Bone Function Structure Mr Lee Van Rensburg Mr Staton Phillips 2015 Function 1Mechanical Role 2Ionic Reservoir 3Haemopoietic Marrow Structure 10%Cells (functional) 90%Matrix (structural) Structure 10%Cells Osteoclasts Osteoblasts Osteocytes Bone Lining cells 90%Matrix Multinucleated giant cells Haemopoetic origin (monocyte progenitors) Resorb bone Osteoclasts Resorb bone by forming: Howships lacunae Integrins attach to bone sealing space Produce H + via carbonic anhydrase Lower PH increases solubility of Hydroxyapatite Organic matrix resorbed by proteolysis Osteoclasts Structure 10%Cells Osteoclasts Osteoblasts Osteocytes Bone Lining cells 90%Matrix Osteoblasts Form bone Undifferentiated mesenchymal cells Line bone surfaces Osteoblasts Osteoblasts affected by: IL PDGF IDGF PTH 1,25 Dihydroxy vitamin D Glucocorticoids Prostaglandins Oestrogen Structure 10%Cells Osteoclasts Osteoblasts Osteocytes Bone Lining cells 90%Matrix Osteocytes 90% of Cells Osteoblasts trapped in matrix Maintain bone Control Extracellular Ca and P Stimulated by Calcitonin Inhibited by PTH Osteocytes Structure 10%Cells Osteoclasts Osteoblasts Osteocytes90% Bone Lining cells 90%Matrix Structure 10%Cells Osteoclasts Osteoblasts Osteocytes90% Bone Lining cells 90%Matrix Structure 10%Cells Osteoclasts Osteoblasts Osteocytes90% Bone Lining cells 90%Matrix Organic 40% Inorganic 60% Organic (40%) Collagen (90%) Proteoglycans Non collagenous matrix proteins Glycoproteins Phospholipids Phosphoproteins Growth factors Cytokines Organic (40%) Collagen (90%) Type - B ONE Polypeptide triple helix Tropocolagen bond together Forming fibrils Most Hydroxyapatite Fills in holes in Collagen Inorganic (60%) Ca 10 (PO 4 ) 6 (OH) 2 Tensile strength Compressive strength Microscopic Primary Immature Woven Secondary Mature Lamellar Woven Bone LOCATION Embryonic Skeleton Neonatal Skeleton Growing Metaphysis in under 4 yr olds Near sutures of skull In tooth sockets Some Tendon insertions Callus PROPERTIES ISOTROPIC SOFT FLEXIBLE RAPID DEPOSITION/TURNOVER HIGH No. OF CELLS uniform physical properties in all directions Microscopic Primary Immature Woven Secondary Mature Lamellar Lamellar Bone LOCATION Throughout the adult skeleton PROPERTIES ANISOTROPIC HARD RIGID SLOW DEPOSITION/TURNOVER LOW No. OF CELLS Properties differ based on the direction that is measured Macroscopic Primary Immature Woven Secondary Mature Lamellar 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) 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 Bone circulation McCarthy I. J Bone Joint Surg 2006:88:4-9 Bone circulation Receives 5-10% of CO Three sources 1.Endosteal (nutrient artery) 2.Metaphyseal epiphyseal system 3.Periosteal system McCarthy I. J Bone Joint Surg 2006:88:4-9 Bone circulation 1.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 Bone circulation 2.2. Metaphyseal epiphyseal system Periarticular vascular plexus eg. geniculate arteries McCarthy I. J Bone Joint Surg 2006:88:4-9 Bone circulation 3.Periosteal system low pressure on periosteum Outer 1/3 rd of cortex Questions ? Biomechanics