heart. The walls of the veins are much thinner and weaker than the arterial ones, but they consist of the same three membranes. However, the elastic and muscular elements in the veins are less developed, so the walls of the veins are more pliable and may collapse. Unlike arteries, many veins have valves. The valves are semi-lunar folds of the inner shell that prevent the reverse flow of blood 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, less in the veins of the trunk and neck. Only both vena cava, veins of the head, renal veins, portal and pulmonary veins do not have valves.

Branchings of the arteries are interconnected, forming arterial anastomoses - anastomoses. The same anastomoses connect the veins. In violation of the inflow or outflow of blood through the main vessels, anastomoses contribute to the movement of blood in various directions. Vessels that provide blood flow bypassing the main path are called collateral (roundabout).

The blood vessels of the body are combined into big and small circles of blood circulation. In addition, additionally allocate 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 away into the capillaries of the organs and tissues of the whole body. Through the walls of the capillaries of the body there is an exchange of substances between the blood and tissues. Arterial blood gives oxygen to the tissues and, saturated with carbon dioxide, turns into venous blood. The systemic circulation ends with two vena cava, which flow into the right atrium.

Small circle of blood circulation (pulmonary) begins with the pulmonary trunk, which departs from the right ventricle. It carries 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. From the lungs, arterial blood flows through 4 pulmonary veins into the left atrium. This is where the pulmonary circulation ends.

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

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

The structure of the heart.

Heart(cor; Greek cardia) - a hollow muscular organ, having the shape of a cone, the top of which is turned down, to the left and forward, and the base is up, to the right and back. The heart is located in the chest cavity between the lungs, behind the sternum, in the region of the anterior mediastinum. Approximately 2/3 of the heart is in the left side of the chest and 1/3 in the right.

The heart has 3 surfaces. Front surface heart adjacent to the sternum and costal cartilage, rear- to the esophagus and thoracic aorta, lower- to the diaphragm.

On the heart, edges (right and left) and grooves are also distinguished: coronal and 2 interventricular (anterior and posterior). The coronal sulcus separates the atria from the ventricles, and the interventricular sulci separate the ventricles. The grooves contain blood vessels and nerves.

The size of the heart varies from person to person. Usually, the size of the heart is compared with the size of the fist of a given person (length 10-15 cm, transverse size - 9-11 cm, anteroposterior size - 6-8 cm). The mass of the heart of an adult is on average 250-350 g.

The wall of the heart is made up of 3 layers:

- inner layer (endocardium) lines the cavity of the heart from the inside, its outgrowths form the valves of the heart. It consists of a layer of flattened, thin, smooth endothelial cells. The endocardium forms the atrioventricular valves, the valves of the aorta, the 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 most powerful part of the heart wall. The thickness of the myocardium is not the same: the largest is in the left ventricle, the smallest is in the atria.

The myocardium of the ventricles consists of three muscle layers - outer, middle and inner; atrial myocardium - from 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 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 is the inner sheet of the pericardial serous membrane - pericardium. The pericardium insulates the heart from surrounding organs, prevents the heart from overstretching, and the fluid between its plates reduces friction during heart contractions.

The human heart is divided by a longitudinal partition into 2 halves (right and left) that do not communicate with each other. At the top of each half is atrium(atrium) right and left, at the bottom – 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. 4 pulmonary veins flow into the left atrium, carrying arterial blood from the lungs. From the right ventricle, the pulmonary trunk exits, 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, equipped 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 are papillary muscles are outgrowths of the myocardium.

Topography of the heart.

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

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

tip heart is determined in the left V intercostal space 1–2 cm medially 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 V right rib to the projection of the apex of the heart.

There are age, constitutional features of the location (in newborns, the heart lies entirely in the left half of the chest horizontally).

The main hemodynamic parameters is volumetric blood flow velocity, pressure in different parts of the vascular bed.

Volumetric velocity- this is the amount of blood flowing through the cross section of the vessel per unit of time and depends on the pressure difference at the beginning and end of the vascular system and on the 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 rises - systolic pressure. At the end of diastole, the diastolic decreases. The difference between systolic and diastolic characterizes the pulse pressure.

Vessels are tubular formations that run throughout the human body. They carry blood. The pressure in the circulatory system is quite large, since the system is closed. The blood circulates through this system very quickly.

After a long period of time, plaques form on the vessels, which hinder the movement of blood. They form on the inside of blood vessels. To overcome the 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 at the moment is no longer able to deliver blood to the organs of the body. It doesn't get the job done. At this stage, there is still the possibility of recovery. Vessels are cleansed of cholesterol deposits and salts.

After cleansing the vessels, their flexibility and elasticity are restored. Most vascular diseases disappear, for example, headaches, paralysis, sclerosis, and a tendency to a heart attack. There is a restoration of vision and hearing, it decreases, the state of the nasopharynx normalizes.

Types of blood vessels

There are three types of blood vessels in the human body: arteries, veins, and blood capillaries. The artery performs 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 travels through the arteries from the heart to various human organs. At the distance farthest from the heart, the arteries divide into fairly small branches. These branches are called arterioles.

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

The inner shell consists of squamous epithelium, the surface of which is very smooth, it adjoins, and also rests on the basal elastic membrane. The middle shell consists of muscular smooth tissue and elastic developed tissues. Thanks to muscle fibers, a change in the arterial lumen is carried out. Elastic fibers provide strength, resilience and elasticity to arteries.

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 provide the possibility of their existence at a sufficiently high blood pressure. Such arteries include the aorta, the pulmonary trunk. The small arteries in the middle layer have practically no elastic fibers, but they are supplied with a muscular layer, which 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, they are also farther from the rest of the vessels from the heart. The length of the capillaries is in the range of 0.1 - 0.5 mm, the lumen is 4-8 microns. A huge number of capillaries in the heart muscle. And in the muscles of skeletal capillaries, on the contrary, there are very few. There are more capillaries in the human head in gray than in white matter. This is due to the fact that the number of capillaries increases in tissues that have a high degree of metabolism. Capillaries merge to form venules, the smallest veins.

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 the veins do not need to withstand high blood pressure, there are much fewer muscle and elastic fibers in these vessels than in the arteries. In veins, there is also significantly more on the inner wall of the venous valves. Similar 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 in the working process of skeletal muscles.

VIDEO

Folk methods for the treatment of vascular diseases

garlic treatment

It is necessary to crush one garlic head with a garlic press. Then chopped garlic is laid out in a jar and poured with a glass of unrefined sunflower oil. If possible, it is better to use fresh linseed oil. Let the composition brew for one day in a cold place.

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

The course of treatment should 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 intended for the treatment of blood vessels, the prevention of blood clots, as well as for the prevention and infarction. Datura tincture is one such remedy.

Datura fruit 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 stem of the plant two centimeters from the ground with petroleum jelly or fat. Seeds after drying are stored for three years.

Recipe: 85 g of dry (100 g of ordinary seeds) is poured with moonshine in the amount of 0.5 liters (moonshine can be replaced with medical alcohol diluted with water in a ratio of 1: 1). The tool must be allowed to brew for fifteen days, while every day it must be shaken. It is not necessary to strain the tincture. Store in a dark bottle at room temperature, protected from direct sunlight.

Method of application: daily in the morning 30 minutes before a meal, 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, you want to drink very much. Therefore, you need to drink a lot of water.

Blue iodine for the treatment of blood vessels

A lot of people talk about blue iodine. In addition to its use in 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 at 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% tincture of iodine 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 after meals once a day for five days, 6 teaspoons. Then there is a five-day break. The medicine can be taken every other day. If an allergy occurs, 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 with its excessive use it increases in the amount of mucus, there are signs of a cold or. In such cases, you need to stop the intake of blue iodine.

Special balm for blood vessels

Among the people, there are two ways to treat blood vessels using balms that can help with deep atherosclerosis, hypertension, coronary heart disease, spasms of cerebral vessels, and stroke.

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

Recipe 2: 100 ml of alcohol tinctures of Baikal skullcap root, hop cones, medicinal valerian root, dog nettle, May lily of the valley herb are mixed.

How to use the balm: 1 tablespoon 3 times a day 15 minutes before meals.

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Outside of 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 the vessels, the elastic fibers form, as it were, a thin plate (membrana elastica interna, membrana elastica externa).

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

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

The distribution of blood throughout the human body is carried out due to the work of the cardiovascular system. Its main organ is the heart. Each of his blows contributes to the fact that the blood moves and nourishes all organs and tissues.

System structure

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

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

Principle of operation

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

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

Veins are divided into superficial and deep. The first are close to the surface of the skin. Through them, blood enters the deep veins, which return it to the heart.

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

How does blood flow

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

The circulatory system includes two circles: small and large. The first of them is designed to saturate the blood with oxygen, and the second - for its transportation throughout the orgasm, delivery to every cell.

Requirements for the circulatory system

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

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

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

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

Vessel classification

To understand how the circulatory system works, it is necessary to understand how each of its components functions. So, the pulmonary and hollow veins, the pulmonary trunk and the aorta are the main ways of moving the necessary biological fluid. And all the rest are able to regulate the intensity of the inflow and outflow of blood to the tissues due to the ability to change their lumen.

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

arteries

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

The first type includes those vessels that are directly connected with the heart and exit from its ventricles. This is the pulmonary trunk, pulmonary and carotid arteries, aorta.

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

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

Other types of blood vessels are also isolated. These include muscular-elastic or mixed arteries. They can contract very well, but at the same time they have high elasticity. This type includes the subclavian, femoral, iliac, mesenteric arteries, celiac trunk. They contain both elastic fibers and muscle cells.

Arterioles and capillaries

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

The thinnest vessels are the capillaries. Together, they represent the longest part of the entire circulatory system. It is they who connect the venous and arterial channels.

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

The density of their placement is also not the same. The highest concentration of capillaries is noted in the myocardium and brain, for every 1 mm 3 there are up to 3,000 of them. At the same time, there are only up to 1000 of them in the skeletal muscle, and even less in the bone tissue. It is also important to know that in an active state, under normal conditions, blood does not circulate in all capillaries. About 50% of them are in an inactive state, their lumen is compressed to a minimum, only plasma passes through them.

Venules and veins

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

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

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

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

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

Also, a characteristic difference between the veins is the presence of valves that prevent the backflow of blood under the influence of gravity. True, they are not in those vessels that are in the head, brain, neck and internal organs. They are also absent in the hollow and small veins.

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

The structure of the walls of the arteries

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

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

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

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

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

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

The outer layer consists of loose connective tissue, in which collagen and elastic fibers are located, they are located obliquely and longitudinally in it. Nerves, lymphatic and blood vessels pass through it.

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

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

The structure of the veins

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

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

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 smoothness to the inner surface of the vessels.
The middle layer is the thickest, it has a lot of muscle, elastic and collagen fibers. This layer provides strength to the 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, the aortic arch and the descending aorta. The aortic arch, in turn, divides 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, divides into the external carotid artery and the internal carotid artery.
  - The external carotid artery gives a number of branches, which, according to their topographic features, are divided into four groups - anterior, posterior, medial and a group of terminal branches that supply blood to the thyroid gland, muscles of the hyoid bone, sternocleidomastoid muscle, muscles of the mucous membrane of the larynx, epiglottis, tongue, palate, tonsils, face, lips, ear (external and internal), nose, occiput, 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 large brain and the ophthalmic artery depart from the internal carotid artery, supplying the brain and eye.
  The subclavian artery is a steam room, 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 one). In the subclavian artery, three departments are topographically distinguished, each of which gives its own branches:
  - The branches of the first section - the vertebral artery, the internal thoracic artery, the thyroid-cervical trunk - each of which gives its own branches that supply the brain, cerebellum, neck muscles, thyroid gland, etc.
  - Branches of the second section - here only one branch departs from the subclavian artery - the costal-cervical trunk, which gives rise to arteries that supply blood to the deep muscles of the neck, spinal cord, back muscles, intercostal spaces
  - Branches of the third section - one branch also departs here - the transverse artery of the neck, the blood supplying part of the back muscles
- Arteries of the upper limb, forearm and hand
- Trunk arteries
- Pelvic arteries
- Arteries of the lower limb
Veins of the systemic circulation [show]
- Superior vena cava system
  - Trunk veins
  - Veins of the head and neck
  - Veins of the upper limb
- Inferior vena cava system
  - Trunk veins
- Veins of the pelvis
  - Veins of the lower extremities
Vessels of the pulmonary circulation [show]
The vessels of the small, pulmonary, circle of blood circulation include:
- pulmonary trunk
- pulmonary veins in the amount of 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 sent to the gate of the corresponding lung, bringing venous blood to it from the right ventricle.
The right artery is somewhat longer and wider than the left. Entering 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 divides into two main branches that enter the gate of the corresponding lobe of the left lung.
From the pulmonary trunk to the aortic arch is a fibromuscular cord (arterial ligament). In the period of intrauterine development, this ligament is an arterial duct, 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 specified ligament.
Pulmonary veins, right and left, - carry arterial blood from the lungs. They leave the gates 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, and flow into the left atrium.

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

Groups of vessels according to the structural features of the wall

arteries

The blood vessels that go from the heart to the organs and carry blood to them are called arteries (aer - air, tereo - contain; arteries on corpses 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 of the arteries are divided into two groups:

Arteries of the elastic type - the arteries closest to the heart (the aorta and its large branches) perform mainly the function of conducting blood. In them, counteraction to stretching by a mass of blood, which is ejected by a cardiac impulse, comes to the fore. Therefore, mechanical structures are relatively more developed in their wall; 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 the arteries elastic properties that cause a continuous flow of blood throughout the vascular system. The left ventricle pumps out more blood at high pressure during contraction than flows from the aorta into the arteries. In this case, the walls of the aorta are stretched, and it contains all the blood ejected by the ventricle. When the ventricle relaxes, the pressure in the aorta drops, and its walls, due to the elastic properties, subside slightly. Excess blood contained in the distended aorta is pushed from the aorta into the arteries, although no blood is flowing from the heart at this time. Thus, the periodic ejection 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 push causes vibrations that propagate throughout the system. In the circulatory system, such an impetus is the impact of blood ejected by the heart against the walls of the aorta. The oscillations arising from this propagate along the walls of the aorta and arteries at a speed of 5-10 m/s, which significantly exceeds the speed of blood in the vessels. In areas of the body where large arteries come close to the skin - on the wrists, temples, neck - you can feel the vibrations of the walls of the arteries with your fingers. This is the arterial pulse.
Muscular-type arteries are medium and small arteries in which the inertia of the cardiac impulse weakens and its own contraction of the vascular wall is required to further move the blood, which is ensured by the relatively large development of smooth muscle tissue in the vascular wall. Smooth muscle fibers, contracting and relaxing, narrow and expand the arteries and thus regulate the blood flow in them.

Widely anastomosing with each other, 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 vessels

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

shock-absorbing vessels (vessels of elastic type)
resistive 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

In humans, unlike animals, there is no true depot in which blood could linger in special formations and be thrown out as necessary (an example of such a depot is the spleen of a dog).

Shunt vessels are arteriovenous anastomoses present in some tissues. When these vessels are open, blood flow through the capillaries either decreases or stops completely (see figure above).

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

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;
main vessels that serve to distribute blood throughout the body. These are large and medium extraorganic arteries of the muscular type and extraorganic veins;
organ vessels that provide exchange reactions between the blood and the parenchyma of organs. These are intraorgan arteries and veins, as well as capillaries