<P> 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 . </P>
<P> 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 . </P>
what is the purpose of t3 and t4
what is the purpose of t3 and t4
regulation of metabolism
regulation of metabolism