The Pituitary-Thyroid Regulatory System
The pituitary thyroid regulatory system is a classical example of a hypothalamic-pituitary-endocrine gland feedback loop. As one of the earliest such systems recognized and one which has proven to be so useful clinically, it has been widely studied. The critical elements in the system are shown in the diagram in Figure 1. The best recognized level of feedback regulation is that of thyroid hormone on pituitary thyrotropin (TSH) production. However, results of recent studies reviewed below demonstrate conclusively that there is also feedback regulation of thyrotropin-releasing hormone (TRH) synthesis by thyroid hormone. This complex system is exquisitely sensitive to changes in ambient thyroid hormone levels and serves to maintain the serum hormone concentration in an extremely narrow range in a given individual.
KeywordsThyroid Hormone Deiodinase Activity Iopanoic Acid Thyrotropin Secretion Thyroid Hormone Administration
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