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MEDICAL ANIMATION TRANSCRIPT: 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 trabeculae. 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 built 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 phosphorous, 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 mid-life, bone resorption and bone formation are balanced. Hormones and other factors influence bone remodeling. For example, estrogen hormone suppresses osteoclasts, inhibiting resorption to help maintain bone strength. After mid-life, 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 trabeculae 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 adds stress to bone, promoting remodeling. ♪ [music] ♪