1. BONE DEVELOPMENT and REPAIR From fetal development through growth and repair of damage…

2. Fetal Skeletal Development (< 8 weeks) Skeletal tissues derived from mesoderm cells Skeletal tissues derived from mesoderm cells Composed mostly of cartilage at the start Composed mostly of cartilage at the start

3. Fetal Skeletal Development (~12 weeks) Gradual hardening process Gradual hardening process  ossification Starts in specific areas and spreads Starts in specific areas and spreads Continues throughout life into early adulthood Continues throughout life into early adulthood

4. Fetal Ossification of Flat Bones Chondrocytes transform into osteoblasts Chondrocytes transform into osteoblasts Osteoblasts form hard bony material Osteoblasts form hard bony material Process finishes after birth to form sutures Process finishes after birth to form sutures

5. Long Bone Development Step 1 Chondrocytes in center enlarge and change Matrix calcifies Chondrocytes die leaving cavities

6. Long Bone Development Step 2 Blood vessels grow around the cartilage Chondrocytes convert to osteoblasts Outer layers of shaft are sheathed in bone d el

7. Long Bone Development: Step 3 Blood vessels penetrate cartilage Invade hollow areas formed in Step 1 Blood brings fibroblasts that change to osteoblasts Ossification now forms spongy bone areas

8. Long Bone Development: Step 4 Osteoclasts remove bone from center  Forms marrow cavity Walls of shaft thicken Cartilage at epiphyses replaced by hard bone Length and diameter continue to increase Marrow Cavity

9. Long Bone Development: Step 5 Capillaries grow into epiphyses Osteoblasts also migrate to epiphyses Creates secondary ossification centers

10. Long Bone Development: Step 6 Epiphyses fill with spongy bone Articular cartilage remains exposed at ends Cartilaginous plates form separation between epiphysis and diaphysis

11. Long Bone Development: Final Stages Growth continues from epiphyseal plates Major growth spurts occur during puberty Ossification complete and end of growth by age 25 in males Epiphyseal plate

12. REPAIR OF FRACTURES STEP 1: Break through blood vessels leads to bleeding Break through blood vessels leads to bleeding Hematoma forms Hematoma forms STEP 1.

13. REPAIR OF FRACTURES Internal callus forms Internal callus forms Stabilizing network of spongy bone forms Stabilizing network of spongy bone forms External callus of bone and cartilage forms External callus of bone and cartilage forms STEP 2..

14. REPAIR OF FRACTURES Cartilage of external callus is replaced Cartilage of external callus is replaced Spongy bone unites broken ends Spongy bone unites broken ends Fragments removed by osteoclasts Fragments removed by osteoclasts STEP 3

15. Final Stage of Fracture Repair Initially swelling at site of repair Osteoclasts re-sculpt the callus to smooth out bone STE P 4