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Skeletal System. Endochondral Ossification. “inside cartilage” Form within hyaline cartilage Cartilage framework for organized ossification ~ 6 wks thru ~ 25 yrs Growth pattern of long bones. Fetal Bone Development. Infant to ~25 yrs Long Bone –Epiphyseal Plate. Endochondral Ossification.
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Endochondral Ossification • “inside cartilage” • Form within hyaline cartilage • Cartilage framework for organized ossification • ~ 6 wks thru ~ 25 yrs • Growth pattern of long bones
Endochondral Ossification • Mesenchymal model forms during development • Mesenchymal differentiate into chondroblasts at center of growing cartilage • Chondroblasts grow (hypertrophy) enlarged lacunae create reduce matrix to thin struts that calcify • Vascularization of cartilage • Perichondrium cells convert to osteoblasts • Blood vessels penetrate cartilage bringing blood supply & osteoblasts • Oteoblasts produce spongy bone • Remodelling of spongy bone to compact bone
Mesenchyme Cells Differentiate to Chondroblasts Chondroblasts Convert tissue to Cartilage
Cartilage Grows in Length & Girth Length Growth is Called interstitial growth Width Growth is Called appositional growth
Proliferation vs Hypertrophy Center Edges
Endochondral Ossification • Cartilage framework initial step • As cartilage grows (proliferation) centrally located chondrocytes grow (hypertrophy) and rupture • Begins ossification of cartilage • At margins cartilage model continues to grow
Hypertrophied Cells Burst Stimulating Calcification of Matrix
Hypertrophied Cells Burst Stimulating Calcification of Matrix
Osteoblast Produce Bone Collar Vascularization Stimulates Mesenchymal Cells to Convert to Osteoblasts
Vascularization of Tissue Carries Osteoblast into Matrix Forming Primary Ossification Center
Primary Ossification Center Continues to Grow at Edges Ossification begins in diaphysis & migrates toward the epiphysis
Cartilage Continues to Grow & Ossification Continues towards ends of Diaphysis
Ossification of Cartilage Continues Towards ends of shaft Center Ends
Endochondral Ossification • Blood vessels & osteoblasts migrate into epiphysis • Secondary ossification centers • Bone ossification remains incomplete • Epiphyseal plate • Site of continued bone growth • Produces VERY structured compact bone
Secondary Ossification Centers Form Ossification of epiphysis
Metaphysis • Location of epiphyseal plate • Site of bone elongation • Growing cartilage plate persists • Zone of proliferation • Zone of Hypertrophy
Bone Elongation • Chondrocytes divide and produce new cartilage • Diaphysis- chondrocytes replaced by invading osteoblasts • During growth stage chondrocyte activity matches osteocyte activity • At maturation osteocyte invasion is FASTER than chondrocyte division • Puberty- Sex hormones stimulate osteoblast & chondrocyte activity aka growth “spurt”
Bone Growth Disorders • Achondroplastic dwarf • Results from slow epiphyseal plate growth & early plate closure • Chondrocytes have slower activity • Results in normal trunk growth & stunted long bone growth
Bone Growth Disorders • Marfan’s syndrome • Dominant genetic disorder • Abnormal connective tissue growth • Hyperactive chondrocytes & epiphyseal plate • Symptoms- long thin limbs