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Lecture 5

Week 5 - Bone Tissue

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Simon Fraser University
Biological Sciences
BISC 101
Derek Bingham

Week 5 – Bone Tissue 1 Functions of Bone and the Skeletal System: Bone consists of 18% of our total body weight 1. Support, structure and attachment points for skeletal muscle 2. Protection of internal organs 3. Assistance with movement – skeletal muscles are attached to bones so when they contract, the bones move 4. Mineral storage – especially calcium and phosphorous; bone stores 99% of the body’s calcium; bone releases minerals into blood to maintain mineral homeostasis 5. Blood cell production – red bone marrow produces RBC’s, WBC’s and platelets (known as hemopoiesis) 6. Triglyceride storage – yellow bone marrow consists of adipocytes that store triglycerides  potential chemical energy reserve Structure of Bone – Typical Long Bone 1. DIAPHYSIS– the shaft 2. EPIPHYSIS– proximal and distal ends 3. M ETAPHYSIS– regions between diaphysis and epiphysis that contain an epiphyseal growth plate - Epiphyseal growth plate – a layer of hyaline cartilage that allows diaphysis to grow in length - When the bone stops growing in length around 18-21, the cartilage is replaced by bone. o Resultant bony structure  the epiphyseal line 4. ARTICULAR CARTILAGE – thin layer of hyaline cartilage that reduces friction and absorbs shock at freely movable joints - Lacks perichondrium and blood vessels, so repair is slow. 5. PERIOSTEUM – tough connective sheath associated with blood supply - Surrounds bone (not cartilage) - Protects bone, assists in fracture repair, nourishes bone tissue, and serves as an attachment point for ligaments and tendons - Attached to underlying bone by Sharpey’s fibers – thick bundles of collagen extending from periosteum into the bone matrix - Made up of o Outer fibrous layer – dense irregular CT o Inner osteogenic layer – consists of cells that enable bone to grow in thickness and not length 6. Medullary cavity – hollow, cylindrical space within the diaphysis that contains yellow bone marrow and many blood vessels in adults - Minimizes weight of bone by reducing dense material where it isn’t needed - The long bone’s tubular structure provides maximum strength with minimum weight. Week 5 – Bone Tissue 2 7. Endosteum – thin membrane that lines the medullary cavity - Single layer of bone-forming cells with a small amount of CT Histology of Bone Tissue 80% of the skeleton is compact bone and 20% is spongy bone. Bone, like other CT’s, contains an extracellular matrix that surrounds widely separately cells.  Composed of: o 15% water o 30% collagen fibers o 55% crystallized mineral salts – most abundant is calcium phosphate Many small spaces between bone cells and matrix components – some purposes are: - Channels for blood vessels that supply nourishment - Storage areas for red bone marrow Calcification – deposition of mineral salts in the matrix in which the tissue hardens; Initiated by osteoblasts – the bone-building cells - The mineral salts first crystallize between the collagen fibers of the matrix. - Then they start crystallizing around the fibers - The crystallized mineral salts are responsible for the bone’s hardness. The collagen fibers are responsible for a bone’s flexibility – they provide the resistance to be stretched or torn apart Four types of cells are present in bone tissue: 1. Osteogenic cells – unspecialized bone cells derived from mesenchyme (tissue that CTs are formed from) - Only bone cells that undergo cell division - Eventually develop into osteoblasts - Found along inner portion of periosteum, in the endosteum, and in canals within bone that contain blood vessels 2. Osteoblasts – bone-building cells that secrete organic components (mainly collagen fibers) that are needed to build the bone matrix - Initiate calcification - As
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