The thyroid is a gland which is responsible for the production of thyroid hormones. These hormones are essential for the regulation of body metabolism. If the thyroid hormone levels are not in the normal range various signs and symptoms may occur. The thyroid gland uses the iodine from the diet to produce the thyroid hormones. Over activity of thyroid glands can result in excessive production of thyroid hormones. This is called as hyperthyroidism. If under activity of the thyroid gland occurs it can result in hypothyroidism.