Regulatory Mechanisms of Bone Development and Function

Bone is metabolically active organ where 10% of it is normally and constantly replaced. Bone constitutes the trabecular or spongy bone (25%) and cortical or compact bone (75%). Trabecular bone is metabolically active and forms the internal supportive elements of the bone. The outer capsule is made up of cortical bone and is particularly present in the shafts of long bones. At the structural level, two different forms of bone can be distinguished, i.e. cortical or compact bone−which forms the diaphysis of long bones and provides protection for the medullary cavity− and trabecular, cancellous, or spongy bone, which is found at the ends of the long bones (epiphyses). The total skeleton comprises about 20% of trabecular bone. Trabecular bone has a porosity of 50%– 90%, while cortical bone of 10% [1].