What is the basic unit of compact bone?

• A. Osteoclast
• B. Osteocytes
• C. Osteon
• D. Trabecula

Answer: (C)

In compact bone, the structure is built from repeating units that give it strength and organized organization. The basic unit is the osteon, also called the Haversian system. An osteon is a cylindrical pillar around a central Haversian canal that contains blood vessels and nerves. The bone matrix around this canal is arranged in concentric lamellae, with small spaces called lacunae housing osteocytes. Tiny channels called canaliculi connect these osteocytes, allowing nutrients and signals to pass through the bone tissue. Multiple osteons sit side by side, with interstitial lamellae between them, all oriented to resist bending along the length of the bone.

Osteoclasts are cells that resorb bone during remodeling, not the repeating unit itself. Osteocytes are the mature cells embedded within the bone matrix, housed in lacunae inside the lamellae, but they are individual cells within the unit rather than the unit as a whole. Trabeculae are the lattice-like structures of cancellous (spongy) bone, not the compact bone’s basic unit.