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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]
Materials picked up by osteocytes adjacent to blood vessels are distributed throughout the bone matrix via the canaliculi. Diameter of canaliculi in human bone is approximately 200 to 900 nm. [ 1 ] In bovine tibia diameter of canaliculi was found to vary from 155 to 844 nm (average 426 nm). [ 2 ]
In an ordinary microscopic section, viewed by transmitted light, they appear as fusiform opaque spots. Each lacuna is occupied during life by a branched cell, termed an osteocyte, bone-cell or bone-corpuscle. Lacunae are connected to one another by small canals called canaliculi. A lacuna never contains more than one osteocyte.
Diagram of a typical long bone showing both cortical (compact) and cancellous (spongy) bone. Haversian canals [i] (sometimes canals of Havers, osteonic canals or central canals) are a series of microscopic tubes in the outermost region of bone called cortical bone. They allow blood vessels and nerves to travel through them to supply the osteocytes.
Osteoblasts are mononucleate bone-forming cells. They are located on the surface of osteon seams and make a protein mixture known as osteoid, which mineralizes to become bone. [23] The osteoid seam is a narrow region of a newly formed organic matrix, not yet mineralized, located on the surface of a bone. Osteoid is primarily composed of Type I ...
Feedback from physical activity maintains bone mass, while feedback from osteocytes limits the size of the bone-forming unit. [33] [34] [35] An important additional mechanism is secretion by osteocytes, buried in the matrix, of sclerostin, a protein that inhibits a pathway that maintains osteoblast activity. Thus, when the osteon reaches a ...
Osteocytes, the most common cell type within mature cortical bone, actively participate in the growth and maintenance of TCVs through the transfer of mitochondria to endothelial cells. Scanning electron microscopy images have revealed that osteocytes possess numerous dendritic processes with expanded, endfoot-like structures. These endfeet ...
This results in an increased bone resorption rate and a decreased bone mineral density due to increased pit numbers and pit areas in the bone. [18] [19] [20] Research has shown that viable osteocytes (another type of bone cell) may prevent osteoclastogenesis, whereas apoptotic osteocytes tend to induce osteoclast stimulation. Stimulation of ...