Bone is formed by the gradual addition of calcium and phosphorus salts to cartilage, a type of dense connective tissue. This process of ossification begins before birth and continues to adulthood. Although bone appears to be inert, it is actually living tissue that is constantly being replaced and remodeled throughout life. Three types of bone cells are involved in these changes: osteoblasts are the cells that produce bone; osteocytes are mature bone cells; and osteoclasts are involved in the breakdown of bone tissue to release needed minerals or to allow for reshaping and repair. The process of destroying bone so that its components can be taken into the circulation is called resorption. This process occurs normally throughout life; in disease states, resorption may occur more rapidly or more slowly than bone production.

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