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
peptide, and the precursor of adrenomedullin.
The hormone participates in calcium (Ca2+)
and phosphorus metabolism. In many ways, calcitonin counteracts
parathyroid hormone (PTH).
To be specific, calcitonin affects blood Ca2+
levels in four ways:
- Inhibits Ca2+ absorption by the
- Inhibits osteoclast activity in bones
- Inhibits phosphate reabsorption by the kidney tubules
- Increases absolute Ca2+ and Mg2+ reabsorption by the kidney tubules, calcitonin is a
renal Ca-conserving hormone.
Secretion of calcitonin is stimulated by:
- an increase in serum gastrin and pentagastrin.
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