<P> Iodine 's main role in vertebrate biology is as constituents of the thyroid hormones , thyroxine ( T4 ) and triiodothyronine ( T3 ) . These are made from addition condensation products of the amino acid tyrosine , and are stored prior to release in an iodine - containing protein called thyroglobulin . T4 and T3 contain four and three atoms of iodine per molecule , respectively . The thyroid gland actively absorbs iodine from the blood to make and release these hormones into the blood , actions which are regulated by a second hormone TSH from the pituitary . Thyroid hormones are phylogenetically very old molecules which are synthesized by most multicellular organisms , and which even have some effect on unicellular organisms . </P>
<P> Iodine 's main role in vertebrate biology is as constituents of the thyroid hormones , thyroxine ( T4 ) and triiodothyronine ( T3 ) . These are made from addition condensation products of the amino acid tyrosine , and are stored prior to release in an iodine - containing protein called thyroglobulin . T4 and T3 contain four and three atoms of iodine per molecule , respectively . The thyroid gland actively absorbs iodine from the blood to make and release these hormones into the blood , actions which are regulated by a second hormone TSH from the pituitary . Thyroid hormones are phylogenetically very old molecules which are synthesized by most multicellular organisms , and which even have some effect on unicellular organisms . </P>
where is the most of the iodine in the body concentrated
where is the most of the iodine in the body concentrated
thyroid gland
thyroid gland