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1. Osteocytes
These cells are
mature bone cells that maintain the protein
and mineral content of the surrounding bone
matrix. |
Osteocytes
occupy spaces called lacunae that are
sandwiched between mineralized layers of
matrix called lamellae. Osteocytes
communicate with each other by cytoplasmic
processes that extend through narrow
passageways in the bony matrix called canaliculi.
Canaliculi
permit the exchange of nutrients and waste
products between the osteocytes and
blood vessels and provide a means for
signals to be transferred from one osteocyte
to another. |
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2. Osteoblasts
Osteoblasts are
precursor cells that are found on the inner
and outer surfaces of bone. These cells
secrete the organic components of bone
matrix called osteoid. The osteoid
then becomes mineralized to form bone. |
The process of
bone formation is called osteogenesis. When the osteoblast is surrounded by bone
matrix it differentiates into an osteocyte. |
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3. Osteoprogenitor Cells
These cells are mesenchymal,
or stem, cells that can divide
and differentiate into osteoblasts. |
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4. Osteoclasts
Osteoclasts are
giant cells with 50 or more nuclei and are
derived from the stem cells that also
produce monocytes and macrophages. They secrete
acids that dissolve bone matrix and release
calcium and phosphorus into the body fluids. |
The process of
bone erosion by the activities of
osteoclasts is called osteolysis.
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