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Osteoclasts lie in small cavities called Howship's lacunae, formed from the digestion of the underlying bone. The sealing zone is the attachment of the osteoclast's plasma membrane to the underlying bone. Sealing zones are bounded by belts of specialized adhesion structures called podosomes.
Minor, but important, amounts of small proteins, including osteocalcin and osteopontin, are secreted in bone's organic matrix. [21] Osteocalcin is not expressed at significant concentrations except in bone, and thus osteocalcin is a specific marker for bone matrix synthesis. [22] These proteins link organic and mineral component of bone matrix ...
The Haversian canal contains the bone's blood supplies. The boundary of an osteon is the cement line. Each Haversian canal is surrounded by varying number (5-20) of concentrically arranged lamellae of bone matrix. Near the surface of the compact bone, the lamellae are arranged parallel to the surface; these are called circumferential lamellae.
Type I collagen composes 90–95% of the organic matrix, with the remainder of the matrix being a homogenous liquid called ground substance consisting of proteoglycans such as hyaluronic acid and chondroitin sulfate, [29] as well as non-collagenous proteins such as osteocalcin, osteopontin or bone sialoprotein. Collagen consists of strands of ...
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 that result in a decrease in bone mass can either be caused by an increase in resorption or by a decrease in ossification. During childhood, bone formation exceeds resorption.
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 ...
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The radiating processes of the osteocytes (called filopodia) project into these canals. These cytoplasmic processes are joined together by gap junctions. Osteocytes do not entirely fill up the canaliculi. The remaining space is known as the periosteocytic space, which is filled with periosteocytic fluid. This fluid contains substances too large ...