The thyroid is also called the thyroid gland. It is an endocrine gland regulating many hormonal systems by the secretion of 3 hormones: triiodothyronine (T3) in very small quantities, thyroxine (T4) and calcitonin which is involved in calcium metabolism. The greatest production of T3 is obtained by the conversion of T4 in the liver, for the largest quantity, and the intestines for the rest. The thyroid produces T3 directly for only 10-20%. The production of these hormones is governed by the thyroid stimulating hormone (TSH) produced by the pituitary gland and requires an iodine supply. In humans, the thyroid gland is located on the front of the neck. Thyroid hormones regulate the metabolism in all cells of the body and are part of the hormonal system that regulates body temperature, body weight, muscle strength, appetite, respiration, growth, the reproductive system as well as heart, brain and kidney function.