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Bone resorption is a process involving the breakdown of bone by specialized cells known as osteoclasts. It occurs on a continual level inside the body, with the broken down bone being replaced by new bone growth. As people age, the rate of resorption tends to exceed the rate of replacement, leading to conditions like osteoporosis. In addition, certain medical conditions such as hormone imbalances can cause bone resorption to increase, leading to increased susceptibility to fractures.
Osteoclasts work by attaching themselves to individual bone cells and secreting compounds to break the cells down, releasing their mineral contents. The minerals enter the bloodstream, where they are processed for recycling to build new bone or eliminated with other bodily wastes. Osteoclasts break down bone in response to inflammation, disease, and injury, removing damaged bone to allow it to be replaced with new bone.
In cases where bone resorption becomes accelerated, bone is broken down faster than it can be renewed. The bone becomes more porous and fragile, exposing people to the risk of fractures. Depending on the location of the bone resorption, additional problems like tooth loss can also arise. The rate of resorption can increase with disuse, as seen when people experience fractures and the bone tends to shrink, or in astronauts, who don't work their musculoskeletal systems while in zero gravity and experience losses in bone density as a result.
Applying pressure to a bone can also contribute to bone resorption, as can failing to treat chronic inflammation and bone injuries. In healthy individuals, the bone may be able to rebuild itself, but in people with chronic untreated conditions, the bone can thin and fragility increases.
There are a number of ways to assess for bone resorption. A blood test can reveal the presence of unusually high numbers of minerals in the blood, suggesting a high rate of bone loss. X-rays can reveal losses in bone density, as can bone density scans, performed specifically to look for losses in density. A physical examination can sometimes provide information about bone loss, as seen when dentists check patients with dentures for signs of damage to the jaw.
If bone resorption is identified, treatment options can be discussed. It may be possible to address the underlying cause to stop the rate of bone loss, and add supplements to help the patient's body build new bone. In other cases, treatment may be focused on supportive care to limit the risks associated with losses in bone density.
The osteoblast and osteoclast are often confusing terms for me. I remember them based on an old trick. "Osteoblasts" take collagen and "blast" it together with calcium to make bone! Easy mental trick.