Source: Joost Van Durme, Glycoprotein-hormone Receptor Information System (http://gris.ulb.ac.be/).
Thyroid-stimulating hormone, also known as thyrotropin, is a hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid gland. Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3). The production of TSH is inhibited by the production of somatostatin by the hypothalamus. T3 and T4 also inhibit TSH production and secretion, creating a regulatory negative feedback loop. The release of TSH is stimulated by the production of thyrotropin-releasing hormone (TRH).
In the digram shown here, pink = TSH receptor extracellular domain, green = beta subunit of TSH hormone, blue = alpha subunit of TSH hormone.