Picture of Thyroid

The thyroid is a gland that sits on the bottom of the front of the neck. It is shaped like a butterfly and it wraps around the trachea. The thyroid produces thyroid hormone, which is necessary for the proper functioning of every cell in the body. Thyroid hormone controls metabolism and affects heart rate, growth, and body temperature. The thyroid needs iodine to make thyroid hormones, T4 (thyroxine) and T3 (triiodothyronine). T4 is the inactive form of thyroid hormone and T3 is the active form.