andrew richards & ryan swenson. endochondral ossification-”within cartilage” start with...
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Andrew Richards & Ryan Swenson
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Endochondral Ossification-”within cartilage”
• Start with Hyaline cartilage model in similar shape as the bone• Primary ossification center expands from the center
Vasculature, bone marrow cells, osteoblast, and osteoclasts spread throughout diaphysis
• Osteoblasts deposit matrix, results in spongy trabeculae, then medullary cavity
• Blood vessels penetrate epiphysis to form secondary ossification center• Cartilage remains between two ossification centers-epiphyseal plate• Most bones form in this way
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Intramembranous Ossification-”within membrane”• Mesenchymal cells differentiate into osteoblasts• Form ossification center, and secrete bone matrix
• Osteoblasts encased in matrix become osteocytes• Network of trabeculae forms around blood vessels• Trabeculae thicken to form plates of compact bone• Bones of skull and clavicle form in this way
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Osteoclast-resorb old bone• Dissolve and digest, form lacunae and Haversian
canals Osteoblast-synthesize new bone matrix
• Encase themselves in matrix Osteocyte-terminal osteoblasts
• Lie within mineralized bone, no longer produce matrix
• Function as support structure and metabolism
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Longitudinal growth• Occurs at the Epiphyseal plate• Childhood and adolescence
Radial Growth Occurs during modeling inresponse to environmental Factors (Adapt)
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Process of resorbing old bone and forming new Occurs throughout lifespan
• Body usually in “bone balance”• In older age negative balance, bones become
brittle Resorption, Reversal, and Formation
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Resorption• Osteoclasts are activated to resorb bone
through many chemical reactions• Result in lacunae in trabecular bone and
Haversian canals in cortical bone• Resorption cycles last approximately 2-4
weeks
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Reversal• Process transitions to bone formation• Resorpton cavities (lacuna and canals)
contain a variety of mononuclear cells Ex. monocytes, and preosteoblasts
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Formation• Osteoblasts synthesize new collagenous
matrix• Encase themselves in their matrix • Become osteocytes
Percentage undergo apoptosis and become bone lining cells