Her hypothyroidism medication replaces a hormone normally produced by which cells?

Correct answer: C. Thyroid follicular cells

• A. Parafollicular or C cells produce CALCITONIN, which lowers serum calcium by inhibiting osteoclastic resorption. They are also the cell of origin of medullary thyroid carcinoma.
• B. Parietal cells of the renal glomerulus line Bowman's capsule and have no endocrine secretory role. Gastric parietal cells secrete hydrochloric acid and intrinsic factor.
• C. CORRECT. Levothyroxine is synthetic T4. THYROID FOLLICULAR CELLS synthesise thyroglobulin, iodinate it, and release T4 and T3 into the circulation. T4 is the main secretory product and is converted peripherally to the more active T3. Follicular cells are also the cells that concentrate iodide, which is the basis of radioiodine therapy and imaging.
• D. Chief cells occur in two places, neither of which is the thyroid: gastric chief cells secrete pepsinogen, and PARATHYROID chief cells secrete parathyroid hormone — the direct antagonist of calcitonin.

Note: Untreated or under-treated hypothyroidism matters dentally: these patients are sensitive to CNS depressants, so sedatives and opioids should be dosed cautiously, and severe untreated disease carries a risk of myxoedema coma under stress.