What are the walls of the arteries. The structure of the vascular wall. Functional groups of vessels

arteries- these are the vessels through which blood flows, ejected by the heart and continuously supplied to the tissues of the body: in order to reach all tissues, the arteries narrow to the smallest capillaries. Arteries carry blood away from the heart, with the exception of the pulmonary artery and umbilical arteries, which carry oxygenated blood. It is worth noting that the heart has its own blood supply system - the coronary circle, which consists of coronary veins, arteries and capillaries. Coronary vessels are identical to other similar vessels of the body.

FEATURES OF THE STRUCTURE OF ARTERIES

The walls of the arteries are composed of three layers of different tissues, which determine their special characteristics:

• The inner layer consists of a layer of epithelial cell tissue called the endothelium, which lines the lumen of the vessels, and a layer of the inner elastic membrane, which is covered on top with elastic longitudinal fibers.
• The middle layer consists of an internal elastic thin membrane, a thick layer of muscle fibers and transverse fibers of a thin elastic outer layer. Taking into account the structure of the middle shell, the arteries are divided into elastic, muscular, hybrid and mixed types.
• The outer layer consists of loose connective fibrous tissue, which contains blood vessels and nerves.

ARTERIAL PULSE POINTS

The force with which the heart ejects blood with each contraction is necessary for the continuous flow of blood, which must overcome resistance, since all subsequent vessels from the aorta to the capillaries narrow in diameter. With each contraction, the left ventricle ejects a certain amount of blood into the aorta, which stretches due to the elastic walls and narrows again; blood is thus pushed into vessels of smaller diameter - this is how a continuous circle of blood circulation functions.

Since there are certain fluctuations in the cardiac cycle, blood pressure is not always the same. Therefore, two parameters are taken into account for measuring blood pressure; the maximum pressure, which corresponds to the moment of systole, when the left ventricle ejects blood into the aorta, and the minimum, corresponding to the moment of diastole, when the left ventricle expands to refill with blood. It must be said that blood pressure changes during the day and its value increases with age, although under normal conditions it is maintained within certain limits.

CAPILLARY

It is a continuation of small arterioles. Capillaries have a small diameter and very thin walls, and consist of only one layer of cells, so thin that it allows the exchange of oxygen and nutrients between the blood and tissues. The function of the cardiovascular system is the continuous exchange of substances between blood cells and tissues.

Everyone knows that in the human body the function of transferring blood to all tissues from the heart muscle is performed by the vessels. The peculiarity of the structure of the circulatory system allows you to ensure the constant operation of all systems. The length of all the vessels of the human body is thousands of meters, or more precisely, about a hundred thousand. This channel is represented by capillaries, veins, aorta, arteries, venules and arterioles. What are arteries and what is their structure? What function do they perform? What are the types of human arteries?

Human vascular system

Blood vessels are a kind of tubes of different sizes and different structures through which blood circulates. These organs are very durable and able to withstand significant chemical exposure. High strength is ensured by the special structure of the vessels, consisting of an inner layer, middle and outer layers. Inside, the vessels consist of the thinnest epithelium, which provides smoothness to the vascular walls. The middle layer is somewhat thicker than the inner one and consists of muscle, collagen and elastic tissues. Outside, the vessels are covered with a fibrous tissue that protects the loose texture from damage.

Division of vessels into types

Medicine divides the vessels according to the type of structure, functions and some other characteristics into veins, arteries and capillaries. The largest artery is called the aorta, and the largest veins are the pulmonary veins. What are arteries and what are they? In anatomy, there are three types of arteries: elastic, muscular-elastic and muscular. Their walls consist of three shells: outer, middle and inner.

elastic arteries

The vessels of the elastic type exit from the ventricles of the heart. These include: aorta, pulmonary trunk, carotid and pulmonary arteries. The walls of these channels contain many elastic cells, due to which they have elasticity and are able to stretch when blood leaves the heart under pressure and at great speed. At the moments of rest of the ventricles, the stretched walls of the vessels are reduced. This principle of operation helps to maintain normal vascular pressure until the ventricle is filled with blood from the arteries.

The structure of elastic arteries

What is an artery, what is its structure? As you know, the vessels consist of three shells. The inner layer is called the intima. In the elastic type of vessels, it occupies about twenty percent of their walls. This membrane is lined with endothelium located on the basement membrane. Under this layer is the connective tissue, which contains macrophages, muscle cells, fibroblasts, intercellular substance. In those places where the arteries depart from the heart, there are special valves. These types of formations are also observed along the aorta.

The middle layer of the artery is formed from elastic tissue with a large number of membranes. With age, their number increases, and the middle layer itself thickens. Between adjacent membranes are smooth muscle cells that are capable of producing collagen, elastin and some other substances.

The outer shell of the arteries is very thin and is formed by fibrous connective tissue. It protects the vessel from rupture and overstretching. In this place, there are multiple nerve endings, small vessels that feed the outer and middle shells of the arteries.

Muscular type of arteries

The pulmonary column and the aorta are divided into numerous branches that deliver blood to different parts of the body: to the skin, internal organs. Also, arteries of the lower extremities depart from these branches. Parts of the body experience different stress, which is why they need different amounts of blood. Arteries must be able to change lumen to deliver the right amount of blood at different times. Because of this feature, a layer of smooth muscles must be well developed in the arteries, capable of contracting and reducing the lumen.

These types of vessels are of the muscular type. Their diameter is controlled by the sympathetic nervous system. This type includes the arteries of the neck, brachial, radial, vessels and some others.

The structure of the vessels of the muscular type

The walls of the vessels of the muscular type consist of endothelium lining the lumen of the channel, and there is also a connective tissue and an elastic inner membrane. In the connective tissue, elastic and collagen cells, an amorphous substance, are well developed. This layer is best developed in large and medium-sized vessels. Outside of the connective tissue is an internal elastic membrane, which is clearly manifested in large arteries.

The middle layer of the vessel is formed by smooth muscle cells arranged in a spiral. With their contraction, the volume of the lumen decreases, and the blood begins to push through the channel to all parts of the body. Muscle cells are interconnected by an intercellular substance containing elastic fibers. They are located between muscle fibers and are associated with the outer and inner membranes. This system forms an elastic framework that gives elasticity to the walls of the arteries.

Outside, the shell is formed by a loose type of connective tissue, in which there are many collagen fibers. Here are the nerve endings, lymphatic and blood vessels that feed the walls of the arteries.

Muscular-elastic arteries

What are mixed arteries? These are vessels that, in function and structure, occupy an intermediate position between muscular and elastic species. These include the femoral, iliac vessels, as well as the celiac trunk and some other vessels.

The middle layer of mixed arteries consists of elastic fibers and fenestrated membranes. In the deepest places of the outer shell, there are bundles of muscle cells. Outside, they are covered with connective tissue and well-developed collagen fibers. These types of arteries are distinguished from others by their high elasticity and the ability to contract strongly.

As the arteries approach the place of division into arterioles, the lumen decreases, the walls become thinner. There is a decrease in the thickness of the connective tissue, the inner elastic membrane, muscle cells, the elastic membrane gradually disappears, the thickness of the outer shell is disturbed.

The movement of blood through the arteries

During a contraction, the heart pushes blood with great force into the aorta, and from there it enters the arteries, spreading throughout the body. As the vessels fill with blood, the elastic walls contract together with the heart, pushing blood through the vascular bed. The pulse wave is formed during periods of ejection of blood from the left ventricle. At this time, the pressure in the aorta rises sharply, the walls begin to stretch. Then the wave propagates from the aorta to the capillaries, passes through the vertebral artery and other vessels.

Initially, blood is ejected by the heart into the aorta, the walls of which are stretched, and it passes on. With each contraction, the ventricle ejects a certain amount of blood: the aorta stretches, then narrows. Thus, the blood passes further along the channel, to other vessels of smaller diameter. When the heart relaxes, the blood tries to return back through the aorta, but this process is prevented by special valves located in large vessels. They close the lumen from the reverse flow of blood, and the narrowing of the lumen of the channel contributes to further movement.

There are certain fluctuations in the cardiac cycle due to which blood pressure is not always the same. Based on this, two parameters are distinguished: diastole and systole. The first is the moment of relaxation of the ventricle and its filling with blood, and systole is the contraction of the heart. You can determine the strength of blood flow through the arteries by placing your hand on the places of palpation of the pulse: at the base of the thumb, on the carotid or popliteal artery.

In the human body, there are coronary arteries that feed the heart. They begin the third circle of blood circulation - coronary. Unlike small and large, it only nourishes the heart.

Arterioles

As you approach the arterioles, the lumen of the vessels decreases, their walls become thinner, and the outer membrane disappears. After the arteries, arterioles begin - these are small vessels that are considered a continuation of the arteries. Gradually they pass into the capillaries.

The walls of the arterioles have three layers: inner, middle and outer, but they are very weakly expressed. Then the arterioles are divided into even smaller vessels - capillaries. They fill the whole space, penetrate into all cells of the body. It is from here that metabolic processes occur that help maintain the vital activity of the body. Then the capillaries increase in volume and form venules, then veins.

Blood vessels are organs of a layered type. Consists of three shells:

internal;

medium (muscular);

external (adventitial).

Blood vessels are divided into:

arteries that carry blood away from the heart

veins that carry blood to the heart

vessels of the microvasculature.

The structure of blood vessels depends on hemodynamic conditions. Hemodynamic conditions are the conditions for the movement of blood through the vessels. They are determined by the following factors: blood pressure, blood flow velocity, blood viscosity, the influence of the Earth's gravitational field, the location of the vessel in the body.

Hemodynamic conditions determine such morphological features of vessels as:

wall thickness (it is larger in arteries, and smaller in capillaries, which facilitates the diffusion of substances);

the degree of development of the muscular membrane and the direction of smooth myocytes in it;

the ratio in the middle shell of the muscular and elastic components;

the presence or absence of internal and external elastic membranes;

the depth of the vessels;

the presence or absence of valves;

the ratio between the thickness of the vessel wall and the diameter of its lumen;

the presence or absence of smooth muscle tissue in the inner and outer shells.

According to the diameter, the arteries are divided into small, medium and large caliber arteries.

According to the quantitative ratio in the middle shell of the muscular and elastic components, they are divided into arteries:

elastic;

muscular

mixed types.

Elastic type arteries

These vessels include the aorta and pulmonary arteries, they perform a transport function and the function of maintaining pressure in the arterial system during diastole. In this type of vessels, the elastic framework is highly developed, which allows the vessels to be strongly stretched, while maintaining the integrity of the vessel.

Elastic type arteries are built according to the general principle of the structure of vessels and consist of:

internal;

• outer shells.

The inner shell is quite thick and is formed by three layers: endothelial, subendothelial and a layer of elastic fibers. In the endothelial layer, the cells are large, polygonal, they lie on the basement membrane. The subendothelial layer is formed by loose fibrous unformed connective tissue, in which there are many collagen and elastic fibers. There is no internal elastic membrane. Instead, on the border with the middle shell, there is a plexus of elastic fibers, consisting of an inner circular and outer longitudinal layers. The outer layer passes into the plexus of elastic fibers of the middle shell.

The middle shell consists mainly of elastic elements. In an adult, they form 50-70 fenestrated membranes, which lie at a distance of 6-18 microns from each other and each have a thickness of 2.5 microns. Between the membranes is a loose fibrous unformed connective tissue with fibroblasts, collagen, elastic and reticular fibers, smooth myocytes. In the outer layers of the middle shell are the vessels of the vessels that feed the vascular wall.

The outer adventitia is relatively thin, consists of loose fibrous unformed connective tissue, contains thick elastic fibers and bundles of collagen fibers running longitudinally or obliquely, as well as vascular vessels and vascular nerves formed by myelinated and non-myelinated nerve fibers.

Arteries of mixed (muscular-elastic) type

An example of a mixed artery is the axillary and carotid arteries. Since the pulse wave gradually decreases in these arteries, along with the elastic component, they have a well-developed muscular component to maintain this wave. The wall thickness in comparison with the diameter of the lumen of these arteries increases significantly.

The inner shell is represented by endothelial, subendothelial layers and an internal elastic membrane. In the middle shell, both muscular and elastic components are well developed. The elastic elements are represented by individual fibers forming a network, fenestrated membranes and layers of smooth myocytes lying between them, running spirally. The outer shell is formed by loose fibrous unformed connective tissue, in which bundles of smooth myocytes meet, and the outer elastic membrane, which lies immediately behind the middle shell. The outer elastic membrane is somewhat less pronounced than the inner one.

Muscular type arteries

These arteries include arteries of small and medium caliber, lying near the organs and intraorganically. In these vessels, the strength of the pulse wave is significantly reduced, and it becomes necessary to create additional conditions for the promotion of blood, so the muscle component predominates in the middle shell. The diameter of these arteries can decrease due to contraction and increase due to relaxation of smooth myocytes. The wall thickness of these arteries significantly exceeds the diameter of the lumen. Such vessels create resistance to the moving blood, so they are often called resistive.

The inner shell has a small thickness and consists of endothelial, subendothelial layers and an internal elastic membrane. Their structure is generally the same as in the mixed type arteries, and the inner elastic membrane consists of a single layer of elastic cells. The middle shell consists of smooth myocytes, arranged in a gentle spiral, and a loose network of elastic fibers, also lying in a spiral. The spiral arrangement of myocytes contributes to a greater reduction in the lumen of the vessel. Elastic fibers merge with the outer and inner elastic membranes, forming a single frame.

The outer shell is formed by an outer elastic membrane and a layer of loose fibrous unformed connective tissue. It contains the blood vessels of the vessels, sympathetic and parasympathetic nerve plexuses.

Cardiovascular complex of organs includes the heart, arteries, vessels of the microvasculature, veins, lymphatic vessels. The heart and a closed network of blood vessels provide blood circulation in the body and transport of lymph to the heart. The activity of the cardiovascular complex is aimed at maintaining the metabolism and constancy of the internal environment of the body - nutrients, oxygen, biologically active substances that regulate their development and functions come from the blood to the tissues and cells; toxins and products of their special activity are removed into the blood and lymph.

Development. The source of the development of blood vessels is the mesenchyme. The first vessels appear outside the body of the embryo - in the wall of the yolk sac and chorion at the beginning of the 3rd week of embryogenesis. Initially, clusters of mesenchymal cells, called blood islands, are formed. The peripheral cells of the islets flatten and, connecting with each other, form primitive vessels in the form of endothelial tubes. Centrally located mesenchymocytes differentiate into primary blood cells (the initial intravascular stage of hematopoiesis). Vessels appear in the body of the embryo later, also from the mesenchyme by the growth of its cells along the walls of the slit-like spaces of the embryo.

At the end of the 3rd week, communication between the primary blood vessels is established. vessels extra-embryonic organs and body of the embryo. After the beginning of blood circulation, the structure of the vessels becomes noticeably more complicated in accordance with the regional hemodynamic conditions. As part of the walls of blood vessels, in addition to the endothelium, other tissues develop (also originating from the mesenchyme), which, when combined, form the inner, middle, and outer shells of the vessels.

Heart bookmark occurs at the beginning of the 3rd week of development in the form of paired mesenchymal tubes. After their fusion, differentiation of the tissues of the inner lining of the heart, the endocardium, begins. The middle and outer shells of the heart are also formed from paired myoepicardial plates - fragments of the right and left visceral sheets of the splanchnotome. Myoepicardial plates approach the anlage of the endocardium, surround it from the outside, and then, merging, differentiate into tissue elements of the myocardium and epicardium.

arteries. Types and structure of arteries.

arteries- Vessels that ensure the movement of blood from the heart to the microcirculatory bed. According to the size of the diameter, they are divided into arteries of small, medium and large caliber. The wall of all arteries consists of three membranes: internal (tunica intima), middle (tunica media) and external (tunica externa). The tissue composition and the degree of development of these membranes in arteries of different calibers are not the same, which is associated with hemodynamic conditions and features of the functions performed by the vessels of certain sections of the arterial bed. According to the quantitative ratio of elastic and muscular elements in the middle shell of the vessel, arteries of elastic, mixed (muscle-elastic) and muscular types are distinguished.

arteries elastic type (aorta and pulmonary artery) perform a transport function and the function of maintaining blood pressure in the arterial system during diastole of the heart. Their wall experiences rhythmic changes in blood pressure. Blood enters these vessels under high pressure (120-130 mm Hg) and at a speed of about 1 m/s. Under these conditions, the strong development of the elastic framework of the wall is fully justified, which allows the vessels to stretch during systole and take their original position during diastole. Returning to its original position, the elastic wall of such vessels contributes to the fact that portions of blood successively ejected from the ventricles of the heart turn into a continuous blood flow.

Inner shell vessels elastic type (for example, the aorta) consists of endothelium, subendothelial layer and plexus of elastic fibers. In the subendothelial layer, poorly differentiated stellate cells of loose connective tissue, individual smooth muscle cells, and a large number of glycosaminoglycans are determined. With age, there is an accumulation of cholesterol. In the middle shell of the aorta, there are up to 50 elastic fenestrated membranes (more precisely, elastic fenestrated cylinders of different diameters inserted into each other), in the openings of which smooth muscle cells and elastic fibers are located. The outer shell consists of loose fibrous connective tissue containing vascular vessels and nerve trunks.

Mixed arteries(muscle-elastic) type are characterized by an approximately equal number of muscle and elastic elements in the composition of the middle shell. Between smooth myocytes lie dense networks of elastic fibrils.

On the border of the inner and middle shells is clearly expressed internal elastic membrane. The outer shell contains bundles of smooth muscle cells, as well as collagen and elastic fibers. Arteries of this type include carotid, subclavian and others.

Muscular type arteries perform not only transport, but also distribution functions, regulating blood flow to organs under conditions of various physiological loads (these are the so-called organ arteries). Muscular type arteries contain smooth myocytes in the middle shell. This allows arteries to regulate blood flow to organs and maintain blood pumping, which is important for blood supply to organs located at a great distance from the heart. Muscular arteries can be of large, medium and small caliber. The inner shell of the wall of these arteries is formed by the endothelium lying on the basement membrane, the subendothelial layer and the internal elastic membrane, however, in small arteries, the internal elastic membrane is poorly expressed.

The middle shell is formed by smooth muscle tissue with a small amount of fibroblasts, collagen and elastic fibers. Smooth myocytes are located in the middle shell in a gentle spiral. Together with radially and arcuately arranged elastic fibers, myocytes create a single springy frame that prevents arteries from collapsing, ensuring their gaping and continuity of blood flow. On the border between the middle and outer shells there is an outer elastic membrane. The latter refers to the outer shell, consisting of loose connective tissue. Collagen fibers have an oblique and longitudinal direction. In the outer shell of the arteries of the muscular type, the blood vessels and nerves that feed them pass.

Using scanning electron microscopy, it was shown that the inner surface of the endothelium arteries has numerous folds and depressions, microscopic outgrowths of various shapes. This creates an uneven and complex microrelief of the inner (luminal) surface of the vessels. Such a microrelief increases the free contact surface of the endothelium with blood, which is of trophic importance and creates favorable conditions for hemodynamics.

The largest artery is. Arteries depart from it, which, as they move away from the heart, branch and become smaller. The thinnest arteries are called arterioles. In the thickness of the organs, the arteries branch up to the capillaries (see). Nearby arteries are often connected, through which collateral blood flow occurs. Usually, arterial plexuses and networks are formed from the anastomosing arteries. An artery that supplies blood to a part of an organ (a segment of the lung, liver) is called segmental.

The wall of the artery consists of three layers: internal - endothelial, or intima, middle - muscular, or media, with a certain amount of collagen and elastic fibers, and external - connective tissue, or adventitia; the wall of the artery is richly supplied with vessels and nerves, located mainly in the outer and middle layers. Based on the structural features of the wall, the arteries are divided into three types: muscular, muscular - elastic (for example, carotid arteries) and elastic (for example, the aorta). Muscular-type arteries include small arteries and arteries of medium caliber (for example, radial, brachial, femoral). The elastic frame of the artery wall prevents its collapse, ensuring the continuity of blood flow in it.

Usually, the arteries lie for a long distance in depth between the muscles and near the bones, to which the artery can be pressed during bleeding. On a superficially lying artery (for example, the radial one), it is palpated.

The walls of the arteries have their own supplying blood vessels (“vessels of the vessels”). The motor and sensory innervation of the arteries is carried out by sympathetic, parasympathetic nerves and branches of the cranial or spinal nerves. The nerves of the artery penetrate into the middle layer (vasomotors - vasomotor nerves) and contract the muscle fibers of the vascular wall and change the lumen of the artery.

Rice. 1. Arteries of the head, trunk and upper limbs:
1-a. facialis; 2-a. lingualis; 3-a. thyreoidea sup.; 4-a. carotis communis sin.; 5-a. subclavia sin.; 6-a. axillaris; 7 - arcus aortae; £ - aorta ascendens; 9-a. brachialis sin.; 10-a. thoracica int.; 11 - aorta thoracica; 12 - aorta abdominalis; 13-a. phrenica sin.; 14 - truncus coeliacus; 15-a. mesenterica sup.; 16-a. renalis sin.; 17-a. testicular sin.; 18-a. mesenterica inf.; 19-a. ulnaris; 20-a. interossea communis; 21-a. radialis; 22-a. interossea ant.; 23-a. epigastric inf.; 24 - arcus palmaris superficialis; 25 - arcus palmaris profundus; 26 - a.a. digitales palmares communes; 27 - a.a. digitales palmares propriae; 28 - a.a. digitales dorsales; 29 - a.a. metacarpeae dorsales; 30 - ramus carpeus dorsalis; 31-a, profunda femoris; 32-a. femoralis; 33-a. interossea post.; 34-a. iliaca externa dextra; 35-a. iliaca interna dextra; 36-a. sacraiis mediana; 37-a. iliaca communis dextra; 38 - a.a. lumbales; 39-a. renalis dextra; 40 - a.a. intercostales post.; 41-a. profunda brachii; 42-a. brachialis dextra; 43 - truncus brachio-cephalicus; 44-a. subciavia dextra; 45-a. carotis communis dextra; 46-a. carotis externa; 47-a. carotis interna; 48-a. vertebralis; 49-a. occipitalis; 50 - a. temporalis superficialis.

Rice. 2. Arteries of the anterior surface of the lower leg and rear of the foot:
1 - a, genu descendens (ramus articularis); 2-ram! musculares; 3-a. dorsalis pedis; 4-a. arcuata; 5 - ramus plantaris profundus; 5-a.a. digitales dorsales; 7-a.a. metatarseae dorsales; 8 - ramus perforans a. peroneae; 9-a. tibialis ant.; 10-a. recurrens tibialis ant.; 11 - rete patellae et rete articulare genu; 12-a. Genu sup. lateralis.

Rice. 3. Arteries of the popliteal fossa and posterior surface of the lower leg:
1-a. poplitea; 2-a. Genu sup. lateralis; 3-a. Genu inf. lateralis; 4-a. peronea (fibularis); 5 - rami malleolares tat.; 6 - rami calcanei (lat.); 7 - rami calcanei (med.); 8 - rami malleolares mediales; 9-a. tibialis post.; 10-a. Genu inf. medialis; 11-a. Genu sup. medialis.

Rice. 4. Arteries of the plantar surface of the foot:
1-a. tibialis post.; 2 - rete calcaneum; 3-a. plantaris lat.; 4-a. digitalis plantaris (V); 5 - arcus plantaris; 6 - a.a. metatarsea plantares; 7-a.a. digitales propriae; 8-a. digitalis plantaris (hallucis); 9-a. plantaris medialis.

Rice. 5. Arteries of the abdominal cavity:
1-a. phrenica sin.; 2-a. gastric sin.; 3 - truncus coeliacus; 4-a. lienalis; 5-a. mesenterica sup.; 6-a. hepatica communis; 7-a. gastroepiploica sin.; 8 - a.a. jejunales; 9-a.a. ilei; 10-a. colica sin.; 11-a. mesenterica inf.; 12-a. iliaca communis sin.; 13 -aa, sigmoideae; 14-a. rectalis sup.; 15-a. appendicis vermiformis; 16-a. ileocolica; 17-a. iliaca communis dextra; 18-a. colica. dext.; 19-a. pancreaticoduodenal inf.; 20-a. colica media; 21-a. gastroepiploica dextra; 22-a. gastroduodenalis; 23-a. gastrica dextra; 24-a. hepatica propria; 25 - a, cystica; 26 - aorta abdominalis.

Arteries (Greek arteria) - a system of blood vessels extending from the heart to all parts of the body and containing oxygen-enriched blood (an exception is a. pulmonalis, which carries venous blood from the heart to the lungs). The arterial system includes the aorta and all its branches down to the smallest arterioles (Fig. 1-5). Arteries are usually designated by topographic feature (a. facialis, a. poplitea) or by the name of the supplied organ (a. renalis, aa. cerebri). Arteries are cylindrical elastic tubes of various diameters and are divided into large, medium and small. The division of arteries into smaller branches occurs according to three main types (V. N. Shevkunenko).

With the main type of division, the main trunk is well defined, gradually decreasing in diameter as the secondary branches depart from it. The loose type is characterized by a short main trunk, quickly disintegrating into a mass of secondary branches. Transitional, or mixed, type occupies an intermediate position. Branches of arteries are often connected to each other, forming anastomoses. There are intrasystemic anastomoses (between branches of one artery) and intersystemic (between branches of different arteries) (B. A. Dolgo-Saburov). Most anastomoses exist permanently as roundabout (collateral) circulatory pathways. In some cases, collaterals may reappear. Small arteries with the help of arteriovenous anastomoses (see) can directly connect to veins.

Arteries are derivatives of the mesenchyme. In the process of embryonic development, muscle, elastic elements and adventitia, also of mesenchymal origin, join the initial thin endothelial tubules. Histologically, three main membranes are distinguished in the wall of the artery: internal (tunica intima, s. interna), middle (tunica media, s. muscularis) and external (tunica adventitia, s. externa) (Fig. 1). According to the structural features, the arteries of the muscular, muscular-elastic and elastic types are distinguished.

Muscular-type arteries include small and medium-sized arteries, as well as most of the arteries of the internal organs. The inner lining of the artery includes the endothelium, subendothelial layers, and the inner elastic membrane. The endothelium lines the lumen of the artery and consists of flat cells elongated along the axis of the vessel with an oval nucleus. The boundaries between cells have the appearance of a wavy or finely serrated line. According to electron microscopy, a very narrow (about 100 A) gap is constantly maintained between cells. Endothelial cells are characterized by the presence in the cytoplasm of a significant number of bubble-like structures. The subendothelial layer consists of connective tissue with very thin elastic and collagen fibers and poorly differentiated stellate cells. The subendothelial layer is well developed in the arteries of large and medium caliber. The internal elastic, or fenestrated, membrane (membrana elastica interna, s.membrana fenestrata) has a lamellar-fibrillar structure with holes of various shapes and sizes and is closely connected with the elastic fibers of the subendothelial layer.

The middle shell consists mainly of smooth muscle cells, which are arranged in a spiral. Between muscle cells there is a small amount of elastic and collagen fibers. In medium-sized arteries, at the border between the middle and outer shells, elastic fibers can thicken, forming an outer elastic membrane (membrana elastica externa). The complex musculo-elastic skeleton of muscular-type arteries not only protects the vascular wall from overstretching and rupture and ensures its elastic properties, but also allows the arteries to actively change their lumen.

Arteries of the muscular-elastic, or mixed, type (for example, the carotid and subclavian arteries) have thicker walls with an increased content of elastic elements. Fenestrated elastic membranes appear in the middle shell. The thickness of the internal elastic membrane also increases. An additional inner layer appears in the adventitia, containing separate bundles of smooth muscle cells.

The vessels of the largest caliber belong to the elastic type arteries - the aorta (see) and the pulmonary artery (see). In them, the thickness of the vascular wall increases even more, especially the middle membrane, where elastic elements predominate in the form of 40-50 powerfully developed fenestrated elastic membranes connected by elastic fibers (Fig. 2). The thickness of the subendothelial layer also increases, and in addition to loose connective tissue rich in stellate cells (Langhans layer), separate smooth muscle cells appear in it. The structural features of the elastic type arteries correspond to their main functional purpose - mainly passive resistance to a strong push of blood ejected from the heart under high pressure. Different sections of the aorta, differing in their functional load, contain a different amount of elastic fibers. The wall of the arteriole retains a strongly reduced three-layer structure. Arteries that supply blood to internal organs have structural features and intraorgan distribution of branches. Branches of the arteries of hollow organs (stomach, intestines) form networks in the wall of the organ. Arteries in parenchymal organs have a characteristic topography and a number of other features.

Histochemically, a significant amount of mucopolysaccharides is found in the ground substance of all the membranes of the arteries, and especially in the inner membrane. The walls of the arteries have their own blood vessels supplying them (a. and v. vasorum, s. vasa vasorum). Vasa vasorum are located in adventitia. The nutrition of the inner shell and the part of the middle shell bordering it is carried out from the blood plasma through the endothelium by pinocytosis. Using electron microscopy, it was found that numerous processes extending from the basal surface of endothelial cells reach muscle cells through holes in the inner elastic membrane. When the artery contracts, many small and medium-sized windows in the internal elastic membrane partially or completely close, which makes it difficult for nutrients to flow through the processes of endothelial cells to muscle cells. Great importance in the nutrition of areas of the vascular wall, devoid of vasa vasorum, is attached to the main substance.

The motor and sensory innervation of the arteries is carried out by sympathetic, parasympathetic nerves and branches of the cranial or spinal nerves. The nerves of the arteries, which form plexuses in the adventitia, penetrate into the middle shell and are designated as vasomotor nerves (vasomotors), which contract the muscle fibers of the vascular wall and narrow the lumen of the artery. The walls of the artery are equipped with numerous sensitive nerve endings - angioreceptors. In some parts of the vascular system, there are especially many of them and they form reflexogenic zones, for example, at the place of division of the common carotid artery in the area of ​​the carotid sinus. The thickness of the walls of the artery and their structure are subject to significant individual and age-related changes. And arteries have a high ability to regenerate.

Pathology of the arteries - see Aneurysm, Aortitis, Arteritis, Atherosclerosis, Coronaritis., Coronarosclerosis, Endarteritis.

See also Blood vessels.

Carotid artery

Rice. 1. Arcus aortae and its branches: 1 - mm. stylohyoldeus, sternohyoideus and omohyoideus; 2 and 22 - a. carotis int.; 3 and 23 - a. carotis ext.; 4 - m. cricothyreoldeus; 5 and 24 - aa. thyreoideae superiores sin. et dext.; 6 - glandula thyreoidea; 7 - truncus thyreocervicalis; 8 - trachea; 9-a. thyreoidea ima; 10 and 18 - a. subclavia sin. et dext.; 11 and 21 - a. carotis communis sin. et dext.; 12 - truncus pulmonais; 13 - auricula dext.; 14 - pulmo dext.; 15 - arcus aortae; 16-v. cava sup.; 17 - truncus brachiocephalicus; 19 - m. scalenus ant.; 20 - plexus brachialis; 25 - glandula submandibularis.

Rice. 2. Arteria carotis communis dextra and its branches; 1-a. facialis; 2-a. occipitalis; 3-a. lingualis; 4-a. thyreoidea sup.; 5-a. thyreoidea inf.; 6-a. carotis communis; 7 - truncus thyreocervicalis; 8 and 10 - a. subclavia; 9-a. thoracica int.; 11 - plexus brachialis; 12-a. transversa colli; 13-a. cervicalis superficialis; 14-a. cervicalis ascendens; 15-a. carotis ext.; 16-a. carotis int.; 17-a. vagus; 18 - n. hypoglossus; 19-a. auricularis post.; 20-a. temporalis superficialis; 21-a. zygomaticoorbitalis.

Rice. 1. Cross section of the artery: 1 - outer shell with longitudinal bundles of muscle fibers 2, 3 - middle shell; 4 - endothelium; 5 - internal elastic membrane.

Rice. 2. Cross section of the thoracic aorta. The elastic membranes of the middle shell are shortened (o) and relaxed (b). 1 - endothelium; 2 - intima; 3 - internal elastic membrane; 4 - elastic membranes of the middle shell.