File:Bone remodeling cycle.jpg

Bone Remodeling Cycle Cartoon

The bone remodeling cycle: Breaking down and rebuilding. Bone is constantly being remodeled by two kinds of cells. Osteoblasts form new bone, while osteoclasts promote resorption, the process by which small packets of bone are broken down and assimilated. These processes permit bone to restructure itself in response to stress and help to maintain strong bones.

• A Quiescent phase - Bone surface is inactive. Neither bone resorption nor bone formation is occurring on this region of bone surface.
• B Resorption phase - Osteoclasts (i.e., bone-resorbing cells) remove a discrete packet of bone, creating a cavity, a temporary weak spot or link.
• C Formation phase - Osteoblasts form a bone matrix, which fills in the cavity. The cement line defines the boundary between the newly formed bone and the surface excavated by osteoclasts at the end of the resorption phase (B).
• D Quiescent phase - Inactive bone surface after a completed remodeling cycle. The new surface may be underfilled (1), exactly filled (2), or overfilled (3), reflecting a local decrease, no change, or increase in bone mass, respectively. The most likely mechanism for alcohol-induced bone loss in adults is underfilling of the resorption cavity during bone remodeling.

Image Source: NIAAA - Effects of Alcohol Use and Estrogen on Bone http://pubs.niaaa.nih.gov/publications/arh25-4/276-281.htm

Copyright Information

Most of the information available on the NIAAA Web site is within the public domain, and unless otherwise noted, may be freely downloaded and reproduced. Citation of the source is appreciated.