Bone Physiology — MFDS Part 1 MCQ

Correct answer: D — Osteoclast

Osteoclasts are the specialised cells responsible for bone resorption. They are multinucleated cells derived from the haematopoietic monocyte–macrophage lineage. After attaching to bone, an osteoclast forms a sealing zone and ruffled border. Proton secretion acidifies the enclosed resorption compartment, dissolving hydroxyapatite, while enzymes such as cathepsin K degrade the organic matrix. Osteoblasts instead produce osteoid and promote bone formation. Osteocytes are mature bone cells that act mainly as mechanosensors and regulators of remodelling. Fibroblasts synthesise connective-tissue matrix, and chondrocytes form and maintain cartilage. Therefore, osteoclast is the single best answer.

Reference: Zhu S, Yan M-Q, Masson A, Chen W, Li Y-P. Cell signaling and transcriptional regulation of osteoclast lineage commitment, differentiation, bone resorption and diseases. Abstract and Figure 6: Osteoclast-mediated bone resorption. 2026. https://pubmed.ncbi.nlm.nih.gov/41559024/