Figure 5.

Bone remodeling compartment and “basic multicellular unit” of the bone-remodeling cycle. The bone remodeling cycle is initiated and orchestrated by osteocytes. Bone remodeling results from changes in mechanical load, structural microdamage, or exposure to systemic or paracrine factors. Monocyte/macrophage precursors differentiate to mature osteoclasts and resorb bone. Differentiation is induced by M-CSF and RANKL and inhibited by OPG. During reversal, osteoblastic progenitors are recruited to the site of resorption, synthesize osteoid, and mineralize new bone to repair the defect.