Functional state of the thyroid gland

Diseases of the thyroid gland occupy the second place among endocrine diseases after diabetes mellitus by prevalence. They develop as a result of violations of the regulation of thyroid function, changes in the biosynthesis of thyroid hormones or their action in tissues.

Inorganic iodine and amino acid tyrosine are necessary for the formation of thyroid hormones. Every day 30-40% of iodine consumed with food concentrates in the thyroid gland together with iodine, formed as a result of peripheral destruction of thyroid hormones. Remains of iodine are excreted in the urine. In the body, it is in the form of inorganic iodine and in a protein-related form. If necessary, iodine is captured by the thyroid gland and oxidized into molecular iodine, which combines with a specific protein called thyroglobulin. In the free form, 1-2% of iodine remains. Iodine is concentrated in the thyroid gland in both colloid follicles and in epithelial cells. Proteolytic cleavage of thyroglobulin leads to the release of T4 and T3, as well as the release of iodinated amino acids - mono- and diiodotyrosine. T4 and T3 in the blood are reversibly associated with a specific protein - thyroxin-binding -

globulin( TSG).When the thyroid hormone content rises, the excess binds to other proteins - prealbumin and albumin. In the blood, a balance is created between bound and free hormones. Protein-bound T4 and T3 represent a kind of hormone depot from which they are released as needed. Biological effect has only free blood hormones.

The thyroid function is controlled by the TRH secreted by the hypothalamus. Secretion of TTG is stimulated by TRH, which,

Fig. Regulation of secretion of thyroid hormones

Liver and other cells Thyroid

Fig. Regulation of the secretion of thyroid hormone

secreted by the cells of the hypothalamus, binds to the membrane receptors of the pituitary cells, activating the adenylate cyclase and causing the proliferation of glandular cells of the adenohypophysis. Under the influence of TSH thyroglobulin passes into follicular cells of the thyroid gland, then it is hydrolyzed by proteolytic enzymes with the formation of T4 and T3.A change in the sensitivity of the adenohypophysis thyrotrophs to the stimulating effect of TRH, depending on the concentration of free thyroid hormones in the blood, is the main mechanism for regulating thyroid function.

Thyroid hormones affect various metabolic processes in the body. They increase the utilization of carbohydrates, potentiating the action of insulin, increase the absorption of glucose by muscles. In physiological quantities, thyroid hormones stimulate protein synthesis, including the synthesis of specific enzymes;increase lipolysis and oxidation of fatty acids;potentiate the action of certain hormones.

Thyroid dysfunction leads to the development of symptoms caused by impaired metabolism.