Osteoblast

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Osteoblast

Osteoblasts and osteoclasts on trabecula of lower jaw of calf embryo.

Part of the growing edge of the developing parietal bone of a fetal cat.
Gray's	subject #18 87
MeSH	Osteoblasts
Dorlands/Elsevier	o_08/12600120

An osteoblast (from the Greek words for "bone" and "germ" or embryonic) is a mononucleate cell that is responsible for bone formation. Osteoblasts produce osteoid, which is composed mainly of Type I collagen. Osteoblasts are also responsible for mineralization of the osteoid matrix. Bone is a dynamic tissue that is constantly being reshaped by osteoblasts, which build bone, and osteoclasts, which resorb bone.

1 Osteoblastogenesis
2 Regulation of osteoclasts
3 Morphology and histological staining
4 Osteoblasts and osteocytes
5 External links

[edit] Osteoblastogenesis

Osteoblasts arise when osteoprogenitor cells located in the periosteum and the bone marrow are induced to differentiate under the influence of growth factors, particularly as bone morphogenetic proteins (BMPs). Osteoprogenitor cells express the transcription factor Cbfa1/Runx2. Once osteoprogenitors start to differentiate, they begin to express a range of other bone markers including Osterix, Col1, ALP, osteocalcin, osteopontin, and osteonectin.

Other growth factors including fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-β) may promote the division of osteoprogenitors and potentially increase osteogenesis.

[edit] Regulation of osteoclasts

Osteoblasts produce RANK ligand (RANKL) on their surface and as a secreted factor. RANKL is a potent stimulator of osteoclastogenesis on haematopoietic precursors.

[edit] Morphology and histological staining

The cytoplasm of osteoblasts appears to be basophilic via normal H&E stain due to presence of large amount of rough endoplasmic reticulum A large Golgi apparatus is also present in the centre. The nucleus is spherical and large. Osteoblasts can be stained for type 1 collagen or for the production of alkaline phosphatase.

[edit] Osteoblasts and osteocytes

Main article: osteocyte

Osteoblasts that become trapped in the bone matrix become osteocytes. They cease to generate osteoid and mineralized matrix, and instead act in a paracrine manner on active osteoblasts. They are believed to act in a mechanosensory manner.