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Functional state of the thyroid gland
Last reviewed: 23.04.2024
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Diseases of the thyroid gland by prevalence are the second most endocrine diseases after diabetes mellitus. 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.
To form thyroid hormones, inorganic iodine and amino acid tyrosine are needed. 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 T 4 and T 3, as well as the liberation of iodinated amino acids - mono- and diiodotyrosine. T 4 and T 3 in the blood are reversibly associated with a specific protein - thyroxine-binding globulin (TSH). 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 T 4 and T 3 represent a kind of hormone depot from which they are released as needed. Biological effect has only free blood hormones.
Function of the thyroid gland is under the control of TRH, secreted by the hypothalamus. Secretion of TTG is stimulated by TGH, which, released by 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 T 4 and T 3. 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.
Dysfunction of the thyroid gland leads to the development of symptoms caused by impaired metabolism.
[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]