Which features are found in an osteon?

• A. Interstitial lamellae and osteoclasts only
• B. Central canal with blood vessels and nerves, concentric lamellae, lacunae with osteocytes, and canaliculi
• C. Red marrow and yellow marrow in the central canal
• D. Perforating canals but no central canal

Answer: (B)

An osteon, or Haversian system, is the functional unit of compact bone and is built around a central canal that houses blood vessels and nerves. Surrounding that canal are concentric lamellae, which are rings of bone matrix. Within these lamellae lie lacunae, small cavities that contain osteocytes, and tiny channels called canaliculi that connect lacunae to each other and to the central canal, allowing nutrients and waste to be exchanged. Perforating canals run perpendicular to the osteons to connect adjacent central canals, but they aren’t part of a single osteon. Red marrow and yellow marrow are found in the medullary cavity, not in the central canal, and interstitial lamellae are remnants between osteons rather than features of one osteon. This combination of a central canal with vessels, concentric lamellae, lacunae with osteocytes, and canaliculi defines an osteon.