The structure and functions of the pituitary gland

The pituitary gland, the structure and functions of which will be discussed later, is an organ of the endocrine system. It combines 3 sites. Let us consider in more detail what functions of the pituitary gland of the brain exist. At the end of the article, additional material is presented. In particular, a table has been compiled. The functions of the pituitary gland are characterized in it briefly.

Circulation

How does the pituitary gland get food? Functions, treatment of disorders, organ activity as a whole are determined by the state of blood circulation. Some features of blood supply to an organ have in many cases a decisive influence on the regulation of its activity.

The branches from the carotid (internal) artery and the Vilisium circle formed the upper and lower channels of the organ. The first forms a fairly powerful capillary network in the region of the median elevation of the hypothalamus. Merging, the vessels form a series of portal long veins. They descend into the adenohypophysis along the pedicle and form a plexus of sinusoidal capillaries in the anterior lobe. Therefore, in this part of the organ, direct arterial supply is absent. Blood enters into it from the median elevation through the portal system. These features are of paramount importance for the regulation of each function of the anterior pituitary gland. This is due to the fact that axons in the neurosecretory cells of the hypothalamus in the region of median elevation form axovasal contacts.

Neurosecret and regulatory peptides penetrate the adenohypophysis through the portal vessels. The posterior organ receives blood from the lower artery. In the adenohypophysis, the highest current intensity is noted, its level being higher than in most other tissues.

Venous vessels of the anterior lobe enter the posterior venules. The outflow from the organ is carried out into the venous cavernous sinus in the hard membrane, and then into the common network. A greater volume of blood departs retrograde to the median elevation. This is crucial for the feedback mechanisms between the hypothalamus and the pituitary gland. The sympathetic innervation of arterial vessels is carried out due to postganglionic fibers passing along the network of vessels.

Pituitary gland: structure and functions (briefly)

As mentioned above, in the body in question there are three departments. The anterior is called the adenohypophysis. According to morphological characters, this department is a gland of epithelial origin. It contains endocrine cells of several types.

The posterior lobe is called the neurohypophysis. It is formed in embryogenesis as a bulging of the ventral hypothalamus and is distinguished by a common neuroectodermal origin. In the posterior section, pituicides are collected - spindle-shaped cells and neuronal hypothalamic axons.

The intermediate lobe (similarly to the anterior) has an epithelial origin. This department is practically absent in humans, but quite clearly expressed, for example, in rodents, cattle and small cattle. The function of the intermediate lobe in humans is performed by a small group of cells in the anterior part of the posterior part, functionally and embryologically associated with the adenohypophysis. Next, we consider the parts described above in more detail.

Hormone production

Structurally, the anterior pituitary is represented by eight types of cells, five of which are characterized by secretory function. These elements include, in particular:

• Somatotrophs . These are red acidophilic elements with small granules. They produce growth hormone.
• Lactotrophs . These are yellow acidophilic elements with large granules. They produce prolactin.
• Thyrotrophs are basophilic . These cells produce thyroid stimulating hormone.
• Gonadotrophs are basophilic. These elements produce LH and FSH (gonadotropins: follicle-stimulating and luteinizing hormones).
• Corticotrophs are basophilic. These elements produce the adrenocorticotropic hormone corticotropin. Also here, as in the elements of the intermediate section, melanotropin and beta-endorphin are formed. These compounds are derived from the molecules of the precursors of lipotropin compounds.
  

Corticotropin

It is a cleavage product of a fairly large glycoprotein of proopiomelanocortin, which is formed by basophilic corticotrophs. This protein compound is divided into two parts. The second of them - lipotropin - breaks down and gives, in addition to melanotropin, the endorphin peptide. It is of crucial importance in the activity of the anti-pain (antinociceptive) system and the modulation of the production of hormones of the adenohypophysis.

Physiological effects of corticotropin

They are divided into extrarenal and adrenal glands. The latter are considered the main ones. Under the influence of corticotropin, the synthesis of hormones increases. With their excess, hyperplasia and hypertrophy of the adrenal cortex occurs. Extrarenal action is manifested by the following effects:

• Increased production of growth hormone and insulin.
• Lipolytic effect on adipose tissue.
• Hypoglycemia due to stimulation of insulin secretion.
• Increased deposition of melanin with hyperpigmentation due to the relationship of the hormonal molecule with melanotropin.

With an excess of corticotropin, the development of hypercorticism is noted, accompanied by a predominant increase in the production of cortisol in the adrenal glands. This pathology is called Itsenko-Cushing's disease. Decreased pituitary function provokes glucocorticoid deficiency. It is accompanied by metabolic changes of a pronounced nature and a deterioration in resistance to environmental influences.

Pituitary gonadotropic function

The production of compounds from specific cell granules is clearly cyclical in both men and women. The pituitary gland functions in this case through the adenylate cyclase-cAMP system. Their main influence is directed to the sexual segments. Moreover, the effect extends not only to the formation and secretion of hormones, but also to the functions of the testes and ovaries due to the binding of follitropin to cellular receptors of the primordial follicle. This leads to a clear morphogenetic effect, manifested in the form of growth of follicles in the ovary and proliferation in granulosa cells in women, as well as the development of testicles, spermatogenesis and proliferation of Sertoli elements in men.

In the process of producing sex hormones, follitropin has only an auxiliary effect. Due to it, secretory structures are prepared for the activity of lutropin. In addition, steroid biosynthesis enzymes are stimulated. Lutropin provokes ovulation and development in the ovaries of the corpus luteum, and in the testes stimulating effect on Lading cells. It is considered a key steroid for the activation of the formation and production of androgens, progesterone and estrogens. The optimal development of gonads and the production of steroids is ensured by the synergistic action of lutropin and follitropin. In this regard, they are often combined under the general name "gonadotropins".

Thyrotropin: general information

The secretion of this glycoprotein hormone is carried out continuously with fairly clear fluctuations throughout the day. Its maximum concentration is observed in the hours that precede sleep. Regulation is carried out due to the interaction of the function of the pituitary gland and the thyroid gland. Thyrotropin enhances the secretion of tetraiodothyronine and triiodothyronine. Feedback is closed both at the level of the hypothalamus and due to the function of the pituitary gland. In the latter case, we are talking about suppressing the production of thyrotropin. Also, its secretion is slowed down by glucocorticoids. In an increased volume, thyrotropin is produced under the influence of an elevated temperature on the body. Factors such as anesthesia, pain, or trauma inhibit its secretion.

The effect of thyrotropin

This hormone is able to bind to a specific receptor in the follicular cells of the thyroid gland and cause metabolic reactions. Thyrotropin promotes the change of all types of metabolic processes, the acceleration of iodine uptake, the synthesis of thyroid steroids and thyroglobulin. An increase in the secretion of thyroid hormones occurs due to the activation of thyroglobulin hydrolysis.

Thyrotropin increases organ mass due to increased protein and RNA synthesis. The hormone also has an extra thyroid effect. It is manifested by an increase in the production of glycosaminoglycans in the skin, periorbital and subcutaneous tissue. This, as a rule, occurs due to hormone deficiency, for example, against the background of iodine deficiency. With excessive secretion of thyrotropin, goiter develops, hyperthyroidism with manifestations of an increased content of thyroid steroids (thyrotoxicosis), exophthalmos (effervescence). All this in complex is called Bazedovoy disease.

Growth hormone

This hormone is produced continuously with 20-30 minute outbreaks in adenohypophysial cells. The secretion is regulated by somatostatin and somatoliberin (hypothalamic neuropeptides). An increase in growth hormone production is noted during sleep, especially in its early stages.

Physiological effects

They are associated with the effects of growth hormone on metabolic processes. Most of the physiological effects are mediated by specific humoral factors in bone and liver. They are called somatomedins. If the pituitary gland is impaired in the form of increased and prolonged secretion of the hormone, the effect of these humoral factors on the cartilage tissue persists. However, there are changes in fat and carbohydrate metabolism. As a result, growth hormone provokes hyperglycemia due to the breakdown of glycogen in the liver and muscles, as well as inhibition of utilization in glucose tissues. Due to this hormone, insulin secretion increases. At the same time, growth hormone stimulates the activation of insulinase.

The specified enzyme has a destructive effect on insulin, provoking resistance to it in the tissues. This combination of processes can trigger the development of diabetes (sugar).

The functions of the pituitary gland are also manifested in lipid metabolism. There is a facilitating (permissive) effect of growth hormone on the effects of glucocorticoids and catecholamines. As a result, lipolysis of adipose tissue is stimulated, the concentration of free fatty acids in the blood rises, and ketone bodies in the liver are excessively formed and even infiltrate.

Insulin resistance can be associated with the described disorders of fat metabolism. With a violation of the function of the pituitary gland, expressed in excessive secretion of growth hormone, if it manifests itself in early childhood, gigantism develops with the proportional formation of the trunk and limbs. In adulthood and adolescence, there is an increase in the growth of epiphyseal segments of skeletal bones, areas with incomplete ossification. This process is called acromegaly. With a deficiency of somatotropin of an innate nature, there is dwarfism, which is called the pituitary dwarfism. Such people are also called midgets.

Prolactin

This is one of the most important hormones that the pituitary gland produces. The functions in the body of the specified steroid performs different. Mostly it affects the mammary gland. In addition, the hormone supports the secretory activity of the corpus luteum and the production of progesterone. Prolactin is involved in the regulation of water-salt metabolism, reducing the excretion of water and electrolytes, stimulates the growth and development of internal organs, and promotes the formation of maternal instinct. In addition to enhancing protein synthesis, the hormone increases the release of fat from carbohydrates, which causes postpartum weight gain.

Rear and intermediate departments: a brief description

Neurohypophysis fulfills to a greater extent the accumulative function. The neurohormones of the paraventricular and supraoptic nuclei in the hypothalamus, oxytocin and vasopressin, are also secreted in this section.

As for the intermediate section, melanotropin is formed here. This hormone synthesizes melanin, increases the amount of free pigment in the epidermis, and enhances the color of skin and hair. Melanotropin performs the tasks of the brain peptide in neurochemical processes in memory.

Finally

The table “Pituitary gland functions”, presented below, allows briefly characterizing the tasks of the considered organ by determining the activity of the compounds produced by it.