Remember, bone is a live tissue just like the kidneys, heart, and other organs of the body. Remodeling is under the control of a number of hormones. Remodeling consists of tearing down small parts of the bones, and then re-forming them.
Osteoclasts live in the central portion of the bone.
The osteoblasts are less efficient at making bone than the osteoclasts are at removing it. Any factor which causes a higher rate of bone remodeling will ultimately lead to a more rapid loss of bone mass and thus more fragile bones. The same factors which encouraged bone formation as a youth and teenager affect the maintenance of bone mass during the adult years. The most important influences are calcium intake , reproductive hormone status , normal parathyroid gland function , and physical activity . Each of these are discussed on separate pages.