Resorption is the breakdown and assimilation of old bone in the cycle of bone growth. The process of resorption (remodeling) involves the removal of hard bone tissue by osteoclasts followed by the laying down of new bone cells by osteoblasts. Resorption releases calcium and repairs micro-damage to bones from normal wears and tears. An imbalance between the rate of bone resorption and bone formation can lead to the development of osteoporosis and osteopenia, and possibly result in fractures to the spine, wrist, or hip. The rate of resorption of bone can also be accelerated in patients who smoke.