Final answer:
Osteons are the basic structural units of bone, composed of lamellae and a central canal. Secondary osteons form from pre-existing tunnels as part of bone remodeling.
Explanation:
Osteons are the functional unit of bone, resembling reinforcing rods in concrete. They consist of concentric lamellae surrounding a central canal, the Haversian canal, containing nerves, blood vessels, and osteogenic cells. Secondary osteons form by osteoclasts enlarging pre-existing tunnels for osteoblasts to deposit bone in a centripetal direction.
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