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Skeletal System

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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Skeletal System

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  1. Skeletal System

  2. Endochondral Ossification • “inside cartilage” • Form within hyaline cartilage • Cartilage framework for organized ossification • ~ 6 wks thru ~ 25 yrs • Growth pattern of long bones

  3. Fetal Bone Development

  4. Infant to ~25 yrsLong Bone –Epiphyseal Plate

  5. Endochondral Ossification

  6. Endochondral Ossification • Cartilage model develops • Cartilage grows • Medullary cavity forms • Primary ossification center forms • Secondary ossification center forms

  7. 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

  8. Mesenchyme Cells form Bone Model

  9. Mesenchyme Cells Differentiate to Chondroblasts Chondroblasts Convert tissue to Cartilage

  10. Perichondrium Develops Around Cartilage Model

  11. Cartilage Grows in Length & Girth Length Growth is Called interstitial growth Width Growth is Called appositional growth

  12. Endochondral Ossification • Cartilage framework initial step • As cartilage grows (hypertrophy) centrally located chondrocytes rupture • Begins ossification of cartilage • At margins cartilage model continues to grow • Proliferation vs hypertrophy

  13. Proliferation vs Hypertrophy Center Edges

  14. Cartilage Continues to Grow

  15. Hypertrophied Cells Burst Stimulating Calcification of Matrix

  16. Hypertrophied Cells Burst Stimulating Calcification of Matrix

  17. Osteoblast Produce Bone Collar Vascularization Stimulates Mesenchymal Cells to Convert to Osteoblasts

  18. Perichondrium Converts to Periosteum

  19. Vascularization of Tissue Carries Osteoblast into Matrix Forming Primary Ossification Center

  20. Primary Ossification Center

  21. Primary Ossification Center Continues to Grow at Edges Ossification begins in diaphysis & migrates toward the epiphysis

  22. Cartilage Continues to Grow & Ossification Continues towards ends of Diaphysis

  23. Cartilage Continues Proliferation & Hypertophy

  24. Ossification of Cartilage Continues Towards ends of shaft Center Ends

  25. Calcified Cartilage Matrix

  26. Forms Spongy Bone

  27. Form Trabeculae of Spongy Bone

  28. Osteoclast Remodel Spongy Bone to Compact

  29. Bone Remodeling

  30. Bone Remodeling Forms Medullary Cavity

  31. Forms Haversian System

  32. 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

  33. Blood Vessels Enter into Diaphysis

  34. Secondary Ossification Centers Form Ossification of epiphysis

  35. Secondary Ossification Centers

  36. Cartilage at Edges Persists as Articular Cartilage

  37. Metaphysis • Location- epiphyseal plate • Site of bone elongation • Growing cartilage plate persists • Zone of proliferation • Zone of Hypertrophy

  38. Epiphyseal Plate

  39. Long Bone Elongation

  40. 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”

  41. Chondrocyte Proliferation

  42. Osteocyte Invasion

  43. 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

  44. Bone Growth Disorders • Marfan’s syndrome • Dominant genetic disorder • Abnormal connective tissue growth • Hyperactive chondrocytes & epiphyseal plate • Symptoms- long thin limbs

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