a substance produced by a tadpole's thyroid gland that causes it to metamorphosize. See the thyroxine page.
(T4) -- A chemical substance made by the thyroid gland The thyroid gland uses iodine to make thyroid hormones. Thyroxine (T4), one of the most important thyroid hormones, has four iodine molecules attached to its molecular structure. Thyroid hormones are essential for the function of every cell in the body. They help regulate growth and the rate of chemical reactions (metabolism) in the body.
a hormone secreted by the thyroid gland; it regulates growth and development, organic metabolism, and the activity of the nervous system