The thyroids have a most remarkable capacity to absorb iodine from the circulating blood so that it contains about 20% of the total iodine present in the body. This iodine is used in the manufacture of the hormones Liothyronine (T3) and Levothyroxine (T4). These hormones are released to stimulate the oxidative metabolism in nearly all tissues of the body, the best-known active principle of the Thyroid gland.