Endocrine glands

Management processes occurring in the body is provided not only by the nervous system, but also by the endocrine glands (organs of internal secretion). The latter include specialized in the process of evolution, topographically disjointed, of different origin of the gland, which do not have excretory ducts and secrete the secret produced by them directly into the tissue fluid and blood. The products of the endocrine glands (organs) are hormones. This is a highly biologically active substance, which even in very small quantities can influence the various functions of the body. Hormones (Greek hormao - excite) have a selective function, i.e. Can exert a very definite influence on the activity of target organs. Hormones provide regulatory effects on the growth and development of cells, tissues, organs and the whole body. Excess or insufficient production of hormones causes severe dysfunction in the human body and even leads to diseases.

Anatomically separated endocrine glands can exert a significant influence on each other. In connection with the fact that this influence is provided by hormones that are delivered to the target organs with blood, it is customary to talk about the humoral regulation of the activity of these organs. However, it is known that all the processes occurring in the body are under constant control of the central nervous system (CNS). This double regulation of the activity of organs is called neurohumoral.

Currently accepted is the classification of endocrine organs, depending on their origin from different types of epithelium.

1. Glands of ectodermal origin - from the epithelial lining of the pharyngeal gill (gill pockets). This is the so-called branhyogenic group of endocrine glands: thyroid and parathyroid glands.
2. Glands of endoderm origin - from the epithelium of the trunk part of the embryonic intestinal tube: the endocrine part of the pancreas (pancreatic islets).
3. Glands of mesoderm origin: interrenal system, cortical substance of the adrenal glands and interstitial cells of the gonads.
4. The glands of ectoderm origin are derived from the anterior section of the neural tube (neurogenic group): the pituitary and the pineal body (the epiphysis of the brain).
5. The glands of ectoderm origin are derivatives of the sympathetic department of the nervous system: adrenal medulla and parangenlia.

There is another classification of endocrine organs, which is based on the principle of their functional interdependence.

1. Adenohypophysis group:
   1. thyroid;
   2. cortex of adrenal gland (beam and reticular zones);
   3. endocrine part of the gonads - testicles and ovaries. The central position in this group is adenohypophysis, the cells of which produce hormones that regulate the activity of these glands (adrenocorticotropic, somatotropic, thyrotropic and gonadotropic hormones).
2. A group of peripheral endocrine glands, whose activity does not depend on the hormones of the adenohypophysis:
   1. parathyroid glands;
   2. adrenal cortex (glomerular zone);
   3. pancreatic islets.

These glands are conventionally called self-regulating. So, the hormone of the pancreatic islets insulin lowers the level of glucose in the blood; Increased glucose in the blood stimulates the secretion of insulin.

3. . Group of endocrine organs of "nervous origin" (neuroendocrine glands):
   1. large and small neurosecretory cells with processes that form the nuclei of the hypothalamus;
   2. neuroendocrine cells that do not have processes (chromaffin cells of the cerebral part of the adrenals and paraganglia);
   3. parafollicular, or K-cells of the thyroid gland;
   4. Argyrophilic and enterochromaffin cells in the walls of the stomach and intestines.

Neurosecretory cells combine nerve and endocrine functions. They perceive nerve impulses and, in response, produce a neurosecret that enters the bloodstream or is transported to the target cells by nerve cell processes. Thus, the cells of the hypothalamus produce a neurosecret which, through the processes of the nerve cells, is delivered to the pituitary gland, causing an increase or inhibition of the activity of the cells.

4. Group of endocrine glands of neuroglyal origin (from the embryonic neural tube):
   1. pineal body;
   2. Neurohaemal organs (neurohypophysis and medial elevation).

The secret produced by the cells of the pineal body inhibits the release of gonadotropic hormones by the cells of the adenohypophysis and, thus, depresses the activity of the sexual glands. The cells of the posterior lobe of the pituitary gland do not produce hormones, but provide the accumulation and release into the blood of vasopressin and oxytocin, which are produced by the cells of the hypothalamus.

[1], [2]