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Lecture 6

Week/Lecture 6: Skeletal System.pdf

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BIOL 171

Skeletal System composed of many different tissues cartilage, bone tissue, epithelium, nerve, blood forming tissue, adipose, dense connective tissue dynamic and ever-changing throughout life Bone Functions shape/structure support blood cell formation storage (calcium, fat, minerals) protection mobility/movement Typical Long Bone epiphysis: end of bone (distal and proximal) articular cartilage: protection from friction at joints epiphyseal line: related to bone growth and length spongy bone: contains red bone marrow - blood formation compact (dense) bone: outside of bone medullary cavity: open space in bone cavity containing yellow marrow (adipose tissue) endosteum: lines medullary cavity periosteum: lines outside of medullary cavity nutrient artery: comes from vein Histology of Bone: histology: study of structure of microscopic cells connective tissue: cells separated by hard matrix Bone Cells: related cells: Osteogenic cells: undifferentiated cells found beneath periosteum, endosteum divide to replace themselves or can differentiate to become osteoblasts Osteoblasts cells: found beneath periosteum and endosteum form matrix and collagen fibers but can't divide differentiate into osteocytes when surrounded by matrix and enclosed in lacunae Osteocyte cells: mature bone cells derived from osteoblasts surrounded by matrix and enclosed in lacunae maintain bone tissue but do not produce new matrix matrix: solid; lacunae suspended in matrix: holds extracellular fluid surrounding cell helps heal damage, regulate growth in bones Osteoclast cells huge cells formed from fused monocytes (white blood cells) located beneath endosteum, periosteum secrete enzymes that dissolve bone matrix function in bone growth, maintenance, repair, remodelling Bone Matrix: 15% water 30% organic matrix (collagen fibers give strength, flexibility -- like rebar) 55% inorganic matrix (mineral salts create hardness) mineralization (calcification) hardening of tissue when mineral crystals deposit around collagen fibers bone is not completely solid has small spaces for vessels and red bone marrow spongy bone has many such spaces compact bone has very few Classification of Bone: by density compact bone: dense solid hard layer of bone makes up the shaft of long bones, external layer of all bones resists stresses produced by weight and movement composed of osteons concentric rings (lamellae) of calcified matrix surrounding a Haversian canal tube that runs down osteon carries blood, nerves osteocytes lie between lamellae in lacunae communicate with adjacent cells via processes that extend through canaliculi filled with ECF projections that connect with blood supply network of tubes/holes to connect to extracellular fluid Volkmann's (perforating) canal delivers blood to middle of bone horizontal connections between all Haversian canals, supplying blood spongy (cancellous) bone: porous latticework of thin plates of bone called trabeculae oriented along lines of stress changing stress on body changes areas of strength: trabeculae can move spaces between trabecular filled with red marrow found in ends of long bones and in flat bones Bones that Contain Red Marrow flat bones: cranial bones pelvis ribs sternum proximal humerus and femur Bone Formation (Ossification): intramembranous bone formation formation of bone directly from mesenchymal cells (all embryonic connective tissue begins as mesenchyme) (face and head bones) 1. Ossification centre 1. mesenchymal cells differentiate to osteogenic cells then osteoblasts 2. Calcification: 1. osteoblasts secrete matrix, surround themselves with lacuna, differentiate into osteocytes; matrix hardens 3. Trabeculae develops 1. matrix develops into trabeculae; mesenchyme condenses at surface; red bone marrow formed 4. Condensed mesenchyme 1. creates periosteum; superficial layers of spongy bone are replaced by compact bone endochondral bone formation formation of bone within hyaline cartilage make shape in cartilage, then change it into bone endo: within; chondro: cartilage occurs in embryo 1. Development of cartilage model 1. some mesenchymal cells differentiate to become cartilage tissue 2. Growth of cartilage model 1. cells secreting matrix which become calcified 2. makes it difficult for chondrocytes to survive (no blood supply, so chondrocytes gather nutrients from surrounding fluid, until calcified, then die) 3. Development of primary ossification centre 1. blood vessel growth into tissue 2. some mesenchymal cells become osteogenic cells -- differentiate into osteoblasts which secrete matrix 4. Development of medullary cavity 1. osteoclasts (break down cells) carve out medullary cavity 2. blood vessel system more complex, more bone tissue 5. Development of secondary ossification centre 1. second blood vessel system invades epiphysis 2. again become osteoblasts (replace cartilage tissue with bone tissue at epiphysis) 6. Formation of articular cartilage 1. secondary ossification centre leaves ridge of articular/hyaline cartilage along top of epiphysis (reduces friction) 2. blue line of cartilage between primary and secondary ossification centres 1. becomes epiphyseal plate -- allows bone to grow in length Bone Growth in Length epiphyseal plate (see above) layer of cartilage cartilage cells are produced by mitosis on epiphyseal side (primary ossification centre) of plate plate is growing "taller" as more cells are added cartilage cells are destroyed and replaced by bone on diaphyseal side (secondary ossification centre) of plate plate is shrinking from opposite side as cells are being replaced with bone tissue therefore, plate does not change size, just moves/lengthens bone zones of growth in epiphyseal plate zone of resting cartilage anchors growth plate to bone little mitosis/change zone of proliferating (multiplying/division) cartilage rapid cell division (stacked coins) chondrocytes secrete matrix and surrounded by it matrix calcified around chondrocytes where bone growth is occurring (lenthening) zone of hypertrophic (increase in size)
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