Thymus gland meaning. Anatomy and structure of the thymus gland

THYMUS (thymus; syn.: thymus, thymus gland) - a paired lobular organ located in the upper part of the anterior mediastinum; is the central organ of the immunogenesis system, responsible for the formation and functioning of the cellular immune system.

For a long time V. attributed a wide variety of functions, including influence on growth and sexual development, metabolism, etc. And only since the 60s, after it was proven that the removal of V. before the formation of peripheral lymphoid organs (spleen, lymph, nodes) leads to a halt in the development of the entire system of immunogenesis and to the inability to carry out immune reactions [Miller (I. F. Miller), 1961], it became obvious that V. zh. has a central place in the formation and maintenance of the full functioning of the body's immunogenesis system. The final opinion about V. zh. as the central organ of immunity was formed after the identification and detailed study of congenital immunodeficiency diseases in humans and animals caused by aplasia or hypoplasia of V. g.

V. g. first appears in vertebrates. In higher fish it is already well formed. V. has been studied to a greater extent. in birds and mammals. In birds V. g. consists of ovoid rosaries located on both sides of the neck, the removal of which leads to disruption of cellular immune responses. Most mammals have V. represented by 2-3 lobes and located in the retrosternal region.

Embryology

Rice. 1. Embryonic anlage of the thymus gland in humans (diagram): a - derivatives of gill pouches on the 16th - 18th day of uterine life; b - derivatives of gill pouches at the end of the second month of uterine life (I-V - gill pouches). 1 - rudiment of the thyroid gland; 2 - thyroglossal duct; 3 - rudiment of the parathyroid glands (anterior pair); 4 - rudiment of the parathyroid glands (posterior pair); 5 - rudiments of the thymus gland (indicated in gray); 6 - ultimobranchial bodies (derivatives of the V gill pouch); 7 - auditory (Eustachian) tube and middle ear cavity; 8 - rudiment of the tonsil (the dots indicate the lymphocytes accumulated around it); 9 - parathyroid glands, separated from the III and IV gill pouches; 10 - thymopharyngeal duct; 11 - aortic arch; 12 - right common carotid artery; 13 - right subclavian artery; 14 - left subclavian artery; 15 - lobes of the thymus gland.

V. g. belongs to the group of branchiogenic organs developing from gill pouches (Fig. 1). In humans V. g. appears at 6 weeks intrauterine development in the form of paired protrusions of the III and IV pairs of gill pouches, but the rudiments from the IV pair remain small and can be reduced. It is possible that in the formation of the rudiments of V. zh. the ectoderm of the bottom of the gill furrows also takes part. Epithelial rudiments of the gland grow in the caudal direction. Their distal part thickens, forming the body of the gland, and the proximal part extends into the ductus thymopharyngeus, which subsequently disappears, and the gland is separated from the gill pouch that gave rise to it. With continued growth in length towards the heart, the distal parts of the anlage come closer and are closely adjacent to each other, but their true fusion does not occur, and the described organ has a bilobar structure. By the middle of the 8th week. intrauterine development bookmarks V. g. descend down under the sternum to the mediastinum, where they lie on the anterior surface of the pericardium. The neck part of the tabs remains narrow and is gradually reduced. When persisting cranial cords, additional cervical V. may occur.

In the early stages of embryogenesis, the anlage of V. not much different from the laying of other glands and has the appearance of massive epithelial bands. During the 2nd month. development, compact epithelial strands form outgrowths into the surrounding mesenchyme rich in vessels, and the gland rudiment becomes lobulated. With the beginning of differentiation of the germ tissue, from approximately the 10th week. development, the epithelium of the anlage gradually acquires a loose reticular structure. In the loops of the reticulum there are rounded large basophilic lymphoid cells, which, multiplying, give rise to numerous small lymphocytes (thymocytes). Their number increases rapidly, especially at the beginning of the 3rd month. embryo development. The density of the epithelial reticulum becomes unequal in the central and peripheral parts of the gland, and the peripheral parts are abundantly infiltrated by lymphocytes. In a 10-11 week old embryo in the V. stage. It is already possible to distinguish between the medulla and the cortex. By the 12th week. embryonic development, the first bodies of V. appear in the medulla. (Hassal's bodies), the growing mesenchymal tissue finally separates the epithelial remnants. After 18 weeks embryonic development of V. it looks like a fully formed lobular organ with a clear division into cortical and medulla layers, resembling a lymphoid organ rather than a developing gland.

During the process of embryogenesis, V. it is finally formed before other lymphoid tissues (spleen, limf, nodes) and by birth it turns out to be the largest lymphoid organ of the body.

The epithelial origin of the reticular base of the gland is beyond doubt. The origin of lymphocytes remains unclear. The question of the mesenchymal genesis of lymphocytic cells (A. A. Maksimov, 1909), which was considered resolved, is again being reviewed after the experimental studies of Auerbach (R. Auerbach, 1961 - 1963), which allows for the possibility of the emergence of lymphocytes from the epithelial anlage of V. g. A necessary condition for this transformation, in his opinion, is the inducing influence of the surrounding mesenchyme.

Anatomy

V. g. consists of two lobes of unequal size - right and left, welded together by loose connective tissue. Sometimes an intermediate lobe is wedged between the main lobes. According to the configuration of the V. zh. resembles a pyramid with its apex facing upward. The parenchyma is of a soft consistency, pink-gray in color. There are a body and four horns of the V. gland: two upper (cervical) sharp, sometimes reaching the thyroid gland, and two lower (thoracic) rounded, wide, forming the base of the V. gland. Less commonly, V. may consist of one or three lobes and very rarely of a larger number of lobes (up to 6). The cervical part, narrower, is located along the trachea behind m. sternohyoideus and m. sternothyreoideus and sometimes reaches the thyroid gland. The thoracic part, expanding downwards, descends behind the sternum to the level of the III - IV intercostal space, covering the large vessels of the heart and the upper part of the pericardium. Dimensions and weight V. g. change with age (age-related involution).

The ratio of the weight of the gland to body weight (in newborns 1: 300) shows that from the moment of birth a continuous decrease in its relative weight begins, continuing until approximately 30 years of age. As V. decreases. its parenchyma is gradually replaced by adipose tissue. In old age, the so-called gland is found in place of the gland. a fatty body, the lobules of which are represented by adipose tissue. However, in these lobules, remnants of the parenchyma of the veins remain until old age.

Blood supply of the V. g. carried out from aa. thoracicae int., rr. mediastinales and aa. pericardiacophrenicae. The arteries extending from these trunks (aa. thymicae) enter the gland, branch along the interlobular layers and, penetrating inside the lobules, give off capillaries mainly to the cortex. The medulla is poor in capillaries. Veins (vv. thymicae) run parallel to the arteries and flow into vv. brachiocephalicae and in vv. thoracicae int.

B. f. has a well-developed intraorgan lymph system, represented by a deep and superficial network of capillaries. In the medulla and cortex of the lobules there is a deep capillary network, and capillaries are found around Hassal's bodies (corpusculum thymi, LHN). In the capsule of the gland and directly below it there is a superficial network of capillaries connected to the capillaries of the cortex. There are more lymphs and capillaries in the cortex (E. A. Vorobyova, 1961). Lymph and capillaries collect in the vessels of the interlobular septa, running along the blood vessels. Lymph, vessels V. g. flow into the lymph nodes of the anterior mediastinum and tracheobronchial nodes.

The innervation of the gland is carried out by branches of the vagus nerve, as well as branches of the sympathetic nerve, originating from the lower cervical and upper thoracic nodes (stellate node) of the sympathetic trunk.

Histology

V. g. covered with a connective tissue capsule, partitions (septa) extend from the cut, dividing the parenchyma of the gland into lobules different sizes. The capsule and septa contain collagen and reticular fibers. Along the course of small-caliber blood vessels in the parenchyma of the V. g. a dense network of reticular fibers is detected. In each lobule, regardless of its size, the cortex and medulla are distinguished (Fig. 2). The basis of the lobule is a loose, sponge-like network of stellate epithelial cells, loops a cut are infiltrated by V.'s lymphocytes., similar on structure to small lymphocytes and representing cells to dia. OK. 6 µm with a round optically dense nucleus and narrow basophilic cytoplasm. In a light microscope, they are indistinguishable from lymphocytes of other lymphoid organs, but electron microscopy revealed differences in the volume of the cytoplasm, the number of organelles, the content nucleic acids, alkaline phosphatase. However, these differences are not significant and do not allow differentiation of V.'s lymphocytes. and lymphocytes of other lymphoid organs. In the subcapsular region of the cortex, layers of cells similar to lymphoblasts and characterized by high mitotic activity are visible. In addition, microphages with granules in the cytoplasm are present in this area, which give a positive PAS reaction. The accumulation of lymphocytes between stellate epithelial thymocytes (epithelial cells of the V. g.) gives the cortex a characteristic appearance and dark color in preparations.

The medulla has a lighter color due to the relatively small number of lymphocytes and the predominance of a reticular epithelial base. Characteristic formations for the medulla are Gass' bodies la, which are concentric accumulations of regenerating stellate epithelial cells. There are no Hassall bodies in the cortical layer. Besides, in a brain layer there are large epithelial cells with a round pale kernel and slightly acidophilic cytoplasm, in a cut by means of a submicroscopy the dense granules and vacuoles filled with amorphous substance are revealed. Histochemical analysis shows the presence of acidic and neutral mucopolysaccharides in the detritus of many Hassall bodies. Granules of stellate epithelial thymocytes and Hassall's bodies react positively to glycoproteins, which indicates the active secretory activity of the epithelial formations of the medulla V. g. It has been observed that the formation of Hassall's bodies occurs as a result of the accumulation of flattening epithelial cells around a cell containing a secretion-like substance.

In the cortical and medulla there are macrophages and a small amount of eosinophilic and neutrophilic leukocytes, mast cells. At children of early age in V.. sometimes foci of erythropoiesis are found. Using electron microscopy, it was found that the epithelial reticulum is formed due to the fact that the stretching epithelial thymocytes remain interconnected by their processes. The processes are in close contact with each other and connected with the help of desmosomes (Fig. 3).

Under the capsule, along the interlobular septa and around the vessels, the epithelium forms a continuous layer with a basement membrane that completely separates the B. lymphocytes. from other fabrics. Identified hematothymic barrier, which consists of endothelial cells, endothelial basement membrane, fine-fibrous tissue, basement membrane of the epithelium and a layer of stellate epithelial thymocytes [Pinkel (D. Pinkel), 1968]. Many epithelial cells contain phageated material, including lymphocytes. They maintain a desmo-somal connection with the epithelial base of the lobule.

In a normal state in V.. there are no germinal centers characteristic of limf, nodes and spleen. Proliferation of lymphocytes V. g. occurs without connection with certain reactive centers. Cells V. zh., ch. arr. cortical substance, are characterized by high mitotic activity, much higher than in other tissues of the body. Mitoses in the thymus gland are observed more often than in lymphoid tissues. DNA update in V. zh. occurs more intensely than in other tissues.

Age-related features of the thymus gland

With age in V. involutional processes occur, expressed in a change in the cellular composition of the organ.

Weight V. varies considerably both individually and in different age periods.

According to various authors, newborns have V. weighs from 7.7 to 34.0 g. Significant increase in weight V. g. registered between the ages of 1 and 3 years. In the period from 3 to 20 years, stabilization of the weight of V. is noted. In older people and old people V. g. weighs on average up to 15 g.

With age, the relationship between the cortical and medulla changes. In fetuses at the time of birth, V. characterized by the predominance of the cortex over the brain, an abundance of capillaries penetrating the lobules; each lobule contains 4-8 Hassall bodies. V. has a similar structure. child under 1 year. By this time, Hassal's bodies increase in size to 80-100 microns. V. g. a child of 1-3 years old is represented by brain and cortical layers of equal size, at this age the number of capillaries decreases and the number of large-caliber vessels increases. At the same time, the process of reverse development of V. begins. In short years, up to 3-4 Hassall bodies with a size of 130-170 µm are detected in the lobule. Further narrowing of the cortical substance with the isolation of follicle-like foci occurs at the age of 4-9 years, continuing up to 20 years later due to a decrease in the number of lymphocytes of the V. g., further isolation of follicle-like foci consisting of lymphocytes, Hassal's bodies (1-4 per lobule ), which reach a maximum size (300-400 microns). At the age of 21-30, the number of lymphocytes of the V. declines. At people at senile age cortical substance and the remains of V. almost completely disappear. are represented by epithelial components, in which there are rare Hassall bodies up to 20-50 microns in size. The vascular network is represented by large-caliber arteries and veins. Significantly developed fatty tissue in the interlobular space. However, V. zh. does not completely atrophy, and its areas surrounded by adipose and connective tissue persist until old age.

During development, the functional activity of the cells of the vein changes. in the implementation of immunological reactions. Thus, it has been established that lymphocytes of V. g. begin to react in vitro to phytohemagglutinin (PHA) and in a mixed culture of lymphocytes from the 12th week. human intrauterine development. Maximum activity of lymphocytes V. g. noted at 14-18 weeks. with a subsequent decrease to the 20th week. Histocompatibility antigens were found on B.'s lymphocytes, starting from the 12th week. Intrathymic phagocytosis of lymphocytes, similar to the process occurring in V. W. adult, found in 15-week-old fetuses. The above facts of the development of the functional activity of lymphocytes

V. g. matter for V.'s use. fetus as a transplant for immunocompromised patients. The literature describes cases of the development of a graft-versus-host reaction in children, to which the embryonic thymus was transplanted to treat congenital immunodeficiency.

In the process of involution V. zh. there is a decrease in the activity of the cells of the cortical layer, while the cells of the medulla in the active state are detected in V. g. old people among the cells of adipose and connective tissue.

According to F. Burnet's selection-clonal theory of immunity, V.'s lymphocytes. are immunocompetent cells. In the embryonic period in V. in the presence of antigens of one's own tissues, clones of cells competent for these tissues, i.e., "forbidden" clones, are suppressed. It is assumed that the lymphocytes of the V., evicted in the first days of life from the thymus, give rise to populations of lymphocytes in the peripheral lymphoid organs, retaining the properties obtained in the thymus. F. Burnet believes that a similar mechanism for the suppression of "forbidden" clones exists in adults, but is expressed to a much lesser extent. Animals (eg mice) with V. removed at birth. it is possible to restore immunological reactivity if to enter them during the first week of life lymphocytes of V., a spleen and limf, nodes from immunologically mature donors of the same line. Transplantation into animals that were thymectomized at birth, as well as into adult animals after irradiation of immunologically competent cells from a donor of a different line, causes graft-versus-host disease in the recipient, meaning that the transferred cells develop an immune reaction against the host tissues. Thymectomy after the first week of life causes lymphopenia, but there are no significant disturbances in the reactions of cellular and humoral immunity. However, after a long time (1 - 2 years), a decrease in a number of immune reactions is found in mice that have undergone thymectomy. W. Dameshek believes that the source of the pathological clone of cells that proliferates uncontrollably in immunoproliferative disorders (lymphoid leukemia, lymphosarcomatosis, reticulosarcomatosis, myelosarcomatosis, etc.) are, as in other autoimmune diseases, “forbidden” clones. The above hypothesis, although it does not cover the pathogenesis of all forms of leukemia, is still of significant interest.

The coincidence of periods of increased thymus activity (up to 5 years and puberty) with two waves of increasing frequency, on the one hand, of autoimmune and allergic diseases and, on the other, of leukemia, has been established.

Function of the thymus

Functional activity of V. in the body is mediated by at least, through two groups of factors: cellular (production of T-lymphocytes) and humoral (secretion humoral factor).

Participation of V. zh. in the development and functioning of the immune system has been convincingly proven in experiments on thymectomized animals, observations of athymic animals and children. Thymectomy within the first day of life in some animal species (mice, rats, hamsters, etc.) leads to the development of “wasting syndrome”. There is a lag in weight, hair loss, lesions of the skin and intestines, hemorrhages, atrophic changes in various organs, the development of inflammatory processes. The most characteristic are atrophic changes in the lymphoid organs with a deficiency of lymphocytes and lymphopenia, which results in a violation of the immunological response. First of all, the T-system of immunity suffers (see Immunity, Transplantation immunity).In animals with removed V., there is no rejection of allogeneic skin grafts or grafted tumors, delayed-type hypersensitivity reactions do not develop, and spleen cells are not able to develop a graft-versus-reaction. host ", etc. Later, the B-system of immunity also suffers, the production of antibodies is disrupted. At the age of 3-4 months, such animals die. "Nude" mice, distinguished by the presence of the autosomal recessive gene "pi", also die at the same time; they show signs of wasting syndrome.A characteristic feature of mice homozygous for the pi gene is congenital aplasia of V. g. The Wasting syndrome does not develop after V.'s removal. in adult animals, as well as after neonatal thymectomy in rabbits, dogs and other species of animals in which other lymphoid organs are developed at birth. Removal of the spleen or maximum extirpation of lymph nodes in the neonatal period does not lead to the development of exhaustion syndrome.

Clinical signs of wasting syndrome with deficiency of the T-immune system were identified in children with aplasia or hypoplasia of the V. g. After thymectomy in adults for myasthenia gravis, no obvious signs of wasting syndrome were detected. However, the state of the immune system in patients after V.'s removal. little studied. It should also be taken into account that in 20% of people, ectopic foci of thymic parenchyma associated with the thyroid or parathyroid glands are found, which are capable of functioning after removal of the bulk of the blood. [Havard (S. W. Havard), 1970].

Observations of this kind served as the basis for the conclusion that V. zh. is the central organ of the immunogenesis system, which is formed and matures earlier than other lymphoid formations. Lymphs, nodes and spleen are considered as peripheral organs of the immune system. Before the peripheral lymphoid organs mature, V. is a vital organ; in the adult body V. only replenishes the population of thymus-dependent lymphocytes, but its participation in immune processes is undoubted. It has been established that under the influence of V. a population of T-lymphocytes (thymus-dependent, thymus-derived) is formed, which carries out cellular immunity reactions, while another population - B-lymphocytes (thymus-independent), possibly originating from lymphoid tissue associated with the intestines or bone marrow, participates in humoral immunity reactions (antibody formation ).

The most widely accepted point of view is that in V. zh. the process of differentiation of a pluripotent stem (progenitor) hematopoietic cell of bone marrow origin occurs through a series of stages into an immunocompetent T-lymphocyte. The process of development of T lymphocytes from a hematopoietic stem cell has been reliably traced using radioactively labeled cells, as well as cells carrying a chromosomal marker. The ancestral hematopoietic cell enters the bloodstream through the bloodstream, where, under the influence of cellular and humoral influences, it differentiates into a lymphocyte of the bloodstream, and then into a T-lymphocyte, which acquires the properties of an immunocompetent cell and leaves the bloodstream, forming a population of lymphocytes in so-called thymus-dependent areas of lymph nodes and spleen.

In V. zh. there are four different structural zones in which the formation of T-lymphocytes occurs: the outer subcapsular cortical layer of the cortex, where large lymphoid cells proliferate and new lymphocytes are formed. the inner cortical layer into which newly formed thymocytes migrate; the medulla itself and areas of perivascular connective tissue surrounding the large vessels of the medulla [L. Clark, 1973]. The subcapsular layer of the cortex is considered the main layer; proliferation of stem cells occurs in it with the formation of new lymphocytes. It is assumed that stem cells enter the subcapsular layer through diapedesis from capillaries that form numerous arcades. Most of the cells in this layer are represented by large lymphocytes with unusually high proliferative activity (on average 6 - 9 hours/cycle). The next process of differentiation occurs in the inner layer of the cortex, where weakly proliferating small lymphocytes are found. It is believed that lymphocytes leave the veins. through the medulla through the veins and lymph vessels. Perivascular cells participate in the same process!! connective tissue. Transition of lymphocytes V. from the cortex to the medulla is accompanied by a change in some of their properties: thymus-specific antigenicity and sensitivity to hydrocortisone decreases, the level of histocompatibility antigens increases and the ability to respond to PHA and other stimulants appears. Educated in V. zh. T-lymphocytes enter the lymph and blood and then colonize the thymus-dependent zones in the lymph nodes (paracortical zone) and in the spleen (zone of lymphocytes around the central arteriole of the lymphoid follicle). The process of colonization is not random. As a result of differentiation, V.'s lymphocytes. acquire surface structures that facilitate targeted colonization of thymus-dependent zones. The deficiency of lymphocytes in thymus-dependent areas is most clearly detected in mice thymectomized in the neonatal period, in “nude” mice, in patients with hypo- and aplasia of the V. g. Restoration of the lymphocyte population in these zones is observed in animals and humans after implantation of V. g.

Production of lymphocytes in V. g. is a relatively stable process influenced by age and genetic factors. High activity of thymic lymphocytopoiesis was noted in humans at the end of intrauterine life and in the first years after birth, i.e. during the periods of formation of the immunogenesis system. Then V. undergoes physiological involution with a decrease in lymphocytopoietic activity, Ch. arr. in the cortex. For the production of lymphocytes V. have various influences. Thus, under various stressors (starvation, overheating or hypothermia, severe injury, exhausting physical work, severe inflammatory or infectious diseases, etc.), involution of the bloodstream is observed, accompanied by mass death T-lymphocytes, but if the stress is not prolonged, then V. g. quickly regenerates. A close relationship has been established between the activity of the adrenal cortex and the production of lymphocytes. Hormones of the adrenal cortex play a significant role in limiting the production of T cells. Thus, it was noted that in mice after 2-3 days. after the introduction of hydrocortisone into the V. g. only 5-10% of lymphocytes remain, represented by T cells. On the other hand, facts of the regulatory influence of V. have been established. on the differentiation of endocrine glands, and in particular the adrenal cortex, in early ontogenesis [Pirpaoli, Sorkin (W. Pierpaoli, E. Sorkin)].

Thymus-dependent lymphocytes, which make up the largest portion of recirculating small lymphocytes in the blood and lymph, perform important immunological functions. These cells are capable of recognizing the antigen entering the body and, depending on the characteristics of the latter, through a series of stages of proliferation and differentiation, transform into effector cells that provide the effector phase of the immune response. A similar effector mechanism develops when the body reacts according to the type of cellular immunity (for example, rejection of a foreign transplant, tumor, during protection against a number of bacterial and viral infections). Effector cells, when interacting with specific antigenic material, release a number of nonspecific factors - mediators of cellular immunity (a factor that inhibits macrophage migration, a blastogenic factor, etc.) that participate in the final stage of the immune reaction. Another functional feature of thymus-dependent lymphocytes is their ability to interact with B-lymphocytes after activation by antigen (the so-called thymus-dependent antigens) and direct the differentiation of the latter into plasma cells that produce antibodies. Since the late 60s, the suppressive function of T lymphocytes, which consists in the regulation of antibody production, has been intensively studied. It is assumed that turning off this function of T-lymphocytes may cause the development of autoimmune processes. In addition, T lymphocytes are assigned important role in the elimination of mutated cells from the body, i.e. participation in maintaining genetic homeostasis. Consequently, V. zh. is an organ that produces immunocompetent T-lymphocytes that perform vital immunological functions in the body.

In addition to the production of T-lymphocytes of the liver, it has been established that this organ secretes a humoral factor. Metcalf (D. Metcalf, 1956) showed that blood serum from mice and humans suffering from leukemia stimulates lymphopoiesis in newborn mice. This factor was called lymphocytopoiesis-stimulating and was detected in small quantities in the blood serum of healthy mice and humans. Experiments have proven the influence of this factor on the function of T-lymphocytes: restoration of immune reactions in the neonatal period in thymectomized mice was noted (cells of the lymph nodes, nodes or spleen do not have this ability); extracts of V. g. promote the development of immune processes in thymectomized animals; after incubation with V. extract. spleen cells from mice deprived of the thymus shortly after birth acquire the ability to develop graft-versus-host disease, like cells from normal animals. Thymic factor present in the blood, as well as extracts of V. g. influence the level of rosette-forming cells formed by T-lymphocytes. Miller (J. F. Miller, 1974) presents the results of the action of an extract from V. g., called “thymopoietin”, on the induction of immature prethymic cells into T-lymphocytes.

Incubation of hematopoietic cells in vitro with thymopoietin for short term(2 hours) led to the appearance of cells with surface antigens characteristic of differentiating T lymphocytes. The drug induced only the differentiation of cells with thymus-specific antigens. Due to the fact that the acquisition of thymus-specific antigens occurs during short period incubation, it was concluded that this process does not require cell division, and the appearance of “new” antigens is associated either with their synthesis or with unmasking on the cell surface. It can be considered proven that the soluble factor produced by V. g. affects the functional activity of thymus-dependent lymphocytes, promoting the differentiation of precursor cells into immunocompetent T-lymphocytes. There is evidence that this factor activates enzymes of cell membranes (activation of adenyl cyclase is noted) and increases the cellular level of cyclic adenosine monophosphate, necessary for the induction of immunocompetence [Kook, Trainin (A. Kook, N. Trainin, 1963)].

However, many issues related to the secretion of this thymic factor remain unclear. In various laboratories a preparation of different chemicals was obtained. composition (protein, peptide, etc.), mol. weight (from 400 to 200,000) and with different properties [Luckey (T. D. Luckey), 1973]. It is assumed that the humoral factor is secreted by stellate epithelial thymocytes located in all parts of the liver, in which acidic glycoprotein is found. It is possible that differentiation processes ( stem cell- thymocyte - T-lymphocyte) are influenced by humoral factors produced by the epithelial elements of the liver. There is also an opinion that the release of soluble humoral factor V. may occur with the participation of Hassal's bodies [Kater (P. Kater)].

The participation of V. is also shown. in the regulation of a number of vital functions. So, for example, the hormone V. takes part in the control of neuromuscular transmission, the state of carbohydrate metabolism, and calcium metabolism. V. g. interacts closely with the endocrine glands (pituitary gland, adrenal glands, thyroid gland, gonads, etc.) - In experiments with the removal of various endocrine glands while the V. is preserved. and with the removal of V. in the presence of endocrine organs, a difference in the level of interaction affecting the production of lymphocytes was shown [Kohmza (I. Comsa), 1973]. Antagonism between the thymic hormone and thyroxine, glucocorticoids and V. hormones, and the synergism of the action of the hormone V. are shown. with pituitary growth hormone. Komza provides evidence that in its effect on the production of lymphocytes, the thymic hormone is an antagonist of the corticotropic effect of the anterior pituitary gland and, apparently, inhibits the lympholytic effect of corticotropin, which is mediated by the adrenal cortex.

Thus, it is already possible to summarize the main functional features of this organ. Function of the V. cannot be considered separately from the state of immunity (see), in particular the T-system. Thymus-derived lymphocytes, as antigen-recognizing cells, effector cells, helper cells, or cells that regulate antibody production by antibody-producing cells, are involved in most of the body's immune responses.

Based on the leading role of thymus-dependent lymphocytes in immunity, F. Vernet formulated the concept of immunological surveillance, highlighting the protection of the genetic constancy of the internal environment of the body as the main task of immunity. The consequences of a violation of immunological surveillance in the body can be infectious diseases, autoimmune disorders, and an increased likelihood of tumor diseases. In this regard, the concept of antitumor immunity is gaining new development. Generalized data indicate an increase in the frequency of tumor diseases in children with immunological deficiency (mainly due to damage to the thymus-dependent system), in recipients of homotransplants (mainly kidneys), who have been receiving long-term immunosuppressive therapy(see Immunodepressive conditions), as well as in an experiment in thymectomized animals immediately after birth [Gatti, Good (R. Gatti, G. A. Good)].

A decrease in the functional activity of V., a decrease in the activity of T-lymphocytes in cellular immune reactions, an increase in the frequency of autoimmune diseases and neoplasms served as the basis for putting forward the immunological theory of aging [Walford (R. L. Walford)].

According to S. S. Vasileisky, Yu. M. Lopukhin, R. V. Petrov (1972), V. zh., in addition to the well-known inductive function in relation to the immunogenesis system, has an inhibitory effect in relation to certain systems characteristic of embryonic period. An example of the latter is the synthesis of embryonic proteins, which is derepressed in situations where V. is turned off. (eg, in patients with ataxia-telangiectasia), such as alpha-fetoprotein, beta-fetoprotein, the appearance of the monomeric subunit IgM5 of immunoglobulin M, represented in an adult by a whole pentomer.

Pathological anatomy

Circulatory disorders in the form venous congestion V. g. often found in stillborns and newborns with asphyxia, in infants and young children with acute, mainly respiratory, viral infections, sepsis, toxic dysentery, diphtheria. Parenchyma V. g. swollen, cyanotic, with pinpoint petechial hemorrhages. Significant plethora and swelling with an increase in the volume and weight of the organ can simulate hyperplasia of the hem. In rare cases in newborns and infants massive hemorrhages are observed in the V. g.

Congenital (primary) aplasia and hypoplasia are characterized by the complete absence of parenchyma of the veins. or its extremely weak development. Similar changes are found in children younger age for a number of congenital hereditary diseases, combined into the group of immunodeficiency - “Swiss syndrome”, Di George syndrome, ataxia-telangiectasia (Louis-Bar syndrome), etc. (see below Diseases of the liver).

Characteristic of these diseases is significant damage to the T-lymphocyte system. In cases of aplasia, the parenchyma of the V. g. not detected. With hypoplasia of the V. reduced, the cortex and medulla are indistinguishable due to the small number or complete absence of lymphocytes, thymic bodies V. g. are absent or occur in the form of single atypical structures. With extreme degrees of hypoplasia, the lobules of the gland are represented only by cells and fibers of the stroma (color. Fig. 7). In the peripheral blood of such children, the number of lymphocytes is sharply reduced, the reactions of cellular immunity are suppressed (slow rejection of a foreign graft, decreased delayed-type hypersensitivity reaction and contact skin sensitivity, decreased response of blast transformation of blood lymphocytes to PHA and allogeneic lymphocytes, etc.). In the most severe disease, “Swiss syndrome,” children usually die before the age of 1 year with signs of wasting syndrome.

Atrophy of the thymus gland (secondary, transient or so-called accidental involution of the thymus gland) develops in children with a number of diseases that occur with symptoms of intoxication (for example, severe pneumonia, prolonged purulent-inflammatory processes, etc.), with stress reactions, prolonged corticosteroid therapy, radiation exposure, etc. With accidental involution, a rapid loss of lymphocytes occurs. with a decrease in the weight and volume of the organ.

In the first phase of accidental involution, lymphocytes disintegrate and are partially phagocytosed by macrophages of the bloodstream, the reticuloepithelium hyperplasias, a large number of Hassall bodies are formed, the cortical substance becomes lighter from the loss of lymphocytes (inversion of layers), the weight of the gland falls, its lobules collapse (color fig. 6). Subsequently, atrophy of the epithelium is observed, the number of Hassall's bodies decreases, their contents become hyalinized, calcified, the lobules sharply collapse, and the interlobular connective tissue becomes fibrotic. The degree of atrophy is proportional to the duration and severity of the disease. In the early phases, the process of accidental involution is reversible, while the structure of the lobules of the V. (cortical and medulla) is completely restored. In the phase of significant atrophy, the process is irreversible. Far advanced atrophy of the V. g. usually found in the section of children who have been seriously ill for a long time. Study of the structure of water. in various pathologies of newborns, a parallel study of serum 7-globulins did not reveal any regular changes.

True hypoplasia of the V. should be distinguished from acquired. With true hypoplasia and aplasia of the V. we're talking about about the complete absence or underdevelopment of the epithelial reticulum and thymic lymphocytes, while Hassal's bodies are either completely absent or their number is sharply reduced and they are small. It is difficult to judge hypoplasia only by the number of lymphocytes, since their number also drops sharply with accidental involution.

Hyperplasia of the thymus gland is accompanied by an increase in the number of cells in the cortex and medulla or a disturbance in the structure of the thymus. due to the emergence additional education(eg germinal centers). According to Y. Bierich, true hyperplasia is observed in 1/3 of well-somatically developed children in the first year of life, since it is during this period of V.’s life. most functionally loaded. Hyperplasia V. g. may be associated with a change in the normal structure, which is observed in a number of diseases of the autoimmune type (malignant myasthenia, systemic lupus erythematosus, etc.)* Thus, with malignant myasthenia, in 70-80% of cases an increase in the medulla is detected due to atrophy of the cortical layer, the appearance of germinal centers characteristic of lymph nodes, accumulation of plasma cells around the vessels. Despite the appearance of additional structures, the size of the V. g. may not increase.

Thymomegaly should be distinguished from true hyperplasia (color Fig. 5) with the so-called. status thymicolymphaticus (see). The etiology of congenital thymomegaly is unclear. Thymomegaly is observed in some endocrine diseases(thyrotoxicosis, acromegaly), in some cases bronchial asthma in children. V. g. with thymomegaly it is rich in lymphocytes, its cortical layer is wide, the size and number of Hassall's bodies are reduced, the medulla is narrowed. With thymomegaly V. does not give reactive accidental involution, because the function of regulation of proliferation and decay of lymphocytes of the V. is impaired, edges are normally carried out by the thymic epithelium and Hassal's bodies [Blau, Hirokawa (J. N. Blau, K. Hirokawa)]. Persons suffering from thymomegaly often die in the most unexpected situations (for example, anesthesia, bathing, etc.). At autopsy, they find increased size and weight of the V. g., enlarged lymph nodes, and hypoplasia of the adrenal glands. It is assumed that the death is associated not so much with V.'s thymomegaly as with hypofunction of the adrenal cortex.

Inflammation of the thymus gland (thymitis) usually develops as a complication of purulent-inflammatory diseases of the tissues of the anterior mediastinum. Hron, thymitis can occur as a sclerosing process.

At different malignant tumors in both children and adults in V., in addition to a sharp drop in its weight due to the loss of lymphocytes and collapse of lobules, there is a significant activation of epithelial thymocytes with the formation of very large fused Hassal bodies (Fig. 4) and the presence of plasma cells. The significance of these changes remains unclear.

In lymphoid forms of acute leukemia in children, the leukemic infiltrate relatively often initially appears in the V., the elements of the cut are completely replaced by the leukemic infiltrate. For myeloid, histiomonocytic and other forms of leukemia in V. accidental involution is observed.

Research methods

Research V. zh. should be aimed both at assessing the somatic state of the gland itself and at assessing thymus-dependent lymphocytes.

Structural changes in the veins. can be identified by examining the material obtained from its biopsy.

X-ray examination of the thymus gland. A number of methods are used to determine the size of the vein. using x-ray methods: a typical shadow of the V. g. can be obtained on x-rays taken in direct, lateral or oblique projections; tomography (see) allows you to obtain a series of images, eliminating the effect of summation of shadows; pneumomediastinography (see) with contrasting mediastinal organs with gas (oblique projection is preferable) provides optimal conditions for identifying V.

Normal V. g. usually does not give an isolated image on radiographs and tomograms and can only be detected with pneumomediastinography.

With congenital and acquired (displacement of the gland due to pathological processes in the mediastinal organs) dystopia and with hypertrophy of the gland, it occupies a marginal location on the right or left side of the mediastinum in the form of a protrusion with rounded outlines (Fig. 5); with hypertrophy, there may also be bilateral protrusion of the gland. In the lateral projection, the shadow of the gland appears in the upper part of the anterior mediastinum. Dystopia and hypertrophy should be differentiated from paramediastinal formations (paramediastinal pleurisy, atelectasis of the apical segment of the lung, paratracheal hyperplastic lymph nodes). For discrimination, in addition to multi-projection studies chest, tomography and pneumomediastinography are used. With giant hypertrophy (Fig. 6), the shadow of V. may occupy a significant part of the pulmonary field. It is necessary to differentiate with cysts and tumors of the lungs and mediastinum, for which they resort to tomography, pneumomediastinography and, in rare cases, artificial pneumothorax. The most important radiological symptoms of thymomas: “pancake” shape, bilateral protrusion with lumpy polycyclic outlines and long arcs (other mediastinal tumors have shorter arcs); infiltrative growth of the tumor upward and downward with penetration into neighboring organs. Various types of thymomas - cancerous, sarcomas (lymphosarcoma), lymphoepitheliomas - usually cannot be distinguished only by X-ray data.

There is also a so-called thymolytic test, when repeated radiographic examination of an enlarged V. the child is performed after the administration of corticosteroid hormones: the size of the thymoma remains unchanged after the test.

Functional assessment of T-lymphocytes. A number of in vitro and in vivo methods have been developed to analyze the function of thymus-dependent lymphocytes. The following tests are recommended for assessing T cells in vitro. 1. The reaction of blastotransformation of peripheral blood lymphocytes under the influence of PHA or in a mixed culture of lymphocytes. Lymphocytes isolated from peripheral blood are cultured for 3 days. with FHA or for 6 - 7 days. with allogeneic lymphocytes and by the number of blast forms or by the inclusion of a radioactive label, the activity of thymus-dependent lymphocytes is judged. 2. Rosette formation by lymphocytes. Human T-lymphocytes have the ability to interact in vitro with sheep erythrocytes and form figures called rosettes. Detection of spontaneous rosette-forming cells is used as a test to determine the absolute and relative number of T lymphocytes in peripheral blood. In a healthy adult, approx. 60-70% of circulating lymphocytes form rosettes with sheep erythrocytes. Peripheral blood lymphocytes are incubated with sheep erythrocytes and on fixed preparations the number of lymphocytes that have bound 4 or more sheep erythrocytes is counted. 3. Production by lymphocytes of a factor that inhibits the migration of macrophages. Lymphocytes of patients sensitized by certain antigens (for example, patients with tuberculosis), upon contact with such an antigen, produce a soluble factor, which can be detected by a test for inhibition of macrophage migration. To assess the function of thymus-dependent lymphocytes in vivo, tests such as the development of delayed-type skin hypersensitivity reactions to widespread antigens (tuberculin, trichophyton, candidin, streptokinase-streptodornase, etc.) are recommended; delayed hypersensitivity response to a contact test with 2,4-dinitrochlorobenzene; ability to reject allogeneic transplants. An indirect idea of ​​the state of the thymus-dependent system is provided by the absolute number of lymphocytes in the peripheral blood. The tests listed above have the greatest diagnostic value for diseases associated with switching off V. (eg, immunodeficiency diseases with aplasia or hypoplasia of the veins).

Diseases of the thymus gland

In connection with the establishment of the role of the V. g. system. in the implementation of immunological reactions in the body, targeted identification of clinical forms of damage to V. is carried out. Despite the fact that many diseases have been discovered in which the veins suffer to one degree or another, there is still no clear classification of diseases of the veins. It seems possible to distinguish at least 3 groups of diseases characterized by damage to the vein system: 1) diseases with aplasia or hypoplasia of the vein; 2) diseases with dysplasia of the veins; 3) tumors of the V. g.

Diseases with congenital aplasia or hypoplasia of the thymus

Congenital, or primary, aplasia and hypoplasia of the V. characterized by the complete absence of thymic parenchyma or its extremely weak development. Similar changes are found in children with a number of congenital diseases, combined into the group of immunodeficiency diseases (see Immunological deficiency).

The most pronounced defects in the development of V. found in the following syndromes. 1. Aplasia V. and parathyroid glands or DiGeorge syndrome - a defect in the development of organs originating from III -IV pairs gill pockets. Characteristic signs of the disease are seizures, starting from the neonatal period, and inhibition of reactions mediated by thymus-dependent lymphocytes; Only the lymphoid tissue of the B-system shows the ability to respond to antigenic irritations. 2. Autosomal recessive aplasia V. with lymphopenia, or Nezelof's syndrome. The organs arising from the III - IV gill pouches develop normally, but the V. g. is almost completely absent. A sharp decrease in the reactivity of T-lymphocytes is also detected. 3. Autosomal recessive severe combined immunological deficiency (“Swiss syndrome”), Lymphopenic agammaglobulinemia, aplasia or hypoplasia V. combined with hypoplasia of all lymphoid tissue. Such children have V. difficult to identify, and in some cases a thin epithelial cord is found, devoid of thymocytes and Hassal bodies. Along with a sharp inhibition of cellular immunity reactions, a deficiency of humoral immunity is revealed. Children usually die in the first six months of life.

4. Immunological deficiency with ataxia-telangiectasia, or Louis-Bar syndrome. Hereditary disease of autosomal recessive type. Characterized by progressive cerebellar ataxia, telangiectasia and dysgammaglobulinemia (see Ataxia). V. g. absent or hypoplastic (after the birth of V. of embryonic type). Along with the shutdown of cellular immunity reactions, patients have a selective IgA deficiency. Characteristic for of this disease is a high frequency of neoplasms (usually lymphosarcoma, lymphogranulomatosis, etc.).

All diseases with aplasia or hypoplasia of the V. g. are accompanied by recurrent inflammatory diseases of sinus-pulmonary and intestinal localization, which are often the direct cause of death of patients. Inflammatory and infectious diseases are especially difficult in children with the “Swiss syndrome”.

Children, especially young children, suffering from recurrent inflammatory diseases, should be carefully examined for the functional state of the thymus-dependent immune system. Treatment Measures for the listed syndromes are reduced to transplantation of the veins. alone or with bone marrow (“Swiss syndrome”, Louis-Bar syndrome, Nezelof syndrome), administration of a transfer factor extracted from lymphocytes of sensitized donors and capable of transmitting cellular immunity, as well as symptomatic therapy.

Diseases with thymic dysplasia

This group includes diseases of Ch. arr. autoimmune: malignant myasthenia (see), systemic lupus erythematosus (see), autoimmune hemolytic anemia (see), rheumatoid arthritis (see), Hashimoto's disease (see Hashimoto's disease), etc. In the thymus, developments uncharacteristic for normal B . and. structures: infiltration of the medulla with lymphocytes and plasma cells, the appearance of germinal centers, aggregation of epithelial cells in the medulla, the formation of cysts in Hassal's bodies, an increase in the size of thymic lobules, in some cases the formation of thymomas, etc. The clinical picture presents symptoms characteristic of each autoimmune disease. The significance of changes in V. zh. The pathogenesis of these diseases is not clear. According to Burnet's hypothesis about the role of V. in the development of autoimmune diseases, formation in V. is expected. so-called prohibited clones of immunocompetent cells that react against the antigenic structures of their own body. The basis for this conclusion was studies on NZB mice, which with age develop autoimmune processes similar to those found in humans, for example, with systemic lupus erythematosus. At the same time, in V. zh. germinal centers develop. On the other hand, it is possible that in V. zh. the mechanisms that control the elimination of such clones are disrupted, i.e., a kind of immunodeficiency occurs, the result of which is increased production of antibodies against various antigenic structures of the body. Often, for diseases such as myasthenia gravis, systemic lupus erythematosus, and some others, thymectomy is performed (see). The results of the operation are contradictory; only with myasthenia gravis, thymectomy provides up to 70% of a permanent cure (S. A. Gadzhiev, M. I. Kuzin). In some cases, long-term remissions have been obtained, while in other cases thymectomy does not produce a favorable result. Apparently, the outcome of the operation is influenced by the stage of the disease at which thymectomy is performed. As a treatment measures for myasthenia gravis are sometimes used radiation therapy on the V. area, the effectiveness of the cut is lower than with thymectomy. Often, for the listed autoimmune diseases, immunosuppressive therapy is used, however, if the possibility of inhibition of cellular mechanisms that regulate the production of autoantibodies is not excluded, then this method of suppressing immune reactions can affect the control systems to an even greater extent.

Thymus tumors

Tumors of the thymus gland - thymomas - occur in people of all age groups. According to the literature, the frequency of thymomas varies widely. Among mediastinal tumors in adults, thymomas occur in 5-14% of cases; in children they are more rare (in 8% of cases). Most often, thymomas occur in patients with myasthenia gravis (see) in adulthood and old age; approximately 2/6 of them have tumors of the V. g. (M.I. Kuzin, 1972; B.P. Volkov, 1974).

Most thymomas belong to lymphoepitheliomas (see). Depending on the ratio of lymphoid and epithelial elements in the tumor, thymomas with an equal number of lymphoid and epithelial cells, predominantly epithelial or lymphoid types, and spindle cell type are distinguished. In some cases, the tumor of the V. g. consists of elements of the thymus and adipose tissue, which is part of the lobules of the gland - the so-called. lipothymoma (thymolipoma), usually asymptomatic.

Typically, thymomas grow from the middle part of the lobes of the V. g. and from the lower horns, often fused with the pleura, pericardium, left brachiocephalic (innominate) and superior vena cava. With dystopia V. or a section of its tissue, they can sometimes be in other parts of the mediastinum, the root of the lung, or on the neck. The size of the tumor varies widely, but small ones predominate. With any histological type of tumor structure, foci of necrosis and hemorrhage with subsequent cyst formation and fibrosis are often found in its thickness. Around the vessels and connective tissue trabeculae, accumulations of edematous fluid are found in the form of cuffs, from which cysts can also form. In thymomas with an equal number of epithelial and lymphoid elements, epithelial cells form a loose network, in which thymocytes are diffusely distributed in the cells. In tumors epithelial type Large cells with abundant juicy cytoplasm and an ovoid, chromatin-poor nucleus predominate. The cells adhere tightly to each other, form solid cords, and in some places form rosettes. With histochemical In a study, glycogen, granules of glycoproteins and glycolipids were found in epithelial cells of thymomas, which suggests that they have a hormonal function and high potential activity. In thymomas with a predominance of lymphoid elements, individual epithelial cells or cords formed by them are visible, in places where “foamy” cells of epithelial origin accumulate.

Thymomas have a capsule, do not have expansive growth, slowly increase in size, and, as a rule, do not metastasize. They have few mitotic figures and no cell atypia. This allows us to consider them as relatively benign tumors. It is believed that metastasizing tumor cells are destroyed by antithymic antibodies, which, as a rule, are found in the blood of patients with thymomas. An immunological reaction is indicated by the presence of plasmacytic infiltration of the tumor capsule and surrounding gland tissue, the development of germinal centers, often near the tumor capsule.

Malignant thymoma consists of poorly differentiated elements that are difficult to distinguish from reticulo- and lymphosarcoma. These tumors V. g. metastasize to the nearest lymph. nodes and distant organs. Castleman (B. Castleman), Peabody (J. W. Peabody) believe that distant metastases are not observed in thymomas, and their presence speaks against thymoma. However, the authors indicate that malignant thymomas account for 32%.

The clinical picture of thymomas is very diverse. OK. 50% of tumors V. g. is asymptomatic and accidentally detected during preventive X-ray examinations or manifests itself with symptoms of compression of the organs of the anterior mediastinum [Bernatz (Ph. Bernatz), 1961]. With significant compression, a feeling of tightness appears behind the sternum, discomfort and pain, shortness of breath, swelling of the neck veins, puffiness and bluish coloration of the face. Respiratory disorders are especially pronounced in children due to compression of the relatively narrow, pliable trachea. Most often, thymomas are combined with myasthenia [according to Seybold (W. Seybold, 1950), McDonald (J. McDonald) - 48-84%], less often with agammaglobulinemia, aregenerator anemia, Itsenko-Cushing syndrome. In some cases, myasthenia gravis or other syndromes may develop after removal of an asymptomatic thymoma. Syndromes accompanying thymoma (myasthenia gravis, agammaglobulinemia, etc.) make it necessary to begin a targeted study to detect thymoma, so tumors are detected earlier and have a relatively small sizes. Asymptomatically developing tumors of V. reach significantly larger sizes by the time symptoms of compression of the mediastinal organs are detected or appear.

X-ray examination (a combination of pneumomediastinography and tomography) allows you to identify tumors of the V. g. in 57-76% of patients. Tumors of the V. g. measuring 3 cm in diameter, and smaller ones are usually not detected when x-ray examination even on a pneumomediastinogram. The shadow of the tumor is better visible on profile and oblique photographs. It is most often found in the middle or upper part of the anterior mediastinum and has a round or ovoid shape. Fast increase the size of the shadow of the neoplasm with expansion of the mediastinum in both directions, uneven, finely wavy, unclear contours of the large tumor V. indicate its malignant nature. Introduction contrast agent in the brachiocephalic veins makes it possible to detect compression or displacement of blood vessels by a tumor of the V. g. Simultaneous damage to several vessels indicates malignant tumor growth.

Differential diagnosis is carried out with diseases of the thyroid gland (retrosternal goiter), teratoma, malignant tumors of lymph nodes and mediastinal tissue, as well as tumors of the sternum. In doubtful cases, in order to clarify the diagnosis and select a treatment method, a puncture or open (mediastinoscopy, sternal mediastinotomy) biopsy is performed, followed by histological examination material.

Treatment of benign and some malignant (in particular, highly differentiated, usually radioresistant) tumors of V. g. predominantly surgical. Patients with myasthenia gravis syndrome and other syndromes require careful preoperative preparation. Patients with myasthenia gravis should be under the supervision of both a surgeon and a neurologist. Assign medications to reduce the severity of dysfunction skeletal muscles, elimination of swallowing, breathing, chewing disorders. For the same purpose, some authors recommend preoperative radiation therapy, believing that surgery performed against the background of improvement of myasthenic status is accompanied by less risk and gives top scores. Operations are performed under endotracheal anesthesia. Preference is given to those types of anesthesia in which you can count on a quick recovery from anesthesia without respiratory depression, in particular combined electro-anesthesia (see Electronarcosis). The best access is a median sternotomy with incision of the sternum to the fifth rib or completely (see Mediastinotomy). For large tumors and the need to expand access, the incision can be extended to the right or left (after crossing the sternum) along the corresponding intercostal space (A. Ya. Kabanov). Application of transverse sternotomy and opening of both pleural cavities unreasonably. From this incision it is difficult to remove the upper horns of the V., which extend to the neck. A transpleural anterolateral or lateral approach has no advantage over a complete longitudinal sternotomy. Some surgeons use it in cases where the tumor mainly persists in one of the pleural cavities. Great technical difficulties arise when the tumor fusions with the brachiocephalic or superior vena cava. By carefully dissecting directly next to the vein wall, it is possible in most cases to separate the tumor and remove it. The left brachiocephalic vein can be ligated and divided.

When it grows into the superior vena cava, it is necessary to leave a small layer of tumor above the vessel and carry out radiation therapy in the postoperative period. Regardless of the radicality of the intervention, all patients with myasthenia gravis are subject to further treatment under the supervision of a neurologist. Along with anticholinesterase drugs, steroid hormones are prescribed (B. M. Hecht). For malignant tumors of the abdominal cavity that have high radiosensitivity, radiation treatment is performed using megavolt sources for the purpose of radical or palliative treatment (to relieve compression of the mediastinal organs) with a total focal dose of up to 5000-6500 rad. In some cases, irradiation can be carried out from the front and rear fields in a dose ratio of 2: 1.

Removal of tumor V. g. in patients with myasthenia gravis leads to improvement in 20% of cases, without changes - in 33% of cases. A significant proportion of patients die at various times after surgery from the progression of myasthenia gravis, and not from tumor relapse. To improve results, they resort to glomectomy and denervation of the carotid sinus, as well as massive therapy with steroid hormones prescribed every other day for a long period of time.

Surgeries for diseases of the thymus gland

Surgical interventions associated with V. can be of two types: thymectomy (see) and V. transplantation.

Transplantation of V. g. began to be used in connection with the identification and study of diseases with aplasia and hypoplasia of the thymus. Transplantation of the V. g. recommended for congenital immunodeficiencies with damage to the T-system, as well as for some diseases with a deficiency of the thymus-dependent system (for example, mucocutaneous candidiasis). The action of the transplanted V. g. associated with the production of humoral factor and T-lymphocytes. Cases of the development of a graft-versus-host reaction in children with a switched off T-system after transplantation of embryonic allogeneic hepatitis are described, which indicates the need to select a donor and recipient based on histocompatibility system antigens. The source of V. zh. embryos are used (it is recommended to use V. after 12 weeks of embryonic development) or children who died in the antenatal period.

Two methods of organ transplantation have been developed: in the form of fragments and a whole organ. Fragments of the embryonic thymus several millimeters in size are often transplanted into the region of the rectus abdominis muscle. Transplantation of V. g. in the form of a solid organ was proposed by Yu. I. Morozov (1971). Material from stillborn children is used as a donor. The sternum is excised together with the V. as a single block, preserving the large branches of the aortic arch and superior vena cava. The vascular system of the graft is perfused with a cooled solution of polyglucin with heparin. Transplantation of the thymus-sternum block is performed in femoral area. To do this, a vascular bundle is exposed in the femoral triangle and a series of anastomoses are performed. The deep femoral artery is sutured to one of the branches of the aortic arch of the graft (with a common carotid artery or shoulder-head trunk), and the central end is large saphenous vein sutured to the superior vena cava of the graft. The operation is performed under general anesthesia. Transplantation of the thymus-sternum block is indicated for children with immunological deficiency with ataxia-telangiectasia and other forms of deficiency of the T-immune system.

Transplantation of cell suspension V. g. turned out to be ineffective.

Clinical and diagnostic characteristics of the main anomalies, lesions of the thymus gland and diseases associated with impaired function (table)

The thymus gland, which belongs to two organ systems: endocrine and immune, produces hormones and provides the body’s protective functions.

What is the thymus?

The thymus (thymus gland, thymus gland), together with the bone marrow, serves as the main organ of the immune system, in which stem cells formed in the bone marrow, having undergone several stages of transformation, ultimately become T-lymphocytes.

Next, they are sent to the lymph and biological fluids, settling in the thymus-dependent areas of other organs responsible for immunity (spleen, lymph nodes). The gland also secretes substances that influence the specialization of T-lymphocytes and a number of hormones.

The thymus in childhood and adolescence is soft to the touch, gray-pink in color. As it grows older, it becomes denser, and after 50 years, due to the abundance of fatty structures in it, it again acquires softness.

In 63.4% of cases, the thymus gland is formed from two long, different-sized right and left halves, connecting one to the other in the middle.

In 30.5% of cases, the thymus is a multilobar organ, having from 3 to 5 lobes surrounded by its own capsule.

The monolobar gland occurs in 6.1% of cases. At the top, the halves of the organ narrow and often protrude into the neck in the shape of a fork with two prongs (hence the name of the gland) with poles diverging to the sides. The shape of each half is spindle-shaped.

In humans, left-sided asymmetry predominates. The thymus gland develops its maximum size by adolescence, then it weighs an average of 37.5 g. After reaching 16 years, the size of the thymus slowly decreases, but even in old age the lymphoid tissue of the organ does not disappear completely, although it makes up an insignificant part of it (1.67 – 2.9%), being replaced by fat.

The thymus is covered with a delicate capsule, which inside turns into partitions that divide it into segments. The internal tissue of the organ is divided into a borderline dark-colored cortex and a light-colored medulla occupying the center. The boundary between them is sometimes unclear.

The internal contents of the thymus gland are represented by a plexus of reticular (processed) cells and fibers, as well as stellate epithelial cells - epithelioreticulocytes. This interweaving contains lymphocytes (thymocytes) and small cells that secrete antibodies, macrophages (the first to capture foreign bodies), granulocytes (white blood cells characterized by a large segmented nucleus).

Structure of the thymus gland

In the dark substance, lymphocytes are located more densely than in the light substance. Stem cells enter the organ capsule; Here there are cells with a high ability to divide.

The epithelial cells of the central substance are large, multi-processed and light-colored. Characteristic of the central zone is the presence in it of multilayered Hassal bodies, consisting of highly flattened epithelial cells.

To maintain the thymus in tone, it is necessary to massage the palate, rotating a clean thumb along the upper fornix clockwise. Laughter also has a positive effect on iron.

Organ location

The thymus gland is located at the top of the chest cavity, between the sternum and the spine.

The apical part of the thymus, if it has reached good development, projects into the neck area.

Often the tops of the halves of the organ are at the same level as the lower edges of the thyroid gland or do not reach it by 1 - 1.5 cm.

The anterior surface of the organ is adjacent to the sternum (up to the IV costal cartilage). At the back, the thymus borders on the pericardium and vessels at the base of the heart; on the sides, the anterior edges of the lungs are adjacent to the gland.

Therapists and acupuncturists advise massaging the thymus gland to activate immune forces. To do this, you need to place 2 fingers slightly below the clavicular fossa and tap on this place 10-12 times in the morning for two weeks. You can also rub the area with essential oils, warming it up.

The thymus is part of the endocrine and hormonal system at the same time. Let's look at it in detail in the article.

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Functions of the thymus gland (thymus) in the human body

The thymus performs two functions - immune and hormonal.

The thymus gland is one of the main organs of the immune system. This is where lymphocytes (elements of the immune system) become immunocompetent.

Initially, the lymphoid stem cell - the progenitor of all lymphocytes - forms two types of cells: the precursors of B- and T-lymphocytes. Their transformation takes place in the central organs of immunogenesis: the former are sent to the bone marrow, the latter to the thymus (hence their name).

Precursors of T-lymphocytes, differentiating in the thymus gland, supply three independent subtypes of lymphocytes into the blood:

• T-helpers (helpers), recognizing foreign agents and activating B-lymphocytes;
• T-effectors that directly react with antigens;
• T-suppressors that reduce the intensity of the immune response.

In addition to participating in immune processes, the thymus, being also an endocrine gland, supplies hormones to the blood.

To strengthen the gland, it is important to consume foods rich in fats ( fatty fish, olive oil), vitamins (rose hips, buckwheat, sea buckthorn), proteins (eggs, chicken meat) and zinc (pumpkin seeds, pine nuts) products. Protein serves as a building material, and zinc is involved in the production of T-lymphocytes.

Thymus hormones and their functions

The main hormones produced by the thymus gland are thymosin, thymopoietin and thymulin.

All of them chemical nature are proteins. Under the influence of thymic factors, the lymphoid tissue of the gland develops and lymphocytes acquire the ability to participate in immunological processes.

In addition, hormonal factors have a regulatory effect on almost all physiological processes:

• exchange of minerals, proteins, carbohydrates, fats and vitamins;
• calcium conversion;
• the work of the thyroid gland, gonads, pituitary gland;
• increase the growth of skeletal tissue and cells by enhancing protein synthesis;
• accelerate the breakdown of glucose;
• replenish energy reserves;
• slow down the functioning of the central nervous system;
• reduce heart rate and cardiac output.

Functions of thymic hormones: table

The health of the thymus gland is spoiled by alcohol, fried and canned foods, and fructose.

The condition and viability of the entire organism depends on the activity of the internal secretion organs.

The functions of the liver, thyroid, pancreas and their location are known to almost everyone, as are the symptoms of a violation of their healthy functioning, but not everyone knows what the thymus gland is, or the thymus gland, where this organ is located, and what functions it performs.

However, it is difficult to exaggerate the importance of the functions that this small organ performs.

The thymus is no less important than the bone marrow, part of the immune system of humans and a significant part of mammals. This organ begins to function even before the baby is born, in the sixth month of pregnancy.

It is here that one of the important stages of lymphocytopoiesis occurs: immature T-lymphocytes formed in the bone marrow, migrating to the thymus, develop in its tissues, turning into full-fledged cells capable of actively responding to antigens, but at the same time tolerant to the tissues of the body.

The process of differentiation and selection of lymphocytes is quite strict - only about 2-4% of immature lymphocytes found in the thymus tissues return to the blood, the rest are destroyed.

This protects the body from autoimmune diseases.

In addition to the immune gland, the thymus gland also performs endocrine function, producing hormones.

Unlike most endocrine glands, the thymus is short-lived. At birth, it weighs 13-15 grams, grows actively during the first three years of life and reaches its greatest development during puberty, growing to 20-35 grams.

After puberty, this organ begins to gradually atrophy, being replaced by connective and fatty tissue, due to which immunity decreases in old age.

There are also cases of human congenital immunodeficiency caused by aplasia or insufficiency of the thymus. The following syndromes are observed:

• DiGeorge syndrome is a condition in which aplasia of the thymus is combined with the absence or dysplasia of the parathyroid glands.
• MEDAC syndrome is accompanied by autoimmune dysfunction of the parathyroid glands and adrenal glands.

Most often, they lead to the early death of the patient due to the complete inability of the body to resist infections.

One of the hormones helps slow down the involution of the thymus pineal gland, responsible for circadian rhythms: melatonin. Therefore, maintaining a healthy sleep-wake schedule is very important for the health of the immune system in the future.

Location of the thymus gland

Where is the thymus gland located? The thymus is located in the mediastinum, occupying a place at the very top of the chest, directly below the thyroid gland.

In shape, the organ resembles a two-pronged fork; it consists of two lobes, welded at the bottom and diverging upward, and in some cases it can come into contact with the thyroid gland with the ends of these peculiar teeth.

The size of the thymus is quite small: its maximum weight reaches 35-37 grams, and the length of the gland during the period of its greatest development is about 15-16 centimeters. It is protected by a dense membrane of connective tissue, ribs and sternum in front, the mediastinal pleural membrane is adjacent to it on the sides, and the pericardium is adjacent to it at the back. The lower part of the gland reaches the fourth or fifth rib in children, and the second or third in adults.

With age, gradually being replaced by connective tissue, the thymus becomes much thinner and smaller. And with malignant and benign tumor processes (very rare and currently little studied), it can grow, squeezing nearby organs.

The thymus gland is abundantly innervated.

Branches go to it vagus nerves and the sympathetic nerves of the superior thoracic and stellate ganglia of the sympathetic trunk.

The thymic branches of the large arteries are responsible for supplying it with blood.

A folk remedy for strengthening the immune system is a light massage of the thymus region, stimulating its work.

And in this topic we will consider the signs of thymic hyperplasia. How is an organ abnormality detected?

Photo location

Where the thymus gland is located in humans, see the following image.

One of the most mysterious endocrine glands is the thymus, or thymus.

Its importance is not inferior to many others, but it has not been studied well enough.

The formation of the thymus gland occurs in the sixth week of intrauterine development. After birth, throughout childhood and adolescence, the thymus grows and increases in size.

In adults, the structure of the thymus changes, the growth rate slows down, and the glandular tissue is gradually replaced by fat cells, almost completely atrophying by the end of life. The thymus is the leading organ of the immune system, its functions are described below.

The thymus gland got its name because of its characteristic appearance, reminiscent of a two-pronged fork.

It is a small lobulated pinkish organ adjacent to the trachea.

The upper part is thinner and the lower part is wider. On the radiograph, the image of the thymus is partially covered by the shadow of the heart.

The size of the gland varies depending on age; in children they are approximately five by four centimeters. An increase (thymomegaly) can be observed when exposed to adverse factors (alcohol, nicotine, medications, etc.) both in utero and after birth.

Changes in the size of the thymus can result from:

• Rhesus conflict, or hemolytic disease of newborns;
• asphyxia during childbirth;
• prematurity;
• frequent and prolonged infectious diseases;
• tumors;
• rickets and nutritional disorders;
• surgical interventions.

Infants with thymomegaly require close monitoring by a pediatrician due to the high risk of sudden death syndrome.

Thymus gland: location in the human body

The thymus is located almost in the center of the chest, with its anterior surface adjacent to the sternum, and with its elongated upper ends reaching the thyroid gland.

In children, the lower edge reaches 3-4 ribs and is located close to the pericardium; in adults, due to a decrease in size, it is located in the second intercostal space.

Thymolipoma

Large vessels pass behind the thymus. The location of the gland is examined using a chest x-ray, ultrasound scan or magnetic resonance imaging.

Organ structure

The right and left lobes of the thymus are connected to each other by a connective tissue layer, but can be fused quite tightly. The thymus is covered on top by a dense fibrous capsule, from which cords (septal septa) of connective tissue pass into the body of the gland.

With their help, the parenchyma of the gland is divided into small incomplete lobules with cortical and medulla layers.

Structure of the thymus

Lymphatic drainage, blood supply and innervation

Despite its direct relationship to the lymphatic system of the body, the thymus gland has features of blood supply and lymphatic drainage. This organ has no afferents lymphatic vessels and does not filter lymph, unlike the mediastinal lymph nodes.

Lymphatic drainage occurs through a few capillaries originating in the wall of blood vessels. The thymus is abundantly supplied with blood. From the nearby thyroid, upper thoracic arteries and aorta, smaller and then numerous arterioles depart, feeding the gland.

Structure of the thymus

Arterioles are divided into:

• lobular - supplying one of the lobes of the gland;
• interlobular;
• intralobular - located in the septal septa.

The peculiarity of the structure of the vessels that supply the thymus gland is a denser basal layer, which does not allow large protein formations - antigens - to penetrate the barrier. The arterioles inside the organ disintegrate into capillaries, which smoothly turn into venules - small vessels that carry venous blood out of the organ.

Innervation is carried out through the sympathetic and parasympathetic systems; the nerve trunks run along the blood vessels, forming plexuses surrounded by fibrous connective tissue.

Diseases of the thymus are rare, so many do not even know what functions it performs.

We'll tell you what diseases an ultrasound scan of the thymus gland can detect.

You can read about the reasons for the enlargement of the thymus gland in children. Should you worry?

Tissue structure

The darker layer inside each lobule is called the cortical layer and consists of outer and inner zones formed by a dense accumulation of cells - T-lymphocytes.

They are separated from the thymic capsule by epithelial reticulocytes, so tightly compressed that they completely isolate the cortex from the outside. These cells have processes with which they connect with underlying cells, forming peculiar cells. Lymphocytes are located in them, the number of which is huge.

Thymus tissue

The transition zone between the dark and light substance is called the cortico-medullary zone. This boundary is arbitrary and marks the transition of more differentiated thymocytes to the medulla.

The medulla is a light layer of the organ, consisting of epithelioreticulocytes and a small number of lymphocytes. Their origin is different - the main part is formed in the thymus itself, and a small amount is brought in by the blood flow from other lymphocytic organs. Reticulocytes of the medulla form circular clusters called Hassall's bodies.

In addition to the two main types of cells, the parenchyma of the thymus gland is rich in stellate cells that produce hormones, dendrites that select lymphocytes, and macrophages that protect the gland from foreign agents.

It is known that the thymus is most important for children, because it trains the immune system. undergoes some changes.

You can read more information about the thymus gland. Functions in adults and children.

Thymus: functions

There is still ongoing debate about which system of the body the thymus belongs to: endocrine, immune or hematopoietic (blood-forming).

In utero and in the first days after birth, the thymus gland is involved in the production of blood cells, but gradually this function loses its relevance and the immunological one comes to the fore.

It includes:

• proliferation of lymphoid cells;
• thymocyte differentiation;
• selection of mature lymphocytes for suitability for use.

The cells entering the thymus from the bone marrow do not yet have specificity, and the task of the thymus gland is to “teach” thymocytes to recognize their own and foreign antigens. Differentiation occurs in the following directions: suppressive cells (suppressors), destroying cells (killers) and helping cells (helpers). Even mature thymocytes undergo careful selection. Those with poor discrimination of their own antigens are rejected. Such cells are destroyed without leaving the thymus into the bloodstream in order to prevent the development of autoimmune processes.

Another important function of the thymus is the synthesis of hormones: thymulin, thymopoietin and thymosin. All of them participate in the formation of immunity, and if their production is disrupted, the body’s defenses are significantly reduced, autoimmune diseases arise, and the risk of cancer pathologies increases significantly. Thymosin influences the formation of the musculoskeletal system by regulating mineral metabolism(calcium and phosphorus), thymulin is involved in endocrine processes.

Insufficient production of any thymus hormone causes immunodeficiency and contributes to severe infectious processes.

Thymus hormones influence puberty and indirectly influence the levels of androgens, estrogen and progesterone. The thymus is also involved in carbohydrate metabolism, it produces a substance whose action resembles insulin, thereby lowering blood sugar levels.

The thymus gland is an important organ, the importance of which is sometimes underestimated. When it changes immune status, frequent colds, activation of opportunistic flora, it is recommended to conduct a full examination, taking into account not only cellular immunity, but also the function of the thymus.

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