ABSTRACT
Bone has two main compartments: cortex and trabecular bone. But, in part because of the lack of information on cortical actions of sex steroids, we concentrate on information regarding the trabecular bone or marrow bone. Maintenance of trabecular bone is the result of an interaction between the three different bone cell types: osteoblasts, osteoclasts and osteocytes (Figure 1). Osteoblasts are derived from pluripotent mesenchymal stem cells and are responsible for bone formation and mineralization. The mesenchymal stem cells also give rise to chondrocytes, adipocytes, myoblasts and fibroblasts, as well as hematologic cells and immunocytes. After formation, the osteoblasts may undergo apoptosis, or become bone-lining cells or osteocytes, representing further stages of differentiation9.
