Thyroid Harmones: II
Regulation of Secretion: -Thyroid hormone secretion is controlled by Anterior Pituitary gland via thyrotropin or TSH. -TSH is stimulated by TRH which is secreted from Hypothalamus. -Somatostatin from Hypothalamus, T3 & T4 inhibits Anterior Pituitary gland directly from releasing TSH while only T3 & T4 inhibits Hypothalamus to release TRH. -The action of TRH on Pituitary Gland & TSH on Thyroid gland is mediated by enhanced cAMP synthesis. -Higher concentration of TSH acts via IP3/DAG Pathway & Mediate intracellular calcium pathway in thyroid cell. Mechanism of Action: -Thyroid hormones bind to ligand-binding domain of thyroid hormone receptor (TR) & and it heterodimerizes with retinoid X receptor (RXR). -Then it undergoes conformational changes releasing 'corepressor' & binding with 'coactivator'. -This induces gene transcription followed by Production of ...