What is the functional unit of a bone?

• A. Osteon (Haversian system)
• B. Osteocyte
• C. Haversian canal
• D. Periosteum

Answer: (A)

The functional unit of bone in compact bone is the osteon, also known as the Haversian system. An osteon is a cylindrical structure with a central Haversian canal that contains blood vessels and nerves, surrounded by concentric lamellae of mineralized bone. Within those lamellae reside lacunae holding osteocytes, and tiny channels called canaliculi connect the osteocytes to each other and to the central canal, enabling nutrient and waste exchange.

This organized arrangement provides the bone with strength and the ability to repair and remodel efficiently. The central canal is just a part of the osteon, while the periosteum is the outer covering, and an osteocyte is a cell within the bone matrix—both not the basic structural unit.