Osteoclasts are derived from which cell lineage and are characterized by which ultrastructural feature?

• A Mesenchymal stem cells; extensive rough endoplasmic reticulum
• B Osteoblast precursors via trans-differentiation; abundant alkaline phosphatase
• C Monocyte-macrophage lineage (hematopoietic stem cell); ruffled border (folded membrane facing the bone surface) ✓
• D Neural crest cells; lipid droplets within the cytoplasm

Explanation

Osteoclasts are derived from hematopoietic stem cells of the monocyte-macrophage lineage (fuse to form multinucleated giant cells, similar to macrophage fusion). Their hallmark ultrastructural feature is the ruffled border — a highly folded plasma membrane facing the resorption lacuna (Howship's lacuna), which creates a sealed zone between the cell and bone surface. The osteoclast acidifies this sealed compartment with H+ (via vacuolar H-ATPase) and releases cathepsin K to dissolve both mineral and organic matrix. Osteoblasts are mesenchymal-derived and are rich in alkaline phosphatase.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.