Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulate the endocrine function of the thyroid gland. TSH is a glycoprotein and consists of two subunits, the alpha and the beta subunit, which are non-covalently bound to one another. The alpha subunit of TSH is also present in two other pituitary glycoprotein hormones: Follicle stimulating hormone and luteinizing hormone and, in primates, in the placental hormone chorionic gonadotropin. Each of these hormones also has a unique beta subunit, which provides receptor specificity. In other words, TSH is composed of alpha subunit bound to the TSH beta subunit, and TSH associates only with its own receptor. Free alpha and beta subunits have essentially no biological activity. Anti-TSH reacts with TSH-producing cells (thyrotrophs), and is a useful marker in classification of pituitary tumors and the differential identification of primary and metastatic tumors in the pituitary gland.