Thyroid gland cells have a strong ability to take up iodine. The human body takes 100~200μg of iodine from the diet every day, of which about 1/3 of the iodine enters the thyroid gland. The total amount of iodine in the thyroid gland is about 8000μg, accounting for 90% of the iodine in the whole body, indicating that the thyroid gland has a strong ability to pump iodine. Hyperthyroidism, pump iodine capacity more than normal, iodine intake increased; hypothyroidism is lower than normal, iodine intake decreased. Therefore, the ability of the thyroid gland to take up radioactive iodine (131I) is used as one of the routine methods to check thyroid function. After iodine ion is ingested into the epithelial cells of thyroid follicles, it is rapidly oxidized to activated iodine under the action of peroxidase, and then the tyrosine residues in thyroglobulin are iodinated by iodinase, generating monoiodotyrosine (MIT) and diiodotyrosine (DIT). Under the action of the condensing enzyme, they are condensed to T4 or T3, so that the thyroglobulin containing four tyrosine residues is stored in the follicular lumen.