RT Book, Section A1 Brent, Gregory A. A1 Koenig, Ronald J. A2 Brunton, Laurence L. A2 Hilal-Dandan, Randa A2 Knollmann, Björn C. SR Print(0) ID 1162541618 T1 Thyroid and Antithyroid Drugs T2 Goodman & Gilman's: The Pharmacological Basis of Therapeutics, 13e YR 2017 FD 2017 PB McGraw-Hill Education PP New York, NY SN 9781259584732 LK accessbiomedicalscience.mhmedical.com/content.aspx?aid=1162541618 RD 2024/11/02 AB Thyroid hormone is essential for normal development, especially of the CNS. In the adult, thyroid hormone maintains metabolic homeostasis and influences the functions of virtually all organ systems. Thyroid hormone contains iodine, which must be supplied by nutritional intake. The thyroid gland contains large stores of thyroid hormone in the form of thyroglobulin. These stores maintain adequate systemic concentrations of thyroid hormone despite significant variations in iodine availability and nutritional intake. The thyroidal secretion is predominantly the prohormone T4, which is converted in the liver and other tissues to supply the plasma with the active form, T3. Local activation of T4 also occurs in target tissues (e.g., brain and pituitary) and is increasingly recognized as an important regulatory step in thyroid hormone action. Similarly, local deactivation of T3 is an important regulatory step. Serum concentrations of thyroid hormones are precisely regulated by the pituitary hormone TSH in a negative-feedback system. The predominant actions of thyroid hormone are mediated via nuclear TRs that modulate the transcription of specific genes.