Parathyroid hormone (PTH) is a hormone secreted by the parathyroid glands that is important in bone remodeling, which is an ongoing process in which bone tissue is alternately resorbed and rebuilt over time. It essentially increases blood calcium levels. PTH essentially acts to increase the concentration of calcium in the blood by acting upon the parathyroid hormone 1 receptor, which is present at high levels in bone and kidney, and the parathyroid hormone 2 receptor, which is present at high levels in the central nervous system, pancreas, testis, and placenta. PTH was one of the first hormones to be shown to use the G-protein, adenylyl cyclase second messenger system.
