bone consists of a dense compact layer and a spongy cancellous structure while compact bone forms an organized outer shell cancellous bone consists of thin interlocking plates called tribeculae osteoblasts and osteoclasts are the osteocytes or bone cells that make up bone tissue bone continually renews its structure and strength through remodeling osteoclasts break down existing bone and osteoblasts build up new bone in normal bone adequate physical stress and changing blood calcium levels prompt osteocytes to initiate bone remodeling osteoblasts emit a cytokine that transforms immature osteoclasts into mature osteoclasts in a process called resorption mature osteoclasts use enzymes to remove existing bone tissue then osteoclasts release chemicals that stimulate immature osteoblasts to mature and release osteoprotegerin a protein that deactivates osteoclasts stopping bone resorption in response bone formation occurs mature osteoblasts deposit osteoid a matrix that contains minerals such as calcium and phosphorus and a strong flexible protein called collagen calcium and phosphorus crystallize or mineralize the osteoid then transform into sturdy hydroxyapatite crystals completing the bone formation process in both men and women before midlife bone resorption and bone formation are balanced hormones and other factors bone remodeling for example estrogen hormone suppresses osteoclasts inhibiting resorption to help maintain bone strength after midlife estrogen levels fall and osteoclast activity may go unchecked increased resorption can lead to bone loss osteoporosis is a progressive disease in which the rate of bone resorption exceeds bone formation as a result the tribeculae in cancellous bone become fewer and farther apart the compact bone thins and overall the bone becomes weak fragile and prone to fractures treatments for osteoporosis include calcium and vitamin d supplements to help maintain blood calcium levels anti-resorptive medications that promote bone strength by preventing osteoclast activation and excessive resorption anabolic medications which increase osteoblast activity and promote bone formation and exercise including weight-bearing activities which add stress to bone promoting remodeling