Thyroid Hormone Signaling
T3/T4 regulation of metabolism, growth, and development via nuclear receptors.
Overview
The hypothalamus releases TRH, stimulating TSH from the pituitary, which stimulates the thyroid to produce T4 (thyroxine) and T3 (triiodothyronine). T4 is converted to active T3 by deiodinases (DIO1/2) in target tissues. T3 binds nuclear thyroid hormone receptors (TRα/β), which form heterodimers with RXR on thyroid response elements (TREs) to regulate gene expression. Thyroid hormones increase basal metabolic rate, thermogenesis, and are essential for brain development.
Cellular Location
Hypothalamus → Pituitary → Thyroid → Target tissues
Clinical Significance
Hypothyroidism is one of the most common endocrine disorders; congenital hypothyroidism causes cretinism if untreated; Graves' disease = autoimmune hyperthyroidism; levothyroxine is among the most prescribed drugs worldwide.