Calcitonin is a 32-amino acid linear polypeptide hormone that is produced in humans primarily by the parafollicular cells (also known as C-cells) of the thyroid, and in many other animals in the ultimobranchial body. It acts to reduce blood calcium (Ca2+), opposing the effects of parathyroid hormone (PTH). Synonyms: Monoclonal Calcitonin antibody, Anti-Calcitonin antibody, Calcitonin receptor antibody, calcr antibody, CT receptor antibody, CTR antibody, CTR receptor antibody.