Also called parathormone or parathyrin.
1. Secreted by the chief cells of the parathyroid glands as a polypeptide containing 84 amino acids. It acts to increase the concentration of calcium (Ca2+) in the blood, whereas calcitonin (a hormone produced by the parafollicular cells (C cells) of the thyroid gland) acts to decrease calcium concentration. PTH acts to increase the concentration of calcium in the blood by acting upon the parathyroid hormone 1 receptor (high levels in bone and kidney) and the parathyroid hormone 2 receptor (high levels in the central nervous system, pancreas, testis, and placenta). PTH half-life is approximately 4 minutes. It has a molecular mass of 9.4 kDa. (wikipedia.org)
2. A polypeptide hormone that is released by the chief cells of the parathyroid glands and is involved in raising the levels of calcium ions in the blood. (wiktionary.org)
3. Hormone synthesized and released into the blood stream by the parathyroid glands; regulates phosphorus and calcium in the body and functions in neuromuscular excitation and blood clotting. (wordnetweb.princeton.edu)