The structure of the pituitary gland histology. Histological structure. Features of the hypothalamic-adenohypophyseal blood supply

1. The main stages in the formation of hemacytopoiesis and immunocytopoiesis in phylogenesis.

2. Classification of hematopoietic organs.

3. General morphofunctional characteristics of the hematopoietic organs. The concept of a specific microenvironment in the organs of hematopoiesis.

4. Red bone marrow: development, structure and functions.

5. Thymus is the central organ of lymphocytopoiesis. Development, structure and functions. Age and accidental involution of the thymus.

In the process of evolution, there is a change in the topography of the hematopoietic organs (OCT), the complication of their structure and differentiation of functions.

1. In invertebrates: there is still no clear organ localization of hematopoietic tissue; primitive hemolymph cells (amoebocytes) are diffusely scattered throughout the tissues of organs.

2. In lower vertebrates (cyclostomes): the first isolated foci of hematopoiesis appear in the wall of the digestive tube. The basis of these foci of hematopoiesis is reticular tissue, there are sinusoidal capillaries.

3. In cartilaginous and bony fish, along with foci of hematopoiesis, separate OCT appears in the wall of the digestive tube - the spleen and thymus; there are foci of CT in the gonads, interrenal bodies and even in the epicardium.

4. In highly organized fish, CT foci appear for the first time in the bone tissue.

5. In amphibians, there is an organ separation of myelopoiesis and lymphopoiesis.

6. In reptiles and birds, there is a clear organ separation of myeloid and lymphoid tissue; the main OCT is red bone marrow.

7. In mammals, the main OCT is red bone marrow; in other organs, lymphocytopoiesis.

OCT classification:

I. Central OCT

1. Red bone marrow

II. Peripheral OCT

1. Actually lymphoid organs (along the lymphatic vessels - lymph nodes).

2. Hemolymphoid organs (along the blood vessels - the spleen, hemolymph nodes).

3. Lymphoepithelial organs (lymphoid accumulations under the epithelium of the mucous membranes of the digestive, respiratory, genitourinary systems).

General morphofunctional characteristics of OCT

Despite the significant diversity of OCT, they have much in common - in the sources of development, in the structure and functions:

1. Source of development - all OCTs originate from the mesenchyme; the exception is the thymus - it develops from the epithelium of the 3rd-4th gill pockets.

2. Generality in structure - the basis of all OCT is a connective tissue with special properties - reticular tissue. The exception is the thymus: the basis of this organ is the reticular epithelium (reticuloepithelial tissue).

3. Blood supply OCT - abundant blood supply; have hemocapillaries of the sinusoidal type (diameter 20 or more microns; there are large gaps, pores between endotheliocytes, the basement membrane is not continuous - sometimes absent; blood flows slowly).

Role of reticular tissue in OCT

You remember that RT consists of cells (reticular cells, a small amount of fibroblast-like cells, macrophages, mast and plasma cells, osteogenic cells) and intercellular substance, represented by reticular fibers and the main amorphous substance. Reticular tissue in OCT performs the following functions:

1. Creates a specific microenvironment that determines the direction of differentiation of maturing blood cells.

2. Trophics of maturing blood cells.

3. Phagocytosis and utilization of dead blood cells due to phagocytosis of reticular cells and macrophages.

4. Support-mechanical function - is a supporting frame for maturing blood cells.

RED BONE MARROW - central OCT, where both myelopoiesis and lymphocytopoiesis occur. RCM in the embryonic period is laid from the mesenchyme at the 2nd month, by the 4th month it becomes the center of hematopoiesis. KKM is a tissue of semi-liquid consistency, dark red in color due to the high content of red blood cells. A small amount of BMC for research can be obtained by puncture of the sternum or iliac crest.

The stroma of the RMC is made up of reticular tissue, abundantly permeated with hemocapillaries of the sinusoidal type. In the loops of the reticular tissue, there are islands or colonies of maturing blood cells:

1. Erythroid cells in their islets-colonies will group around macrophages loaded with iron, obtained from old erythrocytes that died in the spleen. Macrophages in the RMC transfer the iron necessary for the synthesis of hemoglobin to erythroid cells.

2. Lymphocytes, granulocytes, monocytes, megakaryocytes are located in separate islets-colonies around sinusoidal hemocapillaries. Islands of different sprouts interspersed with each other and create a mosaic pattern.

Mature blood cells penetrate through the walls into the sinusoidal hamocapillaries and are carried away by the bloodstream. The passage of cells through the walls of blood vessels is facilitated by the increased permeability of sinusoidal hemocapillaries (slits, the absence of a basement membrane in places), high hydrostatic pressure in the reticular tissue of the organ. High hydrostatic pressure is due to 2 circumstances:

1. Blood cells multiply in a closed space limited by bone tissue, the volume of which cannot change and this leads to an increase in pressure.

2. The total diameter of the afferent vessels is greater than the diameter of the efferent vessels, which also leads to an increase in pressure.

Age features of BMC: In children, BMC fills both the epiphyses and diaphyses of tubular bones, the spongy substance of flat bones. In adults, in the diaphysis, the BMC is replaced by yellow bone marrow (adipose tissue), and in old age by gelatinous bone marrow.

Regeneration: physiological - due to class 4-5 cells; reparative - 1-3 classes.

THYMUS is the central organ of lymphocytopoiesis and immunogenesis. Thymus is laid at the beginning of the 2nd month of embryonic development from the epithelium of 3-4 gill pockets as an exocrine gland. In the future, the cord connecting the gland with the epithelium of the gill pockets undergoes reverse development. At the end of the 2nd month, the organ is populated by lymphocytes.

The structure of the thymus - on the outside, the organ is covered with a sdt capsule, from which partitions of loose sdt extend inward and divide the organ into lobules. The basis of the parenchyma of the thymus is the mesh epithelium: epithelial cells are sprouts, connected to each other by processes and form a looped network, in the loops of which lymphocytes (thymocytes) are located. In the central part of the lobule, aging epithelial cells form layered thymus bodies or Hassall bodies - concentrically layered epithelial cells with vacuoles, keratin granules and fibrillar fibers in the cytoplasm. The number and size of Hassall's bodies increases with age. The function of the reticular epithelium:

1. Creates a specific microenvironment for maturing lymphocytes.

2. Synthesis of the hormone thymosin, which is necessary in the embryonic period for the normal formation and development of peripheral lymphoid organs, and in the postnatal period for regulating the function of peripheral lymphoid organs; synthesis of insulin-like factor, cell growth factor, calcitonin-like factor.

3. Trophic - nutrition of maturing lymphocytes.

4. Support-mechanical function - supporting framework for thymocytes.

Lymphocytes (thymocytes) are located in the loops of the reticular epithelium, there are especially many of them along the periphery of the lobule, therefore this part of the lobule is darker and is called the cortical part. The center of the lobule contains fewer lymphocytes, so this part is lighter and is called the medulla of the lobule. In the cortical substance of the thymus, "learning" of T-lymphocytes occurs, i.e. they acquire the ability to recognize "their own" or "someone else's." What is the essence of this training? In the thymus, lymphocytes are formed that are strictly specific (having strictly complementary receptors) for all possible conceivable A-genes, even against their own cells and tissues, but in the process of "learning" all lymphocytes that have receptors for their tissues are destroyed, leaving only those lymphocytes that are directed against foreign antigens. That is why in the cortical substance, along with increased reproduction, we also see a mass death of lymphocytes. Thus, subpopulations of T-lymphocytes are formed in the thymus from the precursors of T-lymphocytes, which subsequently enter the peripheral lymphoid organs, mature and function.

After birth, the mass of the organ rapidly increases during the first 3 years, slow growth continues until the age of puberty, after 20 years the thymus parenchyma begins to be replaced by adipose tissue, but the minimum amount of lymphoid tissue remains until old age.

Accidental involution of the thymus (AIT): The cause of accidental involution of the thymus can be excessively strong stimuli (trauma, infections, intoxication, severe stress, etc.). Morphologically, AIT is accompanied by mass migration of lymphocytes from the thymus into the bloodstream, mass death of lymphocytes in the thymus and phagocytosis of dead cells by macrophages (sometimes phagocytosis of normal, non-dead lymphocytes), growth of the epithelial base of the thymus and increased thymosin synthesis, blurring of the boundary between the cortical and brain parts of the lobules. Biological significance of AIT:

1. Dying lymphocytes are DNA donors, which are transported by macrophages to the lesion and used there by proliferating cells of the organ.

2. The mass death of lymphocytes in the thymus is a manifestation of the selection and elimination of T-lymphocytes that have receptors against their own tissues in the lesion and is aimed at preventing possible autoaggression.

3. Growth of the epithelial tissue base of the thymus, increased synthesis of thymosin and other hormone-like substances are aimed at increasing the functional activity of peripheral lymphoid organs, enhancing metabolic and regenerative processes in the affected organ.

Endocrine organs are classified by origin, histogenesis and histological origin into three groups. The branchiogenic group is formed from the pharyngeal pockets - this is the thyroid group of the adrenal glands - it belongs to the adrenal glands (medulla and cortex), paraganglia and a group of cerebral appendages - this is the hypothalamus, pituitary gland and pineal gland.

It is a functionally regulating system in which there are inter-organ connections, and the work of this entire system has a hierarchical relationship with each other.

History of the study of the pituitary gland

The study of the brain and its appendages was carried out by many scientists in different eras. For the first time, Galen and Vesalius thought about the role of the pituitary gland in the body, who believed that it forms mucus in the brain. In later periods, there were conflicting opinions about the role of the pituitary gland in the body, namely that it is involved in the formation of cerebrospinal fluid. Another theory was that it absorbs cerebrospinal fluid and then secretes it into the blood.

In 1867 P.I. Peremezhko was the first to make a morphological description of the pituitary gland, distinguishing in it the anterior and posterior lobes and the cavity of the cerebral appendages. In a later period in 1984-1986, Dostoevsky and Flesh, studying microscopic fragments of the pituitary gland, found chromophobic and chromophilic cells in its anterior lobe.

Scientists of the 20th century discovered a correlation between the human pituitary gland, whose histology, when studying its secretory secretions, proved this, with the processes occurring in the body.

Anatomical structure and location of the pituitary gland

The pituitary gland is also called the pituitary or pea gland. It is located in the Turkish saddle of the sphenoid bone and consists of a body and a leg. From above, the Turkish saddle closes the spur of the hard shell of the brain, which serves as a diaphragm for the pituitary gland. The pituitary stalk passes through a hole in the diaphragm, connecting it to the hypothalamus.

It is reddish-gray in color, covered with a fibrous capsule, and weighs 0.5-0.6 g. Its size and weight vary according to sex, disease development, and many other factors.

Embryogenesis of the pituitary gland

Based on the histology of the pituitary gland, it is divided into adenohypophysis and neurohypophysis. The laying of the pituitary gland begins at the fourth week of embryonic development, and two rudiments are used for its formation, which are directed at each other. The anterior lobe of the pituitary gland is formed from the pituitary pocket, which develops from the oral bay of the ectoderm, and the posterior lobe from the cerebral pocket, which is formed by the protrusion of the bottom of the third cerebral ventricle.

Embryonic histology of the pituitary gland differentiates already at the 9th week of development the formation of basophilic cells, and at the 4th month of acidophilic.

Histological structure of the adenohypophysis

Thanks to histology, the structure of the pituitary gland can be represented by the structural parts of the adenohypophysis. It consists of an anterior, intermediate, and tuberal portion.

The anterior part is formed by trabeculae - these are branched strands consisting of epithelial cells, between which connective tissue fibers and sinusoidal capillaries are located. These capillaries form a dense network around each trabecula, which provides a close connection with the bloodstream. trabeculae, of which it consists, are endocrinocytes with secretory granules located in them.

The differentiation of secretory granules is represented by their ability to stain when exposed to coloring pigments.

On the periphery of the trabeculae are endocrinocytes, which contain secretory substances in their cytoplasm, which are stained, and they are called chromophilic. These cells are divided into two types: acidophilic and basophilic.

Acidophilic adrenocytes stain with eosin. It's an acid dye. Their total number is 30-35%. The cells are round in shape with a nucleus located in the center, with the Golgi complex adjacent to it. The endoplasmic reticulum is well developed and has a granular structure. In acidophilic cells, there is an intensive protein biosynthesis and hormone formation.

In the process of histology of the pituitary gland of the anterior part in acidophilic cells, when they were stained, varieties were identified that are involved in the production of hormones - somatotropocytes, lactotropocytes.

acidophilic cells

Acidophilic cells include cells that stain with acidic colors and are smaller in size than basophils. The nucleus in these is located in the center, and the endoplasmic reticulum is granular.

Somatotropocytes make up 50% of all acidophilic cells and their secretory granules, located in the lateral sections of the trabeculae, are spherical in shape, and their diameter is 150-600 nm. They produce somatotropin, which is involved in growth processes and is called growth hormone. It also stimulates cell division in the body.

Lactotropocytes have another name - mammotropocytes. They have an oval shape with dimensions of 500-600 by 100-120 nm. They do not have a clear localization in the trabeculae and are scattered in all acidophilic cells. Their total number is 20-25%. They produce the hormone prolactin or luteotropic hormone. Its functional significance lies in the biosynthesis of milk in the mammary glands, the development of the mammary glands and the functional state of the corpus luteum of the ovaries. During pregnancy, these cells increase in size, and the pituitary gland becomes twice as large, which is reversible.

Basophil cells

These cells are relatively larger than acidophilic cells, and their volume occupies only 4-10% in the anterior part of the adenohypophysis. In their structure, these are glycoproteins, which are the matrix for protein biosynthesis. Cells are stained with the histology of the pituitary gland with a preparation that is determined mainly by aldehyde-fuchsin. Their main cells are thyrotropocytes and gonadotropocytes.

Thyrotropes are small secretory granules with a diameter of 50-100 nm, and their volume is only 10%. Their granules produce thyrotropin, which stimulates the functional activity of the thyroid follicles. Their deficiency contributes to an increase in the pituitary gland, as they increase in size.

Gonadotropes make up 10-15% of the volume of the adenohypophysis and their secretory granules are 200 nm in diameter. They can be found in the histology of the pituitary gland in a scattered state in the anterior lobe. It produces follicle-stimulating and luteinizing hormones, and they ensure the full functioning of the sex glands of the body of a man and a woman.

propioomelanocortin

Large secreted glycoprotein measuring 30 kilodaltons. It is propioomelanocortin, which, after its splitting, forms corticotropic, melanocyte-stimulating and lipotropic hormones.

Corticotropic hormones are produced by the pituitary gland, and their main purpose is to stimulate the activity of the adrenal cortex. Their volume is 15-20% of the anterior pituitary gland, they are basophilic cells.

Chromophobic cells

Melanocyte-stimulating and lipotropic hormones are secreted by chromophobic cells. Chromophobic cells are difficult to stain or do not stain at all. They are divided into cells that have already begun to turn into chromophilic cells, but for some reason did not have time to accumulate secretory granules, and cells that intensively secrete these granules. Depleted or without granules are quite specialized cells.

Chromophobic cells also differentiate into small follicle stellate cells with long processes that form a broad network. Their processes pass through endocrinocytes and are located on sinusoidal capillaries. They can form follicular formations and accumulate a glycoprotein secret.

Intermediate and tuberal adenohypophysis

The cells of the intermediate part are weakly basophilic and accumulate a glycoprotein secret. They have a polygonal shape and their size is 200-300 nm. They synthesize melanotropin and lipotropin, which are involved in pigment and fat metabolism in the body.

The tuberal part is formed by epithelial strands that extend into the anterior part. It is adjacent to the pituitary stalk, which is in contact with the medial eminence of the hypothalamus from its lower surface.

neurohypophysis

The posterior lobe of the pituitary gland consists of which they have a fusiform or process shape. It includes the nerve fibers of the anterior zone of the hypothalamus, which are formed by neurosecretory cells of the axons of the paraventricular and supraoptic nuclei. In these nuclei, oxytocin and vasopressin are formed, which enter and accumulate in the pituitary gland.

pituitary adenoma

Benign formation in the anterior pituitary gland This formation is formed as a result of hyperplasia - this is the uncontrolled development of a tumor cell.

Histology of pituitary adenoma is used in the study of the causes of the disease and to determine its variety according to the anatomical lesion of the growth of the organ. Adenoma can affect the endocrinocytes of basophilic cells, chromophobic and develop on several cellular structures. It can also have different sizes, and this is reflected in its name. For example, microadenoma, prolactinoma and its other varieties.

Animal pituitary gland

The pituitary gland of a cat is spherical, and its dimensions are 5x5x2 mm. Histology of the cat's pituitary gland revealed that it consists of an adenohypophysis and a neurohypophysis. The adenohypophysis consists of an anterior and an intermediate lobe, and the neurohypophysis connects to the hypothalamus through a stalk, which is somewhat shorter and thicker in its posterior part.

Staining of microscopic biopsy fragments of the pituitary gland of a cat with the drug at multiple magnification histology allows one to see the pink granularity of acidophilic endocrinocytes of the anterior lobe. These are large cells. The posterior lobe stains poorly, has a rounded shape, and consists of pituicites and nerve fibers.

The study of the histology of the pituitary gland in humans and animals allows you to accumulate scientific knowledge and experience, which will help explain the processes occurring in the body.

Regulates the activity of a number of endocrine glands and serves as a site for the release of hypothalamic hormones of the large cell nuclei of the hypothalamus. Comprises two embryologically, structurally and functionally different parts - neurohypophysis- an outgrowth of the diencephalon and adenohypophysis, the leading tissue of which is the epithelium. The adenohydophysis is divided into a larger anterior lobe, narrow intermediate and underdeveloped tuberal part (Fig. 1).

Rice. 1. Pituitary. PD - anterior lobe, PRD - intermediate lobe, ZD - posterior lobe, PM - tuberal part, K ​​- capsule.

The pituitary gland is covered capsule from dense fibrous tissue. His stroma It is represented by very thin layers of loose connective tissue associated with a network of reticular fibers, which in the adenohypophysis surrounds strands of epithelial cells and small vessels.

In humans, it makes up about 75% of its mass; it is formed by anastomosing strands (trabeculae) adenocytes, closely related to the system sinusoidal capillaries. The shape of adenocytes varies from oval to polygonal. Based color features their cytoplasm secrete:
1)chromophilic(intensely colored) and
2)chromophobic(weakly perceiving dyes) cells, which are contained in approximately equal amounts (Fig. 2).

Figure 2. Anterior pituitary gland. AA - acidophilic adenocytes, BA - basophilic adenocytes, CFA - chromophobic adenocytes, FSC - follicular stellate cells, CAP - capillary.

Rice. 3. Somatotrope ultrastructure: grEPS - granular endoplasmic reticulum, CG - Golgi complex, SG - secretory granules.

1. Chromophilic adenocytes(chromophils) are characterized by a developed synthetic apparatus and accumulation in the cytoplasm of secretory granules containing hormones (Fig. 3). Depending on the color of the secretory granules, chromophils are divided into acidophiles and basophils.

a) acidophiles(about 40% of all adenocytes) - small rounded cells with well-developed organelles and a high content of large granules - include two types:
(1) growth hormones- produce growth hormone (GH) or growth hormone (GH); its effect growth stimulation mediated by special peptides - somatomedins;
(2) lactotropes- produce prolactin (PRL) or lactotropic hormone (LTH), which stimulates mammary gland development and lactation.

b) basophils(10-20%) larger than acidophiles, however, their granules are smaller and are usually found in smaller numbers. Includes gonadotropes, thyrotropes and adrenocorticotropes:
(1) gonadotropes- produce
a) follicle stimulating hormone(FSH), which stimulates the growth of ovarian follicles and spermatogenesis, and
b) luteinizing hormone(LH), which promotes the secretion of female and male sex hormones, ensures the development of ovulation and the formation of the corpus luteum.
(2) thyrotropes- produce thyrotropic hormone (TSH), which enhances the activity of thyrocytes.
(3) corticotropes- produce adrenocorticotropic hormone (ACTH), which stimulates the activity of the adrenal cortex and is a cleavage product of a large molecule Proopiomelanocortin (POMC). POMC also forms MSH and LPG.

2. Chromophobic adenocytes(chromophobes) - a heterogeneous group of cells that includes:

1. chromophils after excretion of secretory granules,
2. undifferentiated cambial elements capable of transforming into basophils or acidophiles,
3. follicular stellate cells- non-secretory, star-shaped, covering secretory cells with their processes and lining small follicular structures. Able phagocytize dying cells and affect the secretory activity of basophils and acidophils.

Intermediate share in humans, it is very poorly developed and consists of narrow intermittent strands basophilic and chromophobic cells that secrete MSH - melanocyte-stimulating hormone(activates melanocytes) and LPG - lipotropic hormone(stimulates fat metabolism). MSH and LPG (as well as ACTH) are breakdown products of POMC. There are cystic cavities lined with ciliated cells and containing a non-hormonal protein substance - colloid.

Tuberal part in the form of a thin (25-60 microns) sleeve covers the pituitary stalk, separated from it by a narrow layer of connective tissue. It is made up of strands chromophobic and chromophilic cells;

posterior lobe contains:

1. processes and terminals of neurosecretory cells of SOYA and PVN the hypothalamus, through which ADH and oxytocin are transported and excreted into the blood; expanded areas along the processes and in the region of the terminals are called accumulative neurosecretory bodies (Herring);
2. numerous fenestrated capillaries;
3. pituicytes- process glial cells (occupy up to 25-30% of the volume of the lobe) - form 3-dimensional networks, cover the axons and terminals of neurosecretory cells and perform supporting and trophic functions, and also, possibly, influence the processes of neurosecretion release.

Pituitary(pituitary gland) together with the hypothalamus makes up the hypothalamic-pituitary neurosecretory system. It is a brain appendage. In the pituitary gland, the adenohypophysis (anterior lobe, intermediate and tuberal parts) and the neurohypophysis (posterior lobe, infundibulum) are distinguished.

Development. The adenohypophysis develops from the epithelium of the roof of the oral cavity. On the 4th week of embryogenesis, an epithelial protrusion is formed in the form of a pituitary pocket (Rathke's pocket), from which a gland with an external type of secretion is first formed. Then the proximal pocket is reduced, and the adenomere becomes a separate endocrine gland. The neurohypophysis is formed from the material of the infundibular part of the floor of the third ventricle of the brain and has a neural origin. These two parts, different in origin, come into contact, forming the pituitary gland.

Structure. The adenohypophysis consists of epithelial strands - trabeculae. Sinusoidal capillaries pass between them. The cells are represented by chromophilic and chromophobic endocrinocytes. Among chromophilic endocrinocytes, acidophilic and basophilic endocrinocytes are distinguished.

acidophilic endocrinocytes- These are medium-sized cells, round or oval in shape, with a well-developed granular endoplasmic reticulum. The nuclei are in the center of the cells. They contain large dense granules stained with acid dyes. These cells lie along the periphery of the trabeculae and make up 30-35% of the total number of adenocytes in the anterior pituitary gland. There are two types of acidophilic endocrinocytes: somatotropocytes, which produce growth hormone (somatotropin), and lactotropocytes, or mammotropocytes, which produce lactotropic hormone (prolactin). Somatotropin stimulates the growth of all tissues and organs.

With hyperfunction of somatotropocytes acromegaly and gigantism may develop, and in conditions of hypofunction - a slowdown in body growth, which leads to pituitary dwarfism. The lactotropic hormone stimulates the secretion of milk in the mammary glands and progesterone in the corpus luteum of the ovary.

Basophilic endocrinocytes- These are large cells, in the cytoplasm of which there are granules stained with basic dyes (aniline blue). They make up 4-10% of the total number of cells in the anterior pituitary gland. The granules contain glycoproteins. Basophilic endocrinocytes are subdivided into thyrotropocytes and gonadotropocytes.

Thyrotropocytes- these are cells with a large number of dense small granules stained with aldehyde fuchsin. They produce thyroid-stimulating hormone. With a lack of thyroid hormones in the body, thyrotropocytes are transformed into thyroidectomy cells with a large number of vacuoles. This increases the production of thyrotropin.

Gonadotropocytes- rounded cells in which the nucleus is mixed to the periphery. In the cytoplasm there is a macula - a bright spot where the Golgi complex is located. Small secretory granules contain gonadotropic hormones. With a lack of sex hormones in the body, castration cells appear in the adenohypophysis, which are characterized by an annular shape due to the presence of a large vacuole in the cytoplasm. Such a transformation of a gonadotropic cell is associated with its hyperfunction. There are two groups of gonadotropocytes that produce either follicle-stimulating or luteinizing hormones.

Corticotropocytes- These are cells of an irregular, sometimes process-shaped form. They are scattered throughout the anterior pituitary gland. In their cytoplasm, secretory granules are defined in the form of a vesicle with a dense core surrounded by a membrane. There is a light rim between the membrane and the core. Corticotropocytes produce ACTH (adrenocorticotropic hormone), or corticotropin, which activates the cells of the fascicular and reticular zones of the adrenal cortex.

Chromophobic endocrinocytes make up 50-60% of the total number of adenohypophysis cells. They are located in the middle of the trabeculae, are small in size, do not contain granules, their cytoplasm is weakly stained. This is a combined group of cells, among which are young chromophilic cells that have not yet accumulated secretory granules, mature chromophilic cells that have already secreted secretory granules, and reserve cambial cells.

Thus, in adenohypophysis a system of interacting cellular differons is found, which form the leading epithelial tissue of this part of the gland.

Average (intermediate) lobe of the pituitary gland in humans, it is poorly developed, accounting for 2% of the total volume of the pituitary gland. The epithelium in this lobe is homogeneous, the cells are rich in mucoid. In places there is a colloid. In the intermediate lobe, endocrinocytes produce melanocyte-stimulating hormone and lipotropic hormone. The first adapts the retina to vision at dusk, and also activates the adrenal cortex. Lipotropic hormone stimulates fat metabolism.

Influence of neuropeptides of the hypothalamus on endocrinocytes is carried out using the hypothalamic-adenohypophyseal circulation system (portal).

into the primary capillary network hypothalamic neuropeptides are secreted from the median eminence, which then enter the adenohypophysis and its secondary capillary network through the portal vein. The sinusoidal capillaries of the latter are located between the epithelial strands of endocrinocytes. So hypothalamic neuropeptides act on target cells of the adenohypophysis.

neurohypophysis has a neuroglial nature, is not a hormone-producing gland, but plays the role of a neurohemal formation in which hormones of some neurosecretory nuclei of the anterior hypothalamus accumulate. In the posterior lobe of the pituitary gland are numerous nerve fibers of the hypothalamic-pituitary tract. These are the nerve processes of the neurosecretory cells of the supraoptic and paraventricular nuclei of the hypothalamus. The neurons of these nuclei are capable of neurosecretion. Neurosecrete (transductor) is transported along the nerve processes to the posterior pituitary gland, where it is detected in the form of Herring's bodies. Axons of neurosecretory cells end in the neurohypophysis with neurovascular synapses, through which neurosecretion enters the blood.

neurosecret contains two hormones: antidiuretic (ADH), or vasopressin (it acts on nephrons, regulating the reverse absorption of water, and also constricts blood vessels, increasing blood pressure); oxytocin, which stimulates contraction of the smooth muscles of the uterus. A drug derived from the posterior pituitary gland is called pituitrin and is used to treat diabetes insipidus. The neurohypophysis contains neuroglial cells called pituitocytes.

Reactivity of the hypothalamic-pituitary system. Combat injuries and accompanying stresses lead to complex disorders of neuroendocrine regulation of homeostasis. At the same time, the neurosecretory cells of the hypothalamus increase the production of neurohormones. In the adenohypophysis, the number of chromophobic endocrinocytes decreases, which weakens the reparative processes in this organ. The number of basophilic endocrinocytes increases, and large vacuoles appear in acidophilic endocrinocytes, indicating their intense functioning. With prolonged radiation damage in the endocrine glands, destructive changes in secretory cells and inhibition of their function occur.

The adenohypophysis develops from the epithelium of the roof of the oral cavity, which is of ectodermal origin. At the 4th week of embryogenesis, an epithelial protrusion of this roof is formed in the form of Rathke's pocket. The proximal pocket is reduced, and the bottom of the 3rd ventricle protrudes towards it, from which the posterior lobe is formed. The anterior lobe is formed from the anterior wall of Rathke's pocket, and the intermediate lobe is formed from the posterior wall. The connective tissue of the pituitary gland is formed from the mesenchyme.

Functions of the pituitary gland:

regulation of the activity of adenohypophysis-dependent endocrine glands;

accumulation of vasopressin and oxytocin for the neurohormones of the hypothalamus;

regulation of pigment and fat metabolism;

synthesis of a hormone that regulates the growth of the body;

production of neuropeptides (endorphins).

Pituitary is a parenchymal organ with a weak development of the stroma. It consists of the adenohypophysis and the neurohypophysis. The adenohypophysis consists of three parts: anterior, intermediate lobes and tuberal part.

The anterior lobe consists of epithelial strands of trabeculae, between which fenestrated capillaries pass. The cells of the adenohypophysis are called adenocytes. In the anterior lobe there are 2 types.

Chromophilic adenocytes are located on the periphery of the trabeculae and contain secretion granules in the cytoplasm, which are intensely stained with dyes and are divided into: oxyphilic and basophilic.

Oxyphilic adenocytes are divided into two groups:

somatotropocytes produce growth hormone (somatotropin), which stimulates cell division in the body and its growth;

lactotropocytes produce lactotropic hormone (prolactin, mammotropin). This hormone enhances the growth of the mammary glands and their secretion of milk during pregnancy and after childbirth, and also promotes the formation of a corpus luteum in the ovary and the production of the hormone progesterone.

Basophilic adenocytes are also divided into two types:

thyrotropocytes - produce thyroid-stimulating hormone, this hormone stimulates the production of thyroid hormones by the thyroid gland;

gonadotropocytes are divided into two types - follitropocytes produce follicle-stimulating hormone, in the female body it stimulates the processes of oogenesis and the synthesis of female sex hormones estrogen. In the male body, follicle-stimulating hormone activates spermatogenesis. Luthropocytes produce luteotropic hormone, which in the female body stimulates the development of the corpus luteum and the secretion of progesterone.

Another group of chromophilic adenocytes is adrenocorticotropocytes. They lie in the center of the anterior lobe and produce adrenocorticotropic hormone, which stimulates the secretion of hormones by the fascicular and reticular zones of the adrenal cortex. Due to this, adrenocorticotropic hormone is involved in the adaptation of the body to starvation, injuries, and other types of stress.

Chromophobic cells are concentrated in the center of the trabeculae. This heterogeneous group of cells, in which the following varieties are distinguished:

immature, poorly differentiated cells that play the role of cambium for adenocytes;

secreted and therefore not stained at the moment chromophilic cells;

follicular-stellate cells - small in size, having small processes, with the help of which they are connected to each other and form a network. Their function is not clear.

The middle lobe consists of discontinuous strands of basophilic and chromophobic cells. There are cystic cavities lined with ciliated epithelium and containing a proteinaceous colloid that lacks hormones. Intermediate lobe adenocytes produce two hormones:

melanocyte-stimulating hormone, it regulates pigment metabolism, stimulates the production of melanin in the skin, adapts the retina to vision in the dark, activates the adrenal cortex;

lipotropin, which stimulates fat metabolism.

The tuberal zone is formed by a thin strand of epithelial cells surrounding the epiphyseal stalk. In the tuberal lobe, the pituitary portal veins run, connecting the primary capillary network of the medial eminence with the secondary capillary network of the adenohypophysis.

The posterior lobe or neurohypophysis has a neuroglial structure. Hormones are not produced in it, but only accumulate. Vasopressin and oxytocinneurohormones of the anterior hypothalamus enter here along the axons and are deposited in Hering's bodies. The neurohypophysis consists of ependymal cells - pituicites and axons of neurons of the paraventricular and supraoptic nuclei of the hypothalamus, as well as blood capillaries and Hering's bodies - extensions of axons of neurosecretory cells of the hypothalamus. Pituicites occupy up to 30% of the volume of the posterior lobe. They are spiky and form three-dimensional networks surrounding the axons and terminals of neurosecretory cells. The functions of pituicites are trophic and maintenance functions, as well as the regulation of neurosecretion release from axon terminals into hemocapillaries.

The blood supply of the adenohypophysis and neurohypophysis is isolated. The adenohypophysis receives its blood supply from the superior pituitary artery, which enters the medial hypothalamus and breaks up into the primary capillary network. On the capillaries of this network, axons of neurosecretory neurons of the mediobasal hypothalamus, which produce releasing factors, end in axovasal synapses. The capillaries of the primary capillary network and axons, together with synapses, form the first neurohemal organ of the pituitary gland. Then the capillaries are collected in the portal veins, which go to the anterior pituitary gland and there break up into a secondary capillary network of a fenestrated or sinusoidal type. Through it, releasing factors reach adenocytes and adenohypophysis hormones are also released here. These capillaries are collected in the anterior pituitary veins, which carry blood with adenohypophysis hormones to target organs. Since the capillaries of the adenohypophysis lie between two veins (portal and pituitary), they belong to the "wonderful" capillary network. The posterior lobe of the pituitary gland is supplied by the inferior pituitary artery. This artery breaks down to capillaries, on which axovasal synapses of neurosecretory neurons are formed - the second neurohemal organ of the pituitary gland. The capillaries are collected in the posterior pituitary veins.