Endocrine organs are classified according to origin, histogenesis and histological origin into three groups. The branchiogenic group is formed from the pharyngeal pockets - these are the thyroid gland, parathyroid glands. The group of adrenal glands - it belongs to the adrenal glands (medulla and cortex), the paraganglia and the group of brain appendages - these are the hypothalamus, pituitary and pineal gland.
The endocrine system is functionally regulatory system in which there are interorganic connections, and the work of this entire system has a hierarchical relationship between each other.
History of the study of the pituitary gland
The study of the brain and its appendages involved many scientists in different eras. For the first time, Galen and Vesalius thought about the role of the pituitary 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 in the body, namely, that it is involved in the formation of cerebrospinal fluid. Another theory claimed that it absorbs cerebrospinal fluid, then secreting it into the blood.
In 1867, P.I. Peremezhko first made a morphological description of the pituitary gland, highlighting in it the anterior and posterior lobes and the cavity of the brain appendages. In a later period in 1984-1986, Dostoevsky and Flash, studying microscopic fragments of the pituitary gland, found chromophobic and chromophilic cells in its anterior lobe.
Scientists of the 20th century found 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 covers the spur of the dura mater, which serves as the diaphragm for the pituitary gland. Through the hole in the diaphragm, the pituitary leg passes, 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, the 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 pituitary gland begins at the fourth week of embryonic development, and two primordia are used for its formation, which are directed at each other. The anterior pituitary gland is formed from the pituitary pocket, which develops from the oral cavity of the ectoderm, and the posterior lobe from the brain pocket, formed by protruding 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 cells.
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 the anterior, intermediate and tuberous parts.
The front part is formed by trabeculae - these are branched strands consisting of epithelial cells, between which are fibers of connective tissue and sinusoidal capillaries. These capillaries form a dense network around each trabeculae, 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.
On the periphery of the trabeculae there 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 a sour dye. Their total amount is 30-35%. The cells have a rounded shape with a nucleus located in the center, with the adjacent Golgi complex. 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 during their staining, the species involved in the production of hormones - somatotropocytes, lactotropocytes - were isolated.
Acidophilus cells
Acidophilic cells include cells that are stained with acidic dyes and smaller than basophils in size. The core 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 have a spherical shape and their diameter is 150-600 nm. They produce growth hormone, 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 sizes of 500-600 at 100-120 nm. They do not have a clear localization in trabeculae and are scattered in all acidophilic cells. Their total amount 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 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, and their volume occupies only 4-10% in the front of the adenohypophysis. In their structure, these are glycoproteins, which are the matrix for protein biosynthesis. Cells are stained during 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 insufficiency 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 detected with a pituitary histology in a diffuse 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 cleavage forms corticotropic, melanocytostimulating 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 basophilic cells.
Chromophobic cells
Melanocytostimulating and lipotropic hormones are secreted by chromophobic cells. Chromophobic cells are poorly stained 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 manage to accumulate secretory granules, and cells that intensively secrete these granules. Depleted or lacking granules are very specialized cells.
Chromophobic cells also differentiate into small ones with long processes forming a broad-net network, follicle-stellate cells. Their processes pass through endocrinocytes and are located on sinusoidal capillaries. They can form follicular formations and accumulate glycoprotein secretion.
Intermediate and tubercular parts of the adenohypophysis
The cells of the intermediate part are weakly basophilic and accumulate 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 tuberous part is formed by epithelial cords, which extend into the anterior part. It is adjacent to the pituitary leg, which is in contact with the medial elevation of the hypothalamus from its lower surface.
Neurohypophysis
The posterior pituitary gland consists of neuroglia, the cells of which have a fusiform or process shape. It includes nerve fibers of the anterior zone of the hypothalamus, which are formed by neurosecretory axon cells of 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 glandular tissue. This formation is formed as a result of hyperplasia - this is the uncontrolled development of a tumor cell.
The histology of the pituitary adenoma is used to study the causes of the disease and to determine its variety according to the cellular structures of the structure and the anatomical damage to organ growth. An adenoma can affect 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.
Pituitary gland animals
The pituitary gland of the cat is spherical, and its size is 5x5x2 mm. The histology of the cat's pituitary gland revealed that it consists of an adenohypophysis and a neurohypophysis. The adenohypophysis is composed of the anterior and intermediate lobes, and the neurohypophysis through the pedicle, which is somewhat shorter and thicker in its posterior part, connects to the hypothalamus.
Staining of microscopic biopsy fragments of the cat's pituitary gland with histology at multiple magnifications allows the pink granularity of acidophilic endocrinocytes of the anterior lobe to be seen. These are large cells. The posterior lobe is weakly stained, has a rounded shape and consists of pituititis and nerve fibers.
Studying the histology of the pituitary gland of humans and animals allows one to accumulate scientific knowledge and experience, which will help explain the processes occurring in the body.