The thyroid gland is located in the neck and consists of two parts located on either side of the trachea or windpipe.  The thyroid gland uses iodine to make thyroid hormones.   Most of the thyroid hormone circulating in the blood is called thyroxine, or T₄.  Thyroxine is taken up by tissues and activated.  Activated thyroid hormones influence every organ in the body.  Just some of the effects that thyroid hormones have include: