Capillaries: continuous, fenestrated, sinusoidal. BUT

capillaries with a continuous endothelial layer - somatic type, localized in the brain, muscles, skin;

fenestrated capillaries - visceral type, with outflows of the cytoplasm of the endothelium - (capillaries of the glomeruli of the kidney, intestinal villi);

capillaries with slit-like holes in the endothelium and basement membrane - capillaries of the sinusoidal type (in the spleen, liver, and other organs).

Arteriovenular anastomoses (ABA). This part microvasculature provides a direct transition of arterial blood into the veins, bypassing the capillaries. ABA are localized in almost all organs.

There are two groups of anastomoses:

true ABAs (shunts) over which the net arterial blood. They, in turn, are divided into two groups according to their structure:

simple ABA - have a border of the transition of the arteriole to the venule, which corresponds to the area where the middle shell of the arteriole ends. The regulation of blood flow is carried out by smooth muscle cells of the middle shell of the arteriole itself without special contractile apparatus;

ABA, which have special contractile devices in the form of rollers or pillows in the subepithelial layer, formed by longitudinally located smooth muscle cells. Contraction of the muscle pads that protrude into the lumen of the anastomosis leads to the cessation of blood flow.

The same subgroup includes epithelioid-type ABAs (simple and complex).

In simple ABAs of the epithelial type, muscle cells are gradually replaced towards the venous end by short oval light cells (E-cells) similar to epithelial cells. In the complex and glomerular, the afferent arteriole divides into two to four branches, which pass into the venous segment.

atypical ABAs (half shunts) are connections between arterioles and venules; through a short capillary vessel. Therefore, the blood discharged into the venous bed is not completely arterial.

The connection of the arterial and venous systems, bypassing the capillaries, has great importance for regulation blood pressure, blood supply to organs, arterialization of venous blood, mobilization of deposited blood, regulation of the flow of tissue fluid into the venous bed.

Venules. There are three types of venules:

post-capillary,

collective,

Muscular.

Postcapillary venules in their structure resemble the venous part of the capillary, but in the wall of these venules there are more pericytes than in the capillaries.

Separate smooth muscle cells appear in the collecting venules and the outer shell is more clearly expressed.

Muscular venules have one or two layers of smooth myocytes in the middle sheath and a relatively well-developed outer sheath.

The venous section of the ICR, together with the lymphatic capillaries, performs a drainage function, regulating the hemolymphatic balance between the blood and the extravascular fluid, removing the products of tissue metabolism. Leukocytes migrate through the walls of venules, as well as through capillaries. Slow blood flow and low blood pressure, as well as the distensibility of these vessels, create conditions for the deposition of blood.

Vienna(venae) ensure the return of blood to the heart, the deposition of blood. The general plan of the structure of the veins is the same as that of the arteries, but has its own characteristics:

the wall of the vein is thinner than that of the corresponding artery;

collagen fibers predominate in the veins, and elastic fibers are poorly developed;

there is no external elastic membrane, the internal elastic membrane is poorly developed;

the lumen of the vein on the preparation is often irregular in shape, while that of the arteries is round;

relatively the largest thickness in the veins is the outer shell, and in the arteries - the middle shell;

the presence of valves in some veins.

Veins are classified depending on the development of muscle elements in its wall:

Non-muscular veins Muscular veins

Veins with weak development of muscular elements

Veins with strong development of muscular elements

Muscleless veins. Veins of this type include muscleless veins of the dura and pia meninges, veins of the retina, spleen, bones and placenta. The wall of blood vessels is lined from the inside with endothelium on the basement membrane. The middle shell is missing. The outer shell is represented by a thin layer of loose fibrous connective tissue that grows together with the surrounding tissues, as a result of which these veins do not collapse and the outflow of blood through them is easy.

Veins with weak development of muscular elements. The peculiarity of the structure of their wall depends on hemodynamic conditions. The blood in them moves under the influence of the force of gravity. These veins have a poorly defined subendothelial layer, and the media contains few smooth muscle cells. Single muscle cells are found in the outer shell of the veins. This group of veins includes: veins of the upper body, neck, face, upper vena cava.

Veins with medium development of muscular elements. An example is the brachial vein. Structural features: the inner shell forms the valvular apparatus, and also contains separate longitudinally directed myocytes, the inner elastic membrane is not expressed, the middle shell is thin, smooth muscle cells are circularly located in it, the outer elastic membrane is absent, therefore, the connective tissue layers of the middle shell pass directly into the loose fibrous connective tissue of the outer shell.

Veins with strong development of muscular elements. These veins are characterized by a strong development of muscle cells in all three membranes. In the inner and outer shells, smooth myocytes are located longitudinally, and in the middle - circular. A characteristic feature of these veins is the presence of valves. These veins include: veins of the lower half of the trunk and legs.

valves- these are pocket-like folds of the inner shell, open towards the heart. They prevent backflow of blood. The basis of the valve is fibrous connective tissue. At the same time, on the side facing the lumen of the vessel, mainly elastic fibers lie under the endothelium, and on the opposite side, there are many collagen fibers. At the base of the valve leaflet, there may not be a large number of smooth myocytes.

inferior vena cava in structure it differs sharply from the veins flowing into it. The inner and middle shells are poorly developed. The outer shell has a large number of longitudinally arranged bundles of smooth muscle cells and is 6-7 times thicker than the inner and middle shells combined. There are no valves in the inferior vena cava, their function is performed by the resulting transverse folds of the outer shell, which prevent the reverse flow of blood.

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

Lymphatic vessels.

The lymphatic system conducts lymph from tissues to the veins. Functionally lymphatic vessels are closely connected with the blood vessels, especially in the area of ​​the location of the vessels of the microvasculature. It is here that the formation of tissue fluid and its penetration into the lymphatic channel.

Classification. Among the lymphatic vessels, there are:

lymph capillaries,

intralymphatic vessels,

extralymphatic vessels,

thoracic duct,

right lymphatic duct.

Lymph capillaries are blindly beginning flattened tubules into which tissue fluid enters from the tissues along with metabolic products. Their wall is formed only by the endothelium. Basement membrane and pericytes absent. The endothelium is connected to the surrounding connective tissue by bundles of anchor, or sling, filaments that prevent capillaries from falling off. There are gaps between endotheliocytes. The diameter of the lymphatic capillaries may vary depending on the degree of their filling with lymph. Lymphatic capillaries perform a drainage function, participating in the processes of absorption of blood plasma filtrate from the connective tissue.

Lymphatic vessels. The structure of the wall of the lymphatic vessels has much in common with the veins, which is explained by similar conditions of lympho- and hemodynamics (low pressure, low flow rate, direction of outflow from the tissues to the heart). There are vessels of muscular and non-muscular type. Medium and large lymphatic vessels have three well-developed membranes (inner, middle and outer) as part of the wall. The inner membrane of the lymphatic vessels forms numerous folds - valves. The dilated portions of the vessels between adjacent valves are called lymphangions. The middle shell is more pronounced in the vessels of the lower extremities. Lymph nodes are located along the course of the lymphatic vessels. A structural feature of the wall of large lymphatic vessels (thoracic duct and right lymphatic duct) is a well-developed outer shell, which is 3-4 times thicker than the inner and middle combined. Longitudinal bundles of smooth muscle cells pass through the outer shell. There are up to 9 semilunar valves along the thoracic duct.

Heart(cor) - the central organ of blood and lymph circulation. Due to the ability to contract, the heart sets the blood in motion.

The wall of the heart is formed by three layers:

endocardium, (internal);

myocardium, (medium);

epicardium, (external).

Endocardium consists of four layers:

endothelium on basement membrane;

subendothelial layer - loose connective tissue rich in poorly differentiated cells;

muscular-elastic layer - formed by smooth myocytes and elastic fibers;

the outer connective tissue layer consists of loose fibrous connective tissue containing elastic, collagen and reticular fibers.

valves.

Valves are located between the atria and ventricles of the heart, as well as the ventricles and large vessels. They are thin fibrous plates covered with endothelium from dense fibrous connective tissue with a small number of cells. The cells covering the valve partially cover each other in the form of a tile or form finger-like depressions of the cytoplasm of one cell into another. The valve walls do not have blood vessels. The structure of the atrial and ventricular parts of the valve leaflets is not the same. The atrial side has a smooth surface, here in the subendothelial layer there is a dense plexus of elastic fibers and bundles of smooth muscle cells. The number of muscle bundles markedly increases at the base of the valve. The ventricular side has an uneven surface. It is equipped with outgrowths from which tendon filaments begin. In this area, only a small number of elastic fibers are located under the endothelium.

Myocardium consists of cardiac muscle tissue and layers of loose fibrous connective tissue with vessels and nerves. There are typical contractile muscle cells - cardiomyocytes and atypical - conducting cardiac myocytes, which are part of the so-called conduction system of the heart. Contractile myocytes are rectangular cells with a centrally located nucleus. In the cytoplasm, myofibrils are arranged longitudinally. The basement membrane is involved in the formation of T-tubules. Striated cardiac muscle tissue, described in the "Muscular tissue" section.

The conduction system of the heart combines muscle cells that form and conduct impulses to contractile cardiomyocytes. It consists of: sinoatrial node, atrioventricular node, atrioventricular bundle of Giss. There are three types of conducting muscle cells:

1. The first type is pacemakers or pacemaker cells capable of spontaneous contraction. They differ in small size, polygonal shape, a small number of randomly located myofibrils. T-systems are absent.

2. Transitional - thin, elongated cells, myofibrils are more developed, oriented in parallel, but not always.

3. The cells of the Hiss bundle are large, there are no T-systems, myofibrils are thin, located in no particular order along the periphery of the cell, the nuclei are localized eccentrically.

Epicardium and pericardium. The outer shell of the heart or epicardium is the visceral layer of the pericardium. The epicardium consists of a thin plate of connective tissue, which is covered with mesothelium.

Between the epicardium and the pericardium there is a slit-like space containing a small amount of fluid that acts as a lubricant. In the pericardium, the connective base is more developed than in the epicardium.

capillaries- these are the terminal branches of blood vessels in the form of endothelial tubules with a very simply arranged membrane. So, the inner shell consists only of the endothelium and the basement membrane; the middle shell is virtually absent, and the outer shell is represented by a thin pericapillary layer of loose fibrous connective tissue. Capillaries 3-10 µm in diameter and 200-1000 µm long form a highly branched network between metarterioles and post-capillary venules.

capillaries- these are places of active and passive transport of various substances, including oxygen and carbon dioxide. This transport depends on various factors, among which the selective permeability of endothelial cells for certain specific molecules plays an important role.

Depending on the structure of the walls, capillaries can be divided into continuous, fenestrated and sinusoidal.

Endothelial cells have flat nuclei that protrude slightly into the capillary lumen; cell organelles are well developed.

In the cytoplasm of endotheliocytes, several actin microfilaments and numerous microvesicles (MB) with a diameter of 50-70 nm are found, which sometimes merge and form transendothelial channels (TCs). The transendothelial transport function in two directions with the help of microvesicles is greatly facilitated by the presence of microfilaments and the formation of channels. Openings (Ov) of microvesicles and transendothelial channels on the inner and outer surfaces of the endothelium are clearly visible.

Rough, 20-50 nm thick basement membrane (BM) is located under the endothelial cells; on the border with pericytes (Pe), it often splits into two sheets (see arrows), which surround these cells with their processes (O). Outside of the basement membrane are isolated reticular and collagen microfibrils (CM), as well as autonomic nerve endings (NO) corresponding to the outer shell.

continuous capillaries found in brown adipose tissue (see figure), muscle tissue, testicles, ovaries, lungs, central nervous system (CNS), thymus, lymph nodes, bones and bone marrow.

Endothelial cells have flattened, elongated perinuclear cytoplasmic zones that protrude slightly into the capillary lumen. The internal structure of endothelial cells is identical to the internal structure of the same cells in continuous capillaries. Due to the presence of actin microfilaments in the cytoplasm, endothelial cells can shrink.

The basement membrane (BM) has the same thickness as in continuous capillaries and surrounds the outer surface of the endothelium. Around fenestrated capillaries, pericytes (Pe) are less common than in continuous capillaries, but they are also located between two sheets of the basement membrane (see arrows).

Reticular and collagen fibers (KB) and autonomic nerve fibers (not shown) run along the outside of the fenestrated capillaries.

Fenestrated capillaries found mainly in the kidneys, choroid plexuses of the ventricles of the brain, synovial membranes, endocrine glands. The exchange of substances between blood and tissue fluid is greatly facilitated by the presence of such intraendothelial fenestrations.

Endothelial cells are connected through nexuses and locking zones, zonulae occludentes, as well as using overlapping zones (indicated by an arrow).

The nuclei of endothelial cells are flattened; the cytoplasm contains well-developed organelles, few microfilaments, and in some organs a noticeable amount of lysosomes (L) and microvesicles (Mv).

The basement membrane of this type of capillaries is almost completely absent, thus allowing the blood plasma and intercellular fluid to mix freely, there is no permeability barrier.

In rare cases, pericytes occur; delicate collagen and reticular fibers (RV) form a loose network around sinusoidal capillaries.

This type of capillaries is found in the liver, spleen, pituitary gland, adrenal cortex. It is believed that endothelial cells sinusoidal capillaries liver and bone marrow exhibit phagocytic activity.

Cordially- vascular system.

The cardiovascular system includes the heart, blood and lymph vessels. The heart and blood vessels ensure the movement of blood through the body, with which nutrients and biologically are delivered. active substances, oxygen, thermal energy and metabolic products are excreted.

The heart is the main organ that moves the blood. Blood vessels carry out a transport function, regulation of blood supply to organs and metabolism between blood and surrounding tissues.

The vascular system is a complex of tubules of different diameters. The activity of the vascular apparatus is regulated nervous system and hormones. Vessels do not form such a dense network in the body that could provide a direct connection with each cell. Nutrients and oxygen are brought to most cells with tissue fluid, into which they enter with blood plasma by seeping it through the walls of capillaries. This fluid carries away metabolic products from the cells and, flowing from the tissues, first moves between the cells and then is absorbed into the lymphatic capillaries. Thus, the vascular system is divided into two parts: circulatory and lymphatic.

In addition, hematopoietic organs are associated with the cardiovascular system, which simultaneously perform protective functions.

Development of the vascular system.

The first blood vessels appear in the mesenchyme of the walls yolk sac at the 2nd - 3rd week of embryogenesis. From the peripheral cells of the blood islands, squamous endothelial cells are formed. Surrounding mesenchymal cells develop into pericytes, smooth muscle cells, and adventitial cells. In the body of the embryo, blood capillaries are laid in the form irregular shape slits filled with tissue fluid. Their wall is the surrounding mesenchyme. When blood flow through the vessels increases, these cells become endothelial, and elements of the middle and outer membranes are formed from the surrounding mesenchyme. Then the vessels of the embryo begin to communicate with the vessels of the extra-embryonic organs. Further development occurs with the beginning of blood circulation under the influence of blood pressure, blood flow velocity, which are created in different parts of the body.

During the entire postembryonic period of life, the vascular system has great plasticity. There is a significant variability in the density of the vascular network, since, depending on the organ's need for nutrients and oxygen, the amount of blood brought in varies widely.

In connection with the change in the speed of blood movement, blood pressure, the walls of the vessels are rebuilt, small vessels can turn into larger ones with characteristic features, or vice versa. At the same time, new vessels can form, and old ones atrophy.

Especially Big changes occur in the vascular system during the development of roundabout or collateral circulation. This is observed when there are any obstacles in the way of blood flow. New capillaries and vessels are formed, and existing ones are transformed into vessels of a larger caliber.

If a section of an artery is cut out from a living animal and a vein is sewn in its place, then the latter, under conditions of arterial circulation, will be rebuilt and turn into an artery.

Classification and general characteristics of vessels.

In the system of blood vessels, there are:

1) arteries, through which blood flows to organs and tissues (rich in O 2, except pulmonary artery);

2) Vienna through which blood returns to the heart (little O 2, except for the pulmonary vein);

3) Microcirculatory bed , providing, along with the transport function, the exchange of substances between blood and tissues. This channel includes not only hemocapillaries, but also the smallest arteries (arterioles), veins (venules), as well as arteriolo-venular anastomoses.

Hemocapillaries connect the arterial link circulatory system with venous, except for the "wonderful systems" in which the capillaries are located between two vessels of the same name - arterial (in the kidneys), or venous (in the liver and pituitary gland).

Arterio-venular anastomoses provide a very rapid transition of blood from the artery to the veins. They are short vessels connecting small arteries with small veins and are capable of rapidly closing their lumen. Therefore, anastomoses play an important role in regulating the amount of blood brought to the organs.

Arteries and veins are built according to a single plan. Their walls consist of three shells: 1) internal, built from the endothelium and elements of connective tissue located above it; 2) middle - muscular or muscular-elastic and 3) external - adventitia, formed from loose connective tissue.

arteries.

According to the structural features of the artery, there are 3 types: elastic, muscular and mixed (muscular-elastic). The classification is based on the ratio of the number of muscle cells and elastic fibers in the media of the arteries.

To elastic type arteries include vessels of large caliber, such as the aorta and pulmonary artery, into which blood flows under high pressure (120 - 130 mm Hg) and at high speed (0.5 - 1.3 m / s). These vessels perform mainly a transport function.

High pressure and high speed of flowing blood determine the structure of the walls of the vessels of the elastic type; in particular, the presence of a large number of elastic elements (fibers, membranes) allows these vessels to stretch during systole of the heart and return to their original position during diastole, and also contributes to the transformation of pulsating blood flow into a constant, continuous one.

Inner shell includes endothelium and subendothelial layer. The endothelium of the aorta is composed of cells of various shapes and sizes. Sometimes cells reach 500 microns in length and 150 microns in width, more often they are single-nuclear, but there are also multi-nuclear (from 2 - 4 to 15 - 30 nuclei). The endothelium secretes anticoagulants and clotting agents, participates in metabolism, releases substances that affect hematopoiesis.

In their cytoplasm, the endoplasmic reticulum is poorly developed, but there are a lot of microfilaments. Beneath the endothelium is the basement membrane.

subendothelial layer It consists of loose, fine-fibrillar connective tissue rich in poorly differentiated stellate cells, macrophages, and smooth myocytes. The amorphous substance of this layer contains many glycosaminoglycans. If the wall is damaged or pathological (atherosclerosis), lipids (cholesterol and esters) accumulate in this layer.

Deeper than the subendothelial layer, as part of the inner shell, there is a dense plexus of thin elastic fibers.

Middle shell The aorta consists of a large number (40-50) of elastic fenestrated membranes interconnected by elastic fibers. Smooth muscle cells lie between the membranes, having an oblique direction with respect to them. This structure of the middle shell creates a high elasticity of the aorta.

outer shell The aorta is built of loose connective tissue with a large number of thick elastic and collagen fibers, which are mainly longitudinal.

In the middle and outer shells of the aorta, as well as in large vessels in general, there are feeding vessels and nerve trunks.

The outer shell protects the vessel from overstretching and rupture.

to muscular arteries includes most of the arteries of the body, i.e., medium and small caliber: the arteries of the body, limbs and internal organs.

The walls of these arteries contain a relatively large number of smooth myocytes, which provides additional pumping power and regulates blood flow to the organs.

Part inner shell includes endothelium, subendothelial layer and internal elastic membrane.

Endothelial cells are elongated along the axis of the vessel and have convoluted borders. The basement membrane follows the endothelial lining and subendothelial layer, consisting of thin elastic and collagen fibers, mainly longitudinally directed, as well as poorly differentiated connective tissue cells and an amorphous substance containing glycosaminoglycans. On the border with the middle shell lies internal elastic membrane. AT

The cardiovascular system is involved in metabolism, provides and determines the movement of blood, serves as a transport medium between body tissues.

As part of the cardiovascular system, there are: the heart is the central organ that sets the blood in constant motion; blood and lymph vessels; blood and lymph. Hematopoietic organs are associated with this system, which simultaneously perform protective functions.

The organs of the cardiovascular system, hematopoiesis and immunity develop from the mesenchyme, and the membranes of the heart - from the visceral sheet of the mesoderm.

HEART

The central organ of the cardiovascular system is the heart; thanks to its rhythmic contractions, blood circulates through the large (systemic) and small (pulmonary) circulations, that is, throughout the body.

In mammals, the heart is located in the chest cavity between the lungs, in front of the diaphragm in the region from the 3rd to the 6th rib in the plane of the center of gravity of the second quarter of the body. Most of the heart is to the left of midline, and on the right are the right atrium and vena cava.

The mass of the heart depends on the type, breed and sex of the animal, as well as on the age and physical activity. For example, in a bull, the mass of the heart is 0.42%, and in a cow - 0.5% of body weight.

The heart is a hollow organ divided internally into four cavities, or chambers: two atrium and two ventricle oval-cone-shaped or oval-rounded. In the upper part of each atrium there are protruding parts - ears. The atria are externally separated from the ventricles by the coronal groove, in which the main branches of the blood vessels pass. The ventricles are separated from one another by interventricular grooves. The atria, ascending aorta, and pulmonary trunk face upward and form the base of the heart; the lowest and most of all protruding to the left pointed section of the left ventricle - the apex of the heart.

In the lateral plates of the cervical region, at the end of the second week of development of the embryo, a paired accumulation of mesenchymal cells is formed (Fig. 78). From these cells, two mesenchymal strands are formed, gradually transforming into two elongated tubes, lined from the inside with endothelium. This is how the endocardium is formed, surrounded by a visceral sheet of mesoderm. Somewhat later, in connection with the formation of the trunk fold, two tubular rudiments of the future heart approach and merge into one common unpaired tubular organ.

From the visceral sheet of the mesoderm in the area adjacent to the endocardium, myoepicardial plates are isolated, which subsequently develop into the rudiments of the myocardium and epicardium.

So, at this stage of development, the unpaired heart is initially a tubular organ, in which there are narrowed cranial and caudal expanded sections. Blood enters through the caudal, and exits through the cranial part of the organ, and already on this early stage development, the first corresponds to the future atria, and the second to the ventricles.

Further formation of the heart is associated with uneven growth of individual sections of the tubular organ, as a result

Rice. 78.

a B C - respectively early, middle, late stages; /-ectoderm; 2-endoderm; 3- mesoderm; -/ - chord; 5-nerve plate; b - paired bookmark of the heart; 7-neural tube; 8- unpaired bookmark of the heart; 9 - esophagus; 10- paired aorta; 11 - endocardium;

12- myocardium

which forms an S-shaped bend. Moreover, the caudal venous section with thinner membranes slightly shifts the dorsal side forward - an atrium is formed. The cranial arterial section, which has more pronounced membranes, remains on the ventral side - a ventricle is formed. So there is a two-chambered heart. A little later, the partitions in the atrium and in the ventricle separate and the two-chamber heart becomes four-chamber. Holes remain in the longitudinal septum: oval - between the atria and small - between the ventricles. The foramen ovale usually heals after birth, while the foramen ovale closes before birth.

The arterial trunk, which is a section of the original heart tube, is divided by a septum formed in the original ventricle, resulting in the aorta and pulmonary artery.

There are three membranes in the heart: the inner one is the endocardium, the middle one is the myocardium and the outer one is the epicardium. The heart is located in the pericardial sac - the pericardium (Fig. 79).

Endocardium (e n doc a rdium) - a membrane lining the inside of the cavity of the heart, muscular papillae, tendon filaments and valves. The endocardium has a different thickness, for example, it is much thicker in the atrium and in the ventricle of the left half. At the mouth of large trunks - the aorta and pulmonary artery, the endocardium is more pronounced, while on the tendon filaments this sheath is very thin.

Microscopic examination reveals layers in the endocardium that have a similar structure to blood vessels. So, from the side of the surface facing the cavity of the heart, the endocardium is lined with endothelium, consisting of endotheliocytes located on the basement membrane. Nearby is the subendothelial layer, formed by loose fibrous connective tissue and containing a lot of poorly differentiated cambial cells. There are also muscle cells - myocytes and intertwining elastic fibers. The outer layer of the endocardium, as in the blood vessels, consists of loose fibrous connective tissue containing small blood vessels.

Derivatives of the endocardium are atrioventricular (atrioventricular) valves: bicuspid in the left half, tricuspid in the right.

The basis, or frame, of the valve leaflet is formed by a thin, but very strong structure - its own, or main, plate, formed by loose fibrous connective tissue. The strength of this layer is due to the predominance of fibrous material over cellular elements. In the areas of attachment of the bicuspid and tricuspid valves, the connective tissue of the valves passes into the fibrous rings. Both sides of the lamina propria are covered with endothelium.

The atrial and ventricular sides of the valve leaflets have a different structure. So, the atrial side of the valves is smooth from the surface, has a dense plexus of elastic fibers and bundles of smooth muscle cells in its own plate. The ventricular side is uneven, with outgrowths (papillae) to which collagen fibers, the so-called tendon fibers, are attached.

Rice. 79.

a- stained with hematoxylin and eosin; b- stained with iron hematoxylin;

BUT - endocardium; B- myocardium; AT- epicardium: / - atypical fibers; 2- cardiomyocytes

threads (chordae tendinae); a small amount of elastic fibers is located only directly under the endothelium.

Myocardium (miocardium) - the middle muscular membrane, represented by typical cells - cardiomyocytes and atypical fibers that form the conduction system of the heart.

cardiac myocytes(myociti cardiaci) perform a contractile function and form a powerful apparatus of striated muscle tissue, the so-called working muscles.

Striated muscle tissue is formed from closely anastomosing (interconnected) cells - cardiomyocytes, which together form a single system of the heart muscle.

Cardiomyocytes have an almost rectangular shape, the length of the cell ranges from 50 to 120 microns, the width is 15...20 microns. In the central part of the cytoplasm there is a large oval nucleus, sometimes binuclear cells are found.

In the peripheral part of the cytoplasm, there are about a hundred contractile protein filaments - myofibrils, with a diameter of 1 to 3 microns. Each myofibril is formed by several hundred protofibrils, which determine the striated striation of myocytes.

Between the myofibrils there are many oval-shaped mitochondria arranged in chains. The mitochondria of the heart muscle are characterized by the presence of a large number of cristae located so close that the matrix is ​​practically invisible. With the presence of a huge number of mitochondria containing enzymes and participating in redox processes, the ability of the heart to work continuously is associated.

Cardiac striated muscle tissue is characterized by the presence of intercalated discs (diski intercalati) - these are areas of contact between adjacent cardiomyocytes. Within the intercalated discs, highly active enzymes are found: ATPase, dehydrogenase, alkaline phosphatase, which indicates an intensive metabolism. There are straight and stepped insert discs. If the cells are limited by straight intercalary discs, then the total length of the protofibrils will be the same; if stepped intercalary discs, then the total length of protofibril bundles will be different. This is explained by the fact that individual bundles of protofibrils are interrupted in the region of the intercalated disks. Intercalated discs are actively involved in the transmission of excitations from cell to cell. With the help of discs, myocytes are connected into muscle complexes, or fibers (miofibra cardiaca).

Between the muscle fibers there are anastomoses that provide contractions of the myocardium as a whole in the atria and ventricles.

In the myocardium, numerous layers of loose fibrous connective tissue are distinguished, in which there are many elastic and very few collagen fibers. Nerve fibers, lymphatic and blood vessels pass here, each myocyte is in contact with two or more capillaries. Muscle tissue is attached to the supporting skeleton located between the atria and ventricles and at the mouths of large vessels. The supporting skeleton of the heart is formed by dense bundles of collagen fibers or fibrous rings.

conduction system of the heart it is represented by atypical muscle fibers (myofibra conducens), which form nodes: the sinoatrial Keith-Fleck, located at the mouth of the cranial vena cava; atrioventricular Ashof-Tavara - near the attachment of the leaflet of the tricuspid valve; the trunk and branches of the atrioventricular system - the bundle of His (Fig. 80).

Atypical muscle fibers contribute to successive contractions of the atria and ventricles throughout the cardiac cycle - automatism of the heart. That's why distinctive feature conducting system is the presence of a dense plexus nerve fibers on atypical muscle fibers.

The muscle fibers of the conduction system have different sizes and directions. For example, in the sinoatrial node, the fibers are thin (from 13 to 17 microns) and densely intertwined in the middle of the node, and as they move away from the periphery, the fibers become more correct location. This node is characterized by the presence of wide layers of connective tissue, in which elastic fibers predominate. The atrioventricular node has a similar structure.

The muscle cells of the conduction system (myociti conducens cardiacus) of the branches of the legs of the trunk of the conduction system (Purkinje fibers) are located in small bundles surrounded by layers of loose fibrous connective tissue. In the region of the ventricles of the heart, atypical fibers have a larger cross section than in other parts of the conduction system.

Rice. 80.

/ - coronary sinus; 2-right atrium; 3 - tricuspid valve; -/- caudal vena cava; 5 - septum between the ventricles; b - branching of the bundle of His; 7- right ventricle; 8- left ventricle; 9- bundle of His; /0 - bicuspid valve; 11- Ashof-Tavar knot; 12- left atrium; 13 - sinoatrial node; //-/-cranial vena cava

Compared with cells of the working muscles, atypical fibers of the conducting system have a number of hallmarks. Fibers of large size and irregular oval shape. The nuclei are large and light, not always occupy a strictly central position. There is a lot of sarcoplasm in the cytoplasm, but few myofibrils, as a result of which, when stained with hematoxylin and eosin, atypical fibers are light. The cell sarcoplasm contains a lot of glycogen, but few mitochondria and ribosomes. Typically, myofibrils are located at the periphery of cells and are densely intertwined, but do not have such a strict orientation as in typical cardiac myocytes.

Epicardium (epicardium) - the outer shell of the heart. It is a visceral sheet of the serous membrane, which is based on loose fibrous connective tissue. In the atrial region, the layer of connective tissue is very thin and mainly of elastic fibers, which are tightly fused with the myocardium. In the epicardium of the ventricles, in addition to elastic fibers, collagen bundles are found that make up the denser superficial layer.

The epicardium lines the inner surface of the mediastinum, forming the outer shell of the pericardial cavity, called the parietal layer of the pericardium. Between the epicardium and the pericardium, a cardiac cavity is formed, filled with a small amount of serous fluid.

The pericardium is a three-layer pericardial sac that contains the heart. The pericardium consists of the pericardial pleura, the fibrous layer of the mediastinum, and the parietal layer of the epicardium. The pericardium is attached to the sternum by ligaments, and to the spinal column by vessels entering and leaving the heart. The basis of the pericardium is also loose fibrous connective tissue, but more pronounced compared to that in the epicardium. From the pericardium of farm animals, substitutes for tanned leather can be obtained.

The surface of the epicardium and the outer surface of the pericardium facing the pericardial cavity are covered with a layer of mesothelium.

The vessels of the heart, mainly the coronary ones, start from the aorta, branch strongly in all membranes into vessels of different diameters, up to the capillaries. From the capillaries, the blood passes into the coronary veins, which flow into the right atrium. In the coronary arteries there are many elastic fibers that create powerful support networks. Lymphatic vessels in the heart form dense networks.

The nerves of the heart are formed from the branches of the border sympathetic trunk, from the fibers vagus nerve and spinal fibers. In all three membranes there are nerve plexuses, accompanied by intramural ganglia. In the heart, there are free as well as encapsulated nerve endings. Receptors are found in connective tissue on muscle fibers and in the membranes of blood vessels. Sensory nerve endings perceive changes in the lumen of blood vessels, as well as signals during contraction and stretching of muscle fibers.

The cardiovascular system includes the heart, blood and lymphatic vessels, blood and lymph. Hematopoietic organs are associated with this system, which simultaneously perform protective functions.

Heart - the central organ that sets the blood in motion, consists of three membranes (endocardium, myocardium, epicardium), is located in a pericardial sac called the pericardium.

Endocardium lines the cavity of the heart and valves from the inside, is represented by the endothelial layer and the underlying loose fibrous irregular connective tissue containing smooth muscle cells.

Myocardium It is represented by striated cells - cardiomyocytes, which form the so-called working muscles, and atypical muscle fibers, which form a conduction system that promotes rhythmic contractions of the atria and ventricles throughout the cardiac cycle (automatism).

epicardium and pericardium - these are serous membranes, at the base of the structure they have a loose fibrous unformed connective tissue, covered on the outside with mesothelium. Blood vessels represented by arteries carrying blood from the heart, veins through which blood flows to the heart, and microvasculature (capillaries, arterioles, venules, arteriovenous anastomoses).

A common pattern in the structure of arteries and veins is the presence of three membranes - internal, middle, external.

Inner shell consists of endothelium and subendothelial layer of loose fibrous unformed connective tissue.

Middle shell consists of smooth muscle cells, on the surface of which elastic fibers are located - a kind of "tendons" having a radial and arcuate arrangement, which, when stretched, gives the vessel elasticity, and when squeezed, elasticity. Smooth muscle cells and elastic fibers are arranged in a spiral, which, like a spring, ensures the return of the choroid after stretching by a pulsed blood wave.

Outer sheath (adventitial) formed by loose fibrous irregular connective tissue. This sheath contains blood vessels and nerves. (vasa vasorum, nervi vasorum).

The distinguishing features of arteries and veins are due to the speed of movement and blood pressure. AT arteries muscle elements are more pronounced; in the vessels of the muscular type there are internal and external elastic membranes located on both sides of the muscular membrane; in the arteries of the elastic type in the middle shell there are fenestrated elastic membranes. Vienna have folds of the inner shell - valves, the physiological role of which is associated with a mechanism that promotes the movement of venous blood to the heart and prevents the reverse flow of blood. The basis of the valve is loose fibrous unformed connective tissue, covered on both sides with endothelial cells.

Lymphatic vessels have a similar structure with veins, which is explained by the similarity of lympho- and hemodynamic conditions: the presence low pressure and the direction of fluid flow from the organs to the heart. The main feature of the structure of the lymphatic vessels, like the veins, is the presence of valves, in the location of which the vessels expand.

Lymphatic vessels of the smallest diameter (lymphatic capillaries) have a lumen several times wider than blood vessels. Many capillaries, which are a kind of drainage system, merge into lymphatic vessels that drain lymph from the organs into the largest lymphatic vessels or trunks - the thoracic duct and the right lymphatic duct, which flow into the vena cava.

Bull's Heart(hematoxylin and eosin). At a low magnification of the microscope (x10), the endocardium and a portion of the myocardium are revealed. The inner layer of the endocardium, facing the cardiac cavity, consists of endothelial cells located on the basement membrane; in the subendothelial layer, fibers of loose fibrous connective tissue, poorly differentiated cambial cells, and separately located smooth muscle cells are detected (Fig. 73).

Between the endocardium and muscle cells of typical working muscles, Purkinje fibers are detected. Atypical fibers of the conducting system are characterized by a number of distinguishing features: they are large, have an irregular oval shape, the nuclei are large and light, located along the periphery. There is a lot of sarcoplasm and glycogen in the fibers, few mitochondria and ribosomes, usually a small number of myofibrils is located on the periphery of the cells, as a result of which, when stained with hematoxylin and eosin, the fibers are very light.

Preparation "Capillars, arterioles, venules of the pia mater of the cat's brain"(hematoxylin and eosin). For a more complete picture of the vessels of the microvasculature, it is necessary to consider the total preparation, where all layers of the vessels would be visible - both from the surface and in the optical section. Examining the preparation at a low magnification of the microscope (x10), one can identify thin tubes of various diameters that form a network. With a strong magnification of the microscope (x40), nuclei of endothelial cells are detected in all vessels in the inner layer (Fig. 74). Arterioles are smaller in diameter than venules and are characterized by the presence of a middle layer consisting of smooth muscle cells whose nuclei

Rice. 73

/ - endocardium; II- myocardium: 7 - Purkinje fibers; 2- cardiomyocytes

Rice. 74. Vessels of the microvasculature:

• 7 - capillary; 2 - arteriole; 3 - venule;
• 4 - endothelial layer;
• 5 - adventitial cells;
• 6 - smooth muscle cells;
• 7 - adventitial cells arranged in a spiral, which gives the vessel a characteristic striated appearance. The venule has a wide lumen with a large number of erythrocytes. The outer layer of all vessels is formed by separately located adventitial cells.

A drug " femoral artery cats"(hematoxylin and eosin). With a low magnification of the microscope (x10), in the artery of the muscular type, the inner, middle and outer shells are distinguished. With a strong magnification of the microscope (x40) in inner shell find, draw and label: endothelial layer, subendothelial layer and internal elastic membrane (Fig. 75, a).

Middle shell consists of smooth muscle cells, on the surface of which elastic fibers are located; emerging

Rice. 75a- artery: 7 - nuclei of endothelial cells; 2 - internal elastic membrane; 3 - smooth muscle cells; 4 - outer elastic membrane; 5 - adventitial shell; 6 - vascular vessels; 6 - vein: 7 - nuclei of endothelial cells; 2 - smooth muscle cells; 3 - adventitial membrane; 4 - vessels with a single elastic frame creates a constant open lumen to the vessel and the continuity of blood flow. On the border between the middle and outer shells, there is an outer elastic membrane, consisting of longitudinally arranged intertwining elastic fibers, which sometimes take the form of a continuous membrane. outer shell consists of loose fibrous unformed connective tissue, the fibers of which have a predominantly oblique and longitudinal direction. Between the fibers are adventitial and fat cells.

Preparation "Femoral vein of a cat"(hematoxylin and eosin). With a low magnification of the microscope (x10), in a muscular vein with a strong development of muscle elements, the inner, middle and outer shells are distinguished (Fig. 75, b). With a strong magnification of the microscope (x40), the inner shell reveals the endothelium and the subendothelial layer, in which there are bundles of smooth muscle cells arranged in longitudinal layers. The middle shell contains bundles of smooth muscle cells arranged in circular layers; above the base of the valve, the middle shell becomes thinner. Below the insertion of the valve, the muscle bundles cross, creating a thickening. In the outer shell, formed by loose fibrous irregular connective tissue, bundles of smooth muscle cells are located longitudinally. The lumen of the veins is collapsed, and blood cells are detected here, mainly orange-colored erythrocytes.

Preparation "Aorta of the pig"(hematoxylin and picroindigocarmine). With a low magnification of the microscope (x10), in the vessel of the elastic type, the inner, middle and outer shells are distinguished, the relative thickness of which significantly predominates compared to those of the vessels of the muscular type (Fig. 76). Studying the preparation, with a strong magnification of the microscope (x40), compare the structure of the membranes of the aorta and the muscular artery, clarifying and relating the morphological differences with the functional features of vessels of different diameters.

Inner shell It is lined with endothelium, consisting of cells of various shapes and sizes. The subendothelial layer of Langgans is very pronounced, consisting of loose fibrous unformed connective tissue with many star-shaped adventitial cells that perform a cambial function. The inner shell forms the semilunar valves. In the intercellular substance of the inner membrane, a large amount of acid mucopolysaccharides and phospholipids, represented by cholesterol and fatty acids, is detected.

Middle shell consists of 40-50 elastic fenestrated membranes ( membranae fenestratae), interconnected by elastic

Rice. 76. Aorta:

/ - endothelial and subendothelial layers;

• 2 - elastic membranes;
• 3 - adventitial membrane;
• 4 - vascular vessels: 4a- artery; 46 - vein; 5 - fat cells

fibers. Between the membranes there are a small number of fibroblasts and smooth muscle cells, which have an oblique direction with respect to the membranes. The structure of the middle shell ensures the elasticity of the aorta and softens the jolts of blood pushed into the vessel during the systole of the left ventricle of the heart, and also helps to maintain the tone of the choroid during diastole.

outer shell It is built from loose fibrous unformed connective tissue with a significant content of elastic and collagen fibers, which have a mainly longitudinal direction. Vessels of blood vessels and nerve trunks pass in the middle and outer shell.

test questions

• 1. What is the structure of the endocardium?
• 2. What is the structure of typical cardiomyocytes and atypical conductive myocardial fibers?
• 3. What are the structural features of the vessels of the microvasculature?
• 4. How to distinguish arterioles from venules on preparations?
• 5. What General characteristics And what are the differences between arteries and veins of the muscular type?
• 6. What signs are typical for vessels of the elastic type?
• 7. What explains the similarity of the structure and the presence of valves in venous and lymphatic vessels?