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An osteoclast (from Ancient Greek ὀστέον (osteon) 'bone' and κλαστός (clastos) 'broken') is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodeling of bones of the vertebral skeleton .
Osteocytes synthesize sclerostin, a secreted protein that inhibits bone formation by binding to LRP5/LRP6 coreceptors and blunting Wnt signaling. [16] [7] Sclerostin, the product of the SOST gene, is the first mediator of communication between osteocytes, bone forming osteoblasts and bone resorbing osteoclasts, critical for bone remodeling. [20]
Osteoclasts are multinucleated cells that derive from hematopoietic progenitors in the bone marrow which also give rise to monocytes in peripheral blood. [6] Osteoclasts break down bone tissue, and along with osteoblasts and osteocytes form the structural components of bone. In the hollow within bones are many other cell types of the bone marrow.
Bone remodeling is a process which maintains bone strength and ion homeostasis by replacing discrete parts of old bone with newly synthesized packets of proteinaceous matrix. [5] Bone is resorbed by osteoclasts, and is deposited by osteoblasts in a process called ossification. [6] Osteocyte activity plays a key role in this process. Conditions ...
Many believed osteoclasts and osteoblasts came from the same progenitor cell. Because of this, osteoclasts were thought to be derived from cells in connective tissue. Studies that observed that bone resorption could be restored by bone marrow and spleen transplants helped prove osteoclasts' hematopoietic origin. [3]
The origin of the osteoblasts and osteoclasts is from primitive precursor cells found in bone marrow. [22] Like osteoclast cells, osteoblast cell activity is directly related to extracellular pH mirroring of osteoclast activity. At pH 7.4, where osteoclasts are inactive, osteoblast are at peak activity.
Bone tissue undergoes constant remodeling and is kept in balance (homeostasis) by osteoblasts creating bone and osteoclasts destroying bone. Bisphosphonates inhibit the digestion of bone by encouraging osteoclasts to undergo apoptosis , or cell death, thereby slowing bone loss.
Bone tissue is removed by osteoclasts, and then new bone tissue is formed by osteoblasts. Both processes utilize cytokine (TGF-β, IGF) signalling.In osteology, bone remodeling or bone metabolism is a lifelong process where mature bone tissue is removed from the skeleton (a process called bone resorption) and new bone tissue is formed (a process called ossification or new bone formation).