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High Yield Notes
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Calcitonin is synthesized and secreted by the or C cells of the thyroid gland.

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The body’s blood calcium level stays stable thanks to three hormones: parathyroid hormone, vitamin D, and calcitonin.

Parathyroid hormone and vitamin D help increase calcium levels, whereas calcitonin helps lower them. Let’s focus on the role of calcitonin.








Now, calcitonin is a polypeptide hormone involved in regulating blood calcium levels.

Calcitonin comes from the parafollicular cells, or C cells, of the thyroid gland which is a gland located in the neck that looks like two thumbs hooked together in the shape of a “V”.


C cells are adjacent to follicles, more precisely in the connective tissue that separates the follicles.

C cells synthesize preprocalcitonin, a peptide with 141 amino acids, which becomes procalcitonin after a signal peptide is cut off by an enzyme via proteolytic cleavage, leaving 116 amino acids.

From there, procalcitonin is cleaved again into the 33 amino acid-long immature calcitonin, and finally cleaved one more time into mature calcitonin, which has 32 amino acids.

It’s then stored in secretory granules in C cells, waiting to be released.

Normally total blood calcium is between 8.5 to 10 mg/dl.

And changes in calcium levels are detected by a calcium-sensing surface receptor on C cells.

  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  5. "On the Origin of Cells and Derivation of Thyroid Cancer: C Cell Story Revisited" European Thyroid Journal (2016)
  6. "Calcitonin Receptor Plays a Physiological Role to Protect Against Hypercalcemia in Mice" Journal of Bone and Mineral Research (2008)