Bone Disorders

Bone is the most well-differentiated organ that originates from mesenchymal tissue. It is alive and dynamic. In terms of function, bone is primarily a structural, load-bearing organ. It provides protection to vital organs and bears loads that the body experiences, both from external forces and those that occur from muscle contraction. Bone provides the anchor point for that muscle contraction through its specialized tendon insertion sites (entheses). Bone's ligament insertion sites, which have the same structure as its tendon insertion sites (and are also classified as entheses), are essential to the function of joints. The articular cartilage that covers the ends of long bones, and which constitutes the bearing surfaces of joints, allows locomotion by the lower extremities and the positioning of the hands in space by the upper extremities. Bone also acts as a metabolic organ in its role as the storage depot of calcium and phosphate. It is the largest reservoir of calcium in the body, and the constant remodeling of bone mobilizes its calcium as one component of the process that tightly mediates calcium homeostasis. Bone remodeling also serves a structural purpose. The remodeling process positions the available mineralized bone tissue in an optimum distribution to bear the loads experienced by the skeleton. The spaces between bony struts and plates that make up trabecular bone (also called spongy or cancellous bone) contain the bone marrow, which produces and stores cells with multiple hematologic and regenerative body functions.