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Britannica Sources used in this answer

How does negative feedback regulate thyroid hormone secretion?

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A labeled diagram highlights the periodic table entry for iodine, atomic number 53, symbol I, atomic weight 126.90447, and electron configuration. It shows iodine as a solid halogen with an orthorhombic crystal structure and strongly acidic higher-valence oxides, using color and shape keys for classification.
iodine

The thyroid gland functions as part of the hypothalamic-pituitary-thyroid axis, a negative feedback system that maintains hormone levels within a narrow range.1

The process is regulated as follows:

  • Stimulation: The hypothalamus releases thyrotropin-releasing hormone, which triggers the anterior pituitary gland to secrete thyrotropin. Thyrotropin then stimulates the thyroid gland to synthesize and release thyroxine and triiodothyronine.12
  • Inhibition: When thyroid hormone concentrations in the blood rise, these hormones act on the pituitary gland and the hypothalamus to inhibit the further production and secretion of thyrotropin and thyrotropin-releasing hormone.12
  • Correction: If thyroid hormone levels drop, the reduction in negative feedback allows for increased secretion of thyrotropin, which in turn stimulates the thyroid to produce more hormone, restoring balance.12

Because iodine is an essential component of these hormones, this regulatory system is critical for ensuring the body maintains appropriate metabolic function.32