Osteoclasts excavate resorption lacunae (Howship lacunae) into bone surface. Which combination of features at the ruffled border enables dissolution of both mineral and organic matrix?
- A Proton pump mediated acidification of the sealed compartment plus lysosomal cathepsin K degradation of collagen ✓
- B Alkaline phosphatase secretion and osteocalcin deposition under the ruffled border
- C Carbonic anhydrase driven bicarbonate secretion plus matrix metalloproteinase activation outside the seal
- D Reactive oxygen species generation plus tartrate resistant acid phosphatase acting extracellularly on hydroxyapatite
Correct answer: A. Proton pump mediated acidification of the sealed compartment plus lysosomal cathepsin K degradation of collagen
Explanation
The osteoclast seals off a resorption compartment between its ruffled border and bone using integrin based podosomes (sealing zone). B vacuolar H plus ATPase pumps protons into this compartment, aided by cytoplasmic carbonic anhydrase II generating intracellular protons, dissolving hydroxyapatite. Lysosomal enzymes, chiefly cathepsin K, then degrade the exposed organic matrix. TRAP serves as a histochemical marker rather than the effector of mineral dissolution, and alkaline phosphatase marks osteoblasts, not osteoclasts.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.