Osteoprogenitor cells (also known as osteogenic cells) are mesenchymal stem cells that develops into osteoblasts. They are small, spindle-shaped cells residing in all non-resorptive bone surface layer. They constitute the deep layer of the periosteum that invests each bone and also the endosteum that lines the medullary cavity that contains the marrow. The endosteum is a single layer of flat osteoprogenitor cells without a fibrous layer. These cells take part, with those of the periosteum, in repairing broken bones.
Osteoprogenitor cells of the periosteum and endosteum that are stimulated to proliferate develop into osteoblasts in regions that are well vascularized, and into chondroblasts, in regions that are unvascularized. Osteoprogenitor stem cells are self-renewing and they persist in adult life, constituting a potential source of new bone tissue for the repair of broken bone. Self renewal of these bipotential stem cells keep the supply of osteoprogenitor cells for further bone growth and fracture repair.
Once osteoprogenitor cells have developed into osteoblasts, they synthesize and secrete the organic constituents of bone matrix. Their cell bodies and cytoplasmic cell processes create the lacunae and canaliculi in this matrix. They characterize growing surfaces and are distinguishable from the osteoprogenitor cells by their large size, rounded to polygonal outline, and eccentric nucleus. Their cytoplasm is markedly basophilic, usually with a distinct negative Golgi image.
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| A schematic image that shows osteoprogenitor cells differentiating into osteoblasts |
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