Q.51 Calcitonin is produced by
1. Follicular cells of the thyroid gland
2. Parafollicular cells of the thyroid gland
3. Parathyroid gland
4. Follicular cells of the ovary
Calcitonin is produced by parafollicular cells (C cells) of the thyroid gland. These cells lower blood calcium by inhibiting osteoclasts and promoting renal calcium excretion.
Calcitonin Function Overview
Calcitonin (CT), a 32-amino-acid peptide hormone, opposes parathyroid hormone by reducing serum calcium/phosphate via osteoclast inhibition and diuresis.
Secreted in response to hypercalcemia, it plays a minor role in humans but is clinically relevant in medullary thyroid carcinoma markers.
C cells derive from neural crest, embedded between thyroid follicles.
Correct Answer: 2. Parafollicular cells of the thyroid gland
Parafollicular (C) cells synthesize and release calcitonin, confirmed via immunostaining, RT-PCR, and thyroid histology.
They express calcium-sensing receptors (CaR) for hypercalcemia detection.
Distinguishes from follicular cells’ thyroxine production.
Option Breakdown
| Option | Explanation | Correct? |
|---|---|---|
| 1. Follicular cells of thyroid | Produce thyroid hormones T3/T4; surround colloid follicles; no calcitonin. | No |
| 2. Parafollicular cells thyroid | C cells; primary calcitonin source via CALC-1 gene splicing. | Yes |
| 3. Parathyroid gland | Chief cells produce PTH (raises calcium); oxyphil cells ancillary. | No |
| 4. Follicular cells of ovary | Granulosa/theca cells; produce estrogen/progesterone; no calcitonin role. | No |
Clinical Relevance
Elevated calcitonin screens for medullary thyroid cancer (from C cell origin).
Synthetic salmon calcitonin treats hypercalcemia/Paget’s disease.
