The pituitary gland, the structure and functions of which will be discussed later, is an organ of the endocrine system. It contains 3 sections. Let us consider in more detail what functions of the pituitary gland of the brain exist. Additional material is provided at the end of the article. In particular, a table has been compiled. The functions of the pituitary gland are briefly described in it.
Circulation
How is the pituitary gland nourished? Functions, treatment of disorders, the activity of the organ as a whole are determined by the state of blood circulation. Some features of the supply of blood to an organ in many cases have a decisive influence on the regulation of its activity.
The branches from the carotid (internal) artery and the circle of Willis formed the upper and lower canals of the organ. The first forms a sufficiently powerful capillary network in the region of the median eminence of the hypothalamus. Merging, the vessels form a series of portal long veins. They descend into the adenohypophysis along the stalk and form a plexus of sinusoidal capillaries in the anterior lobe. Consequently, there is no direct arterial supply in this part of the organ. Blood enters it from the median eminence through the portal system. These features are of paramount importance for the regulation of each function of the anterior lobe.pituitary. This is due to the fact that axons in the neurosecretory cells of the hypothalamus in the area of the median eminence form axovasal junctions.
Neurosecret and regulatory peptides through the portal vessels penetrate into the adenohypophysis. The posterior part of the organ receives blood from the inferior artery. The adenohypophysis has the highest current intensity, and its level is higher than in most other tissues.
The venous vessels of the anterior lobe enter the venules of the posterior lobe. The outflow from the organ is carried out into the venous cavernous sinus in a hard shell, and then into the general network. Most of the blood drains retrograde to the median eminence. This is of decisive importance in the operation of feedback mechanisms between the hypothalamus and the pituitary gland. Sympathetic innervation of arterial vessels is carried out by postganglionic fibers passing along the network of vessels.
Pituitary gland: structure and functions (briefly)
As mentioned above, there are three departments in the body in question. The anterior is called the adenohypophysis. According to morphological features, this section is a gland of epithelial origin. It contains several types of endocrine cells.
The posterior lobe is called the neurohypophysis. It is formed in embryogenesis as a bulging of the ventral hypothalamus and is distinguished by its common neuroectodermal origin. The posterior section contains pituicids - spindle cells and neuronal hypothalamic axons.
The intermediate lobe (similar to the anterior lobe) has an epithelialorigin. This department is practically absent in humans, but is 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 region, functionally and embryologically related to the adenohypophysis. Next, consider the parts described above in more detail.
Production of hormones
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:
- 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.
- Basophilic gonadotrophs. These elements produce LH and FSH (gonadotropins: follicle-stimulating and luteinizing hormones).
- Basophilic corticotrophs. These elements produce 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 precursor molecule of lipotropin compounds.
Corticotropin
It is a cleavage product of a fairly large glycoprotein proopiomelanocortin, which is formed by basophilic corticotrophs. This protein compound is divided into twoparts. The second of them - lipotropin - splits and gives endorphin peptide in addition to melanotropin. It is essential in the activity of the anti-pain (antinociceptive) system and in the modulation of the production of adenohypophysis hormones.
Physiological effects of corticotropin
They are divided into extra-adrenal and adrenal. The latter are considered the main ones. Under the action of corticotropin, the synthesis of hormones increases. With their excess, hyperplasia and hypertrophy of the adrenal cortex occur. Extra-adrenal action is manifested by the following effects:
- Increased production of somatotropin 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 hypercortisolism 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 function of the pituitary gland provokes insufficiency of glucocorticoids. It is accompanied by metabolic shifts of a pronounced nature and a deterioration in resistance to environmental influences.
Gonadotropic function of the pituitary gland
The production of compounds from specific cell granules is characterized by a clearly pronounced cyclicity in both men and women. The functions of the pituitary gland are realized in this case through the adenylate cyclase-cAMP system. Their mainthe influence is directed to the sexual segments. In this case, the action 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 the cellular receptors of the primordial follicle. This leads to a distinct morphogenetic effect, manifested as the growth of follicles in the ovary and proliferation in granulosa cells in women, as well as testicular development, spermatogenesis and proliferation of Sertoli elements in men.
In the process of producing sex hormones, follitropin has only an auxiliary effect. Due to it, the secretory structures are prepared for the activity of lutropin. In addition, steroid biosynthesis enzymes are stimulated. Lutropin provokes ovulation and development of the corpus luteum in the ovaries, and in the testes it stimulates the Leiding cells. It is considered a key steroid for activating the formation and production of androgens, progesterone and estrogens. Optimal development of the gonads and 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 noted 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 closes both at the level of the hypothalamus and due to the function of the pituitary gland. In the latter case, we are talking about the suppression of thyrotropin production. Also, its secretion is slowed down by glucocorticoids. In an increased volume, thyrotropin is produced under the influence of elevated temperature on the body. 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 thyroid follicular cells and cause metabolic reactions. Thyrotropin contributes to the change of all types of metabolic processes, the acceleration of iodine uptake, the implementation of 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 by increasing protein and RNA synthesis. The hormone also has an extrathyroidal effect. It is manifested by an increase in the production of glycosaminoglycans in the skin, extraorbital and subcutaneous tissue. This, as a rule, occurs due to a lack of hormones, for example, against the background of iodine deficiency. With excessive secretion of thyrotropin, goiter develops, hyperfunction of the thyroid gland with manifestations of an increased content of thyroid steroids (thyrotoxicosis), exophthalmos (bulging eyes). All this in the complex is called Graves' disease.
Somatotropin
This hormone is produced continuously with 20-30 minute bursts in adenohypophyseal cells. Secretion is regulated by somatostatin and somatoliberin(hypothalamic neuropeptides). An increase in the production of somatotropin is noted during sleep, especially in its early stages.
Physiological effects
They are associated with the effect of somatotropin on metabolic processes. Most of the physiological effects are mediated by specific bone and liver humoral factors. They are called somatomedins. If the function of 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 is preserved. However, there are changes in fat and carbohydrate metabolism. As a result, somatotropin provokes hyperglycemia due to the breakdown of glycogen in the liver and muscles, as well as inhibition of glucose utilization in tissues. This hormone increases insulin secretion. At the same time, somatotropin stimulates the activation of insulinase.
This enzyme has a destructive effect on insulin, provoking resistance to it in tissues. This combination of processes can trigger the development of diabetes (diabetes).
The functions of the pituitary gland are also manifested in lipid metabolism. There is a facilitating (permissive) effect of somatotropin 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 increases, there is an 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. If the function of the pituitary gland is impaired, expressed in excessive secretion of somatotropin, if it manifests itself in the earlychildhood, gigantism develops with a 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, dwarfism occurs, which is called pituitary dwarfism. Such people are also called Lilliputians.
Prolactin
This is one of the most important hormones produced by the pituitary gland. This steroid performs different functions in the body. It mainly 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-s alt metabolism, reducing the excretion of water and electrolytes, stimulates the growth and development of internal organs, and contributes to the formation of the maternal instinct. In addition to enhancing protein synthesis, the hormone increases the release of fat from carbohydrates, which causes postpartum weight gain.
Posterior and intermediate departments: a brief description
The neurohypophysis performs more of a cumulative function. This section also secretes the neurohormones of the paraventricular and supraoptic nuclei in the hypothalamus - oxytocin and vasopressin.
As for the intermediate section, melanotropin is formed here. This hormone synthesizes melanin, increases the amount of free pigment in the epidermis, enhances the color of the skin and hair. Melanotropin performs the tasks of the brainpeptide in neurochemical processes in memory.
In closing
The table "Functions of the pituitary gland", presented below, allows you to briefly characterize the tasks of the considered organ by determining the activity of the compounds produced by it.
| Hormone | Action |
| Adrenocorticotropic | Regulation of hormone secretion in the adrenal cortex |
| Vasopressin | Regulate urine output and control blood pressure |
| Growth Hormone | Managing development and growth processes, stimulating protein synthesis |
| LH and FSH | Management of reproductive functions, control of sperm production, egg maturation and menstrual cycle; the formation of female and male sexual characteristics of the secondary type |
| Oxytocin | Causes muscle contractions in the uterus and mammary ducts |
| Prolactin | Causes and maintains milk production in the glands |
| Thyrotropic hormone | Stimulating the production and secretion of thyroid hormones |
