Bone is a dynamic tissue. Ninety-nine percent of the body's calcium is found in bone as a complex mixed salt called hydroxyapetite [(Ca5(PO4)3(OH)]. Because the crystal unit cell has two molecules of hydroxyapatite, it is also written as Ca10(PO4)6(OH)2. Bone is the body's calcium reservoir with calcium constantly being removed by osteoclast cells (bone resorption) and laid down by osteoblast cells (calcium deposition). The former are derived from monocyte-macrophage cell lines. Together, bone resorption and calcium deposition are known as bone remodeling. The large bones such as the femur and hip harbor the body's marrow containing stem cells that produce a wide variety of cells including erythro-cytes, platelets, B cells, T cells, neutrophils, basophils, eosinophils, monocytes, and mast cells.
It should not be surprising that bone, being a dynamic tissue, is subject to several diseases, and there are pharmacological treatments for these diseases. These diseases range from deterioration of bone structure, defects in bone remodeling, and malignancies. Some of these pathological conditions have a genetic basis, others can be ascribed to lifestyle, and some attributed to an aging population. This chapter will be restricted to those bone diseases for which there are approved drug treatments. Antineoplastic agents used to treat malignancies of the bone are discussed in Chapter io.
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