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Hard tissue formation
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Hard tissue formation

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  • 1. Hard Tissue FormationCell Types of Bone• Osteoprogenitor cells ---- undifferentiated cells• Can divide to replace themselves can becomeosteoblasts• Found in inner layer of periosteum and endosteum• Osteoblasts--form matrix collagen fibers butcant divide• Osteocytes ---mature cells that no longer secretematrix• Osteoclasts---- huge multinucleated cells, function in bone resorption atsurfaces such asendosteumMatrix of Bone• Inorganic mineral salts provide bones hardness• Hydroxyapatite (calcium phosphate) calciumcarbonate• Organic collagen fibers provide bonesflexibility• Their tensile strength resists being stretched ortorn• Remove minerals with acid rubbery structureresults• Calcification is hardening of tissue when mineralcrystals deposit around collagen fibers• Bone is not completely solid since it has smallspaces for vessels and red bone marrow• Spongy bone has many such spaces• Compact bone has very few2
  • 2. Bone Formation or Ossification• Intramembranous bone formation, formation ofbone directly• from mesenchymal cells.• All embryonic connective tissue begins asmesenchyme.• Endochondral ossification formation of bonefrom hyaline• cartilage.Some Important Points• When the chondrocytes die during bone lengthening, their extracellularmatrix gets very tough. The reason is that it gets loaded with calciumsalts, which make it harder. This hardening process is calledcalcification.In order for the osteoblasts to be able to get into the region of dead chondrocytes,they have to get through the calcified cartilaginous matrix. They cannot.Therefore, yet another type of cell, the osteoclast, is enlisted to help. The osteoclastis specialized in endocytosis-- taking in and chewing up material that is around it.These cells are derived from the blood; a certain type of blood cell, the monocyte,differentiates into osteoclasts in bone. Therefore, the osteoclasts clear the way forthe invasion of osteoblasts.Secondary Bone Remodelling3