Hormones, Mechanism of action of hormones, Classification of...


Hormones are organic substances of a diverse structure that have a regulating effect on the metabolism and physiological functions of organs.

Hormones are secreted by the organs - glands of internal secretion, they do not have excretory ducts and release hormones directly into the blood.

Mechanism of action of hormones

The hormones themselves do not directly affect any cell responses. Only by contacting a specific, receptor-specific, hormone, causes a certain effect.

Hormones are divided into water- and fat-soluble. Belonging to one of these classes determines their mechanism of action. This is because fat-soluble hormones can safely penetrate through the cell membrane, which consists primarily of lipid bilayer, and water-soluble it can not. In this connection, the receptors for water- and fat-soluble hormones have different sites of localization (membrane or cytoplasm). By contacting the membrane receptor, the hormone causes a cascade of reactions in the cell itself, but does not affect the genetic material. The complex of the cytoplasmic receptor and hormone can affect the nuclear receptors and cause changes in the genetic apparatus, which leads to the synthesis of new proteins.

The influence of hormones can change in the case of metabolic disorders, changes in the physico-chemical parameters of the body (temperature, acidity, osmotic pressure) and concentrations of the most important substrates that arise from diseases, as well as in the performance of muscular work. The consequence of this is the strengthening or weakening of the influence of hormones on the appropriate organs.

Classification of hormones

1. Hormones of protein nature (proteins and polypeptides): hormones of the hypothalamus, pituitary gland, calcitonin of the thyroid gland, parathyroid hormone, pancreatic hormones.

2. Hormones are derivatives of the amino acid tyrosine: iodine-containing hormones of the thyroid gland, hormones of the adrenal medulla.

3. Hormones of the steroid structure: hormones of the adrenal cortex, gonads.

Regulation of the formation of hormones

Synthesis and release of hormones into the blood are controlled by the nervous system. In a simplified form, the relationship between the hormonal (endocrine) and nervous systems can be represented as follows. When external factors are influenced by the organism, or when there are changes in the blood and in various organs, the corresponding information is transmitted along the afferent (sensitive) nerves in the central nervous system. In response to the information obtained in the hypothalamus (part of the intermediate brain), biologically active substances (hormones of the hypothalamus) are produced, which then enter the pituitary (brain appendage) and stimulate or inhibit the secretion of the so-called tropic hormones (hormones of the anterior lobe). Tropic hormones are released from the pituitary gland into the blood, transported to the glands of internal secretion and cause in them the synthesis and secretion of the corresponding hormones, which then act on the target organs. Thus, the body has a single neuro-hormonal or neurohumoral regulation.

All glands of internal secretion function in concert and exert mutual influence on each other. The introduction of hormones into the body not only affects the function of the gland that produces the hormone that is being introduced, but it can also have a negative effect on the state of the entire neuro-hormonal regulation as a whole. Therefore, the use of hormonal drugs as doping is dangerous for the health of athletes.

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