Osteoclasts are derived from the same stem cells that produce macrophages. RANK (receptor activator for nuclear factor-κB) receptors on osteoclast precursors bind RANK ligand (RANKL) expressed by osteoblasts and marrow stromal cells. Along with macrophage colony-stimulating factor (M-CSF), the RANK-RANKL interaction drives the differentiation of functional osteoclasts. Stromal cells also secrete osteoprotegerin (OPG) that acts as a decoy receptor for RANKL, preventing it from binding the RANK receptor on osteoclast precursors. Consequently OPG prevents bone resorption by inhibiting osteoclast differentiation. Paracrine mechanisms regulating osteoclast formation and function.
Osteoporotic vertebral body (right) shortened by compression fractures, compared with a normal vertebral body. Note that the osteoporotic vertebra has a characteristic loss of horizontal trabeculae and thickened vertical trabeculae.
Osteoprosis
Here is a "compressed" fracture of the vertebral column. The middle vertebral body shown here is greatly reduced in size. Such fractures are common in persons with osteoporosis in which there is accelerated bone loss, particularly older women, and can occur with even minor trauma.
Osteoprosis
The trabecular bone in the vertebral bodies is very thin and the two lower vertebrae show the effects of crush fracture - a complication of this condition.
Osteoprosis
Lt. This vertical slice through the thoracic spine shows severe osteoporosis of the vertebrae, with the characteristic 'bowing' or 'curvature' of the spine caused by collapse of the anterior portions of the vertebral bodies. Osteoporosis of this severity is more common in postmenopausal women. It is frequently associated with nerve pain caused by compression of the nerves as they pass through the intervertebral foramina. Rt. X-ray of the patient shown taken some months before his death.
Osteoprosis