The thyroid gland makes and releases two hormones: triiodothyronine (T) (o - (4 - Hydroxy - 3, 5 - iodophenyl) 3, 5 - diiodophenyl tyrosine) and thyroxine (T) (o - (4 - Hydroxy - 3, 5 - diiodophenyl) 3, 5diiodophenyl tyrosine). They are tyrosine - based hormones that are primarily responsible for regulation of metabolism. T and T are partially composed of iodine (see molecular model). A deficiency of iodine leads to decreased production of T and T, enlarges the thyroid tissue and will cause the disease known as simple goitre. The major form of thyroid hormone in the blood is thyroxine (T), which has a longer half - life than T. In humans, the ratio of T to T released into the blood is sometimes claimed to be quite high, but thyroid removal patient data suggests it to vary between 4: 1 to 2: 1, the average being 100: 36 (roughly 2.8: 1). T is converted to the active T (three to four times more potent than T) within cells by deiodinases (5 ' - iodinase). These are further processed by decarboxylation and deiodination to produce iodothyronamine (T a) and thyronamine (T a). All three isoforms of the deiodinases are selenium - containing enzymes, thus dietary selenium is essential for T production. Edward Calvin Kendall was responsible for the isolation of thyroxine in 1915.
what is the purpose of t3 and t4
regulation of metabolism