The thyroid gland primarily secretes two hormones, thyroxine and triiodothyronine, commonly known as T4 and T3.

ALTHOUGH much of the progress in thyroid hormone biochemistry is due to the use of thyroxine and 3 : 5 : 3′-triiodothyronine labelled with iodine-131, the high metabolic lability of the iodine ...