- A hormone produced by the thyroid gland that lowers the levels of calcium and phosphate in the blood and promotes the formation of bone. Bone is in a constant state of remodeling whereby old bone is removed by cells called osteoclast and new bone is laid down by cells called osteoblasts. Calcitonin inhibits bone removal by the osteoclasts and at the same time promotes bone formation by the osteoblasts. Calcitonin is given in hypercalcemia (high blood calcium) to lower the calcium level; in osteoporosis to increases bone density and decrease the risk of a fracture; and in Paget disease to decrease bone turnover and bone pain. Calcitonin is also called thyrocalcitonin.
* * *A peptide hormone, of which eight forms in five species are known; composed of 32 amino acid s and produced by the parathyroid, thyroid, and thymus glands; its action is opposite to that of parathyroid hormone in that c. increases deposition of calcium and phosphate in bone and lowers the level of calcium in the blood; its level in the blood is increased by glucagon and by Ca2+ and thus opposes postprandial hypercalcemia. SYN: thyrocalcitonin. [calci- + G. tonos, stretching, + -in]
* * *cal·ci·to·nin .kal-sə-'tō-nən n a polypeptide hormone esp. from the thyroid gland that tends to lower the level of calcium in the blood plasma called also thyrocalcitonin
* * *n.a hormone, produced by C cells in the thyroid gland, that lowers the levels of calcium and phosphate in the blood. Calcitonin is given by injection to treat hypercalcaemia and Paget's disease of the bone. Compare parathyroid hormone.
* * *cal·ci·to·nin (kal″sĭ-toґnin) a 32-amino-acid polypeptide hormone elaborated by the parafollicular cells of the thyroid gland in response to hypercalcemia; it lowers plasma calcium and phosphate levels, inhibits bone resorption, and acts as an antagonist to parathyroid hormone. It is secreted in lower vertebrates by the ultimobranchial bodies. Called also thyrocalcitonin.
Medical dictionary. 2011.