Is Bone Actively Modified

Bone is often considered dead or at least inactive tissue. Maybe this comes from images of skeletons at Halloween or the bone fossils of animals that lived long ago. Whatever the case, bone is actually fairly active. It is constantly engaged in remodeling processes by bone cells called osteoblasts and osteoclasts. The osteoblasts are responsible for making and laying down new collagen protein and other substances. The collagen provides the network for the deposition of calcium and phosphorus mineral complexes such as hydroxyapatite to cling to. This is an important and often overlooked point, because without collagen you cannot properly mineralize bone. For this reason the osteoblasts are said to be active in making new bone tissue and are often called "bone makers."

Osteoporosis is caused by a general loss of minerals and protein from bone, rending it weaker.

Osteoclasts, on the other hand, are primarily responsible for initiating the events leading to the breakdown of bone substances. For this reason they are often called "bone destroyers." Osteoclasts ooze acids that will dissolve the mineral complexes as well as enzymes (collagenase) that will dissolve collagen. The actions of osteoclasts may seem destructive, but their role in bone remodeling is pivotal. Furthermore, when osteoclasts break down bone mineral complexes, the minerals can become available to the blood. This can be important in maintaining blood calcium levels if diet levels are low.

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