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Medical Definition of Thyroid hormones
1. Chemical substances made by the thyroid gland which is located in the front of the neck. The thyroid gland uses iodine to make thyroid hormones. 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. The two most important thyroid hormones are thyroxine (t4) and triiodothyronine (T3). (12 Dec 1998)