90 what tissue forms the stroma of the thymus lobule. Thymus: development, structure, functions. The lymph nodes. General morphofunctional characteristics. Characteristics of cortical substance. B- and t-dependent zones

The thymus performs the following functions:

Antigen-independent differentiation of T-lymphocytes occurs in the thymus, that is, it is the central organ of immunogenesis;

The thymus produces the hormones thymosin, thymopoietin, and thymic serum factor.

The thymus reaches its greatest development in childhood. The functioning of the thymus is especially important in early childhood. After puberty, the thymus undergoes age-related involution and is replaced by adipose tissue, but does not completely lose its functions even with old age.

Development

The thymus differs from other hematopoietic organs in that its stroma is epithelial in nature. Originates from the epithelium of the anterior part of the primary intestine.

From here, several epithelial strands begin to grow at once: the rudiments of the respiratory system, adenohypophysis, thyroid and parathyroid glands, and among them the paired rudiment of the thymus stroma. As for the hemal component of the thymus, it originates from unipotent T cell precursors that migrate to the thymus from the red bone marrow.

Structure

The thymus is a parenchymal lobular organ. On the outside it is covered with a connective tissue capsule. The septa extending from the capsule divide the organ into lobules, but this division is incomplete. The basis of each lobule is made up of branched epithelial cells called reticuloepitheliocytes. Loose fibrous unformed connective tissue is present only perivascularly. There are two types of reticuloepitheliocytes:

Nurse cells or nurse cells are located in the subcapsular zone;

Epithelial dendritic cells lying in the deep cortex zone.

Each lobule is divided into cortex and medulla.

The cortex consists of two zones: the subcapsular or outer zone and the deep cortex zone. Pre-T lymphocytes enter the subcapsular zone from the red bone marrow. They turn into lymphoblasts and begin to proliferate, coming into close contact with nurse cells. At this time, the cells do not yet have a T-cell receptor on their surface. Nurse cells produce thymosin and other hormones that stimulate the differentiation of T lymphocytes, that is, the transformation of precursors into mature T lymphocytes. As they differentiate, T lymphocytes begin to express receptors on their surface and gradually move to deeper zones of the cortex.

In the deep cortex, thymocytes begin to contact epithelial dendritic cells. These cells control the formation of autoreactive lymphocytes. If the resulting lymphocyte is capable of reacting against the body's own antigens, then such a lymphocyte receives a signal from the epithelial dendritic cell for apoptosis and is destroyed by macrophages. Lymphocytes tolerant to their own antigens penetrate into the deepest zones of the cortex, at the border with the medulla, through postcapillary veins with high endothelium, they enter the blood and then into the T-dependent zones of the peripheral lymphoid organs, where antigen-dependent lymphocytopoiesis occurs. The function of the cortex is antigen-independent differentiation and selection of T lymphocytes.

The medulla contains connective tissue stroma, reticuloepithelial base and lymphocytes. Which are much smaller (3-5% of all thymic lymphocytes). Some lymphocytes migrate here from the cortex in order to leave the thymus at the border with the cortex through postcapillary venules. Another part of the medulla lymphocytes may be lymphocytes coming from the peripheral organs of immunogenesis. The medulla contains epithelial thymic corpuscles of Hassall. They are formed by layering epithelial cells on top of each other. The size of Hassall's bodies and their number increases with age and under stress. Their possible functions are:

Formation of thymic hormones;

Destruction of autoreactive T lymphocytes.

Vascularization of the thymus

The arteries entering the thymus branch into interlobular, intralobular, and then arcuate vessels. The arcuate arteries split into capillaries, forming a deep network in the cortex. A smaller part of the cortical capillaries at the border with the medulla passes into postcapillary veins with high endothelium. Lymphocytes are recirculated through them. Most of the capillaries do not enter postcapillary venules with high endothelium, but continue into subcapsular venules. Venules pass into efferent veins.

Histology of the oral cavity. Formation, development and eruption of permanent teeth. Changing teeth. Physiological and reparative regeneration of dental tissues. Features of the development of multi-rooted teeth.

The organs of the oral cavity include lips, cheeks, gums, teeth, tongue, hard and soft palate, tonsils. The excretory ducts of the large salivary glands open into the oral cavity.

Functions of the anterior section: mechanical and chemical (partial) processing of food, determining its taste, swallowing and moving food into the esophagus.

Features of the structure:

The mucous membrane (cutaneous mucosa) consists of stratified squamous non-keratinizing epithelium and the lamina propria of the mucous membrane. Performs a barrier-protective function, there is no muscle plasticity;

The submucosa may be absent (in the gums, hard palate, on the upper and lateral surfaces of the tongue);

The muscularis propria is formed by striated muscle tissue.

The main sources of tooth development are the epithelium of the oral mucosa (ectoderm) and mesenchyme. In humans, there are two generations of teeth: milk and permanent. Their development proceeds in the same way from the same sources, but at different times. The formation of primary teeth occurs at the end of the second month of embryogenesis. In this case, the process of tooth development occurs in stages. There are three periods in it:

The period of formation of tooth germs;

The period of formation and differentiation of tooth germs;

The period of histogenesis of dental tissues.

Period I - the period of formation of tooth germs includes 2 stages:

Stage 1 - the stage of formation of the dental plate. It begins in the 6th week of embryogenesis. At this time, the epithelium of the gingival mucosa begins to grow into the underlying mesenchyme along each of the developing jaws. This is how epithelial dental plates are formed.

Stage 2 - toothball (bud) stage. During this stage, the cells of the dental lamina multiply in the distal part and form dental balls at the end of the dental lamina.

Period II - the period of formation and differentiation of tooth germs - is characterized by the formation of the enamel organ (dental cup). It includes 2 stages: the “cap” stage and the “bell” stage. In the second period, the mesenchymal cells lying under the dental ball begin to multiply intensively and create increased pressure here, and also induce, due to soluble inducers, the movement of the dental bud cells located above them. As a result, the lower cells of the dental bud protrude inward, gradually forming a double-walled dental cup. At first it has the shape of a cap (cap stage), and as the lower cells move inside the kidney it becomes bell-shaped (bell stage). In the resulting enamel organ, three types of cells are distinguished: internal, intermediate and external. Internal cells multiply intensively and subsequently serve as a source for the formation of ameloblasts - the main cells of the enamel organ that produce enamel. Intermediate cells, as a result of the accumulation of fluid between them, acquire a structure similar to the structure of mesenchyme and form the pulp of the enamel organ, which for some time carries out the trophism of ameloblasts, and subsequently is a source for the formation of the cuticle and tooth. The outer cells have a flattened shape. Over a larger extent of the enamel organ, they degenerate, and in its lower part they form an epithelial root sheath (Hertwig’s sheath), which induces the development of the tooth root. The dental papilla is formed from the mesenchyme lying inside the dental cup, and from the mesenchyme surrounding the enamel organ-dental sac. The second period for primary teeth is completely completed by the end of the 4th month of embryogenesis.

III period - the period of histogenesis of dental tissues. Dentin forms the earliest of the hard tissues of the tooth. Adjacent to the internal cells of the enamel organ (future ameloblasts), the connective tissue cells of the dental papilla, under the inductive influence of the latter, turn into dentinoblasts, which are arranged in one row like epithelium. They begin to form the intercellular substance of dentin - collagen fibers and ground substance, and also synthesize the enzyme alkaline phosphatase. This enzyme breaks down blood glycerophosphates to form phosphoric acid. As a result of the connection of the latter with calcium ions, hydroxyapatite crystals are formed, which are released between collagen fibrils in the form of matrix vesicles surrounded by a membrane. Hydroxyapatite crystals increase in size. Dentin mineralization gradually occurs.

Internal enamel cells, under the inductive influence of dentinoblasts of the dental papilla, transform into ameloblasts. At the same time, a reversal of physiological polarity occurs in the internal cells: the nucleus and organelles move from the basal part of the cell to the apical part, which from this moment becomes the basal part of the cell. On the side of the cell facing the dental papilla, cuticle-like structures begin to form. They then undergo mineralization with the deposition of hydroxyapatite crystals and turn into enamel prisms - the main structures of the enamel. As a result of the synthesis of enamel by ameloblasts and dentin by dentinoblasts, these two types of cells move further and further away from each other.

The dental papilla differentiates into the dental pulp, which contains blood vessels, nerves and provides nutrition to the dental tissues. Cementoblasts are formed from the mesenchyme of the dental sac, which produce the intercellular substance of cement and participate in its mineralization according to the same mechanism as in the mineralization of dentin. Thus, as a result of differentiation of the rudiment of the enamel organ, the formation of the main tissues of the tooth occurs: enamel, dentin, cement, pulp. The dental ligament, the periodontium, is also formed from the dental sac.

In the further development of the tooth, a number of stages can be distinguished.

The stage of growth and eruption of primary teeth is characterized by the growth of dental anlages. In this case, all tissues above them gradually undergo lysis. As a result, teeth break through these tissues and rise above the gum - they erupt.

The stage of loss of milk teeth and their replacement with permanent ones. The formation of permanent teeth is formed in the 5th month of embryogenesis as a result of the growth of epithelial cords from the dental plates. Permanent teeth develop very slowly, located next to the milk teeth, separated from them by a bony septum. By the time the baby teeth change (6-7 years), osteoclasts begin to destroy the bone septa and roots of the baby teeth. As a result, baby teeth fall out and are replaced by rapidly growing permanent teeth.

Root resorbent cells are located in bone lacunae, large, multinucleated, with a characteristic corrugated border, mitochondria and lysosomal enzymes in the cytoplasm. At the initial stage, demineralization of the bone matrix of the root tissue - cement and dentin - occurs, and subsequently there is extracellular destruction and intracellular utilization of the decay products of their organic component. Dentin destruction accelerates as dentinoclast processes penetrate the dentinal tubules. The pulp of a resorbed tooth remains viable and actively participates in the processes of root destruction. Dentinoclasts differentiate in it, which destroy dentin from the inside, from the pulp side. The process begins at the root and involves the coronal pulp.

Periodontal destruction of a temporary tooth occurs within a short time and occurs without signs of an inflammatory reaction. Fibroblasts and histiocytes die by apoptosis and are replaced by new cellular elements. Periods of active resorption of the temporary root are interspersed with periods of relative rest, i.e. the process proceeds in waves.

Permanent teeth that erupt in place of temporary (replacement) teeth have some features: their development occurs simultaneously and depending on the resorption of the roots of milk teeth. Such replacement teeth have a special anatomical structure that facilitates their eruption - a conductor canal, or conductor cord. The anlage of such a permanent tooth is initially located in the same bone alveolus with its temporary predecessor. Subsequently, it is almost completely surrounded by alveolar bone, with the exception of a small canal containing the remains of the dental plate and connective tissue; these structures are called conductive channels; it is assumed that in the future it contributes to the directional movement of the tooth during its eruption.

It is necessary to note the features of the morphogenesis of chewing teeth with a complex crown configuration. First of all, attention is drawn to the fact that in these teeth the process of differentiation of the enamel organ occurs more slowly. In addition, their rudiments are characterized by a larger volume of pulp of the enamel organ. In this case, the importance of the spatial relationships of the cellular elements of the rudiment again manifests itself. The formation of dentin begins precisely in those areas of the dental papilla that are located closer to the outer layer of the enamel organ. Such areas correspond to its lateral sections. This leads to the formation of several points of dentin formation, corresponding to the future cusps of the crown. In this case, the formation of enamel in them begins no earlier than the corresponding section of the papilla with a layer of dentin substance and ameloblasts located on top of it comes as close as possible to the outer epithelium of the enamel organ. Consequently, in this case, the pattern of spatial movements observed during the development of incisors and leading to the onset of amelogenesis is repeated. It is characteristic that the areas located between the tubercles are the most distant from the outer layers of cells of the enamel organ. Apparently, for this reason, there is a delay in the final differentiation of enameloblasts and, accordingly, the beginning of enamel formation.

When the roots of multi-rooted teeth are formed, the initial wide root canal is subdivided into two or three narrower canals due to outgrowths of the edges of the epithelial diaphragm, which, in the form of two or three tongues, are directed towards each other and ultimately merge.

At the beginning of the last century, doctors considered the thymus to be the thymus gland. This was due to the fact that it was located near the thyroid gland.

Then no one suspected the true the importance of this organ. So what is the thymus, and what role does it play in the human body?

What kind of organ is this and where is it located?

Thymus (or thymus gland) – one of the main organs of the immune system. It received its second name because of its resemblance to a two-pronged fork. It is in the thymus that immune cells are formed and mature. The organ is located above the collarbone behind the sternum.

The thymus is surrounded by a durable capsule, which consists of connective tissue. Two jumpers extend from it, dividing the organ into two lobules. The slices can be of different sizes. Both have cortex and medulla.

The cortex consists of networks of epithelial cells containing thymus lymphocytes. Epithelial cells produce hormones, cells involved in the maturation of lymphocytes and supporting cells. The medulla consists of flattened keratinized cells.

It is difficult to say about the size of the thymus gland, since it is size changes throughout life. In a newborn baby, the thymus gland is fully developed and during the first year of life its weight can reach 20 grams. For children from 6 to 16 years old – up to 35 grams.

Thymus grows until puberty. From about 16 years of age, the process of involution (aging) begins, and by the age of twenty, the tissue of the thymus gland is partially replaced by fatty tissue. The thymus begins to shrink. By the age of 60, his weight is less than 15 grams. By age 70 – less than 7 grams.

There is no need to be afraid of the extinction of the thymus, this is a natural process. During the first few years of fruitful work, the thymus produces enough T-lymphocytes; this amount will last the body for the rest of its life.

It is worth noting that in some people the thymus ages earlier, in others later. Doctors attribute this to two factors: genetic predisposition and lifestyle. In rare cases, the thymus does not disappear at all; in its place, an accumulation of connective, lymphoid and adipose tissue remains.

Look video about the thymus gland:

Functions and hormones of the thymus gland

The thymus secretes hormones:

The table shows the functions of hormones:

Timalin	Responsible for the ratio of T- and B-lymphocytes, affects the processes of regeneration and hematopoiesis.
Thymosin	Affects the metabolism of carbohydrates and calcium in the blood. Regulates the development and growth of the skeleton.
Thymopoietin I, thymopoietin II	Delays premature maturation, participates in the formation of T-lymphocytes
Homeostatic thymic hormone	Affects growth hormone, ACTH (Adrenocorticotropic hormone) and thyroid hormone.
Humoral thymic hormone	Activates T cell responses to antigens.

Familiarize yourself with the main functions of the thymus:

If the thymus gland has the “secret of beauty,” then why is no one considering a thymus transplant as one of the methods of rejuvenation? The whole problem is that Thymus transplant operations are very complex and quite traumatic.

Doctors have found a less dangerous way of rejuvenation - enough inject embryonic stem cells into the thymus. This procedure restores the thymus gland, which subsequently entails rejuvenation of the patient.

Diseases

Thymus disease is a rare phenomenon. Possible hyperplasia, hypoplasia and aplasia of the thymus:

Degeneration of the thymus is possible suspend replenishment of zinc reserves. To restore and maintain the thymus, there are methods of external influence: rubbing in essential ointments, warm compresses, physiotherapy. But it is not recommended to get carried away with such methods - no more than 10 days.

There is another fairly simple method - lightly tap your fingers on the area where the thymus is located. About 20 taps several times a day are enough and you will soon feel a noticeable surge of vigor and strength.

The thymus, despite its early involution and atrophy, is an amazing organ. During the first couple of years after birth, a person acquires a set of cellular receptors that can resist foreign antigens throughout life.

To maintain the longevity of the thymus consume more animal proteins and B vitamins, foods containing large amounts of zinc and try to avoid stress. A good one will help keep the whole body in good shape.

Blood supply and innervation of the thymus. The rr extend to the thymus from the internal mammary artery, aortic arch and brachiocephalic trunk. thymici. In the interlobular septa, they are divided into smaller branches, which penetrate into the lobules, where they branch to capillaries. The veins of the thymus drain into the brachiocephalic veins, as well as into the internal mammary veins.

Lymphatic capillaries of the thymus, which are more numerous in the cortex, form networks in the parenchyma of the organ, from which lymphatic vessels are formed that flow into the anterior mediastinal and tracheobronchial lymph nodes.

The thymic nerves are branches of the right and left vagus nerves, and also originate from the cervicothoracic (stellate) and superior thoracic ganglia of the sympathetic trunk.

2.3. Histology of the thymus

Externally, the thymus gland is covered with a connective tissue capsule. Partitions extend from it into the organ, dividing the gland into lobules. Each lobule contains a cortex and a medulla. The organ is based on epithelial tissue consisting of process cells - epithelioreticulocytes. All epithelioreticulocytes are characterized by the presence of desmosomes, tonofilaments and keratin proteins, products of the major histocompatibility complex on their membranes.

Epithelioreticulocytes, depending on their location, differ in shape and size, tinctorial features, hyaloplasm density, content of organelles and inclusions. Secretory cells of the cortex and medulla, non-secretory (or supporting) cells and cells of epithelial layered bodies - Hassall's bodies (Gassal's bodies) are described.

Secretory cells produce regulating hormone-like factors: thymosin, thymulin, thymopoietins. These cells contain vacuoles or secretory inclusions.

Epithelial cells in the subcapsular zone and outer cortex have deep invaginations in which lymphocytes are located, as in a cradle. The layers of cytoplasm of these epithelial cells - “feeders” or “nannies” between lymphocytes can be very thin and extended. Typically, such cells contain 10-20 lymphocytes or more.

Lymphocytes can move in and out of intussusceptions and form tight junctions with these cells. Nurse cells are capable of producing α-thymosin.

In addition to epithelial cells, auxiliary cells are distinguished. These include macrophages and dendritic cells. They contain products of the major histocompatibility complex and secrete growth factors (dendritic cells) that influence the differentiation of T lymphocytes.

Cortex - the peripheral part of the thymus lobules contains T-lymphocytes, which densely fill the lumens of the reticular epithelial framework. In the subcapsular zone of the cortex there are large lymphoid cells - T-lymphoblasts, which migrated here from the red bone marrow. They proliferate under the influence of thymosin secreted by epithelioreticulocytes. New generations of lymphocytes appear in the thymus every 6-9 hours. It is believed that T-lymphocytes of the cortex migrate into the bloodstream without entering the medulla. These lymphocytes differ in the composition of their receptors from the T-lymphocytes of the medulla. With the bloodstream, they enter the peripheral organs of lymphocytopoiesis - lymph nodes and spleen, where they mature into subclasses: antigen-reactive killers, helpers, suppressors. However, not all lymphocytes formed in the thymus enter the circulation, but only those that have undergone “training” and acquired specific cytoreceptors for foreign antigens. Lymphocytes that have cytoreceptors for their own antigens, as a rule, die in the thymus, which serves as a manifestation of the selection of immunocompetent cells. When such T-lymphocytes enter the bloodstream, an autoimmune reaction develops.

The cells of the cortex are in a certain way delimited from the blood by the blood-thymus barrier, which protects the differentiating lymphocytes of the cortex from excess antigens. It consists of endothelial cells of hemocapillaries with a basement membrane, a pericapillary space with single lymphocytes, macrophages and intercellular substance, as well as epithelioreticulocytes with their basement membrane. The barrier is selectively permeable to antigen. When the barrier is disrupted, single plasma cells, granular leukocytes and mast cells are also found among the cellular elements of the cortex. Sometimes foci of extramedullary myelopoiesis appear in the cortex.

The medulla of the thymus lobule on histological preparations has a lighter color, since it contains a smaller number of lymphocytes compared to the cortex. Lymphocytes in this zone represent a recirculating pool of T lymphocytes and can enter and exit the bloodstream through postcapillary venules.

The number of mitotically dividing cells in the medulla is approximately 15 times less than in the cortex. A feature of the ultramicroscopic structure of branched epithelioreticulocytes is the presence in the cytoplasm of grape-shaped vacuoles and intracellular tubules, the surface of which forms microprotrusions.

In the middle part of the medulla there are layered epithelial bodies (corpusculum thymicum) - Hassal's bodies. They are formed by concentrically layered epithelioreticulocytes, the cytoplasm of which contains large vacuoles, keratin granules and bundles of fibrils. The number of these bodies in humans increases during puberty, then decreases. The function of the taurus has not been established.

5. Thymus diseases

Microscopic structure of the thymus gland

The stroma of the thymus is of epithelial origin, originating from the epithelium of the anterior part of the primary intestine. Two cords originate from the third branchial arch and grow into the anterior mediastinum. Sometimes the thymic stroma is also formed by additional cords from the fourth pair of gill arches. Lymphocytes originate from blood stem cells that migrate to the thymus from the liver in the early stages of fetal development. Initially, proliferation of various blood cells occurs in the thymus tissue, but soon its function is reduced to the formation of T-lymphocytes. The thymus gland has a lobular structure; the tissue of the lobules is divided into the cortex and medulla. The cortex is located on the periphery of the lobule and appears dark in a histological microslide. The cortex contains arterioles and blood capillaries that have a blood-thymus barrier that prevents the introduction of antigens from the blood.

The cortex contains cells:

• epithelial origin:
  • supporting cells: form the “framework” of the tissue, form the blood-thymus barrier;
  • stellate cells: secrete soluble thymic hormones - thymopoietin, thymosin and others, regulating the processes of growth, maturation and differentiation of T cells and the functional activity of mature cells of the immune system.
  • “nurse” cells: have invaginations in which lymphocytes develop;
• hematopoietic cells:
  • lymphoid series: maturing T-lymphocytes;
  • macrophage series: typical macrophages, dendritic and interdigitating cells.

Directly under the capsule, dividing T-lymphoblasts predominate in the cellular composition. Deeper are the maturing T-lymphocytes, which gradually migrate to the medulla. The ripening process takes approximately 20 days. During their maturation, genes are rearranged and a gene encoding TCR is formed.

Next, they undergo positive selection: in interaction with epithelial cells, “functionally suitable” lymphocytes are selected, the TCR and its coreceptors of which are able to interact with HLA; During development, the lymphocyte differentiates into a helper or killer, i.e. either CD4 or CD8 remains on its surface. Next, in contact with stromal epithelial cells, cells capable of functional interaction are selected: CD8+ lymphocytes capable of receiving HLA I, and CD4+ lymphocytes capable of receiving HLA II.

The next stage - negative selection of lymphocytes - occurs at the border with the medulla. Dendritic and interdigitating cells - cells of monocyte origin - select lymphocytes capable of interacting with antigens of their own body and trigger their apoptosis.

The medulla mainly contains maturing T-lymphocytes. From here they migrate into the bloodstream of venules with high endothelium and disperse throughout the body. The presence of mature recirculating T-lymphocytes is also assumed here.

The cellular composition of the medulla is represented by supporting epithelial cells, stellate cells, and macrophages. There are also efferent lymphatic vessels and Hassall's corpuscles.

Thymus- the central organ of lymphoid hematopoiesis and immune defense of the body. In the thymus, antigen-independent differentiation of bone marrow precursors of T-lymphocytes into immunocompetent cells - T-lymphocytes - occurs. The latter carry out cellular immune reactions and participate in the regulation of humoral immunity, which occurs, however, not in the thymus, but in the peripheral organs of hematopoiesis and immune defense. In addition, more than 20 biologically active substances, including distant ones, were found in thymus extracts, which makes it possible to classify the thymus as a gland of the endocrine system.

Thymus development. The thymus is formed in the 2nd month of embryogenesis in the form of small protrusions of the walls of the 3rd and 4th pairs of gill pouches. At the 6th week, the gland primordium has a clearly defined epithelial character. At week 7, it loses contact with the wall of the head intestine. The epithelium of the gland anlage, forming outgrowths into mesenchyme, acquires a network-like structure. Initially, the dense epithelial lining of the gland is loosened due to its colonization with lymphocytes. Their number quickly increases, and the gland acquires the structure of a lymphoepithelial organ.

Growing mesenchyme with blood vessels subdivides thymus into slices. Each lobule contains a cortex and a medulla. During the histogenesis of the thymus, layered epithelial formations are formed in the medulla of the lobules - epithelial pearls, or Hassal's bodies. They contain dense epithelial cells, concentrically layered on top of each other.

Structure of the thymus. Externally, the thymus gland is covered with a connective tissue capsule. The partitions extending from it - septa - divide the thymus into lobules. The basis of the lobule is made up of branched epithelial cells - epithelioreticulocytes, in the reticular framework of which there are thymic lymphocytes (thymocytes). The source of development of T-lymphocytes are bone marrow hematopoietic stem cells. Next, the precursors of T-lymphocytes (prethymocytes) enter the thymus with the blood and transform into lymphoblasts.

10- Thymus gland (thymus) produces hormones:
1- Thymosin
2- Tmopoietin
3- Connection with the Anahata chakra
4- Connection of the Anahata chakra with the Soul body
5- Areas controlling upper blood pressure
6- Areas that control lower blood pressure
7- Areas that control heart rate

STROMA

• dense stroma:

· soft stroma: reticuloepithelial tissue; in the cortex there are special types of cells of the reticuloepithelial stroma - epithelial nurse cells, dendritic epithelial cells of the cortex; the medulla also contains special types of cells of the reticuloepithelial stroma - interdigital dendritic cells, epithelial cells of the medulla, Hassall's bodies

FUNCTIONS OF RETICULOEPITHELIAL STROMA CELLS- participation in the differentiation of T-lymphocytes, which is ensured through contact interactions with lymphocytes and through the production of thymic hormones (thymosin, thymalin, thymopoietin)

PARENCHYMA the structural element of the parenchyma is thymus lobule consisting of cortex and medulla

• cortex: formed by precursor cells of T-lymphocytes, T-lymphoblasts, T-lymphocytes at different levels of differentiation, dying T-lymphocytes, macrophages lying in the cells of the reticuloepithelial stroma due to the presence of a large number of cells, stains intensely and looks darker compared to the brain substance
  Features: antigen-independent differentiation of T-lymphocytes, recognition and destruction of T-lymphocytes aimed at interacting with self-antigens (censor function)
• medulla: formed by T-lymphocytes, macrophages, sometimes plasma cells are found
  Features: exact functions are unknown, perhaps some stages of antigen-independent differentiation of T lymphocytes

FEATURES OF BLOOD SUPPLY

• the cortex and medulla are supplied with blood separately
• blood from the cortex, without entering the medulla, immediately flows out of the thymus
• in the cortex there is blood barrier; the structure of its wall:
  1. (blood-->) capillary endothelium--> 2. basement membrane of the capillary, there may be pericytes and adventitial cells --> 3. pericapillary space --> 4. basement membrane of reticuloepithelial cells --> 5. reticuloepithelial cells -->(parenchyma)

INVOLUTION OF THE THYMUS
During life, the thymus undergoes reverse development - this is age involution; occurs under stress and under the influence of glucocorticoid hormones rapid or accidental involution thymus; both types of involution involve the death of lymphoid cells, a decrease in organ mass and the replacement of parenchyma with connective tissue

SOURCES OF DEVELOPMENT

• mesenchyme- capsule and septa

· epithelium of 3rd and 4th gill pouches- reticuloepithelial stroma

Bone marrow- parenchyma (lymphoid cells, macrophages)

89)SPLEEN

STROMA

· dense stroma: the capsule and septa (septa in the spleen are called trabeculae) are formed by dense fibrous connective tissue, where there are many elastic fibers, and SMCs are found

• soft stroma: reticular tissue; in the white pulp - in the lymphoid follicles - there are special types of reticular stroma cells - dendritic cells And interdigital cells; dendritic cells located in the proliferation center of the lymphoid follicle, participate in the differentiation of B-lymphocytes; interdigital cells are located in the periarterial zone of the follicle, participate in the differentiation of T-lymphocytes

PARANCHYMA (PULPA) formed by white and red pulp

• white pulp: presented lymphoid follicles, they distinguish the following zones:
• breeding center- here there are mainly B-lymphocytes at different levels of differentiation, dendritic cells of the reticular stroma; in this area antigen-dependent differentiation of B-lymphocytes occurs (B-zone)
• periarterial zone- there are mainly T-lymphocytes at different levels of differentiation, interdigital cells of the reticular stroma; antigen-independent differentiation of T-lymphocytes occurs (T-zone) SUCH A ZONE exists only in the follicles of the spleen
• - interaction between T and B lymphocytes occurs, which is necessary for their differentiation

Features: antigen-dependent differentiation of T and B lymphocytes

• red pulp: represented by blood, which is located in the sinusoids and perisinusoidal spaces
  Features:
• death of old erythrocytes - old erythrocytes have reduced osmotic resistance (resistance to a decrease in the osmotic pressure of the blood plasma), and in the sinusoids of the spleen the osmotic pressure of the plasma may decrease, old erythrocytes cannot withstand such changes in osmotic pressure and undergo hemolysis, after which their remains are phagocytosed by macrophages; in addition, old red blood cells have few sialic acids in the cytomembrane glycocalyx; they are recognized by macrophages and are phagocytosed
• death of old platelets that are recognized and phagocytosed by macrophages
• blood depot - due to the presence of arterial and venous sphincters, blood can be deposited in the red pulp, this is facilitated by the extensibility of the capsule and trabneculae of the spleen
• final stages of antigen-dependent differentiation of lymphocytes (plasmocytopoiesis)

BLOOD SUPPLY

1. splenic artery
2. segmental arteries
3. trabecular artery
4. pulpal artery
5. central artery - the part of the pulp artery passing through the lymphoid follicle is called the central artery
6. brush arterioles (there are precapillary sphincters)
7. short capillaries
8. BLOOD CAN FURTHER FLOW IN TWO WAYS
   venous sinusoidal capillary
   OR
   blood enters directly into the pulp, into the perisinusoidal space
9. pulpal venule (there are sphincters)
10. trabecular vein
11. segmental veins
12. splenic veins

structure of the wall of the venous sinusoidal capillary of the spleen:

· fenestrated endothelium, to which a huge number of macrophages are attached;

• fenestrated basement membrane
• reticular fibers

SOURCES OF DEVELOPMENT

• mesenchyme- stroma (capsule, trabeculae, reticular tissue)

red bone marrow- red and white pulp cells

90) THE LYMPH NODES

STROMA

• dense stroma: the capsule and septa are formed by PBST
• soft stroma: reticular tissue; in the cortex - in lymphoid follicles there is a special type of reticular stroma cells - dendritic cells, which are involved in the differentiation of B lymphocytes; V paracortical zone There are special types of reticular stroma cells - interdigital cells, which are involved in the differentiation of T lymphocytes

PARENCHYMA educated cortical, medulla And paracortical zone

• cortex: represented by lymphoid follicles; in the follicle there are:
• breeding center where antigen-dependent differentiation of B lymphocytes occurs
• mantle layer, marginal layer- in these layers the interaction of T- and B-lymphocytes occurs, which is necessary for their differentiation

In lymphoid follicles, mainly antigen-dependent differentiation of B-lymphocytes occurs, therefore this part is called the B-zone of the lymph node

• paracortical zone: formed by accumulations of lymphoid tissue on the internal surfaces of the follicles; antigen-dependent differentiation of T lymphocytes occurs here, which is why this area is called the T zone
• medulla: formed from accumulations of lymphoid tissue in the internal parts of the lymph node; they are called medullary cords; the final stages of differentiation of T and B lymphocytes may occur in the medulla

SINES OF LYMPH NODE- channels through which lymph flows inside the lymph node

The following sines are distinguished: subcapsular, cortical, medullary, portal

structure of the sinus wall:

• fenestrated endothelium to which many macrophages are attached
• fenestrated basement membrane (sometimes absent)
• reticular fibers, reticular cells (there may be a small number of SMCs in the portal sinus)

SOURCES OF DEVELOPMENT

• mesenchyme- stroma (capsule, septa, reticular tissue)

red bone marrow- parenchyma

91) Human respiratory system- a set of organs that provide the function of external respiration (gas exchange between inhaled atmospheric air and blood circulating in the pulmonary circulation).

Gas exchange takes place in the alveoli of the lungs, and is normally aimed at capturing oxygen from the inhaled air and releasing carbon dioxide formed in the body into the external environment.
Respiratory system

Part one. General plan of the building, development; structure of the airways.

The respiratory system is a set of organs that provide external respiration in the body, as well as a number of important non-respiratory functions.
(Internal respiration is a complex of intracellular redox processes).

The respiratory system includes various organs that perform air-conducting and respiratory (i.e., gas exchange) functions: the nasal cavity, nasopharynx, larynx, trachea, bronchi and lungs. Thus, in the respiratory system we can distinguish:

• extrapulmonary airways;
• and lungs, which in turn include:
• -intrapulmonary airways (the so-called bronchial tree);
• - the actual respiratory part of the lungs (alveoli).

The main function of the respiratory system is external respiration, i.e. absorbing oxygen from the inhaled air and supplying it to the blood, as well as removing carbon dioxide from the body. This gas exchange is carried out by the lungs.

Among the non-respiratory functions of the respiratory system, the following are very important:

• thermoregulation,
• deposition of blood in the abundantly developed vascular system of the lungs,
• participation in the regulation of blood coagulation due to the production of thromboplastin and its antagonist - heparin,
• participation in the synthesis of certain hormones, as well as inactivation of hormones;
• participation in water-salt and lipid metabolism;
• participation in voice formation, smell and immune defense.

The lungs take an active part in the metabolism of serotonin, which is destroyed under the influence of monoamine oxidase (MAO). MAO is detected in macrophages and mast cells of the lungs.>

In the respiratory system, inactivation of bradykinin, synthesis of lysozyme, interferon, pyrogen, etc. occur. With metabolic disorders and the development of pathological processes, some volatile substances are released (acetone, ammonia, ethanol, etc.).

The protective filtering role of the lungs is not only to retain dust particles and microorganisms in the airways, but also to trap cells (tumor, small blood clots) in the vessels of the lungs (“traps”).

Development

The respiratory system develops from the endoderm.

The larynx, trachea and lungs develop from one common rudiment, which appears at the 3-4th week by protrusion of the ventral wall of the foregut. The larynx and trachea are formed in the 3rd week from the upper part of the unpaired sac-like protrusion of the ventral wall of the foregut. In the lower part, this unpaired rudiment is divided along the midline into two sacs, giving rise to the rudiments of the right and left lungs. These bags, in turn, are later subdivided into many interconnected smaller protrusions, between which mesenchyme grows. At the 8th week, the rudiments of the bronchi appear in the form of short, even tubes, and at the 10-12th week their walls become folded, lined with cylindrical epithelial cells (a tree-like branched system of bronchi is formed - the bronchial tree). At this stage of development, the lungs resemble a gland (glandular stage). At the 5-6th month of embryogenesis, the development of final (terminal) and respiratory bronchioles, as well as alveolar ducts, surrounded by a network of blood capillaries and growing nerve fibers (tubular stage) occurs.

From the mesenchyme surrounding the growing bronchial tree, smooth muscle tissue, cartilaginous tissue, fibrous connective tissue of the bronchi, elastic, collagen elements of the alveoli, as well as layers of connective tissue growing between the lobules of the lung are differentiated. From the end of the 6th - beginning of the 7th month and before birth, part of the alveoli and the alveolocytes of the 1st and 2nd types lining them are differentiated (alveolar stage).

During the entire embryonic period, the alveoli have the appearance of collapsed vesicles with insignificant lumen. At this time, from the visceral and parietal layers of the splanchnotome, the visceral and parietal layers of the pleura are formed. When a newborn takes his first breath, the alveoli of the lungs straighten, as a result of which their cavities sharply increase and the thickness of the alveolar walls decreases. This promotes the exchange of oxygen and carbon dioxide between the blood flowing through the capillaries and the air of the alveoli.

Airways

These include the nasal cavity, nasopharynx, larynx, trachea and bronchi. In the airways, as the air moves, it is purified, moistened, warmed, receives gas, temperature and mechanical stimuli, as well as regulates the volume of inhaled air.

The wall of the airways (in typical cases - in the trachea, bronchi) consists of four membranes:

1. mucous membrane;
2. submucosa;
3. fibrocartilaginous membrane;
4. adventitia.

In this case, the submucosa is often considered as part of the mucous membrane, and they speak of the presence of three membranes as part of the wall of the airways (mucosal, fibrocartilaginous and adventitial).