The hormone TSH (thyrotropin, thyroid stimulating hormone) stimulates the development and activity of the thyroid gland. This substance was first isolated from the pituitary gland extract. Thyrotropin is a glycoprotein with a molecular weight of 23,000 to 32,000 daltons, is highly soluble in water, inactivated by pepsin, trypsin and chymotrypsin. The hormone TSH consists of Ξ± and Ξ² subunits. The Ξ±-subunits have the same structure not only in different hormones (lutropin and thyrotropin), but also in hormones of different animal species. They differ from each other only in the structure of the carbohydrate parts of the molecule. The specific biological activity of the hormone is determined by the properties of the Ξ²-subunit. However, this activity is determined only after the binding of the Ξ± and Ξ² subunits.
With an increase in the concentration of thyroid hormones in the blood, the synthesis of thyrotropin decreases according to the principle of negative feedback: in the hypothalamus the synthesis of thyrolibirin decreases, in the pituitary gland - melanotropin, in the thyroid gland - thyroxine.
The hormone TSH stimulates the growth and development of the epithelium of the thyroid gland follicles, activates the activity of organelles, which take part in the biosynthesis of its hormones. The mechanism of its action consists of several stages: first, the hormone TSH activates the formation of cAMP, it, in turn, the biosynthesis of thyroglobulins. Thyrotropin promotes the "capture" of iodine by follicle cells and the breakdown of thyroglobulins into individual hormones and a protein residue.
The hormone stimulates the absorption of oxygen by the cells of the thyroid gland and increases their permeability to monosaccharides, amino acids and other biological compounds.
In diseases of the anterior pituitary gland, the synthesis of TSH decreases, which subsequently leads to inhibition of the biosynthesis of thyroid hormones. This can trigger the development of diseases such as myxedema and goiter.
The morphological and functional parts of the thyroid gland are epithelial cells and follicles, which are filled with a viscous yellow fluid - a colloid. Its biochemical composition is mainly represented by protein - thyroglobulin. It refers to glycoproteins with a molecular weight of 660,000 daltons. Its composition includes tyrone, which is formed as a result of the condensation of two tyrosine molecules (amino acid). Tyrone is the main material for the construction of iodinated thyroid hormones - thyroxine (T4, tetraiodothyronine) and triiodothyronine (T3), which are synthesized in the follicles of the gland.
In the blood, these hormones combine with plasma proteins and circulate in the body. Upon contact with target cells, the proteins break down and hormones are released into the intercellular fluid. Most of the hormones in the cell are concentrated in the hyaloplasm, a smaller one in the mitochondria and ribosomes.
Low hormone TSH in the blood of a young body can cause cretinism and a violation of the proportionality of the body. In adults, myxedema occurs. In this case, puffiness forms, water is retained in the tissues, the main metabolism decreases, general weakness, pathological obesity and premature aging occur . If hypothyroidism occurs with iodine deficiency in food and water, then endemic goiter develops , the thyroid gland increases in size.
With hyperfunction of the thyroid gland, a bazedova disease (diffuse toxic goiter) occurs. The reasons may be different: chronic intoxication, infectious diseases, etc. Under the influence of hormones, the permeability of cell membranes, especially mitochondria, increases. In this case, all types of metabolism are disturbed, intoxication develops.
In cases where the hormone TSH is elevated, treatment must be done on time. In the process of treating this pathology, hormone therapy is prescribed using iodine-containing drugs.