An osteoclast on a bone surface lies within a shallow depression it has excavated in the mineralized matrix. What is the correct name for this depression, and which enzyme released at the ruffled border degrades the organic matrix?

• A Howship lacuna, tartrate-resistant acid phosphatase ✓
• B Howship lacuna, alkaline phosphatase
• C Volkmann canal, matrix metalloproteinase
• D Resorption canal, cathepsin K only

Explanation

Osteoclasts sit in shallow resorption pits called Howship lacunae, sealed off by an actin ring beneath the ruffled border into which protons and lysosomal enzymes are pumped. Tartrate-resistant acid phosphatase (TRAP) is the histochemical marker used to identify osteoclasts, and cathepsin K is the key collagen-degrading enzyme. Alkaline phosphatase marks osteoblasts, Volkmann canals are vascular channels in compact bone, and option D names only one enzyme where TRAP is the defining marker.

Reference: Junqueira's Basic Histology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.