Caption

Osteoporosis. Computer artwork sequence of an osteoclast (green, bone-removing cell) destroying a piece of bone. This process (bone resorption), is a normal part of the continual rebuilding of a human skeleton, but it can get out of control and lead to excessive bone loss in disorders such as osteoporosis. The osteoclast has a ruffled edge that it attaches to the bone (top), secreting acids and enzymes (middle) to remove the mineral and collagen of the bone. The bone is rebuilt by osteoblasts (bone-building cells), but if this does not happen then the bone units (trabeculae) become fragile and may break (bottom).