On electron microscopy of compact bone, which structure runs longitudinally and contains collagen fibrils and mineral hydroxyapatite crystals, forming concentric lamellae around the Haversian canal?

• A Perforating (Volkmann's) canals
• B Osteons (Haversian systems) with concentric lamellae ✓
• C Lacunae containing osteoblasts
• D Trabeculae of cancellous bone

Explanation

The structural unit of compact bone is the osteon (Haversian system), consisting of a central Haversian canal containing blood vessels and nerves, surrounded by concentric lamellae of mineralized matrix. Each lamella consists of collagen fibrils oriented in alternating directions with hydroxyapatite crystals deposited along the fibril length. Osteocytes (mature bone cells) occupy lacunae between lamellae and communicate via canaliculi. Volkmann's canals run transversely, connecting adjacent Haversian canals and the periosteum. This architecture provides compressive and torsional strength to cortical bone.

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

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