Calcitonin participates in calcium homeostasis alongside PTH and vitamin D. Which statement about calcitonin is correct?
- A It is secreted by parafollicular C cells of the thyroid and lowers serum calcium mainly by inhibiting osteoclastic bone resorption ✓
- B It is secreted by chief cells of the parathyroid gland in response to hypercalcemia
- C It increases renal tubular reabsorption of calcium, thereby raising serum calcium
- D Its secretion is stimulated by hypocalcemia and it acts synergistically with PTH
Correct answer: A. It is secreted by parafollicular C cells of the thyroid and lowers serum calcium mainly by inhibiting osteoclastic bone resorption
Explanation
Calcitonin is synthesized by the parafollicular C cells of the thyroid, which derive from the neural crest. It is released when serum calcium rises and acts on osteoclasts to inhibit bone resorption, producing a mild fall in serum calcium. Option B is wrong because chief cells secrete PTH, not calcitonin, and respond to hypocalcemia. Option D fails because calcitonin opposes, rather than synergizes with, PTH. In humans its physiologic importance is modest, since thyroidectomy does not cause hypercalcemia.
Reference: Ganong Review of Medical Physiology, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.