Capillary networks in the human body. Structure of capillaries
The thickness of this layer is so thin that it allows molecules of oxygen, water, lipids and more to pass through. Bodily products (such as carbon dioxide and urea) can also pass through the capillary wall to be transported to the site of excretion from the body. The permeability of the capillary wall is influenced by cytokines.
The functions of the endothelium also include the transfer of nutrients, messenger substances and other compounds. In some cases, large molecules may be too large to diffuse through the endothelium and the mechanisms of endocytosis and exocytosis are used to transport them.
In the mechanism of the immune response, endothelial cells expose receptor molecules on their surface, retaining immune cells and helping their subsequent transition to the extravascular space to the focus of infection or other damage.
The blood supply of organs occurs due to the "capillary network". The more metabolic activity of the cells, the more capillaries will be required to meet the demand for nutrients. Under normal conditions, the capillary network contains only 25% of the volume of blood that it can hold. However, this volume can be increased by self-regulatory mechanisms by relaxing smooth muscle cells. It should be noted that the walls of the capillaries do not contain muscle cells and therefore any increase in the lumen is passive. Any signaling substances produced by the endothelium (such as endothelin for contraction and nitric oxide for dilation) act on the muscle cells of nearby large vessels, such as arterioles.
Kinds
There are three types of capillaries:
continuous capillaries
Intercellular connections in this type of capillaries are very dense, which allows only small molecules and ions to diffuse.
Fenestrated capillaries
In their wall there are gaps for the penetration of large molecules. Fenestrated capillaries are found in the intestines, endocrine glands and other internal organs, where there is an intensive transport of substances between the blood and surrounding tissues.
Sinusoid capillaries (sinusoids)
The wall of these capillaries contains gaps (sines), the size of which is sufficient for erythrocytes and large protein molecules to exit outside the lumen of the capillary. There are sinusoidal capillaries in the liver, lymphoid tissue, endocrine and hematopoietic organs such as the bone marrow and spleen. The sinusoids in the hepatic lobules contain Kupffer cells, which are capable of trapping and destroying foreign bodies.
- The total cross-sectional area of the capillaries is 50 m², which is 25 times the surface of the body. In the human body, there are 100-160 mld. capillaries.
- The total length of the capillaries of an average adult is 42,000 km.
- The total length of the capillaries exceeds the double perimeter of the Earth, i.e., the capillaries of an adult person can wrap the Earth through its center more than 2 times.
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See what "Capillaries" are in other dictionaries:
- (from lat. capillaris hair), the smallest vessels (diam. 2.5 30 microns), penetrating the organs and tissues of animals with a closed circulatory system. For the first time K. were described by M. Malpighi (1661) as the missing link between the venous and arterial vessels ... Biological encyclopedic dictionary
- (from lat. hair capillaris) 1) tubes with a very narrow channel; a system of communicating pores (for example, in rocks, foams, etc.). 2) In anatomy, the smallest vessels (diameter 2.5 30 microns) penetrating organs and tissues in many animals and humans. ... ... Big Encyclopedic Dictionary
Modern Encyclopedia
Capillaries are tiny blood vessels that connect arteries and veins. The walls of the capillaries consist of only one layer of cells, which allows the exchange of dissolved oxygen and other nutrients (or carbon dioxide and ... ... Scientific and technical encyclopedic dictionary
capillaries- - a system of communicating pores and very narrow channels. [Terminological dictionary for concrete and reinforced concrete. Federal State Unitary Enterprise "Research Center" Construction "NIIZHB and M. A. A. Gvozdev, Moscow, 2007 110 pages] Term heading: General terms Encyclopedia headings: ... ... Encyclopedia of terms, definitions and explanations of building materials
capillaries- (from the Latin capillaris hair), 1) tubes with a very narrow channel; a system of communicating small pores (in rocks, foam plastics, etc.). 2) The thinnest blood vessels (diameter 2.5-30 microns); connecting link between venous and arterial ... ... Illustrated Encyclopedic Dictionary
- (from lat. hair capillaris), 1) tubes with a very narrow channel; a system of communicating pores (for example, in rocks, foam plastics, etc.). 2) (Anat.) the smallest vessels (diameter 2.5 30 microns) penetrating organs and tissues in many animals and ... ... encyclopedic Dictionary
- (from lat. capilla hair-like), the thinnest, almost transparent blood vessels are the terminal branches of the vascular system. They depart from the arterioles (the smallest components of the arterial system), 10 20 capillaries from each arteriole. Capillaries... ... Collier Encyclopedia
- (from Latin capillaris hair) blood, the smallest vessels penetrating all human and animal tissues and forming networks (Fig. 1, I) between arterioles that bring blood to the tissues and venules that drain blood from tissues. Through the wall... Great Soviet Encyclopedia
See hair vessels... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron
Books
- Vessels, capillaries, heart. Methods of cleansing and healing, Anatoly Malovichko. The book of the traditional healer and hereditary naturopath Anatoly Malovichko, whose nutrition and cleansing systems have helped hundreds of thousands of people gain health, is not only devoted to the most pressing problem ...
Marcello Malpighi(Italian biologist and physician) discovered capillaries in 1678, thus completing the description of a closed vascular system.
hemocapillaries, depending on the organs in which they are located, they can have a different diameter.
The smallest capillaries(diameter 4-7 microns) are found in striated muscles, lungs, nerves;
wider capillaries.(diameter 8-11 microns) - in the skin and mucous membranes;
even wider capillaries - sinusoids(diameter 20-30 microns) are located in the organs of hematopoiesis, endocrine glands, liver;
the widest capillaries-gaps(diameter more than 30 microns) are located in the columnar zone of the rectum and in the cavernous bodies of the penis.
Capillaries, intertwined with each other, form a network. In addition, they can be in the form of a loop (in the villi of the intestine, papillae of the skin, villi of the joint capsules). The end of a capillary that branches off from an arteriole is called arterial, and which flows into the venule - venous. The arterial end is always narrower, and the venous end is wider, sometimes 2-2.5 times. There are more mitochondria and microvilli in endotheliocytes of the venous end.
Capillaries can form glomeruli (in the kidneys). Capillaries may arise from an arteriole and flow into an arteriole (the afferent and efferent arterioles of the kidneys) or depart from a venule and flow into a venule (the pituitary portal system). If the capillaries are located between two arterioles or two venules, then this is called a miraculous network (rete mirabile).
The number of capillaries per unit volume in different tissues can be different. So, for example, in skeletal muscle tissue on a cross-sectional area of \u200b\u200b1 mm 2, up to 2000 sections of capillaries are found, in the skin - about 40.
Each tissue has approximately 50% of the capillaries in reserve. These capillaries are called non-functioning; they are in a collapsed state, only blood plasma passes through them. With an increase in the functional load on the organ, part of the non-functioning capillaries turns into functioning ones.
Wall The capillaries are made up of 3 layers:
1) endothelium, 2) layer of pericytes and 3) layer of adventitial cells.
endothelial layer consists of flattened polygonal cells of various sizes (from 5 to 75 microns in length). On the luminal surface (the surface facing the lumen of the vessel), covered with a plasmolemmal layer (glycocalix), there are microvilli that increase the surface of the cells. The cytolemma of endotheliocytes forms many caveolae, in the cytoplasm - many pinocytic vesicles. Microvilli and pinocytic vesicles are a morphological sign of intensive metabolism. At the same time, the cytoplasm is poor in organelles of general importance, there are microfilaments that form the cytoskeleton of the cell, and there are receptors on the cytolemma. Endotheliocytes are connected to each other by means of interdigitations and adhesion zones. Among the endotheliocytes there are fenestrated, i.e., endotheliocytes that have fenestrations. Fenestrated capillaries are found in the pituitary gland and glomeruli of the kidneys. ALP and ATPase are found in the cytoplasm of endotheliocytes. Endotheliocytes of the venous end of the capillary form folds in the form of valves that regulate blood flow.
The functions of the endothelium are numerous:
1) athrombogenic (negative charge of the glycocalyx and the synthesis of prostaglandin inhibitors that prevent platelet aggregation);
2) participation in the formation of the basement membrane;
3) barrier, due to the presence of the cytoskeleton and receptors;
4) participation in the regulation of vascular tone, due to the presence of receptors and the synthesis of factors that relax/contract vascular myocytes;
5) vasoforming, due to the synthesis of factors that accelerate the proliferation and migration of endotheliocytes;
6) secretion of lipoprotein lipase and other substances.
basement membrane The capillaries are about 30 nm thick and contain ATPase. Basement membrane function- ensuring selective permeability (exchange), barrier. Some capillaries have holes or gaps in the basement membrane.
Pericytes located in the crevices of the basement membrane, have a process shape. Their cytoplasm is capable of osmotic swelling - they squeeze the lumen. The processes have contractile filaments. The processes of pericytes cover the capillary, they end with efferent nerve endings. There are contacts between pericytes and endotheliocytes. In the place where the contact is located, there is a hole in the basement membrane.
Functions of pericytes:
1) contractile, due to the presence of contractile filaments;
2) supporting, due to the presence of a cytoskeleton;
3) participation in regeneration due to the ability to differentiate into smooth myocytes;
4) control of endotheliocyte mitosis due to contacts between pericytes and endotheliocytes;
5) participation in the synthesis of basement membrane components, due to the presence of granular EPS.
adventitial layer It is represented by adventitial cells immersed in an amorphous matrix around a capillary, in which thin collagen and elastic fibers pass.
Classification of capillaries depending on the structure of their wall. Currently, there are 3 types of capillaries:
1st type - continuous lined capillaries, somatic, characterized by the absence of fenestra in the endothelium and holes in the basement membrane - these are the capillaries of the skeletal muscles, lungs, nerve trunks, mucous membranes;
2nd type - fenestrated capillaries, characterized by the presence of fenestra in the endothelium and the absence of holes in the basement membrane - these are the capillaries of the glomeruli of the kidneys and intestinal villi;
3rd type - sinusoidal capillaries, perforated, are characterized by the presence of fenestra in the endothelium and holes in the basement membrane; these are sinusoidal capillaries of the liver and hematopoietic organs, due to the large width of which (diameter up to 130-150 microns), increased permeability of the wall and slow blood flow in the hematopoietic organs, migration of mature formed elements occurs into the sinusoids.
Capillary function - exchange of substances and gases between the lumen of capillaries and surrounding tissues. 4 factors contribute to this:
1) thin wall of capillaries;
2) slow blood flow (0.5 mm/s);
3) a large area of contact with surrounding tissues (6000 m 2);
4) low intracapillary pressure (20-30 mm Hg).
In addition to these four factors, the intensity of metabolism depends on the permeability of the basement membrane of capillaries and the ground substance of the surrounding connective tissue. Permeability increases when exposed to histamine and hyaluronidase, which destroys hyaluronic acid, which contributes to an increase in metabolism. Snake venom and the venom of poisonous spiders contain a lot of hyaluronidase, so these poisons easily penetrate the body. Vitamin C and Ca 2+ ions increase the density of basement membranes and the main intercellular substance.
capillaries(from lat. capillaris - hair) are the thinnest vessels in the human body and other animals. Their average diameter is 5-10 microns. Connecting arteries and veins, they are involved in the exchange of substances between blood and tissues. The blood capillaries in each organ are approximately the same size. The largest capillaries have a lumen diameter of 20 to 30 microns, the narrowest - from 5 to 8 microns. On transverse sections, it is easy to see that in large capillaries the lumen of the tube is lined with many endothelial cells, while the lumen of the smallest capillaries can be formed by only two or even one cell. The narrowest capillaries are in the striated muscles, where their lumen reaches 5-6 microns. Since the lumen of such narrow capillaries is smaller than the diameter of erythrocytes, when passing through them, erythrocytes, of course, must experience deformation of their body. Capillaries were first described in Italian. naturalist M. Malpighi (1661) as the missing link between venous and arterial vessels, the existence of which was predicted by W. Harvey. The walls of the capillaries, which consist of separate, closely adjoining and very thin (endothelial) cells, do not contain a muscular layer and are therefore incapable of contraction (they have this ability only in some lower vertebrates, such as frogs and fish). The capillary endothelium is permeable enough to allow the exchange of various substances between the blood and tissues.
Normally, water and substances dissolved in it easily pass in both directions; cells and blood proteins are retained inside the vessels. Bodily products (such as carbon dioxide and urea) can also pass through the capillary wall to be transported to the site of excretion from the body. Cytokines influence the permeability of the capillary wall. Capillaries are an integral part of any tissues; they form a wide network of interconnected vessels that are in close contact with cellular structures, supply the cells with the necessary substances and carry away the products of their vital activity.
In the so-called capillary bed, the capillaries are connected to each other, forming collective venules - the smallest components of the venous system. Venules merge into veins that carry blood back to the heart. The capillary bed functions as a unit, regulating the local blood supply according to the needs of the tissue. In the vascular walls, at the place where the capillaries branch off from the arterioles, there are clearly defined rings of muscle cells that play the role of sphincters that regulate the flow of blood into the capillary network. Under normal conditions, only a small part of these so-called. precapillary sphincters, so that blood flows through few of the available channels. A characteristic feature of blood circulation in the capillary bed is periodic spontaneous cycles of contraction and relaxation of smooth muscle cells surrounding arterioles and precapillaries, which creates intermittent, intermittent blood flow through the capillaries.
IN endothelial functions also includes the transfer of nutrients, messenger substances and other compounds. In some cases, large molecules may be too large to diffuse through the endothelium, and endocytosis and exocytosis are used to transport them. In the mechanism of the immune response, endothelial cells expose receptor molecules on their surface, retaining immune cells and helping their subsequent transition to the extravascular space to the focus of infection or other damage. Organs are supplied with blood by "capillary network". The more metabolic activity of the cells, the more capillaries will be required to meet the demand for nutrients. Under normal conditions, the capillary network contains only 25% of the volume of blood that it can hold. However, this volume can be increased by self-regulatory mechanisms by relaxing smooth muscle cells.
It should be noted that the walls of the capillaries do not contain muscle cells, and therefore any increase in the lumen is passive. Any signaling substances produced by the endothelium (such as endothelin for contraction and nitric oxide for dilation) act on the muscle cells of nearby large vessels, such as arterioles. Capillaries, like all vessels, are located among loose connective tissue, with which they are usually quite firmly connected. The exceptions are the capillaries of the brain, surrounded by special lymphatic spaces, and the capillaries of the striated muscles, where tissue spaces filled with lymphatic fluid are developed no less powerfully. Therefore, both from the brain and from the striated muscles, capillaries can be easily isolated.
The connective tissue surrounding the capillaries is always rich in cellular elements. Fat cells, and plasma cells, and mast cells, and histiocytes, and reticular cells, and cambial cells of the connective tissue are usually located here. Histiocytes and reticular cells, adjacent to the capillary wall, tend to spread and stretch along the length of the capillary. All connective tissue cells surrounding capillaries are referred to by some authors as capillary adventitia(adventitia capillaris). In addition to the typical cellular forms of connective tissue listed above, a number of cells are also described, which are sometimes called pericytes, sometimes adventitial, sometimes simply mesenchymal cells. The most branched cells adjacent directly to the wall of the capillary and covering it from all sides with their processes are called Rouge cells. They are found mainly in precapillary and postcapillary ramifications, passing into small arteries and veins. However, it is not always possible to distinguish them from elongated histiocytes or reticular cells.
The movement of blood through the capillaries Blood moves through the capillaries not only as a result of the pressure that is created in the arteries due to the rhythmic active contraction of their walls, but also due to the active expansion and narrowing of the walls of the capillaries themselves. Many methods have been developed to monitor the blood flow in the capillaries of living objects. It is shown that the blood flow here is slow and does not exceed 0.5 mm per second on average. As for the expansion and contraction of the capillaries, it is assumed that both expansion and contraction can reach 60-70% of the capillary lumen. In recent times, many authors are trying to connect this ability to contract with the function of adventitial elements, especially Rouget cells, which are considered special contractile cells of capillaries. This point of view is often given in physiology courses. However, this assumption remains unproven, since the properties of adventitial cells are quite consistent with the cambial and reticular elements.
Therefore, it is quite possible that the endothelial wall itself, having a certain elasticity, and possibly contractility, causes changes in the size of the lumen. In any case, many authors describe that they were able to see the reduction of endothelial cells just in those places where Rouget cells are absent. It should be noted that in some pathological conditions (shock, severe burns, etc.), capillaries can expand 2-3 times against the norm. In dilated capillaries, as a rule, a significant decrease in the rate of blood flow occurs, which leads to its deposition in the capillary bed. The reverse can also be observed, namely capillary constriction, which also leads to a cessation of blood flow and to some very slight deposition of erythrocytes in the capillary bed.
Types of capillaries There are three types of capillaries:
- continuous capillaries Intercellular connections in this type of capillaries are very dense, which allows only small molecules and ions to diffuse.
- Fenestrated capillaries In their wall there are gaps for the penetration of large molecules. Fenestrated capillaries are found in the intestines, endocrine glands and other internal organs, where there is an intensive transport of substances between the blood and surrounding tissues.
- Sinusoid capillaries (sinusoids) In some organs (liver, kidneys, adrenal glands, parathyroid gland, hematopoietic organs), the typical capillaries described above are absent, and the capillary network is represented by the so-called sinusoidal capillaries. These capillaries differ in the structure of their walls and the great variability of the inner lumen. The walls of the sinusoidal capillaries are formed by cells, the boundaries between which cannot be established. Adventitial cells never accumulate around the walls, but reticular fibers are always located. Very often, the cells lining the sinusoidal capillaries are called the endothelium, but this is not entirely true, at least in relation to some sinusoidal capillaries. As is known, the endothelial cells of typical capillaries do not accumulate dye when it is introduced into the body, while the cells lining the sinusoidal capillaries in most cases have this ability. In addition, they are capable of active phagocytosis. With these properties, the cells lining the sinusoidal capillaries approach macrophages, to which they are referred by some modern researchers.
The structure of arterioles
Topic: Microvasculature: arterioles, capillaries, venules and arteriolo-venular anastomoses. Features of the structure of the walls of blood vessels. Types of capillaries, structure, localization. Heart. Sources of development. The structure of the membranes of the heart. Age features.
The vessels of the microcirculatory bed include: arterioles, capillaries, venules and arteriolo-venular anastomoses.
The functions of the vessels of the microvasculature are:
1. Exchange of substances and gases between blood and tissues.
2. Regulation of blood flow.
3. Deposition of blood.
4. Drainage of tissue fluid.
The microcirculatory bed begins with arterioles, into which arteries pass as the diameter of the lumen and wall thickness decrease.
Arterioles- These are small vessels with a diameter of 100 to 50 microns. They are similar in structure to the arteries of the muscular type.
The wall of an arteriole consists of three layers:
1. The inner shell is represented by endothelium located on the basement membrane. Below it are single cells of the subendothelial layer and a thin internal elastic membrane with holes (perforations) through which endothelial cells contact with smooth myocytes of the middle layer to transmit signals from endothelial cells about a change in the concentration of biologically active substances that regulate arteriole tone.
2. The middle shell is represented by 1 - 2 layers of smooth myocytes.
3. The outer shell is thin, merges with the surrounding connective tissue.
The smallest arterioles less than 50 µm in diameter are called precapillary artererioles or precapillaries. Their wall consists of endothelium lying on the basement membrane, separate smooth myocytes and external adventitial cells.
At the point where the precapillaries branch into capillaries, there are sphincters, which are several layers of smooth myocytes that regulate blood flow into the capillaries.
Functions of arterioles:
Regulation of blood flow in organs and tissues.
regulation of blood pressure.
capillaries- These are the thinnest-walled vessels of the microcirculatory bed, through which blood is transported from the arterial bed to the venous.
The capillary wall consists of three layers of cells:
1. The endothelial layer consists of polygonal cells of various sizes. On the luminal (facing into the lumen of the vessel) surface, covered with glycocalyx, which adsorbs and absorbs metabolic products and metabolites from the blood, there are villi.
Functions of the endothelium:
Athrombogenic (synthesize prostaglandins that prevent platelet aggregation).
Participation in the formation of the basement membrane.
Barrier (it is carried out by the cytoskeleton and receptors).
Participation in the regulation of vascular tone.
Vascular (synthesize factors that accelerate the proliferation and migration of endotheliocytes).
Synthesis of lipoprotein lipase.
1. A layer of pericytes (process-shaped cells containing contractile filaments and regulating the lumen of capillaries), which are located in the clefts of the basement membrane.
2. A layer of adventitial cells immersed in an amorphous matrix, in which thin collagen and elastic fibers pass.
Classification of capillaries
1. According to the diameter of the lumen
Narrow (4-7 microns) are found in the striated muscles, lungs, and nerves.
Wide (8-12 microns) are in the skin, mucous membranes.
Sinusoidal (up to 30 microns) are found in the hematopoietic organs, endocrine glands, liver.
Lacunas (more than 30 microns) are located in the columnar zone of the rectum, the cavernous bodies of the penis.
2. According to the structure of the wall
Somatic, characterized by the absence of fenestra (local thinning of the endothelium) and holes in the basement membrane (perforations). Located in the brain, skin, muscles.
Fenestrated (visceral type), characterized by the presence of fenestra and the absence of perforations. They are located where the processes of molecular transfer occur most intensively: glomeruli of the kidneys, intestinal villi, endocrine glands).
Perforated, characterized by the presence of fenestra in the endothelium and perforations in the basement membrane. This structure facilitates the transition through the cell capillary wall: sinusoidal capillaries of the liver and hematopoietic organs.
Capillary function- the exchange of substances and gases between the lumen of the capillaries and the surrounding tissues is carried out due to the following factors:
1. Thin wall of capillaries.
2. Slow blood flow.
3. Large area of contact with surrounding tissues.
4. Low intracapillary pressure.
The number of capillaries per unit volume in different tissues is different, but in each tissue there are 50% of non-functioning capillaries that are in a collapsed state and only blood plasma passes through them. When the load on the body increases, they begin to function.
There is a capillary network that is enclosed between two vessels of the same name (between two arterioles in the kidneys or between two venules in the portal system of the pituitary gland), such capillaries are called the “miraculous network”.
When several capillaries merge, they form postcapillary venules or postcapillaries, with a diameter of 12-13 microns, in the wall of which there is a fenestrated endothelium, there are more pericytes. When postcapillaries merge, they form collecting venules, in the middle shell of which smooth myocytes appear, the adventitial shell is better expressed. Collecting venules continue into muscle venules, in the middle shell of which contains 1-2 layers of smooth myocytes.
Venule function:
· Drainage (receipt of metabolic products from the connective tissue into the lumen of the venules).
Blood cells migrate from the venules into the surrounding tissue.
The microcirculation includes arteriolo-venular anastomoses (AVA)- These are the vessels through which blood from the arterioles enters the venules bypassing the capillaries. Their length is up to 4 mm, diameter is more than 30 microns. AVAs open and close 4 to 12 times per minute.
AVAs are classified into true (shunts) through which arterial blood flows, and atypical (semi-shunts) through which mixed blood is discharged, tk. when moving along the half-shunt, a partial exchange of substances and gases with the surrounding tissues occurs.
Functions of true anastomoses:
Regulation of blood flow in capillaries.
Arterialization of venous blood.
Increased intravenous pressure.
Functions of atypical anastomoses:
· Drainage.
· Partial exchange.
development of blood vessels.
Primary blood vessels (capillaries) appear on the 2-3rd week of intrauterine development from the mesenchymal cells of the blood islands.
Dynamic conditions that determine the development of the vessel wall.
The blood pressure gradient and blood flow velocity, the combination of which in different parts of the body causes the appearance of certain types of vessels.
Classification and function of blood vessels. Their general building plan.
3 shells: inner; average; outdoor.
Distinguish between arteries and veins. The relationship between arteries and veins is carried out by the vessels of the microcirculation.
Functionally, all blood vessels are divided into the following types:
1) conduction-type vessels (conducting department) - main arteries: aorta, pulmonary, carotid, subclavian arteries;
2) vessels of the kinetic type, the totality of which is called the peripheral heart: arteries of the muscular type;
3) vessels of the regulatory type - "cranes of the vascular system", arterioles - maintain optimal blood pressure;
4) vessels of the exchange type - capillaries - carry out the exchange of substances between tissue and blood;
5) vessels of the reverse type - all types of veins - ensure the return of blood to the heart and its deposition.
Capillaries, their types, structure and function. The concept of microcirculation.
Capillary - a thin-walled blood vessel with a diameter of 3-30 microns, with its entire being immersed in the internal environment.
The main types of capillaries:
1) Somatic - tight contacts between the endothelium, no pinocytic vesicles, microvilli; characteristic of organs with a high metabolism (brain, muscles, lungs).
2) Visceral, fenestrated - the endothelium is thinned in places; characteristic of the organs of the endocrine system, kidneys.
3) Sinusoidal, slit-like - there are through holes between endotheliocytes; in the organs of hematopoiesis, liver.
The wall of the capillary is built:
A continuous layer of endothelium; basement membrane formed by collagen types IV-V, immersed in proteoglycans - fibronectin and laminin; in the splits (chambers) of the basement membrane lie pericytes; adventitial cells are located outside of them.
Functions of the capillary endothelium:
1) Transport - active transport (pinocytosis) and passive (transfer of O2 and CO2).
2) Anticoagulant (anticoagulant, antithrombogenic) - determined by glycocalyx and prostocycline.
3) Relaxing (due to the secretion of nitric oxide) and constrictor (conversion of angiotensin I to angiotensin II and endothelium).
4) Metabolic functions (metabolizes arachidonic acid, turning it into prostaglandins, thromboxane and leukotrienes).
109. Types of arteries: the structure of arteries of muscular, mixed and elastic types.
According to the ratio of the number of smooth muscle cells and elastic structures, the arteries are divided into:
1) elastic type arteries;
2) arteries of the muscular-elastic type;
3) muscular type.
The wall of muscular arteries is built as follows:
1) The inner lining of muscle type arteries consists of endothelium, subendothelial layer, internal elastic membrane.
2) The middle shell - smooth muscle cells located obliquely transversely, and the outer elastic membrane.
3) Adventitial sheath - dense connective tissue, with oblique and longitudinally lying collagen and elastic fibers. In the shell is the neuro-regulatory apparatus.
Features of the structure of the arteries of the elastic type:
1) The inner shell (aorta, pulmonary artery) is lined with large-sized endothelium; binuclear cells lie in the aortic arch. The subendothelial layer is well defined.
2) The middle shell is a powerful system of fenestrated elastic membranes, with obliquely arranged smooth myocytes. There are no inner and outer elastic membranes.
3) Adventitial connective tissue sheath - well developed, with large bundles of collagen fibers, includes its own blood vessels of the microcirculation and the nervous apparatus.
Features of the structure of the arteries of the muscular-elastic type:
The inner shell has a pronounced subendothelium and an internal elastic membrane.
The middle shell (carotid, subclavian artery) has an approximately equal number of smooth myocytes, spirally oriented elastic fibers and fenestrated elastic membranes.
The outer shell consists of two layers: the inner, containing separate bundles of smooth muscle cells, and the outer, longitudinally and obliquely arranged collagen and elastic fibers.
In the arteriole, weakly expressed three membranes characteristic of the arteries are distinguished.
Features of the structure of veins.
Vein classification:
1) Veins of the non-muscular type - veins of the dura mater and pia mater, retina, bones, placenta;
2) muscle-type veins - among them there are: veins with a small development of muscle elements (veins of the upper body, neck, face, superior vena cava), with strong development (inferior vena cava).
Features of the structure of veins of the non-muscular type:
The endothelium has tortuous borders. The subendothelial layer is absent or poorly developed. There are no inner and outer elastic membranes. The middle shell is minimally developed. The elastic fibers of the adventitia are few and longitudinally directed.
Features of the structure of veins with a small development of muscle elements:
Poorly developed subendothelial layer; in the middle shell a small number of smooth myocytes, in the outer shell - single, longitudinally directed smooth myocytes.
Features of the structure of veins with a strong development of muscle elements:
The inner shell is poorly developed. In all three shells, bundles of smooth muscle cells are found; in the inner and outer shells - longitudinal direction, in the middle - circular. The adventitia is thicker than the inner and middle shells combined. It contains many neurovascular bundles and nerve endings. The presence of venous valves is characteristic - duplication of the inner shell.
