A specialized bone cell that absorbs bone, allowing for the deposition of new bone and maintenance of bone strength. Osteoclasts secrete enyzmes that dissolve the matrix of old bone tissue and acids that dissolve bone salts, which contain calcium and phosphorus. Except in growing bone, the rate of bone deposition and bone absorption equal each other so that bone mass remains constant. A mass of osteoclasts absorbs bone from the outer surfaces inward for about three weeks. The osteoclasts are then converted into osteoblasts that form new bone to fill in the cavities. See also osteoblast.
