Structure and function of the pituitary gland

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

Circulation

How does the pituitary gland feed? Functions, treatment of violations, the activity of the body as a whole are determined by the state of the circulation. Some features of supplying the organ with blood have in many cases a determining influence on the regulation of its activity.

The branches from the carotid (inner) artery and the vilizium circle form the upper and lower channels of the organ. The first forms a sufficiently powerful capillary network in the region of the mid elevation of the hypothalamus. Fusing, the vessels form a series of portal long veins. They descend into the adenohypophysis by the leg and form in the anterior lobe a wreath of sinusoidal capillaries. Consequently, there is no direct arterial supply in this part of the body. The blood enters from the middle elevation through the portal system. These features are of paramount importance for the regulation of each function of the anterior lobe of the pituitary gland. This is due to the fact that the axons in the neurosecretory cells of the hypothalamus in the region of the mid elevation form axovasal contacts.

Neurosecret and regulatory peptides penetrate the adenohypophysis via portal vessels. The posterior part of the organ receives blood from the lower artery. The adenohypophysis shows the highest current intensity, its level is higher than in most other tissues.

The venous vessels of the anterior lobe enter the venules of the posterior. Outflow from the organ is carried out into the venous cavernous sinus in a hard shell, and then into a common network. The larger volume of blood retrograde to the middle elevation. This is of decisive importance in the work of feedback mechanisms between the hypothalamus and the pituitary gland. Sympathetic innervation of arterial vessels is carried out by postganglionic fibers passing along the vascular network.

Pituitary: structure and function (briefly)

As was said above, there are three divisions in the body under consideration. Anterior is called adenohypophysis. According to morphological signs, 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 the bulging of the ventral hypothalamus and differs from its common neuroectodermal origin. In the posterior section, pituitary-spindle cells and neuronal hypothalamic axons are collected.

The intermediate part (similarly to the anterior one) has an epithelial origin. This department is practically absent in humans, but it is quite clearly expressed, for example, in rodents, large 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, consider the parts described above in more detail.

Hormone production

Structurally, the anterior lobe of the pituitary gland is represented by eight types of cells, five of which have a secretory function. These elements include, in particular:

• Somatrophic growths . 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 a thyroid-stimulating hormone.
• Gonadotrophs are basophilic. These elements produce LH and FSH (gonadotropins: follicle-stimulating and luteinizing hormones).
• Corticotrophs are basophilic. These elements produce adrenocorticotropic hormone corticotropin. Also here, as in the elements of the intermediate department, melanotropin and beta-endorphin are formed. These compounds originate from a molecule of precursors of lipotropin compounds.

Corticotropin

It is the product of the cleavage of a sufficiently large glycoprotein of proopiomelanocortin, which is formed by basophilic corticotrophs. This protein compound is divided into two parts. The second of these - lipotropin - splits and gives peptide endorphin in addition to melanotropin. It is of paramount importance in the activity of the antiseptic (antinociceptive) system and the modulation of the production of hormones of the adenohypophysis.

Physiological effects of corticotropin

They are divided into the adenadrenal and adrenal glands. The latter are considered basic. Under the influence of corticotropin, the synthesis of hormones increases. With their excess, there is hyperplasia and hypertrophy of the adrenal cortex. The extra-adrenal effect is manifested by the following effects:

• Increased production of somatotropin and insulin.
• Lipolytic effects on adipose tissue.
• Hypoglycemia in connection with the stimulation of insulin secretion.
• Increased melanin deposits with hyperpigmentation due to the kinship of the hormonal molecule with melanotropin.

With excess corticotropin, there is a development of hypercorticism, accompanied by a predominant increase in cortisol production in the adrenal glands. This pathology is called the disease of Itenko-Cushing. Decreased function of the pituitary gland provokes insufficiency of glucocorticoids. It is accompanied by metabolic shifts of a pronounced character and a deterioration in resistance to external influences.

Gonadotropic function of the pituitary gland

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

In the process of producing sex hormones in follitropin, only an auxiliary effect is noted. Due to it, secretory structures are prepared for lutropin activity. In addition, enzymes of steroid biosynthesis are stimulated. Lutropin provokes ovulation and development in the ovaries of the yellow body, and in the testes stimulates the cells of Leyding. It is considered a key steroid for the activation of education and the production of androgens, progesterone and estrogens. The optimal development of gonads and production of steroids is provided by the synergistic action of lutropine and follitropin. In this regard, they are often combined under the common name of "gonadotropins."

Thyrotropin: general information

The secretion of this glycoprotein hormone is carried out continuously with fairly clear fluctuations throughout the day. Maximum concentration is noted in the hours that precede sleep. Regulation is carried out due to the interaction of the pituitary and thyroid gland function. Thyrotropin increases the secretion of tetraiodothyronine and triiodothyronine. The feedback is closed both at the hypothalamus level and due to the function of the pituitary gland. In the latter case, it is a question of inhibiting the production of thyrotropin. Also, its secretion is slowed down by glucocorticoids. In an increased volume, thyrotropin is produced by exposure to an elevated temperature organism. Factors such as anesthesia, pain or trauma suppress its secretion.

The effect of thyrotropin

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

Thyrotropin increases the weight of the organ due to increased synthesis of protein and RNA. The hormone exerts and vnesetreoidnoe action. It is manifested by an increase in the production of glycosaminoglycans in the skin, in the zorbital and subcutaneous tissue. This, as a rule, arises from the inadequacy of hormones, for example, against the background of iodine deficiency. With excessive secretion of thyrotropin, goiter develops, hyperthyroidism with manifestations of increased content of thyroid steroids (thyrotoxicosis), exophthalmos (pchego-eyes). All this in the complex is called Based's disease.

Somatotropin

This hormone is produced continuously with 20-30-minute flares in adenohypophyseal cells. The secretion is regulated by somatostatin and somatoliberin (hypothalamic neuropeptides). An increase in the production of somatotropin is noted during the sleep period, especially in its early stages.

Physiological effects

They are associated with the influence of somatotropin on metabolic processes. Most of the physiological effects are mediated by specific humoral factors of bone tissue and liver. They are called somatomedines. When the pituitary gland function is disturbed in the form of increased and prolonged hormone secretion, the effect of these humoral factors on the cartilaginous tissue is preserved. However, changes in fat and carbohydrate metabolism are observed. As a result, somatotropin provokes hyperglycemia caused by decay in the liver and muscles of glycogen, as well as depression of utilization in the tissues of glucose. This hormone increases the secretion of insulin. At the same time, somatotropin stimulates the activation of insulinase.

This enzyme acts destructively on insulin, provoking resistance to it in tissues. This combination of processes can trigger the development of diabetes (sugar).

Functions of the pituitary gland also appear in the metabolism of lipids. There is a facilitating (permissive) effect of somatotropin on the effects of glucocorticoids and catecholamines. Because of this, lipolysis of adipose tissue is stimulated, the concentration of fatty free acids in the blood increases, there is excessive formation of ketone bodies in the liver and even its infiltration.

Insulin resistance can also be associated with the described disorders of fat metabolism. When the pituitary gland function is abnormal, expressed in excessive secretion of somatotropin, if it manifests itself in early childhood, gigantism develops with proportional formation of the trunk and extremities. 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 deficit of congenital somatotropin, dwarfism takes place, which is called hypophysis nazmom. Such people are also called Lilliputians.

Prolactin

This is one of the most important hormones that the pituitary gland produces. Functions in the body indicated by the steroid performs different. Mostly it affects the mammary gland. In addition, the hormone maintains the secretory activity of the yellow body and the production of progesterone. Prolactin is involved in the regulation of water-salt metabolism, reducing the excretion of water and electrolytes, stimulating the growth and development of internal organs, contributes to the formation of a maternal instinct. In addition to enhancing protein synthesis, the hormone increases the release of fat from carbohydrates, which causes postnatal weight gain.

Rear and intermediate departments: brief description

The neurohypophysis performs a more accumulative function. In this department, the neurohormones of the paraventricular and supraoptic nucleus in the hypothalamus, oxytocin and vasopressin, are also secreted.

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

Finally

Table "Functions of the pituitary gland", presented below, allows us to briefly characterize the problems of the considered organ by determining the activity of the compounds produced by it.