Capillary networks in the human body. The structure of capillaries
The thickness of this layer is so thin that it allows molecules of oxygen, water, lipids and many others to pass through it. Products produced by the body (such as carbon dioxide and urea) can also pass through the capillary wall to transport them to the site of elimination from the body. The permeability of the capillary wall is influenced by cytokines.
The functions of the endothelium also include the transport of nutrients, messenger substances and other compounds. In some cases, large molecules may be too large to diffuse across the endothelium and the mechanisms of endocytosis and exocytosis are used to transport them.
In the immune response mechanism, endothelial cells exhibit receptor molecules on their surface, trapping immune cells and helping their subsequent transition into the extravascular space to the site of infection or other damage.
Blood supply to organs occurs due to the “capillary network”. The greater the metabolic activity of cells, the more capillaries will be needed to meet nutrient needs. Under normal conditions, the capillary network contains only 25% of the blood volume that it can accommodate. However, this volume can be increased due to self-regulatory mechanisms by relaxing smooth muscle cells. It should be noted that the capillary walls 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 large vessels located in close proximity, such as arterioles.
Species
There are three types of capillaries:
Continuous capillaries
The intercellular connections in this type of capillary are very tight, which allows only small molecules and ions to diffuse.
Fenestrated capillaries
In their walls there are gaps for the penetration of large molecules. Fenestrated capillaries are found in the intestines, endocrine glands and other internal organs, where intensive transport of substances occurs between the blood and surrounding tissues.
Sinusoidal capillaries (sinusoids)
The wall of these capillaries contains slits (sinuses), the size of which is sufficient for red blood cells and large protein molecules to exit outside the lumen of the capillary. Sinusoidal capillaries are found 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. There are 100-160 billion in the human body. capillaries.
- The total length of the capillaries of the average adult is 42,000 km.
- The total length of the capillaries exceeds twice the perimeter of the Earth, i.e. the capillaries of an adult can wrap the Earth through its center more than 2 times.
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See what “Capillaries” are in other dictionaries:
- (from Latin capillaris capillaris), the smallest vessels (dia. 2.5-30 microns), penetrating the organs and tissues of animals with a closed circulatory system. K. were first described by M. Malpighi (1661) as the missing link between the venous and arterial vessels... Biological encyclopedic dictionary
- (from Latin capillaris hair) 1) tubes with a very narrow channel; a system of communicating pores (for example, in rocks, foam plastics, 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, the smallest BLOOD VESSELS connecting arteries and veins. The walls of the capillaries consist of only one layer of cells, which ensures the ease of 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 of concrete and reinforced concrete. FSUE "National 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 Latin capillaris pilosa), 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 Latin capillaris hair), 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 Latin capilla hair-like), the thinnest, almost transparent blood vessels are the final branches of the vascular system. They extend from arterioles (the smallest components of the arterial system), 10 to 20 capillaries from each arteriole. Capillaries... ... Collier's Encyclopedia
- (from the Latin capillaris capillaris) blood vessels, the smallest vessels that penetrate all tissues of humans and animals and form networks (Fig. 1, I) between arterioles that bring blood to the tissues and venules that drain blood from the tissues. Through wall K... 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 by folk healer and hereditary naturopath Anatoly Malovichko, whose nutrition and cleansing systems have helped hundreds of thousands of people gain health, is dedicated not only to the most pressing problem...
Marcello Malpighi(Italian biologist and physician) discovered capillaries in 1678, thereby completing the description of a closed vascular system.
Hemocapillaries, depending on which organs they are located in, they can have different diameters.
The smallest capillaries(diameter 4-7 microns) are found in striated muscles, lungs, and 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 hematopoietic organs, 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 intertwining with each other form a network. In addition, they can have the shape of a loop (in the intestinal villi, skin papillae, villi of joint capsules). The end of the capillary that arises from the 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. The endothelial cells of the venous end have more mitochondria and microvilli.
Capillaries can form glomeruli (in the kidneys). Capillaries can arise from an arteriole and enter an arteriole (the afferent and efferent arterioles of the kidneys) or arise from a venule and enter a venule (the pituitary portal system). If the capillaries are located between two arterioles or two venules, then this is called the miraculous network (rete mirabile).
The number of capillaries per unit volume may vary in different tissues. For example, in skeletal muscle tissue, in a cross-sectional area of 1 mm2, there are up to 2000 sections of capillaries, in the skin - about 40.
Each tissue has approximately 50% of 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, some of the non-functioning capillaries turn into functioning ones.
Wall capillaries consists 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 (length from 5 to 75 μm). On the luminal surface (the surface facing the lumen of the vessel), covered with the plasmalemmal layer (glycocalyx), there are microvilli that increase the surface of the cells. The cytolemma of endothelial cells forms many caveolae, and in the cytoplasm there are many pinocytotic vesicles. Microvilli and pinocytotic 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 connect to each other using interdigitations and adhesion zones. Among the endotheliocytes there are fenestrated ones, i.e. endotheliocytes that have fenestrae. Fenestrated capillaries are present in the pituitary gland and glomeruli of the kidneys. ALP and ATPase are found in the cytoplasm of endothelial cells. Endothelial cells at 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) atrombogenic (negative charge of the glycocalyx and 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) vessel-forming, due to the synthesis of factors that accelerate the proliferation and migration of endothelial cells;
6) secretion of lipoprotein lipase and other substances.
basement membrane The capillaries are about 30 nm thick and contain an ATPase. Function of the basement membrane- ensuring selective permeability (exchange), barrier. Some capillaries have holes or slits in the basement membrane.
Pericytes are located in the crevices of the basement membrane and have a branched shape. Their cytoplasm is capable of osmotic swelling - they compress the lumen. The processes contain contractile filaments. The pericyte processes cover the capillary and efferent nerve endings end on them. There are contacts between pericytes and endothelial cells. 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, thanks to the ability to differentiate into smooth myocytes;
4) control of endothelial cell mitosis due to contacts between pericytes and endothelial cells;
5) participation in the synthesis of basement membrane components, due to the presence of granular EPS.
Adventitial layer represented by adventitial cells embedded 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 fenestrae in the endothelium and holes in the basement membrane - these are capillaries of skeletal muscles, lungs, nerve trunks, mucous membranes;
2nd type - fenestrated capillaries, characterized by the presence of fenestrae 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, characterized by the presence of fenestrae in the endothelium and holes in the basement membrane - these are sinusoidal capillaries of the liver and hematopoietic organs, due to their large width (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 lumen of the sinusoids.
Capillary function - exchange of substances and gases between the lumen of the capillaries and surrounding tissues. This is facilitated by 4 factors:
1) thin wall of capillaries;
2) slow blood flow (0.5 mm/s);
3) large area of contact with surrounding tissues (6000 m2);
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 the capillaries and the ground substance of the surrounding connective tissue. Permeability increases when exposed to histamine and hyaluronidase, which destroys hyaluronic acid, which helps increase 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 Latin capillaris - hair) are the thinnest vessels in the body of humans and other animals. Their average diameter is 5-10 microns. By connecting arteries and veins, they participate in the exchange of substances between blood and tissues. The blood capillaries in each organ are of approximately the same caliber. The largest capillaries have a lumen diameter from 20 to 30 microns, the narrowest - from 5 to 8 microns. In cross 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 found in striated muscles, where their lumen reaches 5-6 microns. Since the lumen of such narrow capillaries is smaller than the diameter of red blood cells, when passing through them, red blood cells naturally must experience deformation of their body. Capillaries were first described by Italian. naturalist M. Malpighi (1661) as the missing link between the venous and arterial vessels, the existence of which was predicted by W. Harvey. The walls of the capillaries, consisting of individual closely adjacent and very thin (endothelial) cells, do not contain a muscle layer and are therefore incapable of contraction (they have this ability only in some lower vertebrates, such as frogs and fish). The endothelium of the capillaries is sufficiently permeable to allow the exchange of various substances between the blood and tissues.
Normally, water and the substances dissolved in it easily pass in both directions; blood cells and proteins are retained inside the vessels. Products produced by the body (such as carbon dioxide and urea) can also pass through the capillary wall to transport them to the site of elimination from the body. The permeability of the capillary wall is influenced by cytokines. Capillaries are an integral part of any tissue; they form a wide network of interconnected vessels that are in close contact with cellular structures, supply cells with necessary substances and carry away their waste products.
In the so-called capillary bed, capillaries connect with each other, forming collecting venules - the smallest components of the venous system. The venules merge into veins, which return blood to the heart. The capillary bed functions as a single unit, regulating local blood supply according to the needs of the tissue. In the vascular walls, at the point where the capillaries branch 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 ones is open. 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 the smooth muscle cells surrounding the arterioles and precapillaries, which creates an intermittent, intermittent flow of blood through the capillaries.
IN endothelial functions It also includes the transfer of nutrients, messenger substances and other compounds. In some cases, large molecules may be too large to diffuse across the endothelium and the mechanisms of endocytosis and exocytosis are used to transport them. In the immune response mechanism, endothelial cells exhibit receptor molecules on their surface, trapping immune cells and helping their subsequent transition into the extravascular space to the site of infection or other damage. Blood supply to organs occurs due to "capillary network". The greater the metabolic activity of cells, the more capillaries will be needed to meet nutrient needs. Under normal conditions, the capillary network contains only 25% of the blood volume that it can accommodate. However, this volume can be increased due to self-regulatory mechanisms by relaxing smooth muscle cells.
It should be noted that the capillary walls 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 large vessels located in close proximity, such as arterioles. Capillaries, like all vessels, are located among loose connective tissue, with which they are usually quite firmly connected. The exception is the capillaries of the brain, surrounded by special lymphatic spaces, and the capillaries of striated muscles, where tissue spaces filled with lymphatic fluid are no less powerfully developed. Therefore, capillaries can be easily isolated from both the brain and striated muscles.
The connective tissue surrounding the capillaries is always rich in cellular elements. Fat cells, plasma cells, mast cells, histiocytes, reticular cells, and cambial cells of connective tissue are usually located here. Histiocytes and reticular cells, adjacent to the capillary wall, tend to spread out and stretch along the length of the capillary. All connective tissue cells surrounding capillaries are designated 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 described that are sometimes called pericytes, sometimes adventitial, or simply mesenchymal cells. The most branched cells, adjacent directly to the capillary wall and covering it on all sides with their processes, are called Rouget cells. They are found mainly in precapillary and postcapillary branches, which pass into small arteries and veins. However, it is not always possible to distinguish them from elongated histiocytes or reticular cells.
Movement of blood through capillaries Blood moves through the Capillaries not only as a result of the pressure that is created in the arteries as a result of the rhythmic active contraction of their walls, but also as a result of the active expansion and contraction of the walls of the capillaries themselves. Many methods have now been developed to monitor blood flow in the capillaries of living objects. It has been shown that the blood flow here is slow and on average does not exceed 0.5 mm per second. As for the expansion and contraction of capillaries, it is accepted that both expansion and contraction can reach 60-70% of the capillary lumen. In modern 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 the capillaries. This point of view is often given in physiology courses. However, this assumption remains unproven, since in their properties adventitial cells are quite consistent with 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 a reduction in endothelial cells precisely in those places where Rouget cells are absent. It should be noted that in some pathological conditions (shock, severe burn, etc.) the capillaries can expand 2-3 times against the norm. In dilated capillaries, as a rule, there is a significant decrease in the speed of blood flow, which leads to its deposition in the capillary bed. The opposite cases can also be observed, namely, compression of the capillaries, which also leads to a cessation of blood flow and to some very slight deposition of red blood cells in the capillary bed.
Types of capillaries There are three types of capillaries:
- Continuous capillaries The intercellular connections in this type of capillary are very tight, which allows only small molecules and ions to diffuse.
- Fenestrated capillaries In their walls there are gaps for the penetration of large molecules. Fenestrated capillaries are found in the intestines, endocrine glands and other internal organs, where intensive transport of substances occurs between the blood and surrounding tissues.
- Sinusoidal 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 so-called sinusoidal capillaries. These capillaries differ in the structure of their wall and the great variability of the internal lumen. The walls of 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 sinusoidal capillaries are called endothelium, but this is not entirely true, at least in relation to some sinusoidal capillaries. As is known, endothelial cells of typical capillaries do not accumulate dye when it is introduced into the body, while the cells lining 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 are close to macrophages, to which some modern researchers classify them.
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 characteristics.
The vessels of the microvasculature 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. Blood deposition.
4. Drainage of tissue fluid.
The microcirculatory bed begins with arterioles, into which arteries become as the lumen diameter and wall thickness decrease.
Arterioles– these are small vessels with a diameter of 100 to 50 microns. They are similar in structure to muscular arteries.
The arteriole wall consists of three membranes:
1. The inner lining is represented by endothelium located on the basement membrane. Underneath it are single cells of the subendothelial layer and a thin internal elastic membrane that has holes (perforations) through which endothelial cells contact the smooth myocytes of the middle layer to transmit signals from endothelial cells about changes in the concentration of biologically active substances that regulate arteriolar tone.
2. The middle membrane is represented by 1 – 2 layers of smooth myocytes.
3. The outer shell is thin and merges with the surrounding connective tissue.
The smallest arterioles with a diameter of less than 50 microns are called precapillary arterioles or precapillaries. Their wall consists of endothelium lying on the basement membrane, individual smooth myocytes and outer adventitial cells.
At the site where 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 microvasculature, through which blood is transported from the arterial to the venous bed.
The capillary wall consists of three layers of cells:
1. The endothelial layer consists of polygonal cells of various sizes. There are villi on the luminal (facing the lumen of the vessel) surface, covered with glycocalyx, which adsorbs and absorbs metabolic products and metabolites from the blood.
Endothelial functions:
Atrombogenic (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 endothelial cells).
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 splits of the basement membrane.
2. A layer of adventitial cells embedded in an amorphous matrix, in which thin collagen and elastic fibers pass.
Classification of capillaries
1. By lumen diameter
Narrow ones (4-7 microns) are found in transversely striated muscles, lungs, and nerves.
Wide (8-12 microns) are found in the skin and mucous membranes.
Sinusoidal (up to 30 microns) are found in the hematopoietic organs, endocrine glands, and liver.
Lacunae (more than 30 microns) are located in the columnar zone of the rectum and cavernous bodies of the penis.
2. According to the structure of the wall
Somatic, characterized by the absence of fenestrae (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 fenestrae and the absence of perforations. They are located where molecular transfer processes occur especially intensively: glomeruli of the kidneys, intestinal villi, endocrine glands).
Perforated, characterized by the presence of fenestrae in the endothelium and perforations in the basement membrane. This structure facilitates the passage through the wall of the capillary cells: sinusoidal capillaries of the liver and hematopoietic organs.
Capillary function– the exchange of substances and gases between the lumen of the capillaries and 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 varies in different tissues, but in each tissue there are 50% non-functioning capillaries that are in a collapsed state and only blood plasma passes through them. When the load on the organ 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 fenestrated endothelium, more pericytes. When postcapillaries merge, they form collecting venules, in the middle membrane of which smooth myocytes appear, the adventitial membrane is better expressed. Collecting venules continue into muscle venules, the middle shell of which contains 1-2 layers of smooth myocytes.
Function of venules:
· 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 microvasculature consists of arteriolo-venular anastomoses (AVA)- these are vessels through which blood from arterioles enters venules bypassing capillaries. Their length is up to 4 mm, diameter more than 30 microns. AVAs open and close 4 to 12 times per minute.
ABAs are classified into true (shunts), through which arterial blood flows, and atypical (half shunts) through which mixed blood is discharged, because When moving along the half-shunt, a partial exchange of substances and gases occurs with the surrounding tissues.
Functions of true anastomoses:
· Regulation of blood flow in capillaries.
· Arterialization of venous blood.
· Increased intravenular pressure.
Functions of atypical anastomoses:
· Drainage.
· Partially exchangeable.
Development of blood vessels.
Primary blood vessels (capillaries) appear in the 2-3rd week of intrauterine development from the mesenchymal cells of the blood islands.
Dynamic conditions determining 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 structure plan.
3 shells: inner; average; external
There are arteries and veins. The relationship between arteries and veins is carried out by microcircular vessels.
Functionally, all blood vessels are divided into the following types:
1) conductor type vessels (conducting section) - 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 - “faucets of the vascular system”, arterioles - maintain optimal blood pressure;
4) exchange vessels - capillaries - carry out the exchange of substances between tissue and blood;
5) reversion type vessels - 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.
A capillary is a thin-walled blood vessel with a diameter of 3-30 microns, its entire being is immersed in the internal environment.
Main types of capillaries:
1) Somatic - there are tight junctions between the endothelium, there are no pinocytotic vesicles, microvilli; characteristic of organs with 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-shaped - there are through holes between endothelial cells; in the hematopoietic organs, liver.
The capillary wall is built:
Continuous layer of endothelium; basement membrane formed by collagen types IV-V, immersed in proteoglycans - fibronectin and laminin; pericytes lie in the fissures (chambers) of the basement membrane; adventitial cells are located outside of them.
Functions of the capillary endothelium:
1) Transport - active transport (pinocytosis) and passive (O2 and CO2 transfer).
2) Anticoagulant (anticoagulant, antithrombogenic) - determined by glycocalyx and prostocycline.
3) Relaxing (due to the secretion of nitric oxide) and constrictor (conversion of angiotensin I into angiotensin II and endothelium).
4) Metabolic functions (metabolizes arachidonic acid, converting it into prostaglandins, thromboxane and leukotrienes).
109. Types of arteries: the structure of arteries of the muscular, mixed and elastic type.
According to the ratio of the number of smooth muscle cells and elastic structures, arteries are divided into:
1) arteries of elastic type;
2) arteries of the muscular-elastic type;
3) muscular type.
The wall of muscular arteries is built like this:
1) The inner lining of muscular arteries consists of endothelium, subendothelial layer, and internal elastic membrane.
2) The middle shell is smooth muscle cells located obliquely transversely and the outer elastic membrane.
3) The adventitia is a dense connective tissue with obliquely and longitudinally lying collagen and elastic fibers. The neuroregulatory apparatus is located in the membrane.
Features of the structure of elastic arteries:
1) The inner lining (aorta, pulmonary artery) is lined with large endothelium; binucleate 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 located smooth myocytes. There are no internal or external elastic membranes.
3) Adventitial connective tissue membrane - well developed, with large bundles of collagen fibers, includes its own blood vessels of the microcircular bed and the nervous apparatus.
Features of the structure of arteries of the muscular-elastic type:
The inner shell has a pronounced subendothelium and an internal elastic membrane.
The middle membrane (carotid, subclavian arteries) has approximately equal numbers of smooth myocytes, spirally oriented elastic fibers and fenestrated elastic membranes.
The outer shell has two layers: the inner one, containing individual bundles of smooth muscle cells, and the outer one - longitudinally and obliquely located collagen and elastic fibers.
In the arteriole, three weakly defined membranes are distinguished, characteristic of arteries.
Features of the structure of veins.
Vein classification:
1) Veins of the non-muscular type - veins of the dura and pia mater, retina, bones, placenta;
2) veins of the muscular type - among them there are: veins with little 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 non-muscle type veins:
The endothelium has convoluted borders. The subendothelial layer is absent or poorly developed. There are no internal or external elastic membranes. The middle shell is minimally developed. The elastic fibers of the adventitia are few in number and directed longitudinally.
Features of the structure of veins with little development of muscle elements:
The subendothelial layer is poorly developed; in the middle shell there is a small number of smooth myocytes, in the outer shell there are single, longitudinally directed smooth myocytes.
Features of the structure of veins with strong development of muscle elements:
The inner shell is poorly developed. In all three membranes, 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 layers combined. It contains many neurovascular bundles and nerve endings. Characteristic is the presence of venous valves - duplicates of the inner membrane.
