Bone Function Structure

1. BoneFunctionStructure Mr Lee Van Rensburg Mr Staton Phillips 2014

3. Function 1 Mechanical Role 2 Ionic Reservoir 3 Haemopoietic Marrow

5. Structure 10% Cells (functional) 90% Matrix (structural)

6. Structure 10% Cells Osteoclasts Osteoblasts Osteocytes Bone Lining cells 90% Matrix

7. Osteoclasts Multinucleated giant cells Haemopoetic origin (monocyte progenitors) Resorb bone

8. Osteoclasts Resorb bone by forming: Howships lacunae

9. Osteoclasts Integrins – attach to bone sealing space Produce H+ via carbonic anhydrase Lower PH increases solubility of Hydroxyapatite Organic matrix resorbed by proteolysis

10. Structure 10% Cells Osteoclasts Osteoblasts Osteocytes Bone Lining cells 90% Matrix

11. Osteoblasts Form bone Undifferentiated mesenchymal cells Line bone surfaces

12. Osteoblasts Osteoblasts affected by: IL PDGF IDGF PTH 1,25 Dihydroxy vitamin D Glucocorticoids Prostaglandins Oestrogen

13. Structure 10% CellsOsteoclasts Osteoblasts Osteocytes Bone Lining cells 90% Matrix

14. Osteocytes 90% of Cells Osteoblasts trapped in matrix

15. Osteocytes Maintain bone Control Extracellular Ca and P Stimulated by Calcitonin Inhibited by PTH

16. Structure 10% Cells Osteoclasts Osteoblasts Osteocytes 90% Bone Lining cells 90% Matrix

17. Structure 10% Cells Osteoclasts Osteoblasts Osteocytes 90% Bone Lining cells 90% Matrix

18. Structure 10% Cells Osteoclasts Osteoblasts Osteocytes 90% Bone Lining cells 90% Matrix Organic 40% Inorganic 60%

19. Organic (40%) Collagen (90%) Proteoglycans Non collagenous matrix proteins Glycoproteins Phospholipids Phosphoproteins Growth factors Cytokines

20. Organic (40%)Collagen (90%) Type - BONE Polypeptide triple helix Tropocolagen bond together Forming fibrils

22. Inorganic (60%) Most Hydroxyapatite Fills in holes in Collagen Ca10 (PO4)6 (OH)2

23. Tensile strength

24. Compressive strength

25. Microscopic Primary Immature Woven Secondary Mature Lamellar

26. Woven Bone PROPERTIES ISOTROPIC SOFT FLEXIBLE RAPID DEPOSITION/TURNOVER HIGH No. OF CELLS LOCATION Embryonic Skeleton Neonatal Skeleton Growing Metaphysis in under 4 yr olds Near sutures of skull In tooth sockets Some Tendon insertions Callus uniform physical properties in all directions

27. Microscopic Primary Immature Woven Secondary Mature Lamellar

28. Lamellar Bone PROPERTIES ANISOTROPIC HARD RIGID SLOW DEPOSITION/TURNOVER LOW No. OF CELLS LOCATION Throughout the adult skeleton Properties differ based on the direction that is measured

29. Macroscopic Primary Immature Woven Secondary Mature Lamellar

30. Cortical Bone Compact 80% of the adult skeleton 20 times stiffer than cancellous bone Lamellae in concentric rings aligned with lines of force Complex arrangement of canals serving the lamellae (Haversian System)

33. Cancellous Bone trabecular 20% of the adult skeleton 20 times less stiff than cortical bone Lamellae also present aligned with lines of force No Haversian System

35. Bone circulation

36. Bone circulation • Receives 5-10% of CO • Three sources • Endosteal (nutrient artery) • Metaphysealepiphyseal system • Periosteal system McCarthy I. J Bone Joint Surg 2006:88:4-9

37. Bone circulation • Nutrient artery Enters diaphysis to medullary cavity Ascending and descending arterioles Centrifugal high pressure Inner 2/3rds of cortex McCarthy I. J Bone Joint Surg 2006:88:4-9

38. Bone circulation • 2. Metaphyseal epiphyseal system Periarticular vascular plexus eg. geniculate arteries McCarthy I. J Bone Joint Surg 2006:88:4-9

39. Bone circulation • Periosteal system low pressure on periosteum Outer 1/3rd of cortex McCarthy I. J Bone Joint Surg 2006:88:4-9

40. Questions ?

41. Biomechanics