Histological structure and blood supply of the spleen. Spleen. development of the spleen. The structure of the spleen The structural components of the spleen are

The spleen is an unpaired organ located in the abdominal cavity on the greater curvature of the stomach, in ruminants - on the scar. Its shape varies from flat elongated to rounded; in animals of different species, the shape and size may be different. The color of the spleen - from intense red-brown to blue-violet - is due to the large amount of blood contained in it.

Rice. 212. Palatine tonsils:

A- dogs, B- sheep (according to Ellenberger and Trautman); A- pits of the tonsils; b- epithelium; V- reticular tissue; d - lymphatic follicles; d- loose connective tissue; e- glands; and- bundles of muscle fibers.

The spleen is a multifunctional organ. In most animals, this is an important organ of lymphocyte formation and immunity, in which, under the influence of antigens present in the blood, cells are formed either producing humoral antibodies or participating in cellular immunity reactions. In some animals (rodents), the spleen is a universal organ of hematopoiesis, where cells of lymphoid, erythroid and granulocytic sprouts are formed. The spleen is a powerful macrophage organ. With the participation of numerous macrophages, it destroys blood cells and especially erythrocytes ("erythrocyte graveyard"), the decay products of the latter (iron, proteins) are reused in the body.

Rice. 213. Spleen of a cat (according to Ellenberger and Trautnan):

a - capsule; b- trabeculae; V- trabecular artery; G- trabecular vein; d- light center of the lymphatic follicle; e- central artery; and- red pulp; h- vascular sheath.

The spleen is an organ of blood storage. The depositing function of the spleen in horses and ruminants is especially pronounced.

The spleen develops from clusters of rapidly multiplying mesenchymal cells in the dorsal part of the mesentery. In the initial period of development in the anlage, a fibrous framework, a vascular bed, and a reticular stroma are formed from the mesenchyme. The latter is populated by stem cells and macrophages. Initially, this is the organ of myeloid hematopoiesis. Then there is an intensive invasion of lymphocytes from the central lymphoid organs, which are first distributed evenly around the central arteries (T-zone). B-zones are formed later, which is associated with the concentration of macrophages and lymphocytes on the side of the T-zones. Simultaneously with the development of lymphatic nodules, the formation of the red pulp of the spleen is also observed. In the early postembryonic period, an increase in the number and volume of nodules, the development and expansion of reproduction centers in them are noted.

Microscopic structure of the spleen. The main structural and functional elements of the spleen are the musculoskeletal apparatus, represented by a capsule and a system of trabeculae, and the rest of the intertrabecular part is the pulp, built mainly from reticular tissue. There are white and red pulp (Fig. 213).

The spleen is covered with a serous membrane, tightly fused with the connective tissue capsule. Crossbars - trabeculae, forming a kind of network-like frame, depart from the capsule inside the organ. The most massive trabeculae are at the hilum of the spleen, they contain large blood vessels - trabecular arteries and veins. The latter belong to the veins of the non-muscular type and on the preparations they quite clearly differ in structure from the wall of the arteries.

The capsule and trabeculae are composed of dense fibrous connective and smooth muscle tissue. A significant amount of muscle tissue develops and is contained in the spleen of the depositing type (horse, ruminants, pigs, carnivores). The contraction of smooth muscle tissue promotes the expulsion of deposited blood into the bloodstream. In the connective tissue of the capsule and trabeculae, elastic fibers predominate, allowing

spleen to change its size and withstand a significant increase in its volume.

White pulp (pulpa lienis alba) macroscopically and on unstained preparations represents a collection of light gray round or oval formations (nodules) irregularly dispersed throughout the spleen. The number of nodules in different animal species is different. There are many of them in the spleen of cattle and they are distinctly separated from the red pulp. Less nodules in the spleen of the horse and pig.

With light microscopy, each lymph nodule is a formation consisting of a complex of lymphoid tissue cells located in the adventitia of the artery and numerous hemocapillaries extending from it. The nodule artery is called the central artery. however, more often it is located eccentrically. In a developed lymphatic nodule, several structural and functional zones are distinguished: periarterial, light center with a mantle zone, and a marginal zone. The periarterial zone is a kind of clutch, consisting of small lymphocytes, closely adjacent to each other and interdigitating cells. The lymphocytes of this zone belong to the recirculating fund of T-cells. Here they penetrate from hemocapillaries, and after antigenic stimulation they can migrate into the sinuses of the red pulp. Interdigitizing cells are special process macrophages that absorb antigen and stimulate blast transformation, proliferation, and the conversion of T-lymphocytes into effector cells.

The light center of the nodule in structure and function corresponds to the follicles of the lymph node and is a thymus-independent area. Here there are lymphoblasts, many of which are at the stage of mitosis, dendritic cells that fix the antigen and retain it for a long time, as well as free macrophages containing absorbed lymphocyte decay products in the form of stained bodies. The structure of the light center reflects the functional state of the lymph node and can significantly change with infections and intoxications. The center is surrounded by a dense lymphocytic rim - the mantle zone.

There is a marginal zone around the entire nodule. which contains T- and B-lymphocytes and macrophages. It is believed that functionally this zone is one of the areas of cooperative interaction of different cell types in the immune response. As a result of this interaction, B-lymphocytes located in this zone and stimulated by the corresponding antigen proliferate and differentiate into antibody-forming plasma cells that accumulate in the strands of the red pulp. The shape of the splenic nodule is maintained by a network of reticular fibers - in the thymus-independent area they are located radially, and in the T-zone - along the long axis of the central artery.

Red pulp (pulpa lienis rubra). An extensive part (up to 70% of the mass) of the spleen, located between the lymph nodes and trabeculae. Due to the content of a significant amount of erythrocytes in it, it has a red color on unstained preparations of the spleen. It consists of reticular tissue with free cellular elements in it: blood cells, plasma cells and macrophages. Numerous arterioles, capillaries and peculiar venous sinuses (sinus venosus) are found in the red pulp, a wide variety of cellular elements are deposited in their cavity. The red pulp is rich in sinuses on the border with the marginal zone of lymph nodes. The number of venous sinuses in the spleen of animals of different species is not the same. There are many of them in rabbits, guinea pigs, dogs, less in cats, cattle and small cattle. The areas of red pulp located between the sinuses are called splenic. or pulp cords, which contain many lymphocytes and the development of mature plasma cells occurs. Pulp cord macrophages carry out phagocytosis of damaged erythrocytes and are involved in iron metabolism in the body.

Circulation. The complexity of the structure and multifunctionality of the spleen can only be understood in connection with the peculiarities of its blood circulation.

Arterial blood is sent to the spleen via the splenic artery. which enters the organ through the gate. Branches extend from the artery, which run inside large trabeculae and are called trabecular arteries. In their wall there are all the membranes characteristic of the arteries of the muscular type: intima, media and adventitia. The latter fuses with the connective tissue of the trabeculae. From the trabecular artery, arteries of small caliber depart, which enter the red pulp and are called pulp arteries. Around the pulpal arteries, elongated lymphatic sheaths are formed, as they move away from the trabeculae, they increase and take on a spherical shape (lymph nodule). Inside these lymphatic formations, many capillaries depart from the artery, and the artery itself is called the central one. However, the central (axial) location is only in the lymphatic sheath, and in the nodule it is eccentric. Upon exiting the nodule, this artery splits into a number of branches - brush arterioles. Around the end sections of the cystic arterioles are oval clusters of elongated reticular cells (ellipsoids, or sleeves). In the cytoplasm of the endothelium of ellipsoid arterioles, microfilaments were found, which are associated with the ability of ellipsoids to contract - a function of peculiar sphincters. Arterioles further branch into capillaries. some of them flow into the venous sinuses of the red pulp (the theory of closed circulation). According to the open circulation theory, arterial blood

from the capillaries it enters the reticular tissue of the pulp, and from it it seeps through the wall into the cavity of the sinuses. The venous sinuses occupy a significant part of the red pulp and can have different diameters and shapes depending on their blood supply. The thin walls of the venous sinuses are lined with discontinuous endothelium located on the basal plate. Reticular fibers run along the surface of the sinus wall in the form of rings. At the end of the sinus, at the site of its transition to the vein, there is another sphincter.

Depending on the reduced or relaxed state of the arterial and venous sphincters, the sinuses can be in various functional states. With the contraction of the venous sphincters, the blood fills the sinuses, stretches their wall, while the blood plasma passes through it into the reticular tissue of the pulp cords, and blood cells accumulate in the cavity of the sinuses. In the venous sinuses of the spleen, up to 1/3 of the total number of red blood cells can be retained. With both sphincters open, the contents of the sinuses enter the bloodstream. Often this occurs with a sharp increase in oxygen demand, when there is excitation of the sympathetic nervous system and relaxation of the sphincters. This is also facilitated by contraction of the smooth muscles of the capsule and trabeculae of the spleen.

The outflow of venous blood from the pulp occurs through the system of veins. The wall of the trabecular veins consists only of endothelium, closely adjacent to the connective tissue of the trabeculae, that is, these veins do not have their own muscular membrane. This structure of the trabecular veins facilitates the expulsion of blood from their cavity into the splenic vein, which exits through the gate of the spleen and flows into the portal vein.

The spleen lies along the course of the blood vessels and is an organ of great variation in size. From the surface, the spleen is covered with a connective tissue capsule, which reaches its greatest thickness in the region of the gate. The capsule contains smooth muscle cells, the number of which increases sharply in some representatives of the living world, including horses, predators, etc. The surface of the capsule is covered with mesothelium. All this creates a completely mobile capsule design. Numerous layers of loose, unformed connective tissue, trabeculae, depart from the capsule. These trabeculae contain numerous blood vessels and smooth myocytes. Trabeculae can anastomose with each other. The stroma of the spleen is formed by reticular tissue. There are white and red pulp, which are based on reticular tissue.

white pulp represented by numerous lymphoid follicles scattered throughout the spleen. The white pulp makes up about one-fifth of the mass of the spleen. Lymphoid follicles of the spleen are built from lymphoid tissue and are called Malpighian bodies. Lymphoid follicles of the spleen differ in structure from the follicles of the lymph node. Each lymphoid follicle of the spleen contains a central artery, which, due to a corkscrew-like course, can enter the cut several times. In the Malpighian body, 4 zones are distinguished, including the periarterial zone, the light center, the mantle zone, and the marginal zone. The light center (reactive center, reproduction center) and the mantle zone represent the B-zone, in which the antigen-dependent stage of maturation of B-lymphocytes occurs. This zone is characterized by a specific microenvironment, including type 1 dendritic cells, macrophages, and a small number of T-lymphocytes. In the light center, blast transformation and reproduction of B-lymphocytes occur, and in the mantle zone, cooperation of T- and B-lymphocytes and accumulation of memory B-cells occur. The periarterial zone is the T-zone. Here, an antigen-dependent stage of maturation of T-lymphocytes occurs under the influence of a specific microenvironment (type 2 dendritic cells, macrophages, a small number of B-lymphocytes). This zone increases significantly with a cell-type immune response. The marginal zone is common for T- and B-lymphocytes. The marginal (marginal) sinuses are adjacent to it. In the marginal zone, cooperative interactions of T- and B-lymphocytes occur. In addition, T- and B-lymphocytes, as well as antigens, which are captured by macrophages, enter the white pulp through this zone. Plasma cells migrate through this zone into the red pulp. The cellular composition of this zone is represented by lymphocytes (mainly B-lymphocytes and precursors of plasma cells), macrophages and reticular cells.

red pulp represented by numerous blood vessels, including venous sinuses. Venous sinuses have a diameter of up to 40 microns and resemble sinusoidal capillaries in structure (lined with endothelium lying on a discontinuous basement membrane). The red pulp also includes splenic cords containing erythrocytes, granular and non-granular leukocytes, plasmocytes at different stages of development, that is, the destruction of old erythrocytes, the maturation of plasmocytes occurs here. It has been established that blood cells from the capillaries enter the splenic cords, and then migrate through the gaps between the endothelial cells of the wall of the venous sinus into its lumen. This is facilitated by increased blood pressure due to its constant influx and periodic contractions of bundles of smooth muscle cells in the wall of the trabecular arteries and the spleen capsule.

The spleen has an abundant blood supply. About 800 ml of blood flows through the spleen every minute. The splenic artery enters the gates of the spleen, which splits into numerous trabecular arteries, the latter pass into the pulp arteries, in the adventitia of which there are accumulations of lymphoid tissue (lymphoid sheaths) related to the white pulp. The pulpal artery enters the lymphoid follicle, acquires a corkscrew course and is called the central artery. In the Malpighian follicle, the central artery gives rise to numerous capillaries to nourish its tissues. Leaving the follicle, the central artery splits into many branches, which are called brush arteries. The cystic arteries are surrounded by periarterial muffs composed of reticular cells, macrophages, and lymphocytes. At the ends of the cystic arteries, sphinctors are formed, consisting of accumulations and reticular cells. The cystic arteries pass into capillaries, from which blood enters the venous sinuses. Sphinctors are located at the ends of the venous sinuses. From the venous sinuses, blood enters the pulpal veins, trabecular veins, and splenic veins. Trabecular veins and venous sinuses do not have a muscular membrane, therefore, when damaged, vessels do not collapse, which leads to the development of parenchymal bleeding.

Distinguish open and closed blood supply spleen. When awake, blood flows in the spleen, without leaving the red pulp (closed blood supply). At rest and rest, part of the blood is deposited, including in the venous sinuses, which creates conditions for the release of part of the blood into the red pulp, where old erythrocytes die.

The spleen regenerates well both under physiological conditions and after injury. Under experimental conditions, the possibility of complete recovery of the spleen even after removal of 80-90% of its volume has been shown. However, a complete restoration of the shape and size of the spleen does not occur.

Functions of the spleen.

1. Hematopoietic function: the formation of T- and B-lymphocytes.

2. Immune function: due to lymphocytes, it participates in the regulation of cellular and humoral immune response.

3. Blood depot: due to the double sphincter system.

4. Here, the death of most red blood cells occurs.

6. Depot of blood stem cells.

B-lymphocytopoiesis.

In the bone marrow, B-lymphocyte progenitor cells sequentially proliferate and differentiate into B-lymphoblasts, B-prolymphocytes, and B-lymphocytes. The formed B-lymphocytes from the bone marrow with the blood flow enter the peripheral organs of hematopoiesis, where they populate the B-zones. Under the influence of antigens, an antigen-dependent stage of the formation of B-lymphocytes is carried out here. In this case, blast forms are formed, and then plasma cells that produce antibodies.

T-lymphocytopoiesis.

Precursor cells of T-lymphocytes and T-lymphoblasts from the red bone marrow enter the subcapsular zone of the thymus. T-lymphocytes proliferate and differentiate in the thymus. In this case, the formation of T-prolymphocytes and T-lymphocytes occurs sequentially. The resulting T-lymphocytes with the blood flow then enter the peripheral organs of hematopoiesis, where they populate the T-zones. In the T-zones, the antigen-dependent stage of T-lymphocytopoiesis occurs.

Morphological features of the spleen in children

The spleen begins to function as a hematopoietic organ in the embryonic period. However, the spleen of a newborn child has a number of significant morphological features.

First of all, a newborn child of the first years of life, as a rule, has several additional spleens, ranging in size from the head of a needle to the size of an average apple. In a newborn child, the mass of the spleen is 8-12 grams. After the birth of a child, an increase in the mass of the spleen is noted, as a result of which by the age of 5 this figure reaches 35–40 g, and by the period of puberty it is already 80–90 g. cells. From the capsule depart single weakly expressed, thin layers of connective tissue - trabeculae. After birth, the spleen capsule gradually thickens, the number of elastic and muscular elements increases, and the trabeculae become wider. The capsule is finally formed by the age of 7–10 years, and the trabeculae by 18–20 years.

In the spleen of a newborn child, there are few, immature lymphoid follicles, most of which are small with indistinct contours. Light centers in the lymphoid follicles are formed only by the end of the first year of a child's life. In 85% of newborn children, the spleens have a lobed structure. After birth, the lobular nature of the structure of the spleen is gradually erased, an increase in the number of lymphoid follicles with pronounced light centers is noted. This process continues until the age of 18-20.

Spleen- peripheral organ of the hematopoietic and immune systems. In addition to performing hematopoietic and protective functions, it participates in the death of erythrocytes, produces substances that inhibit erythropoiesis, and deposits blood.

Development of the spleen. The laying of the spleen occurs at the 5th week of embryogenesis by the formation of a dense accumulation of mesenchyme. The latter differentiates into reticular tissue, germinates with blood vessels, and is populated by hematopoietic stem cells. At the 5th month of embryogenesis in the spleen, the processes of myelopoiesis are noted, which by the time of birth are replaced by lymphocytopoiesis.

The structure of the spleen. The spleen is covered on the outside with a capsule consisting of mesothelium, fibrous connective tissue and smooth myocytes. Crossbars - trabeculae, anastomosing with each other, depart from the capsule inward. They also have fibrous structures and smooth myocytes. The capsule and trabeculae form the musculoskeletal apparatus of the spleen. It makes up 5-7% of the volume of this organ. Between the trabeculae is the pulp (pulp) of the spleen, which is based on reticular tissue.

stem hematopoietic cells are determined in the spleen in an amount of approximately 3.5 per 105 cells. There are white and red pulps of the spleen.

White pulp of the spleen- this is a collection of lymphoid tissue, which is formed by lymphatic nodules (B-dependent zones) and lymphatic periarterial sheaths (T-dependent zones).

white pulp macroscopic examination of sections of the spleen It looks like light gray rounded formations that make up 1/5 of the organ and are diffusely distributed over the cut area.

Lymphatic periarterial sheath surrounds the artery after it exits the trabeculae. It contains antigen-presenting (dendritic) cells, reticular cells, lymphocytes (mainly T-helpers), macrophages, and plasma cells. Lymphatic primary nodules are similar in structure to those in the lymph nodes. This is a round formation in the form of an accumulation of small B-lymphocytes that have undergone antigen-independent differentiation in the bone marrow, which are in interaction with reticular and dendritic cells.

Secondary nodule with germinal center and the crown occurs with antigenic stimulation and the presence of T-helpers. In the crown there are B-lymphocytes, macrophages, reticular cells, and in the germinal center - B-lymphocytes at different stages of proliferation and differentiation into plasma cells, T-helpers, dendritic cells and macrophages.

Regional, or marginal, zone of nodules is surrounded by sinusoidal capillaries, the wall of which is penetrated by slit-like pores. In this zone, T-lymphocytes migrate along the hemocapillaries from the periarterial zone and enter the sinusoidal capillaries.

red pulp- a set of various tissue and cellular structures that make up the entire remaining mass of the spleen, with the exception of the capsule, trabeculae and white pulp. Its main structural components are reticular tissue with blood cells, as well as blood vessels of the sinusoidal type, which form bizarre labyrinths due to branching and anastomoses. In the reticular tissue of the red pulp, two types of reticular cells are distinguished - poorly differentiated and phagocytic cells, in the cytoplasm of which there are many phagosomes and lysosomes.

between reticular cells blood cells are located - erythrocytes, granular and non-granular leukocytes.
Part erythrocytes is in a state of degeneration or complete decay. Such erythrocytes are phagocytized by macrophages, which then transfer the iron-containing part of hemoglobin to the red bone marrow for erythrocytopoiesis.

Sinuses in the red pulp of the spleen represent part of the vascular bed, the beginning of which gives the splenic artery. This is followed by segmental, trabecular and pulpal arteries. Within the lymphoid nodules, the pulpal arteries are called central. Then come brush arterioles, arterial hemocapillaries, venous sinuses, pulpal venules and veins, trabecular veins, etc. There are thickenings in the wall of brush arterioles called sleeves, couplings or ellipsoids. There are no muscle elements here. Thin myofilaments were found in the endothelial cells lining the lumen of the sleeves. The basement membrane is very porous.

The bulk of the thickened sleeves make up reticular cells with high phagocytic activity. It is believed that arterial sleeves are involved in filtering and neutralizing arterial blood flowing through the spleen.

Venous sinuses form a significant part of the red pulp. Their diameter is 12-40 microns. The wall of the sinuses is lined with endotheliocytes, between which there are intercellular gaps up to 2 microns in size. They lie on a discontinuous basement membrane containing a large number of holes with a diameter of 2-6 microns. In some places, the pores in the basement membrane coincide with the intercellular gaps of the endothelium. Due to this, a direct communication is established between the lumen of the sinus and the reticular tissue of the red pulp, and the blood from the sinus can exit into the surrounding reticular stroma. Important for the regulation of blood flow through the venous sinuses are the muscle sphincters in the wall of the sinuses at the point of their transition into the veins. There are also sphincters in the arterial capillaries.

Contractions of these two types of muscle sphincters regulates blood supply to the sinuses. The outflow of blood from the microvasculature of the spleen occurs through a system of veins of increasing caliber. A feature of trabecular veins is the absence of a muscle layer in their wall and the fusion of the outer shell with the connective tissue of the trabeculae. As a result, the trabecular veins constantly gape, which facilitates the outflow of blood.

Age-related changes in the spleen. With age, atrophy of the white and red pulp is noted in the spleen, the number of lymphatic follicles decreases, and the connective tissue stroma of the organ grows.

Reactivity and regeneration of the spleen. Histological features of the structure of the spleen, its blood supply, the presence in it of a large number of large dilated sinusoidal capillaries, the absence of a muscular membrane in the trabecular veins should be taken into account in case of a combat injury. When the spleen is damaged, many vessels are in a gaping state, and the bleeding does not stop spontaneously. These circumstances may determine the tactics of surgical interventions. The spleen tissues are very sensitive to the action of penetrating radiation, to intoxications and infections. However, they have a high regenerative capacity. Recovery of the spleen after injury occurs within 3-4 weeks due to the proliferation of cells of the reticular tissue and the formation of foci of lymphoid hematopoiesis.

Hematopoietic and immune systems extremely sensitive to various damaging influences. Under the action of extreme factors, severe injuries and intoxications, significant changes occur in the organs. In the bone marrow, the number of hematopoietic stem cells decreases, lymphoid organs (thymus, spleen, lymph nodes) are emptied, cooperation of T- and B-lymphocytes is inhibited, helper and killer properties of T-lymphocytes change, differentiation of B-lymphocytes is disturbed.

Functions of the lymph nodes:

hematopoietic function consists in antigen-dependent differentiation of lymphocytes;

barrier-protective function - non-specific protection against antigens consists in their phagocytosis from the lymph by numerous macrophages and "coastal" cells; a specific protective function is the implementation of specific immune responses;

drainage function, the lymph nodes collect lymph from the bringing vessels coming from the tissues. If this function is impaired, peripheral edema is observed;

the function of deposition of lymph, normally a certain amount of lymph lingers in the lymph node and is turned off from the lymph flow;

metabolic functionparticipation in the metabolism of proteins, fats, carbohydrates and other substances.

Structure

The total number of lymph nodes in the human body is approximately 1000, which is about 1% of body weight. Their average size is 0.5-1 cm. Lymph nodes are kidney-shaped, lie regionally in relation to the organs, in groups. From the convex surface of the lymph node, the afferent lymphatic vessels enter it, and from the opposite side, which is called the gate, the efferent lymphatic vessels exit. In addition, arteries and nerves enter the gates of the lymph node, and veins exit.

Lymph nodes are parenchymal zonal organs. The following structural and functional components can be distinguished in them:

trabeculae extending from the capsule, anastomosing with each other, they form the framework of the lymph node;

reticular tissue filling the entire space between the capsule and trabeculae;

in the lymph node, two zones are distinguished: the peripheral cortical substance, and the central one - the medulla;

between the cortical and medulla - the paracortical zone or deep cortex;

sinuses - a collection of lymphatic vessels through which lymph moves. The sequence of passage of lymph through the lymph node and the location of the sinuses is as follows: the afferent lymphatic vessels - the marginal or subcapsular sinus - the intermediate cortical sinuses - the intermediate cerebral sinuses - the portal sinus - the efferent lymphatic vessel in the region of the gate.

^ The cortical substance of the lymph node is represented by an accumulation of lymphoid tissue, which includes lymphoid follicles, or nodules, and an interfollicular plateau. Lymphoid nodules are round, up to 1 mm in size. Distinguish primary without a reactive center, and secondary lymphoid follicles with a reactive center (reproduction center, light center).

Primary follicles consist mainly of small "naive" B-lymphocytes associated with reticular and follicular dendritic cells. When the antigen enters, blast transformation of "naive" B-lymphocytes occurs, and secondary nodules are formed. They consist of a breeding center and a crown, or mantle, on the periphery. The crown is formed by small memory B-lymphocytes, as well as small "naive" lymphocytes of bone marrow origin. The reactive center at the height of the immune response is divided into dark and light zones. The dark zone faces the paracortical zone. Here, cells divide mitotically, move to a light, more peripheral zone, where there are already more mature, migrating cells. Plasma cell precursors leave the follicle through the lateral zones of the corona to the interfollicular plateau, and then move through the paracortical zone to the medulla (into the pulp cords), where they mature into plasma cells.

^ The paracortical zone or zone of the deep cortex is located on the border of the cortical and medulla. It is the thymus-dependent zone (T-zone) of the lymph node. It contains predominantly T-lymphocytes, however, plasmocytes migrating into the pulpy strands of the medulla at different stages of development are found here. The entire paracortical zone can be divided into separate units. Each unit consists of a central and peripheral parts. In the center, blast transformation and reproduction of T-lymphocytes take place. On the periphery there are postcapillary veins with high epithelium. Through them, lymphocytes migrate from the blood to the lymph node and, possibly, back.

^ The medulla consists of two structural and functional components: the cerebral and pulpy cords and the cerebral intermediate sinuses. Brain cords are B-dependent zone. This is where the maturation of the precursors of plasma cells migrating from the cortex into plasma cells takes place. Plasma cells accumulating in the brain cords during the immune response secrete antibodies into the lymph. Outside, the cerebral sinuses are adjacent to the cerebral cords.

^ The structure of the sinuses of the lymph node

All sinuses of the lymph node are slit-like spaces that are lined with endothelium capable of phagocytosis. In addition to endotheliocytes, retethelial cells are involved in the formation of the walls of the lymphatic sinuses. They have a process shape. At the same time, the processes cross all the spaces of the sinus and form extensions in the form of platforms on its opposite side, which, along with the littoral cells, form a discontinuous lining of the sinuses. There is no basement membrane in the lining of the sinuses. The processes of retethelial cells form a three-dimensional network that slows down the flow of lymph, which contributes to its more complete purification by macrophages. The network is also formed by reticular fibers going in different directions. There are many free macrophages and lymphocytes in the sinuses, which can be fixed in the network.

^ Blood supply to the lymph node

The blood vessels enter the gate of the node. Capillaries depart from the arteries into the capsule and trabeculae, as well as to the nodules. They have superficial and deep capillary networks. The capillary networks continue into high endothelial venules and then into veins that exit through the hilum of the node. Normally, blood never enters the sinuses. With inflammation, trauma and other pathological conditions, a similar phenomenon is possible.

( The spleen is a peripheral organ of the hematopoietic and immune systems. In addition to performing hematopoietic and protective functions, it participates in the death of erythrocytes, produces substances that inhibit erythropoiesis, and deposits blood. development of the spleen. The laying of the spleen occurs at the 5th week of embryogenesis by the formation of a dense accumulation of mesenchyme. The latter differentiates into reticular tissue, germinates with blood vessels, and is populated by hematopoietic stem cells. At the 5th month of embryogenesis in the spleen, the processes of myelopoiesis are noted, which by the time of birth are replaced by lymphocytopoiesis. The structure of the spleen. The spleen is covered on the outside with a capsule consisting of mesothelium, fibrous connective tissue and smooth myocytes. Crossbars - trabeculae, anastomosing with each other, depart from the capsule inward. They also have fibrous structures and smooth myocytes. The capsule and trabeculae form the musculoskeletal apparatus of the spleen. It makes up 5-7% of the volume of this organ. Between the trabeculae is the pulp (pulp) of the spleen, which is based on reticular tissue. Hematopoietic stem cells are found in the spleen at about 3.5 per 105 cells. There are white and red pulps of the spleen. The white pulp of the spleen is a collection of lymphoid tissue, which is formed by lymphatic nodules (B-dependent zones) and lymphatic periarterial sheaths (T-dependent zones). Macroscopically examining spleen sections, the white pulp looks like light gray rounded formations that make up 1/5 of the organ and are diffusely distributed over the section area. The lymphatic periarterial sheath surrounds the artery after it exits the trabeculae. It contains antigen-presenting (dendritic) cells, reticular cells, lymphocytes (mainly T-helpers), macrophages, and plasma cells. Lymphatic primary nodules are similar in structure to those in the lymph nodes. This is a round formation in the form of an accumulation of small B-lymphocytes that have undergone antigen-independent differentiation in the bone marrow, which are in interaction with reticular and dendritic cells. A secondary nodule with a germinal center and a crown occurs with antigenic stimulation and the presence of T-helpers. In the crown there are B-lymphocytes, macrophages, reticular cells, and in the germinal center - B-lymphocytes at different stages of proliferation and differentiation into plasma cells, T-helpers, dendritic cells and macrophages. The marginal, or marginal, zone of nodules is surrounded by sinusoidal capillaries, the wall of which is permeated with slit-like pores. In this zone, T-lymphocytes migrate along the hemocapillaries from the periarterial zone and enter the sinusoidal capillaries. Red pulp - a collection of various tissue and cellular structures that make up the entire remaining mass of the spleen, with the exception of the capsule, trabeculae and white pulp. Its main structural components are reticular tissue with blood cells, as well as blood vessels of the sinusoidal type, which form bizarre labyrinths due to branching and anastomoses. In the reticular tissue of the red pulp, two types of reticular cells are distinguished - poorly differentiated and phagocytic cells, in the cytoplasm of which there are many phagosomes and lysosomes. Between the reticular cells are blood cells - erythrocytes, granular and non-granular leukocytes. Part of the red blood cells is in a state of degeneration or complete decay. Such erythrocytes are phagocytized by macrophages, which then transfer the iron-containing part of hemoglobin to the red bone marrow for erythrocytopoiesis. The sinuses in the red pulp of the spleen represent part of the vascular bed, which originates from the splenic artery. This is followed by segmental, trabecular and pulpal arteries. Within the lymphoid nodules, the pulpal arteries are called central. Then come brush arterioles, arterial hemocapillaries, venous sinuses, pulpal venules and veins, trabecular veins, etc. There are thickenings in the wall of brush arterioles called sleeves, couplings or ellipsoids. There are no muscle elements here. Thin myofilaments were found in the endothelial cells lining the lumen of the sleeves. The basement membrane is very porous. The bulk of the thickened sleeves are reticular cells with high phagocytic activity. It is believed that arterial sleeves are involved in filtering and neutralizing arterial blood flowing through the spleen. Venous sinuses form a significant part of the red pulp. Their diameter is 12-40 microns. The wall of the sinuses is lined with endotheliocytes, between which there are intercellular gaps up to 2 microns in size. They lie on a discontinuous basement membrane containing a large number of holes with a diameter of 2-6 microns. In some places, the pores in the basement membrane coincide with the intercellular gaps of the endothelium. Due to this, a direct communication is established between the lumen of the sinus and the reticular tissue of the red pulp, and the blood from the sinus can exit into the surrounding reticular stroma. Important for the regulation of blood flow through the venous sinuses are the muscle sphincters in the wall of the sinuses at the point of their transition into the veins. There are also sphincters in the arterial capillaries. The contraction of these two types of muscle sphincters regulates the blood supply to the sinuses. The outflow of blood from the microvasculature of the spleen occurs through a system of veins of increasing caliber. A feature of trabecular veins is the absence of a muscle layer in their wall and the fusion of the outer shell with the connective tissue of the trabeculae. As a result, the trabecular veins constantly gape, which facilitates the outflow of blood. Age-related changes in the spleen. With age, atrophy of the white and red pulp is noted in the spleen, the number of lymphatic follicles decreases, and the connective tissue stroma of the organ grows. Reactivity and regeneration of the spleen. Histological features of the structure of the spleen, its blood supply, the presence in it of a large number of large dilated sinusoidal capillaries, the absence of a muscular membrane in the trabecular veins should be taken into account in case of a combat injury. When the spleen is damaged, many vessels are in a gaping state, and the bleeding does not stop spontaneously. These circumstances may determine the tactics of surgical interventions. The spleen tissues are very sensitive to the action of penetrating radiation, to intoxications and infections. However, they have a high regenerative capacity. Recovery of the spleen after injury occurs within 3-4 weeks due to the proliferation of cells of the reticular tissue and the formation of foci of lymphoid hematopoiesis. The hematopoietic and immune systems are extremely sensitive to various damaging effects. Under the action of extreme factors, severe injuries and intoxications, significant changes occur in the organs. In the bone marrow, the number of hematopoietic stem cells decreases, lymphoid organs (thymus, spleen, lymph nodes) are emptied, cooperation of T- and B-lymphocytes is inhibited, helper and killer properties of T-lymphocytes change, differentiation of B-lymphocytes is disturbed.

human spleen

Spleen (lie, splen)- an unpaired, elongated peripheral organ of lymphoid hematopoiesis and immune defense, located deep in the back of the left hypochondrium. The length of the spleen is 10-12 cm, width 8-9 cm, thickness 4-5 cm, weight 150-200 g. The spleen is projected onto the chest between the 9th and 11th ribs, its long axis is oblique and in most cases corresponds to the direction of the 10th rib .

The main functions of the spleen:

1. Anatomy of the spleen

In the spleen, diaphragmatic and visceral surfaces are distinguished. With its diaphragmatic surface, the spleen is adjacent to the lower surface of the diaphragm, visceral - to the bottom of the stomach, left kidney, left adrenal gland and in the colon. On the visceral surface of the spleen is a recess - the gate of the liver, through which the splenic artery, nerves, veins and lymphatic vessels pass. The spleen is covered on all sides by the peritoneum, which forms connections. Two ligaments diverge from the gates of the spleen: gastrosplenic and diaphragmatic-splenic, which runs in the lumbar part of the diaphragm. In addition, the diaphragmatic-colic ligament runs from the diaphragm to the left flexure of the colon, which supports the anterior root of the spleen.

2. Histology of the spleen

The spleen is covered on the outside with a connective tissue capsule, from which trabeculae extend inward, forming a kind of mesh frame. The capsule and trabeculae form the musculoskeletal apparatus of the spleen. They consist of dense fibrous connective tissue dominated by elastic fibers that allow the spleen to change its size and withstand a significant increase in volume. The capsule and trabeculae contain bundles of smooth myocytes, the contraction of which contributes to the expulsion of deposited blood into the bloodstream. Between the trabeculae is the stroma of the spleen, which is represented by reticular tissue, and in its loops there are parenchyma cells. The parenchyma includes two sections with different functions:

• white pulp
• red pulp

From so, the spleen refers to the human parenchymal organs.

2.1. white pulp

The white pulp of the spleen is represented by lymphoid tissue, lymph nodes (follicles), and lymphatic periarterial sheaths.

Lymph follicles are B-dependent zones, which are formed by spherical accumulations of lymphocytes, plasma cells, macrophages, dendritic and interdigitating cells. They are surrounded by a capsule, which is formed by reticuendothalial cells. In the lymphatic follicles of the white pulp of the spleen, the following zones are distinguished:

Lymphatic periarterial sheaths are an elongated accumulation of lymphocytes, which in the form of clutches cover the artery of the white pulp of the spleen and continue into the lymphatic follicle. B-lymphocytes and plasmocytes are located in the central part of the vagina, small T-lymphocytes are located along the periphery.

2.2. red pulp

Occupies the space between the white pulp and connective tissue trabeculae. It consists of blood cells that are located among the reticular stroma. red pulp includes:

3. Blood supply to the spleen

Provided by the splenic artery - a branch of the celiac trunk. The initial section of the artery is located behind the upper edge of the pancreas, and at the level of the tail of the gland, the artery emerges from under it and divides into 2-3 branches that go to the gates of the spleen. Along the way, the splenic artery gives off branches to the pancreas, and at the gates of the spleen, the short arteries of the stomach and the left gastroepiploic artery depart from it. The splenic vein has a diameter twice that of the eponymous artery and is often located below the artery. Behind the head of the pancreas, the splenic vein merges with the superior mesenteric vein to form the main trunk of the portal vein.

4. Lymph drainage of the spleen

Regional lymph nodes of the first order are located in the gastrosplenic ligament at the hilum of the spleen, as well as at the tail of the pancreas. Further, the lymph flows into the subscapular nodes, and then into the lymph nodes located around the root of the abdominal trunk.

5. Innervation of the spleen

The spleen is innervated by branches of the splenic plexus located around the splenic artery. The abdominal, left diaphragmatic and left adrenal nerve plexuses participate in the formation of this plexus.