What is the fundamental functional unit of cortical bone, structured as a column of rings of bone matrix with a central (Haversian) canal?

• A. Calcaneus
• B. Osteon
• C. -plasty
• D. Endosteum

Answer: (B)

The fundamental functional unit of cortical bone is the osteon, also known as the Haversian system. An osteon is a cylindrical column of bone matrix organized into concentric lamellae that surround a central Haversian canal containing blood vessels and nerves. Osteocytes reside in lacunae between the lamellae and communicate through tiny canaliculi, enabling nutrient and signal exchange. Many osteons align to form the dense outer layer of bone, with interstitial lamellae filling the spaces between them. In contrast, calcaneus is a bone in the heel, -plasty is a surgical repair suffix, and endosteum is the innermost lining of bone; none of these describe the basic unit of cortical bone.