<Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (April 2016) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (April 2016) (Learn how and when to remove this template message) </Td> </Tr> <P> Thyroid hormones (T and T) are produced by the follicular cells of the thyroid gland and are regulated by TSH made by the thyrotropes of the anterior pituitary gland . The effects of T in vivo are mediated via T (T is converted to T in target tissues). T is 3 - to 5 - fold more active than T . </P> <P> Thyroxine (3, 5, 3', 5' - tetraiodothyronine) is produced by follicular cells of the thyroid gland . It is produced as the precursor thyroglobulin (this is not the same as thyroxine - binding globulin (TBG)), which is cleaved by enzymes to produce active T . </P>

Thyroid hormones (t3 and t4) are produced by