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). It
has been found in fish, reptiles, birds, and mammals. Its
importance in humans has not been as well established as its
importance in other animals, as its function is usually not
significant in the regulation of normal calcium homeostasis.
Calcitonin was purified in 1962 by Copp and Cheney. While it was
initially considered a secretion of the parathyroid glands, it
was later identified as the secretion of the C-cells of the
thyroid gland. Calcitonin is formed by the proteolytic cleavage
of a larger prepropeptide, which is the product of the CALC1
gene (). The CALC1 gene belongs to a superfamily of related
protein hormone precursors including islet amyloid precursor
protein, calcitonin gene-related peptid