Organization of bone Claudia Stanescu Ph D Office Hours in Gittings 108 Tue 10 11am and Thurs 1 2pm or by appointment Objectives 1 List the components of the matrix of bone and describe how each component contributes to the bone s strength 2 Describe the differences between compact and spongy bone in terms of location function and composition 3 Describe the microscopic structure of compact bone the osteon and understand the purpose of its organization Composition of bone Connective tissue Extracellular Matrix Ground Substance Contains organic and inorganic components Noncollagenous proteins Fibers Organic component Collagen Fibers Cells Osteogenic cells Osteoblasts Osteocytes Osteoclasts Extracellular matrix Organic components secreted by osteoblasts Ground substance glycosaminoglycans GAG Glycoproteins polysaccharide protein Chondroitin sulfate and Hyaluronic acid Negatively charged trap water Collagen fibers type I Fibrous protein arranged in helical form Very resistant to pulling forces Provides flexibility and a framework for deposition of calcium crystals Type I Collagen T A Einhorn Bone metabolism and metabolic bone disease In Orthopaedic Knowledge Update 4 Home Study Syllabus J W Frymoyer ed Am Acad Orthop Surg Rosemont 69 88 1994 http www ncbi nlm nih gov books NBK26810 Extracellular matrix Inorganic components Water Attracted to ground substance Makes up 25 of the extracellular matrix Hydroxyapatite Ca10 PO4 6 OH 2 Ca3 PO4 2 Ca OH 2 Calcium phosphate and calcium hydroxide other minerals calcium carbonate and some ions Mg F K Organization of the organic inorganic components Salts hydroxyapatite are deposited within collagen fibers As the hydroxyapatite condenses other inorganic salts and ions precipitate in the matrix to fill in the spaces between fibers Organization of mineral 1 The collagen fiber contains mineralized fibrils 2 The fibrils contain small mineral plates bound by helical noncollagenous proteins collagen cross links Principles of bone biology 3rd ed Seeman Modeling and remodeling 2008 Collagen and minerals provide strength to the matrix Collagen provides flexibility Minerals provide firmness Experiments Soak bone in weak acid vinegar remove minerals from bone bone becomes rubbery flexible Apply proteolytic enzymes denature protein remove collagen from bone bone becomes brittle crumbly Bone needs both collagen and minerals for maximum strength Skeletal disorders Rickets inorganic component deficient Calcium deficiency due to lack of vitamin D leads to flexible bones bowed legs Scurvy organic component deficient Problem with collagen synthesis due to vitamin C deficiency leads to brittle bones that can fracture easily 3D arrangement of matrix Spongy bone vs Compact bone Both have the same chemical composition but different organization Spongy bone Organization Irregular lattice of thin plates called trabecullae Osteocytes housed in lacunae Lacuna Lamellae Space for red bone marrow Trabeculae Canaliculi Osteocyte Osteoclast Osteoblasts aligned along trabeculae of new bone Low power scanning electron microscope image of normal bone architecture in the 3rd lumbar vertebra of a 30 year old woman marrow and other cells have been removed to reveal thick interconnected plates of bone Spongy bone Location Epiphyses of long bones Surrounding marrow cavities Flat short irregular bones Functions Withstand forces from many directions trabecullae arranged along lines of stress Lightens the skeleton not as strong as compact bone Contains red marrow for hemopoiesis Compact bone Organization Solid network of bone organized in concentric ring structures called osteons see next slide Location External layer of all bones Diaphysis of long bones Function Gives long bones ability to withstand forces along longitudinal axis Osteon functional unit of compact bone Osteon organization Greenspans s Basic and Clinical endocrinolgy 8th edition Metabolic Bone Disease Dolores Shoback MD Deborah Sellmeyer MD Daniel D Bikle MD PhD 2007 Osteocytes in lacunae and canaliculi Lacuna space Canaliculi little canals Cytoplasmic extension dendrite of osteocyte Osteocyte dendrites in canaliculi Osteoporosis 3rd ed Marcus Feldman Nelson Rosen Osteocytes 2008