What cells make up bone?
Bones are made up of the following types of cells: osteoclasts, osteoblasts and osteocytes
Where do osteoclasts, osteoblasts and osteocytes originate?
- Osteoclasts, which are bone resorbing cells, come from the fusion of monocytes.
- Osteoblasts, which are bone forming cells, come from bone marrow.
- Osteocytes are the mature cells of bone that help to regulate the osteoclasts and osteoblasts.
Osteoclasts are found in something called resorption bays – these are indentations or pits along the surface of the bone. Certain hormones work to regulate osteoclasts. These include calcitonin which originates in the thyroid,and parathyroid hormone or PTH from the parathyroid gland.
Osteoblasts create a mineral from calcium and phosphate that forms into a durable, compact tissue. Osteoblasts are responsible for mineralizing most of the bone matrix. Active osteoblasts play an essential role in active bone formation. When bone synthesis is not actively occurring, osteoblasts are referred to as inactive.
Osteocytes make up greater than 95% of bone cells. They are encased in bone matrix. Bone matrix is a reservoir for many proteins including: collagen, osteocalcin, osteopontin, transforming growth factor and bone morphogenic protein.
Shaped like a star, osteocytes are generally located in mature bone. While the size of osteocytes varies, they are reported to have an average half life of about two and a half decades.
Osteocytes communicate with each other via small canals call canaliculi. Canaliculi have dendrites in them that communicate with the different osteocytes and osteoblasts. Think of the canaliculi has the train tracks between the osteocytes and the dendrites function as the trains.
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