What is Bone?

Contrary to popular belief, bone is not a lifeless structure, but living growing tissue. Throughout life, a dynamic process called "remodeling" occurs in which old bone is removed (resorption) and new bone is laid down (formation). During the resorption phase, bone removing cells (osteoclasts) carve cavities into the surface of the bone, while in the formation phase, bone forming cells (osteoblasts) fill in the cavities with new bone until the bone surface is restored. Beginning in childhood and continuing throughout adulthood, bone formation normally occurs faster than bone removal, so that bones become larger, heavier, denser. In the early to mid-thirties, bone removal overtakes bone replacement leading to a net bone loss of bone tissue.