Abstract
In 1962 Copp proposed the existence of a hypocalcaemic hormone. Subsequent studies have shown him to be right. Calcitonin is a potent inhibitor of bone resorption. By its action it lowers systemic blood calcium. It is secreted in response to hypercalcaemia by a distinct endocrine system within the thyroid in mammals and within the ultimobranchial bodies in fish, amphibia and reptiles. The active principle from pig has now been isolated and found to be a polypeptide composed of thirty-two amino acid residues. Together with parathyroid hormone, the hormone provides precise regulation of calcium concentration in the blood and controls bone remodelling and mineral turnover. Calcitonin in man may be secreted in excessive amounts by medullary carcinoma of the thyroid. In addition, aberrations in its secretion may play a role in pseudohyper-parathyroidism and ostepetrosis.