Thyroxine, also known as tetraiodothyronine or T<sub>4</sub>, is a hormone produced by the thyroid gland. It is the primary form of thyroid hormone found in the blood and acts as a prohormone of the more active thyroid hormone, triiodothyronine (T<sub>3</sub>). Thyroxine and its active metabolites are essential for regulating metabolic rate, supporting heart and muscle function, promoting brain development, and maintaining bone health.
Regulation
Thyroxine has a half-life of approximately one week and hence maintains relatively stable blood levels. Its production and release are controlled through a complex feedback loop involving the hypothalamus, pituitary gland, and thyroid gland. This regulatory system ensures that optimal hormone levels are maintained.
Biosynthesis
[[File:Thyroxine biosynthesis.svg|class=skin-invert-image|thumb|left|Biosynthesis of thyroxine