The amount of bone in the body is continually adjusted to achieve the best balance between lightweight structure and strong support. Bone activity in any stage of life continually undergoes an orderly set of procedures. The first step, activation, is a retraction of the protective lining cells that cover normal resting bone. After the bone is directly exposed to the blood stream, osteoclasts swarm to its raw surface by way of a rich system of blood vessels. Once there, the osteoclasts dissolve the bone, after which they die or become inactive.
Osteoblasts then arrive to rebuild the damage.
They make bone by producing rows of collagen fibers, changing the orientation of the fiber in each row. The osteoblasts remain in the bone tissue where they continue to live. Any remaining osteoclasts transform into harmless lining cells. During any 10-year period, virtually all bones are completely rebuilt. In children, the process of resorption and regrowth allows bone shape to match the child's rapid growth.