Histology of the central organs of the endocrine system. Endocrine system Histological structure of the adenohypophysis
32. Pituitary gland
The pituitary gland has several lobes: adenohypophysis, neurohypophysis.
The adenohypophysis is divided into anterior, middle (or intermediate) and tuberal parts. The anterior part has a trabecular structure. The trabeculae, strongly branching, are woven into a narrow-loop network. 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 are stained with basic dyes on histological preparations.
Among them, there are two main types: gonadotropic and thyrotropic.
Some of the gonadotropic cells produce follicle-stimulating hormone (follitropin), while others are responsible for the production of luteinizing hormone (lutropin).
Thyrotropic hormone (thyrotropin) – has an irregular or angular shape. When there is insufficiency of thyroid hormone in the body, the production of thyrotropin increases, and thyrotropocytes 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 coarse foam. In these vacuoles aldehyde-fuchsinophilic granules are found, larger than the secretory granules of the original thyrotropocytes.
Acidophilic cells, or acidophils, are characterized by large dense granules that are stained in preparations with acidic dyes. Acidophilic cells are also divided into two types: somatotropic, or somatotropocytes, 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 tuberal part is a section of the adenohypophyseal parenchyma adjacent to the pituitary stalk 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 neuroglia. The glial cells of this lobe are represented predominantly by small branched or spindle-shaped cells - pituicytes. The posterior lobe includes the axons of 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 break up into the primary capillary network.
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 infundibulum of the floor of the 3rd ventricle. The adenohypophysis develops from the epithelium of the oral cavity (ectoderm) at 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 pouch is formed. A funnel grows towards the pituitary recess from the bottom of the 3rd ventricle. When the distal end of the infundibulum is aligned with the pituitary recess, the anterior wall of this recess thickens and becomes the anterior lobe, the posterior wall becomes the intermediate part, and the distal end of the infundibulum becomes the posterior lobe of the pituitary gland.
Structure. The pituitary gland consists of the adenohypophysis (anterior lobe, intermediate lobe, tuberal part) and the neurohypophysis (posterior lobe).
Anterior lobe hidden by a connective capsule, from which extend layers of connective tissue that make up the stroma of the organ. The parenchyma of the organ is epithelial cells called adenocytes, which are arranged in cords.
Cells of the anterior lobe:
chromophilic (contain granules that are colored with dyes)
basophilic (10%)
Gonadotropic
Thyrotropic
acidophilic
Somatotropic
Mammatropic
chromophobic (does not contain granules, therefore they are not colored) (60%)
undifferentiated
differentiating
chromophilic mature
stellate-follicular
corticotropic
Gonadotropic endocrinocytes- the largest cells have a round, sometimes angular shape, an oval or round nucleus, shifted to the periphery, since in the center of the cell there is a macula (spot), in which the Golgi complex and the cell center are located. In the cytoplasm, granular EPS, mitochondria and the Golgi complex are well developed, 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 body - on the growth of follicles and the release of estrogens 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 gonads produce insufficient amounts of sex hormones.
Thyrotropic endocrinocytes have an oval or elongated shape, an oval core. Their cytoplasm has a well-developed Golgi complex, granular ER and mitochondria, and contains basophilic granules 80-150 nm in size, stained with aldehyde fuchsin. Thyrotropic endocrinocytes, under the influence of thyroliberin, produce thyrotropic hormone, which stimulates the release of thyroxine by the thyroid gland.
Thyroidectomy cells appear in the pituitary gland when the function of the thyroid gland decreases. In these cells, granular EPS hypertrophies, its cisterns expand, and the secretion of thyroid-stimulating hormone increases. As a result of the expansion of the tubules and EPS cisterns, the cytoplasm of the cells acquires a cellular appearance.
Corticotropic endocrinocytes They are neither acidophilic nor basophilic; they have an irregular shape, a lobed nucleus, and 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 divided into 2 varieties, which are usually round in shape, with an oval or round core located in the center. The cells have a well-developed synthetic apparatus, i.e. the Golgi complex, granular EPS, mitochondria; the cytoplasm contains acidophilic granules.
Somatotropic endocrinocytes contain oval or round granules with a diameter of 400-500 nm, produce somatotropic hormone, which stimulates body growth in childhood and adolescence. With hyperfunction of somatotropic cells after completion of growth, 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 parturient and pregnant women. In non-nursing mothers, the granules are reduced to 200 nm. These adenocytes secrete mammotropic hormone, or prolactin. Functions: 1) stimulates milk synthesis 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%, are smaller in size, do not contain stainable granules, so their cytoplasm is not stained. The composition of chromophobe adenocytes includes 4 groups:
1) undifferentiated (perform a regenerative function);
2) differentiating, i.e. they began to differentiate, but differentiation did not end, only single granules appeared in the cytoplasm, therefore the cytoplasm is weakly stained;
3) chromophilic mature cells that have just released their secretory granules and 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, with their apical surfaces facing each other, secretes a secretion, resulting in the formation of pseudofollicles filled with colloid.
Intermediate part (lobe) of the adenohypophysis It is represented by 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 metabolism of melanin pigment; 2) lipotropic hormone that regulates lipid metabolism.
Tuberal part of the adenohypophysis(pars tuberalis) is located next to the pituitary stalk, consists of intertwined strands of cubic-shaped epithelial cells, and is richly vascularized. Function little studied.
Posterior pituitary gland (neurohypophysis) represented mainly by ependymal glia. Neuroglial cells are called pituicytes. The neurohypophysis does not produce hormones (it is a neurohemal organ). The posterior lobe receives axons from the neurosecretory cells of the supraoptic and paraventricular nuclei. Vasopressin and oxytocin are transported along these axons to the posterior lobe and accumulate on the axon terminals near the blood vessels (it is a depot reservoir for these hormones). These savings are called storage bodies, or Herring's bodies. As needed, hormones flow from these bodies into the blood vessels.
Blood supply. Called the hypothalamic-adenopituitary or pormal system. The afferent 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 axon terminals of the neurosecretory cells of the adenopituitary zone of the hypothalamus contact. The capillaries of the primary plexus are collected in portal veins, running along the pituitary stalk into the anterior lobe, where they break up into sinusoidal capillaries (secondary capillary network), branching between the trabeculae of the gland parenchyma. Finally, the sinusoids of the secondary capillary network are collected in the efferent veins, through which blood, enriched with the hormones of the anterior lobe, enters the general circulation.
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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 forms in the form of Rathke's pouch. The proximal part of the pouch 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 pouch, and the intermediate lobe is formed from the posterior wall. The connective tissue of the pituitary gland is formed from mesenchyme.
Functions of the pituitary gland:
regulation of the activity of the adenohypophyseal-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 body growth;
production of neuropeptides (endorphins).
Pituitary It is a parenchymal organ with weak stroma development. It consists of the adenohypophysis and neurohypophysis. The adenohypophysis includes three parts: the anterior, intermediate lobes and the tuberal part.
The anterior lobe consists of epithelial cords of trabeculae, between which fenestrated capillaries pass. The cells of the adenohypophysis are called adenocytes. There are 2 types of them in the anterior lobe.
Chromophilic adenocytes are located along the periphery of 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 the corpus luteum in the ovary and its 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 its 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 zona fasciculata and reticularis of the adrenal cortex. Thanks to this, adrenocorticotropic hormone is involved in the body’s adaptation to starvation, injury, and other types of stress.
Chromophobe cells are concentrated in the center of the trabeculae. This is a heterogeneous group of cells, in which the following varieties are distinguished:
immature, poorly differentiated cells that play the role of cambium for adenocytes;
chromophilic cells that have secreted a secret and therefore are not stained at the moment;
follicular stellate cells are small in size, having small processes with which they connect to each other and form a network. Their function is not clear.
The middle lobe consists of discontinuous strands of basophilic and chromophobe cells. There are cystic cavities lined with ciliated epithelium and containing a colloid of a protein nature, in which there are no hormones. Adenocytes of the intermediate lobe 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 cord of epithelial cells surrounding the epiphyseal stalk. The pituitary portal veins pass through the tuberal lobe, 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 oxytocin neurohormones of the anterior hypothalamus enter here along axons and are deposited in Hering's bodies. The neurohypophysis consists of ependymal cells - pituicytes and axons of neurons of the paraventricular and supraoptic nuclei of the hypothalamus, as well as blood capillaries and Hering's bodies - extensions of the axons of neurosecretory cells of the hypothalamus. Pituycytes occupy up to 30% of the volume of the posterior lobe. They have a branched shape and form three-dimensional networks, surrounding the axons and terminals of neurosecretory cells. The functions of pituicytes are trophic and supportive functions, as well as regulation of the release of neurosecretion from axon terminals into hemocapillaries.
The blood supply to the adenohypophysis and neurohypophysis is isolated. The adenohypophysis is supplied with blood from the superior pituitary artery, which enters the medial eminence of the hypothalamus and breaks up into the primary capillary network. On the capillaries of this network, the axons of neurosecretory neurons of the mediobasal hypothalamus, which produce releasing factors, end at axovasal synapses. The capillaries of the primary capillary network and axons, together with synapses, form the first neurohemal organ of the pituitary gland. The capillaries then collect into portal veins, which go to the anterior lobe of the pituitary gland and there break up into a secondary capillary network of fenestrated or sinusoidal type. Through it, releasing factors reach adenocytes and adenohypophysis hormones are released here. These capillaries collect in the anterior pituitary veins, which carry blood with adenohypophysial hormones to the target organs. Since the capillaries of the adenohypophysis lie between two veins (portal and pituitary), they belong to the “miraculous” capillary network. The posterior lobe of the pituitary gland is supplied by the inferior pituitary artery. This artery breaks down into capillaries, on which axovasal synapses of neurosecretory neurons are formed - the second neurohemal organ of the pituitary gland. The capillaries collect in the posterior pituitary veins.
Endocrine organs are classified according to their origin, histogenesis and histological origin into three groups. The branchiogenic group is formed from the pharyngeal pouches - these are the thyroid gland, parathyroid glands. The adrenal gland group - it includes the adrenal glands (medulla and cortex), paraganglia and a group of brain appendages - these are the hypothalamus, pituitary gland and pineal gland.
The endocrine system is a functionally regulating system in which interorgan connections exist, 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 studied 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 participates in the formation of cerebrospinal fluid. Another theory stated that it absorbs cerebrospinal fluid, then secreting 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 Flesch, studying microscopic fragments of the pituitary gland, discovered chromophobe 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 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 sella turcica of the sphenoid bone and consists of a body and a stalk. From above, the sella turcica covers the spur of the dura mater, which serves as a diaphragm for the pituitary gland. The pituitary stalk passes through the 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 depending on gender, disease progression, 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 formation of the pituitary gland begins in the fourth week of embryonic development, and for its formation two rudiments are used, which are directed towards each other. The anterior lobe of the pituitary gland is formed from the pituitary recess, which develops from the oral bay of the ectoderm, and the posterior lobe from the medullary recess, formed by the protrusion of the bottom 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.
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 part.
The anterior part is formed by trabeculae - these are branched cords 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. The glandular cells of the trabecula, 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.
Along the periphery of the trabeculae there are endocrinocytes containing in their cytoplasm secretory substances that stain and are called chromophilic. These cells are divided into two types: acidophilic and basophilic.
Acidophilic adrenocytes stain with eosin. This is an acidic dye. Their total number is 30-35%. The cells are round in shape with the nucleus located in the center, with the Golgi complex adjacent to it. The endoplasmic reticulum is well developed and has a granular structure. Acidophilic cells undergo intensive protein biosynthesis and hormone formation.
In the process of histology of the anterior pituitary gland, in acidophilic cells, when staining them, varieties involved in the production of hormones were identified - somatotropocytes, lactotropocytes.
Acidophilus cells
Acidophilic cells include cells that are stained with acidic dyes 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 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 acidophilus cells, and their volume occupies only 4-10% in the anterior part of the adenohypophysis. By their structure, these are glycoproteins, which are the matrix for protein biosynthesis. Cells in the histology of the pituitary gland are stained with a preparation that is determined mainly by aldehyde-fuchsin. Their main cells are thyrocytes 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 the enlargement of 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. In the histology of the pituitary gland, they can be found 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.
Propiomelanocortin
A large secreted glycoprotein measuring 30 kilodaltons. It is propioomelanocortin, which, after its cleavage, 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 makes up 15-20% of the anterior pituitary gland; they belong to basophilic cells.
Chromophobe cells
Melanocyte-stimulating and lipotropic hormones are secreted by chromophobe cells. Chromophobic cells are difficult to stain or cannot be stained 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. Cells that are depleted or lack granules are quite specialized cells.
Chromophobe cells also differentiate into small-sized cells with long processes that form a broadly woven network, follicle-stellate cells. Their processes pass through endocrinocytes and are located on sinusoidal capillaries. They can form follicular formations and accumulate glycoprotein secretions.
Intermediate and tuberal parts of the adenohypophysis
The cells of the intermediate part are weakly basophilic and accumulate glycoprotein secretions. 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 to 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 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 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 of glandular tissue. This formation is formed as a result of hyperplasia - this is the uncontrolled development of a tumor cell. 
The histology of pituitary adenoma is used in studying the causes of the disease and to determine its type based on the cellular structures of the structure and the anatomical damage to the growth of the organ. Adenoma can affect endocrinocytes of basophilic cells, chromophobe cells 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 cat's pituitary gland is spherical and measures 5x5x2 mm. Histology of the cat's 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 a stalk that is somewhat shorter and thicker in its posterior part, connects to the hypothalamus. 
Staining microscopic biopsy fragments of the cat pituitary gland with a preparation for 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 slightly stained, has a rounded shape and consists of pituicytes and nerve fibers.
Studying the histology of the pituitary gland in humans and animals allows us to accumulate scientific knowledge and experience, which will help explain the processes occurring in the body.
Material taken from the site www.hystology.ru
The pituitary gland is a component of the body’s unified hypothalamophyseal system. Produces hormones that regulate the function of many endocrine glands and communicates with the central nervous system. It is located in the pituitary fossa of the sella turcica of the sphenoid bone of the skull; It has a bean-shaped shape and very little mass. So, in cattle it is about 4 g, and in pigs it is less - 0.4 g.
The pituitary gland develops from two embryonic rudiments growing towards each other. The first rudiment - the pituitary pouch - is formed from the roof of the primary oral cavity and is directed towards the brain. This is an epithelial rudiment from which the adenohypophysis subsequently develops.
The second rudiment is a protrusion of the bottom of the cerebral ventricle, therefore it is a brain pocket and the neurohypophysis is formed from it (Fig. 217).
Embryogenesis determined the structure of the organ - the pituitary gland consists of two lobes: the adenohypophysis and the neurohypophysis (Fig. 218, 219).
The adenohypophysis consists of the anterior, intermediate and tuberal parts. The anterior part is built of epithelial cells - adenocytes, forming cords (trabeculae) and delimited by sinusoidal capillaries of the secondary vascular network (color table VII - A- A). The primary vascular network is located in the medial eminence.
Rice. 217. Development of the pituitary gland:
A - early and B - later stages; a - walls of the neural tube; b - walls of the brain bladder; V- epithelium of the oral bay; G- chord; d - intestinal tube; e - mesenchyme; and - pituitary recess; his h- front and And- back walls; k - rudiment of the posterior part.
Rice. 218. Structure of the pituitary gland:
1 - front, 2 - intermediate, 3 - tuberal and 4 - back; 5 - funnel; 6 - hypothalamus.
Rice. 219. Scheme of the medial section of the pituitary gland of domestic animals:
a - horses; b - cattle; c - pigs; g - dogs; d- cats (according to Trautman and Fibiger).
The connective tissue stroma of the adenohypophysis is poorly developed.
Adenocytes perceive dyes differently: cells that stain well are called chromophilic, and cells that stain poorly are called chromophobic (b). Chromophilic adenocytes can perceive either acidic or basic dyes, therefore the former are called acidophilic (b), the latter - basophilic (d).
Acidophilic cells make up 30 - 35% of all cells of the anterior pituitary gland. They have a round or oval shape, larger than chromophobe and smaller than basophilic adenocytes. The cytoplasm of acidophilus contains granules that stain with eosin; the nucleus is located in the center of the cell. It is adjacent to the Golgi complex, a small number of large mitochondria, and a well-developed granular endoplasmic reticulum, which indicates intensive protein synthesis.
Due to the different hormone-producing function and structure, cytoplasmic granularity, three types of acidophilic adenocytes are distinguished: somatotropocytes, lactotropocytes, corticotropocytes. Somatotropocytes produce somatotropic hormone, which stimulates the growth of tissues and the entire organism as a whole. Lactotropocytes produce prolactin (lactotropic hormone), which regulates the lactation process and the functional state of the corpus luteum of the ovary. Corticotropocytes produce corticotropin, which increases the hormone-forming function of the adrenal cortex.
Secretory granules of somatotropocytes are spherical in shape, with a diameter of 200 to 400 nm (Fig. 220). Lactotropocytes have larger oval-shaped secretory granules with a length of 500 - 600 nm and a width of 100 - 120 nm. The secretory granules of corticotropocytes are covered on the outside with a vesicular membrane with a dense core.
Basophilic adenocytes make up 4 - 10% of all cells of the anterior pituitary gland. These are the largest cells of the adenohypophysis. Their secretory granules are glycoprotein in nature and are therefore stained with basic dyes. There are two types of these cells: gonadotropic and thyrotropic. Gonadotropic cells produce follicle-stimulating hormone, which regulates the development of female and male germ cells, the secretion of the female genital organs and luteinizing hormone, which stimulates the growth and development of the corpus luteum in the ovaries and
Rice. 220. Somatotropocyte of the anterior lobe of the adenohypophysis (electron micrograph):
1 - granular endoplasmic reticulum; 2 - Golgi complex; 3 - Forming secretion granules; 4 - core; 5 - mature secretion granules; 6 - ? ;mitochondrion (according to Strizhkov).
Rice. 221. Gonadotropocyte of the anterior lobe of the adenohypophysis:
1 - core; 2 - Golgi complex; 3 - secretory granules; 4 - storage granules; 5 - mitochondria; 6 - tanks of granular endoplasmic reticulum.
interstitial cells in the testes (Fig. 221). The macula is located in the central zone of the gonadotropic basophil. This is an expanded cavity of the Golgi complex, pushing the nucleus, numerous small mitochondria, and endoplasmic reticulum membranes to the cell periphery. Basophilic gonadotropocytes contain granules equal to about 200 - 300 nm in diameter.
With a lack of sex hormones in the body, the diameter of the grain increases. After castration of animals, basophilic gonadotropocytes turn into castration cells: a large vacuole occupies the entire central part of the cell. The latter takes on a ring shape.
Thyroid-stimulating basophils (Fig. 222) are angular cells with fine (80 - 150 nm) granularity filling the entire cytoplasm. If
Rice. 222. Thyrotropocyte of the anterior lobe of the adenohypophysis (electron micrograph):
1 - core; 2 - secretory granules; 3 - somatotropocyte (according to Dolan and Seloshi).
When the body lacks thyroid hormones, thyroidectomy cells develop. They are increased in size, with expanded cisterns of the endoplasmic reticulum, so the cytoplasm has a cellular appearance, larger secretion granules,
Chromophobe cells make up 60 - 70% of all cells of the anterior pituitary gland. This is a combined group, since it includes cells of different importance: cambial, cells at different stages of differentiation; have not yet accumulated specific grain size; cells that secrete the secretion. Acidophilic and basophilic adenocytes subsequently develop from cambial cells.
The intermediate part of the adenohypophysis is represented by several rows of weakly basophilic cells. Produced
By adenocytes, the secretion accumulates in the spaces between the cells, which contributes to the formation of follicle-like structures. The cells of the intermediate part of the adenohypophysis are polygonal in shape and contain small glycoprotein granules measuring 200 - 300 nm. In the intermediate zone, melanotropin, which regulates pigment metabolism, and lipotropin, a stimulator of fat metabolism, are synthesized.
The tuberal part of the adenohypophysis is similar in structure to the intermediate part. It is adjacent to the pituitary stalk and medial eminence. The cells of this zone are characterized by weak basophilia and trabecular arrangement. The function of the tuberal part has not been fully elucidated.
It was said above that the hormone-producing function of the adenohypophysis is regulated by the hypothalamus, with which it forms a single hypothalamoadenopituitary system. Morphofunctionally, this connection is manifested in the following: the superior pituitary artery in the medial eminence forms the primary capillary network. Axons of small neurosecretory cells of the nuclei of the mediobasal hypothalamus form axovascular synapses on the vessels of the primary capillary network. Neurohormones produced by these neurosecretory cells move along their axons to the medial eminence. Here they accumulate and then enter the capillaries of the primary vascular network through axovascular synapses. The latter collect in portal veins, which are directed along the pituitary stalk to the adenohypophysis. Here again they break up and form a secondary capillary network. The sinusoidal capillaries of this network intertwine the trabeculae of secreting adenocytes.
The blood flowing through the veins from the secondary vascular network contains adenohypophyseal hormones, which, through the general blood flow, that is, in a humoral way, regulate the functions of the peripheral endocrine glands.
Neurohypophysis(posterior lobe) develops from the medullary pouch, so it is built from neuroglia. Its cells are fusiform or process-shaped pituicytes. The processes of pituicytes are in contact with blood vessels. The posterior lobe includes large bundles of nerve fibers formed by the axons of neurosecretory cells of the paraventricular and supraoptic nuclei of the anterior zone of the hypothalamus. The neurosecretion formed by these cells moves along the axons into the neurohypophysis in the form of secretory drops. Here they settle in the form of storage bodies, or terminals, which are in contact with the capillaries.
Consequently, the hormones of the neurohypophysis - oxytocin and vasopressin - are synthesized not by the structures of the neurohypophysis, but in the paraventricular and supraoptic nuclei. Then, as mentioned above, hormones travel along nerve fibers to the neurohypophysis, where they accumulate and from where they enter the bloodstream. Therefore, the neurohypophysis and hypothalamus are closely connected and form a single hypothalamic-neurohypophyseal system.
Oxytocin stimulates the function of the smooth muscles of the uterus, promotes the secretion of uterine glands; during childbirth causes a strong contraction of the muscular lining of the uterine wall; regulates the contraction of the muscle elements of the mammary gland.
Vasopressin narrows the lumen of blood vessels and increases blood pressure; regulates water metabolism, as it affects the reabsorption (reabsorption) of water in the kidney tubules.
