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BONES Functions of the skeleton 1 Support 2 Protection 3 Movement 4 Electrolyte acid base balance 5 Blood formation Histology Osteogenic osteoprogenitor cells stem cells from mesenchymal cells Found in endosteum inner layer of periosteum central canals Osteoblasts bone forming cells from mitosis or differentiation of osteogenic cells Found under endosteum and periosteum Synthesize soft organic bone matrix that is later mineralized Secrete osteocalcin stimulate insulin secretion and sensitivity Limit growth of fat Osteocytes trapped in lacunae osteoblasts contact others by gap junctions in canaliculi Resorb and deposit bone matrix maintenance of bone density blood levels of Ca P Strain sensors bone remodeling adapt to stress Osteoclasts bone dissolving cells on bone surface From fusion of several marrow stem cells Remodeling Development Intramembranous ossification produces flat bones of the skull and most of the clavicle Mesenchyme condenses into soft tissue with blood capillaries Mesenchymal cells enlarge differentiate into osteogenic cells network of trabeculae forms Osteogenic cells gather in trabeculae differentiate into osteoblasts soft osteoid tissue Calcium phosphate deposited Osteoblasts trapped osteocytes Mesenchyme on the surface periosteum uncalcified but denser and more fibrous Osteoblasts continue to build trabeculae Osteoclasts resorb and remodel marrow cavity Trabeculae at the surface calcify spaces fill compact bone Endochondral ossification hyaline cartilage replaced by osseous tissue Mesenchyme hyaline cartilage with fibrous perichondrium Pericondrium starts producing osteoblasts bony collar Chondrocytes in the middle enlarge thin walls b w calcify primary ossification center Cells die lacunae merge into a single cavity Blood vessels penetrate the bony collar fill center with blood and stem cells primary marrow cavity Osteoblasts deposit bone wave of cartilage death Osteoclasts enlarge marrow cavity Metaphysis region of transition from cartilage to bone dissolving Secondary ossification center forms in the epiphyses secondary marrow cavity Epiphyses fill with spongy bone left over cartilage epiphyseal plate growth zone for bone elongation till early 20s Bone elongation cartilage growth from within interstitial growth Epiphyseal plate zones of reserve resting cartilage shows no sign of transforming of cell proliferation chondrocytes multiply arrange into longtitudinal columns of cell hypothrophy cease to divide enlarge walls b w lacunae thin of calcification walls become calcified of bone deposition chondrocytes die Walls break channels invaded by blood vessels and marrow Osteoblasts and osteoclasts line up and start remodeling Bone widening and thickening appositional growth Osteoblasts in the inner layer of periosteun deposit osseous tissue parallel to te surface circumferential lamellae Osteoclasts widen the marrow cavity Fracture repair Bleeding fracture hematoma osteoblasts osteogenic cells etc form soft granulation tissue Fibroblasts deposit collagen Osteogenic cells chondroblasts deposit fibrocartilage soft callus Osteogenic cells osteoblasts hard callus bony collar 4 6 weeks to form Next 3 4 months remodeling Calcium homeostasis Ca too low parathyroid hormone PTH osteoclasts resorb bone PTH also promotes Ca reabsorption by kidneys and inhibits osteoblasts Ca too high thyroid hormone calcitonin reduces osteclast activity stimulates osteoblasts weak effect in adults Factors affecting bone growth hormones sex and growth nutrition Functions of the Skeleton Support Protection Movement leverage Electrolyte and acid base balance Blood formation Types of bones Flat bones parietal sternum scapula ribs hip bones Long bones limbs humerus radius ulna upper femur tibia fibula lower fingers metacarpals metatarsals phalanges Levers major body movements Short bones carpal tarsal Patella sesamoid bone Irregular bones vertebrae sphenoid and ethmoid skull Parts of a long bone Diaphysis shaft Epiphysis heads Articular cartilage hyaline Nutrient foramina Periosteum can penetrate into bone matrix perforating fibers Endosteum lines internal marrow cavity surfaces of spongy bone canal system Epiphyseal plate cartilage in children epiphyseal mark adults Separates the marrow spaces of epiphysis and diaphysis Compact bone Osteon central canal joined with others by perforating canals concentric lamellae vs circumferential lamellae interstitial lamellae Helix coiled loose tension bending tight compression Spongy bone Spicules rods or spines Trabeculae thin plates Lined with endosteum filled with bone marrow Few osteons No central canals Joints Bony Snostosis Gap ossifies and becomes one bone fuses With age epiphysis diaphysis cranial bones 1st rib to sternum Fibrous Synarthrosis Collagen fibers emerge from one bone and penetrate into another Sutures Immobile or slightly movable Bones of the skull only Serrate wavy interlocking Lap overlapping edges relatively smooth Plane straight nonoverlapping Gomphoses Tooth in a socket periodontal ligament Syndesmosis Relatively long collagenous fibers slightly more mobility ex Radius and ulna Cartilaginous Amphiarthrosis Two bones are linked by cartilage Synchondrosis The bones are bound by hyaline cartilage 1st rib to sternum Symphysis The bones are joined by fibrocartilage interpubic intervertebral Synovial Diarthrosis Limited to free mobility Anatomy Articulate cartilage hyaline Joint articular cavity with synovial fluid Joint articular capsule encloses the cavity and retains the fluid Fibrous capsule continuous with the periosteum and In a few synovial joints fibrocartilage grows inward forms a pad b w artic bones synovial membrane secretes fluid populated by macrophages articular disc jaw ulna carpal ends of clavicle Meniscus knee doesn t entirely cross the joint Accessory structures Tendons attach muscle to a bone stabilize joints tough collagenous Ligaments attach one bone to another Bursa fibrous sac of synovial fluid cushions muscles help tendons slide more easily over joints sometimes enhance the mechanical effect of a muscle b w muscles b w bone connective tissue and skin where tendon passes over a bone Tendon sheaths elongated cylindrical bursae wrapped around tendons Classes of Synovial Joints Multiaxial Ball and socket joints spheroid Shoulder glenoid cavity of the scapula and hip joints acetabulum ONLY One bone s smooth semispherical head fits into a cuplike socket on the other Flexion extention abduction adduction curcumduction

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