117. Pituitary gland. Development, structure, blood supply and functions of individual lobes.

Development. The pituitary gland develops from: 1) the epithelium of the roof of the oral cavity, which itself develops from the ectoderm, and 2) the distal end of the funnel of the bottom of the 3rd ventricle. From the epithelium of the oral cavity (ectoderm), the adenohypophysis develops in the 4-5th week of embryogenesis. As a result of protrusion of the epithelium of the oral cavity towards the bottom of the 3rd ventricle, a pituitary pocket is formed. A funnel from the bottom of the 3rd ventricle grows towards the pituitary pocket. When the distal end of the funnel is aligned with the pituitary pocket, the anterior wall of this pocket thickens and turns into the anterior lobe, the posterior one into the intermediate part, and the distal end of the funnel into the posterior lobe of the pituitary gland.

Structure. The pituitary gland consists of the adenohypophysis (anterior lobe, intermediate lobe, tubular part) and the neurohypophysis (posterior lobe).

Anterior lobe hidden by a connective capsule, from which the layers of connective tissue, which make up the stroma of the organ, depart. The parenchyma of the organ is epithelial cells of adenocytes, which are recruited into cords.

Anterior lobe cells:

chromophilic (contain granules that stain with dyes)

basophilic (10%)

Gonadotropic

Thyrotropic

acidophilic

Somatotropic

Mammatropic

chromophobic (do not contain granules, therefore do not stain) (60%)

undifferentiated

differentiating

chromophilic mature

stellate follicular

corticotropic

Gonadotropic endocrinocytes - the largest cells have a round, sometimes angular, oval or round nucleus, shifted to the periphery, since the macula (spot) is located in the center of the cell, in which the Golgi complex and the cell center are located The cytoplasm contains well-developed granular EPS, mitochondria and Golgi complex, as well as basophilic granules with a diameter of 200-300 nm, consisting of glycoproteins and stained with aldehyde-fuchsin. It is believed that there are 2 types of gonadotropic endocrinocytes, some of which secrete follitropin, others lutropin.

Folliculotropic hormone (follitropin) in the male body it acts on the initial stage of spermatogenesis, in the female - on the growth of follicles and the release of estrogen in the gonads.

Lutropin stimulates the secretion of testosterone in the male gonads and the development and function of the corpus luteum in the female gonads.

Castration cells appear in the anterior lobe in cases where the sex glands produce an insufficient amount of sex hormones.

Thyrotropic endocrinocytes have an oval or elongated shape, an oval core. In their cytoplasm, the Golgi complex, granular EPS and mitochondria are well developed, they contain basophilic granules 80-150 nm in size, stained with aldehyde fuchsin. Thyrotropic endocrinocytes under the influence of thyroliberin produce thyrotropic hormone, which stimulates the secretion of thyroxine by the thyroid gland.

Thyroidectomy cells appear in the pituitary gland with a decrease in the function of the thyroid gland. In these cells, granular EPS hypertrophies, its cisterns expand, and the secretion of thyrotropic hormone increases. As a result of the expansion of the tubules and cisterns of the EPS, the cytoplasm of the cells acquires a cellular appearance.

Corticotropic endocrinocytes do not belong to either acidophilic or basophilic, they have an irregular shape, a lobular nucleus, their cytoplasm contains small granules. Under the influence of corticoliberins, produced in the nuclei of the mediobasal hypothalamus, these cells secrete corticotropic or adrenocorticotropic hormone (ACTH), which stimulates the function of the adrenal cortex.

Acidophilic endocrinocytes make up 35-40% and are subdivided into 2 varieties, which are usually round in shape, oval or round core located in the center. The cells have a well-developed synthetic apparatus, that is, the Golgi complex, granular EPS, mitochondria; the cytoplasm contains acidophilic granules.

Somatotropic endocrinocytes contain granules of oval or round shape with a diameter of 400-500 nm, produce growth hormone, which stimulates the growth of the body in childhood and adolescence. With hyperfunction of somatotropic cells, after growth is complete, acromegaly develops - a disease characterized by the appearance of a hump, an increase in the size of the tongue, lower jaw, hands and feet.

Mammotropic endocrinocytes contain elongated granules reaching sizes of 500-600 nm in women in labor and pregnant women. In non-breastfeeding mothers, the granules are reduced to 200 nm. These adenocytes secrete mammotropic hormone, or prolactin. Functions: 1) stimulates the synthesis of milk in the mammary glands; 2) stimulates the development of the corpus luteum in the ovaries and the secretion of progesterone.

Chromophobic (main) endocrinocytes make up about 60%, have a smaller size, do not contain stained granules, so their cytoplasm is not stained. The composition of chromophobic adenocytes includes 4 groups:

1) undifferentiated (perform a regenerative function);

2) differentiating, that is, they began to differentiate, but the differentiation did not end, only single granules appeared in the cytoplasm, therefore the cytoplasm is poorly stained;

3) chromophilic mature cells that have just released their secretory granules, therefore, have decreased in size, and the cytoplasm has lost the ability to stain;

4) stellate follicular cells, characterized by long processes spreading between endocrinocytes.

A group of such cells, facing each other with their apical surfaces, secretes secretions, resulting in the formation of pseudofollicles filled with colloid.

The intermediate part (lobe) of the adenohypophysis represented by the epithelium, located in several layers, localized between the anterior and posterior lobes of the pituitary gland. In the intermediate part, there are pseudofollicles containing a colloid-like mass. Functions: 1) secretion of melanotropic (melanocyte-stimulating) hormone, which regulates the exchange of melanin pigment; 2) lipotropic hormone that regulates lipid metabolism.

Tuberous part of the adenohypophysis (pars tuberalis) is located next to the pituitary pedicle, consists of intertwining cords of cubic epithelial cells, richly vascularized. Function little studied.

Posterior pituitary gland (neurohypophysis) represented mainly by ependymal glia. Neuroglial cells are called pituicites... In the neurohypophysis, hormones are not produced (this is a neurohemal organ). The axons of neurosecretory cells of the supraoptic and paraventricular nuclei enter the posterior lobe. These axons transport vasopressin and oxytocin to the posterior lobe and accumulate on the axon terminals near the blood vessels (it is a depot reservoir of these hormones). These savings are called accumulative bodies, or Herring bodies... As needed, hormones from these bodies enter the blood vessels.

Blood supply. It is called the hypothalamic-adenohypophyseal or pituitary system. The supplying pituitary arteries enter the medial eminence of the hypothalamus, where they branch into a network of capillaries (primary capillary plexus). These capillaries form loops and glomeruli, with which the terminals of the axons of neurosecretory cells of the adenohypophyseal zone of the hypothalamus contact. The capillaries of the primary plexus collect in the portal veins that run along the pituitary pedicle into the anterior lobe, where they break up into sinusoidal capillaries (secondary capillary network), branching between the trabeculae of the parenchyma of the gland. Finally, the sinusoids of the secondary capillary network are collected in the outflow veins, through which the blood, enriched with hormones and the anterior lobe, enters the general circulation.

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 gland, parathyroid glands. The adrenal group - it includes the adrenal glands (medulla and cortex), paraganglia and a group of cerebral appendages - the hypothalamus, pituitary gland and pineal gland.

The endocrine system is a functionally regulating system in which there are interorgan connections, and the work of this entire system has a hierarchical relationship with each other.

History of the study of the pituitary gland

Many scientists in different eras have been studying the brain and its appendages. 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, then secreting it into the blood.

In 1867 P.I. Interleaving was the first to make a morphological description of the pituitary gland, highlighting 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, the histology of which, when studying its secretory secretions, proved this, with the processes taking place 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 dura mater, which serves as a diaphragm for the pituitary gland. The pituitary gland passes through the opening in the diaphragm, connecting it to the hypothalamus.

It has a reddish-gray color, is covered with a fibrous capsule, and its weight is 0.5-0.6 g. Its size and weight vary depending on gender, development of diseases and many other factors.

Pituitary embryogenesis

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

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

The 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, an intermediate and a tuberal part.

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

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

On the periphery of the trabeculae are endocrinocytes containing 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 are stained with eosin. It is an acidic dye. Their total number is 30-35%. The cells are round in shape with a nucleus located in the center, with an adjacent Golgi complex. 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 anterior pituitary gland in acidophilic cells during their staining, the species involved in the production of hormones were identified - somatotropocytes, lactotropocytes.

Acidophilic cells

Acidophilic cells include cells that are stained 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 parts of the trabeculae, have a spherical 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.

Basophilic cells

These cells are relatively larger than acidophilic cells, and their volume occupies only 4-10% in the anterior part of the adenohypophysis. By their structure, these are glycoproteins, which are a matrix for protein biosynthesis. Cells are stained in the histology of the pituitary gland with a drug 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 have a diameter of 200 nm. 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 men and women.

Propioomelanocortin

Large secreted glycoprotein measuring 30 kilodaltons. It is a 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 belong to the 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 divide 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 secreted these granules. Depleted or lacking granules are quite specialized cells.

Chromophobic cells also differentiate into small in size with long processes forming a broad-plaited network, follicle-stellate cells. Their processes pass through endocrinacytes and are located on sinusoidal capillaries. They can form follicular formations and accumulate glycoprotein secretions.

The intermediate and tubular parts of the adenohypophysis

The cells of the intermediate part are weakly basophilic and accumulate a glycoprotein secretion. 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 tubular part is formed by epithelial strands that extend into the anterior part. It is adjacent to the pituitary pedicle, which is in contact with the medial elevation of the hypothalamus from its lower surface.

Neurohypophysis

The posterior lobe of the pituitary gland consists of neuroglia, the cells of which are spindle-shaped or process-shaped. It includes nerve fibers of the anterior zone of the hypothalamus, which are formed by the neurosecretory cells of the axons of the paraventricular and supraoptic nuclei. Oxytocin and vasopressin are formed in these nuclei, which enter and accumulate in the pituitary gland.

Pituitary adenoma

A benign mass in the anterior lobe of the pituitary gland of the glandular tissue. This formation is formed as a result of hyperplasia - this is the uncontrolled development of a tumor cell.

The histology of a pituitary adenoma is used in the study of the causes of the disease and to determine its variety according to the cellular structures of the structure and anatomical damage to organ growth. Adenoma can affect the endocrinocytes of basophilic cells, chromophobic, and develop on several cell structures. Also, it can have different sizes, and this is reflected in its name. For example, microadenoma, prolactinoma and its other types.

Animal pituitary gland

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

Staining of microscopic biopsy fragments of the cat's pituitary gland with a drug during histology at multiple magnification allows one to see the pink granularity of acidophilic endocrinocytes of the anterior lobe. These are large cells. The posterior lobe is weakly stained, 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 the accumulation of scientific knowledge and experience, which will help explain the processes occurring in the body.

Several lobes are distinguished in the pituitary gland: adenohypophysis, neurohypophysis.

In the adenohypophysis, the anterior, middle (or intermediate) and tubular parts are distinguished. The anterior part has a trabecular structure. Trabeculae, strongly branching, are woven into a narrow-looped net. The spaces between them are filled with loose connective tissue, through which numerous sinusoidal capillaries pass.

Chromophilic cells are divided into basophilic and acidophilic. Basophilic cells, or basophils, produce glycoprotein hormones, and their secretory granules on histological preparations are stained with basic paints.

Among them, there are two main types: gonadotropic and thyrotropic.

Some of the gonadotropic cells produce follicle-stimulating hormone (follitropin), while others are attributed to the production of luteinizing hormone (lutropin).

Thyrotropic hormone (thyrotropin) - has an irregular or angular shape. With a deficiency in the body of the thyroid hormone, thyrotropin production increases, and thyrotropic cells are partially transformed into thyroidectomy cells, which are characterized by larger sizes and a significant expansion of the endoplasmic reticulum cisterns, as a result of which the cytoplasm takes on the appearance of a coarse-cellular foam. In these vacuoles, aldehyde-fuchsinophilic granules are found, which are larger than the secretory granules of the original thyrotropic cells.

For acidophilic cells, or acidophiles, large dense granules are characteristic, stained on preparations with acidic dyes. Acidophilic cells are also divided into two types: somatotropic, or somatotropic cells, producing growth hormone (somatotropin), and mammotropic, or mammotropocytes, producing lactotropic hormone (prolactin).

Corticotropic cells in the anterior pituitary gland produce adrenocorticotropic hormone (ACTH, or corticotropin), which activates the adrenal cortex.

The tuberous part is the section of the adenohypophyseal parenchyma adjacent to the pituitary pedicle and in contact with the lower surface of the medial eminence of the hypothalamus.

The posterior lobe of the pituitary gland (neurohypophysis) is formed by the neuroglia. The glial cells of this lobe are mainly represented by small process or vein-shaped cells - pituicites. The posterior lobe includes the axons of the neurosecretory cells of the supraoptic and paraventricular nuclei of the anterior hypothalamus.

Innervation. The pituitary gland, as well as the hypothalamus and pineal gland, receive nerve fibers from the cervical ganglia (mainly from the upper) of the sympathetic trunk.

Blood supply. The superior pituitary arteries enter the medial eminence, where they disintegrate into the primary capillary network.

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 the group of cerebral appendages - the hypothalamus, pituitary and pineal gland.

It is a functionally regulating system in which interorgan connections exist, and the work of this entire system has a hierarchical relationship between each other.

History of the study of the pituitary gland

Many scientists in different eras have been studying the brain and its appendages. 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, then secreting it into the blood.

In 1867 P.I. Interleaving was the first to make a morphological description of the pituitary gland, highlighting 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, the histology of which, when studying its secretory secretions, proved this, with the processes taking place 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 dura mater, which serves as a diaphragm for the pituitary gland. The pituitary gland passes through the opening in the diaphragm, connecting it to the hypothalamus.

It has a reddish-gray color, is covered with a fibrous capsule, and its weight is 0.5-0.6 g. Its size and weight vary depending on gender, development of diseases and many other factors.

Pituitary embryogenesis

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

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

The 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, an intermediate and a tuberal part.

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

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

On the periphery of the trabeculae are endocrinocytes containing 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 are stained with eosin. It is an acidic dye. Their total number is 30-35%. The cells are round in shape with a nucleus located in the center, with an adjacent Golgi complex. 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 anterior pituitary gland in acidophilic cells during their staining, the species involved in the production of hormones were identified - somatotropocytes, lactotropocytes.

Acidophilic cells

Acidophilic cells include cells that are stained 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 parts of the trabeculae, have a spherical 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.

Basophilic cells

These cells are relatively larger than acidophilic cells, and their volume occupies only 4-10% in the anterior part of the adenohypophysis. By their structure, these are glycoproteins, which are a matrix for protein biosynthesis. Cells are stained in the histology of the pituitary gland with a drug 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 have a diameter of 200 nm. 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 men and women.

Propioomelanocortin

Large secreted glycoprotein measuring 30 kilodaltons. It is a 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 belong to the 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 divide 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 secreted these granules. Depleted or lacking granules are quite specialized cells.

Chromophobic cells also differentiate into small in size with long processes forming a broad-plaited network, follicle-stellate cells. Their processes pass through endocrinacytes and are located on sinusoidal capillaries. They can form follicular formations and accumulate glycoprotein secretions.

The intermediate and tubular parts of the adenohypophysis

The cells of the intermediate part are weakly basophilic and accumulate a glycoprotein secretion. 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 tubular part is formed by epithelial strands that extend into the anterior part. It is adjacent to the pituitary pedicle, which is in contact with the medial elevation of the hypothalamus from its lower surface.

Neurohypophysis

The posterior lobe of the pituitary gland consists of which they are spindle-shaped or process-shaped. It includes nerve fibers of the anterior zone of the hypothalamus, which are formed by the neurosecretory cells of the axons of the paraventricular and supraoptic nuclei. Oxytocin and vasopressin are formed in these nuclei, which enter and accumulate in the pituitary gland.

Pituitary adenoma

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

Histology of a pituitary adenoma is used in the study of the causes of the disease and to determine its type and anatomical damage to organ growth. Adenoma can affect the endocrinocytes of basophilic cells, chromophobic, and develop on several cell structures. Also, it can have different sizes, and this is reflected in its name. For example, microadenoma, prolactinoma and its other types.

Animal pituitary gland

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

Staining of microscopic biopsy fragments of the cat's pituitary gland with a drug during histology at multiple magnification allows one to see the pink granularity of acidophilic endocrinocytes of the anterior lobe. These are large cells. The posterior lobe is weakly stained, 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 the accumulation of scientific knowledge and experience, which will help explain the processes occurring in the body.

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

2. Classification of hematopoietic organs.

3. General morphological and functional characteristics of the hematopoietic organs. The concept of a specific microenvironment in the organs of hematopoiesis.

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

5. Thymus is the central organ of lymphocytopoiesis. Development, structure and function. Age-related and accidental thymic involution.

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 the hematopoietic tissue; primitive cells of hemolymph (amoebocytes) are diffusely dispersed 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 the reticular tissue, there are sinusoidal capillaries.

3. In cartilaginous and teleost fishes, along with foci of hematopoiesis, separate OCT appear in the wall of the digestive tube - the spleen and thymus; there are CT foci in the gonads, interrenal corpuscles, and even in the epicardium.

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

5. In amphibians, organ separation of myelopoiesis and lymphopoiesis occurs.

6. In reptiles and birds, there is a clear organ separation of myeloid and lymphoid tissues; 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.The lymphoid organs proper (along the lymphatic vessels - lymph nodes).

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

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

General morphological and functional characteristics of OCT

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

1. Source of development - all OCT are laid from the mesenchyme; an exception is the thymus - it develops from the epithelium of the 3-4th branchial pockets.

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

3. OCT blood supply - abundant blood supply; have sinusoidal hemocapillaries (diameter 20 and more microns; there are large gaps, pores between endotheliocytes, the basement membrane is not continuous - in places it is absent; blood flows slowly).

The role of reticular tissue in OCT

You will remember that RT consists of cells (reticular cells, in 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. Trophism 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 is the central OCT, where both myelopoiesis and lymphocytopoiesis take place. CCM in the embryonic period is laid from the mesenchyme at the 2nd month, by the 4th month it becomes the center of hematopoiesis. CCM is a tissue of a semi-liquid consistency, dark red in color due to the high content of red blood cells. A small amount of CCM for research can be obtained by puncture of the sternum or iliac crest.

The stroma of the CCM is the reticular tissue, abundantly penetrated by sinusoidal hemocapillaries. In the loops of the reticular tissue, islets or colonies of maturing blood cells are located:

1. Erythroid cells in their islets-colonies are grouped around macrophages loaded with iron, obtained from old erythrocytes that have died in the spleen. Macrophages in CCM transfer iron to erythroid cells, which is necessary for their synthesis of hemoglobin.

2. Separate islets-colonies around sinusoidal hemocapillaries are lymphocytes, granulocytes, monocytes, megakaryocytes. Islets of different sprouts are interspersed with each other and create a mosaic picture.

Ripe blood cells penetrate through the walls into sinusoidal gamocapillaries and are carried away by the bloodstream. The passage of cells through the walls of the vessels is facilitated by the increased permeability of sinusoidal hemocapillaries (cracks, 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 outflow vessels is greater than the diameter of the outflow vessels, which also leads to an increase in pressure.

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

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

TIMUS is the central organ of lymphocytopoiesis and immunogenesis. The thymus is formed at the beginning of the 2nd month of embryonic development from the epithelium of 3-4 branchial pockets as an exocrine gland. Subsequently, the cord connecting the gland with the epithelium of the branchial pockets undergoes reverse development. At the end of the 2nd month, the organ is colonized by lymphocytes.

The structure of the thymus - on the outside, the organ is covered with a sdt capsule, from which partitions from the loose sdt extend inward and divide the organ into lobules. The basis of the thymus parenchyma is the reticular epithelium: epithelial cells are erect, 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, senescent epithelial cells form layered thymic bodies or Gassal's bodies - concentrically layered epithelial cells with vacuoles, keratin granules and fibrillar fibers in the cytoplasm. The number and size of Hassal's little bodies increases with age. Retinal epithelium function:

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 the regulation of 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 - a supporting frame for thymocytes.

In the loops of the reticular epithelium, lymphocytes (thymocytes) are located, especially there are a lot 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, therefore this part is lighter and is called the brain part of the lobule. In the cortex of the thymus, T-lymphocytes are "trained"; they acquire the ability to recognize "theirs" or "others". 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 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 alien antigens. That is why, in the cortical substance, along with increased reproduction, we also see mass death of lymphocytes. Thus, in the thymus, from the precursors of T-lymphocytes, subpopulations of T-lymphocytes are formed, 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 thymic involution (AIT): Accidental thymic involution can be caused by 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 and normal, non-dead lymphocytes), proliferation of the epithelial base of the thymus and increased synthesis of thymosin, erasure of the border between the cortical and cerebral parts. Biological value of AIT:

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

2. 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 focus and is aimed at preventing possible autoaggression.

3. The proliferation 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.