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Calcitonin — MFDS Part 1 MCQ

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ModeratePhysiologyCalcitoninMFDS Part 1

A rise in ionised serum calcium stimulates calcitonin secretion. Which option correctly pairs the cellular source of calcitonin with its direct skeletal action and expected effect on serum calcium?

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Correct answer: B — Thyroid parafollicular C cells; inhibition of osteoclast activity; lower serum calcium

Calcitonin is secreted by the parafollicular C cells of the thyroid. It acts directly on calcitonin receptors on osteoclasts, inhibiting osteoclast-mediated bone resorption and thereby tending to lower circulating calcium. Parathyroid chief cells instead secrete parathyroid hormone, whose net effect is to raise serum calcium. Thyroid follicular cells produce thyroid hormones rather than calcitonin. Osteoblasts participate in bone formation and regulate osteoclast differentiation but are not the endocrine source of calcitonin. Pancreatic alpha cells secrete glucagon and do not have this role in calcium homeostasis. Although calcitonin has a comparatively limited role in normal adult human calcium regulation, its recognised acute action is hypocalcaemic.

Reference: Mathiesen DS et al. THERAPY OF ENDOCRINE DISEASE: Amylin and calcitonin—physiology and pharmacology. European Journal of Endocrinology. 2022;186(6):R93–R111. https://pubmed.ncbi.nlm.nih.gov/35353712/