The two biologically active hormones secreted by the thyroid gland are thyroxine (also known as tetraiodothyronine, T4) and triiodothyronine (T3). They are a group of iodine-containing tyrosines, which are synthesized in the thyroid gland cells using iodine and tyrosine as raw materials. The thyroid gland cells have a strong capacity to take up iodine. The human body takes in 100 to 200 μg of iodine from the diet every day, of which about 1/3 enters the thyroid gland. The total iodine content of the thyroid gland is about 8,000 μg, accounting for 90% of the total body iodine content, indicating that the thyroid gland has a strong iodine pumping capacity. When the thyroid gland is hyperactive, the iodine pumping capacity exceeds normal and iodine intake increases; when it is low, it is lower than normal and iodine intake decreases. Therefore, the ability of the thyroid gland to take up radioactive iodine (131I) is used clinically as one of the methods to routinely check thyroid function. After iodine ions are taken into the epithelial cells of the thyroid follicles, they are rapidly oxidized to activated iodine by the action of peroxidase, and then iodinated by the action of iodinase to produce monoiodotyrosine (MIT) and diiodotyrosine (DIT) from the tyrosine residues in thyroglobulin. In this way, thyroglobulin containing the four tyrosine residues is stored in the follicular compartment (see the section on biochemistry). When the thyroid gland is affected by TSH and thyroid hormone is released, the glandular epithelial cells first swallow the thyroglobulin in the follicular cavity into the glandular cells by swallowing it, and under the action of lysosomal protein hydrolase, the thyroglobulin is broken down. The amount of T4 on the thyroglobulin molecule is much higher than that of T3, so T4 accounts for about 90% of the total amount of hormone secreted, while the amount of T3 secreted is smaller, but its activity is greater, being five times that of T4. The total amount of T4 secreted daily is about 96μg, while that of T3 is about 30μg. After T4 is released into the blood, part of it is bound to plasma proteins, while the other part is transported in the blood in a free state, and the two can be transformed into each other to maintain T4 The biologically active hormones secreted by the thyroid gland are thyroxine (also known as tetraiodothyronine, T4) and triiodothyronine (T3). They are a group of iodine-containing tyrosines, which are synthesized in the thyroid gland cells using iodine and tyrosine as raw materials. The thyroid gland cells have a strong capacity to take up iodine. The human body takes in 100-200 μg of iodine from the diet every day, of which about 1/3 enters the thyroid gland. The total iodine content of the thyroid gland is about 8,000 μg, accounting for 90% of the iodine content of the whole body, indicating that the thyroid gland has a strong iodine pumping capacity. When the thyroid gland is hyperactive, the iodine pumping capacity exceeds normal and iodine intake increases; when it is low, it is lower than normal and iodine intake decreases. Therefore, the ability of the thyroid gland to take up radioactive iodine (131I) is used clinically as one of the methods to routinely check thyroid function. After iodine ions are taken into the epithelial cells of the thyroid follicles, they are rapidly oxidized to activated iodine by the action of peroxidase, and then iodinated by the action of iodinase to produce monoiodotyrosine (MIT) and diiodotyrosine (DIT) from the tyrosine residues in thyroglobulin. In this way, thyroglobulin containing the four tyrosine residues is stored in the follicular compartment (see the section on biochemistry). When the thyroid gland is affected by TSH and thyroid hormone is released, the glandular epithelial cells first swallow the thyroglobulin in the follicular cavity into the glandular cells by swallowing it, and under the action of lysosomal protein hydrolase, the thyroglobulin is broken down. The number of T4 on the thyroglobulin molecule is much higher than that of T3, so T4 accounts for about 90% of the total amount of hormone secreted, while T3 is secreted in a smaller amount, but its activity is large, five times that of T4. The daily secretion of T4 and the dynamic balance of T3 in the blood, because only the free form, can enter the cells to play a role. after T3 is released into the blood, because of the small affinity with plasma proteins, mainly in the free form. About 50% of T4 is deiodinated into T3 every day, so the role of T3 cannot be ignored. Self-regulation of thyroid function, which refers to the regulation of thyroxine secretion by the thyroid gland itself in response to the amount of iodine supply in the absence of TSH altogether or when the TSH concentration remains basically unchanged. When the iodine supply in food is excessive, it first inhibits the transport of iodine in the process of thyroid hormone synthesis, and also inhibits the synthesis process, causing a significant decrease in thyroid hormone synthesis. If the amount of iodine increases again, its anti-thyroid hormone synthesis effect disappears and thyroid hormone synthesis increases. In addition, excess iodine has the effect of inhibiting the release of thyroid hormones. Conversely, when the supply of exogenous iodine is insufficient, the iodine transport mechanism will be enhanced and the synthesis and release of thyroid hormones will be increased so that thyroid hormone secretion does not become too low. The principle of this action of iodine is not known.