Bone remodeling is basically when old bone is removed and new bone is made.
The process of bone modeling has been taking place since you were a child. Bone grows and changes their shapes. Modeling takes place when new bone forms on the outside of the cortex, while the inside of the bone is reabsorbed.
During remodeling, the formation and resorption are more closely coupled. Bone is removed and replaced at the same site during remodeling. This occurs on the surface of the trabecular bone or on the inside of the cortical bone.
Bone is constantly reshaping itself, building it up and breaking it down. Obviously, you don't even notice this reshaping process because it's happening on a microscopic level.
The major influences involved...
Bone remodeling starts with resorption, which the osteoclasts orchestrate. Osteoclasts break down bone by dissolving mineral and resorbing the matrix that osteoblasts have formed.
More research into the function of these cells will undoubtedly result in new drugs for osteoporosis treatment. Scientists now understand that the process of building up bone and resorption of bone is critical because abnormalities in these processes lead to bone diseases.
Vitamin D is critical for proper bone mineralization. The body mainly absorbs Vitamin D through the skin from sunlight, but also can be absorbed through the stomach by way of diet. When Vitamin D is absorbed in the skin, it requires special changes to occur in both the kidney and liver.
Parathyroid hormone (PTH)
Parathyroid hormone provides the exquisite regulation of calcium metabolism. The parathyroid gland, which is actually a set of four small glands located near your thyroid gland, produces this hormone.
Calcitonin is a hormone produced by the thyroid gland. This hormone inhibits bone removal by osteoclasts and promotes bone formation by osteoblasts. Calcitonin is one of the older drugs that's used to treat osteoporosis.
Estrogen works with the parathyroid glands to keep calcium levels in balance. The drops in estrogen levels at menopause contributes to women developing osteoporosis. Estrogen deficiency contributes to developing bone fragility. For some reason, estrogen deficiency results in the production of more osteoclasts and more active osteoclasts.
Testosterone helps maintain strong bones and muscles. Testosterone also stimulates bone formation. Testosterone deficiency clearly is associated with osteoporosis.
Bone is constantly remodeling, replacing, and repairing itself. Every 7 to 10 years, the entire adult skeleton is replaced. From birth on to adulthood, there is a massive bone remodeling taking place as we grow taller and long bones continue to extend.
After the adolescent growth period, remodeling slows, entering the maintenance phase. After menopause, most women have higher levels of bone remodeling once again. In men, the age related thinning of bones seems to occur about 10 years later than it does in women.
Purpose of Remodeling
Remodeling has two basic purposes...
During the remodeling process, certain chemicals are produced. These chemicals that are produced during the bone formation and resorption are called bone markers.
By measuring an individual's bone markers, researchers gauge if a person's bone resorption is too high or formation is too low. The general consensus about bone markers is it provides potentially useful information to supplement BMD measurement, but can't be used to diagnose osteoporosis or its severity.
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