How is thyroid hormone regulated?
The hypothalamus secretes thyrotropin-releasing hor-mone (TRH), which stimulates the release of thyroid-stimulating hormone (TSH) by the anterior pituitary gland. The thyroid gland, in response to TSH, releases T3 and T4 into the circulation. TSH also causes increased uptake of iodide and increased iodination of thyroglobu-lin. Both T3 and T4 have a negative-feedback effect on the hypothalamus and pituitary glands.