Regulation of Thyroid Function, Synthesis and Function of Thyroid Hormones

Abstract

Thyroid hormone (TH) is a common name for the two products secreted by thyroid follicles, namely the prohormone thyroxine (T4) as the major product and the active hormone triiodothyronine (T3) as the minor product. Most T3 is produced by deiodination of T4 in peripheral tissues. TH is essential for the development of different tissues, in particular the central nervous system, and for the function of the tissues throughout life. The secretion of thyroid hormone is regulated within the hypothalamus-pituitary thyroid axis, but the biological activity of thyroid hormone is largely regulated at the level of the target tissues. This chapter covers various aspects of (a) the neuroendocrine regulation of thyroid function, (b) the biosynthesis of thyroid hormone, in particular T4, (c) the local regulation of bioactive TH in target tissues, and (d) the mechanisms by which T3 exerts its biological activities.