TSH (Thyroid Stimulating Hormone), also known as Thyrotropin, is a heterodimeric glycoprotein hormone. It is composed of a unique beta subunit and a common alpha subunit which is shared with Follicle-Stimulating Hormone, Luteinizing Hormone, and Chorionic Gonadotropin. TSH is produced and secreted by the anterior pituitary gland. Its secretion is controlled by Thyrotropin-Releasing Hormone (TRH) from the hypothalamus. TSH binds to the TSH Receptor in the thyroid gland to stimulate production of Thyroxine (T4), which is converted in peripheral tissues to Triiodothyronine (T3), a more biologically potent form of the thyroid hormone. TSH secretion is also controlled by plasma T3 and T4 via a negative feedback mechanism and by the neurotransmitters dopamine and Somatostatin. TSH is also produced in the bone marrow where it promotes bone strength and quality.