Functional state of the hypothalamic-pituitary system

There is a close relationship between the nervous and endocrine systems. The unity of nervous and humoral regulation in the body is ensured by the close anatomical and functional connection of the pituitary gland and hypothalamus. The hypothalamus is the highest vegetative center that coordinates the functions of various systems to meet the needs of the entire body. It plays a leading role in maintaining the optimal level of metabolism (protein, carbohydrate, fat, water and mineral) and energy, in regulating the body's thermal balance, the functions of the digestive, cardiovascular, excretory, respiratory and endocrine systems. The hypothalamus controls such endocrine glands as the pituitary gland, thyroid gland, sex glands, adrenal glands, and pancreas. The hypothalamus has extensive anatomical and functional connections with other structures of the brain.

Regulation of the secretion of tropic hormones of the pituitary gland is carried out by the release of hypothalamic neurohormones. The hypothalamus forms specific mediators - releasing hormones, which enter the pituitary gland through the vessels of the hypothalamus-pituitary portal system and, acting directly on its cells, stimulate or inhibit the secretion of hormones. The network of blood capillaries related to the hypothalamus-pituitary portal system forms veins that pass along the stalk of the pituitary gland and then divide into a secondary capillary network in the anterior lobe of the pituitary gland. The hormones of the hypothalamus and pituitary gland are protein and peptide hormones.

Hormones of the hypothalamus

The following hypothalamic hormones stimulate the secretion of tropons of the anterior pituitary gland:

• corticotropin-releasing hormone (CRH);
• thyrotropin-releasing hormone (TRH);
• gonadotropin-releasing hormone (GnRH);
• prolactin-releasing hormone (PRH);
• somatotropin-releasing hormone (STH);
• Melanotropin-releasing hormone. Pituitary hormone secretion blockers include:
• somatostatin;
• gonadotropin-releasing inhibitory hormone (GRIH);
• prolactin-releasing inhibitory hormone (PRHI);
• melanostatin.

The biosynthesis of the above neurohormones occurs not only in the hypothalamus, for example, somatostatin is formed by D-cells of the pancreatic islets and intestinal mucosa, as well as cerebral neurosecretory cells. TRH is formed, in addition to the hypothalamus, in other parts of the CNS. In addition to the named hormones, the hypothalamus also synthesizes ADH, oxytocin and neurophysin, which migrate along the nerve pathways of the pituitary stalk and enter the tissue depots of the posterior pituitary gland. The hypothalamus regulates the release of these peptides into the bloodstream.

Pituitary hormones

The pituitary gland secretes hormones with a wide range of effects.

• The anterior pituitary gland synthesizes:
  • ACTH;
  • STH, or growth hormone;
  • TSH;
  • FSH;
  • LG;
  • prolactin;
  • β-lipotropic hormone;
  • propiomelanocortin.
• In the cells of the middle part of the pituitary gland (intermediate lobe) the following are synthesized:
  • melanocyte-stimulating hormone (α-MSH);
  • corticotropin-binding midlobe peptide;
  • β-endorphin.
• The posterior lobe of the pituitary gland secretes:
  • ADH (arginine vasopressin);
  • oxytocin;
  • neurophysin (the exact functions have not been established, it promotes the transport and transition to reserve forms in the posterior pituitary gland of ADH and oxytocin.

Pituitary hormones can also be formed in other tissues of the body, mainly in malignant and benign tumors. Tumors of various organs are capable of secreting ACTH, ADH, prolactin, TSH, STH, etc.

Regulation of secretion of hormones of the hypothalamus and pituitary gland

Regulation of the secretion of pituitary hormones is carried out by the nervous system, as well as by the principle of feedback. Only stimulants are known for the secretion of ACTH, LH, FSH, TSH, inhibition of their secretion is carried out by hormones of target glands (corticosteroids, sex steroids, T4 ₎. Secretion of a tropic hormone is usually inhibited by an increase in the concentration of the hormone of the target gland in the blood. This negative feedback can either directly inhibit the secretion of the hypothalamic hormone or change its effect on the pituitary cells. An increase in the secretion of the tropic hormone of the adenohypophysis can inhibit the secretion of the releasing hormone of the hypothalamus.

Disruption of secretion of hormones of the hypothalamus and pituitary gland

The basis of disturbances in the synthesis and secretion of hormones of the hypothalamus and pituitary gland is the action of the following pathogenetic mechanisms.

• Violation of the ratio of neurotransmitters in the central nervous system.
• Local disturbances in the synthesis of hormones, changes in their properties and the response of cells to the action of hormones in the hypothalamus and pituitary gland.
• Pathological changes in hormone receptors of pituitary cells.
• Disorders of the functions of peripheral endocrine glands and their receptors.
• Pathological resistance (areactivity) of target cells to the action of hormones.

The main cause of hypothalamic-pituitary diseases is a disruption in the relationship between the central nervous system, hypothalamus, pituitary gland and peripheral endocrine glands. To select effective treatment methods, it is necessary to establish at what level the disruption in the relationship in the hormonal regulation system occurred.

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