Chapter 6 Bone and Skeletal Tissue PDF

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Chapter 6: Bone and Skeletal Tissue Skeletal Cartilages -

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Structure, types, locations o All types of skeletal cartilages have chrondos, extracellular matrix, fibers o Hyaline Cartilage  Most common  Flexible  Resilient  Contain fine collagen fibers  Articular, costal, respiratory, nasal  Glassy smooth and shiny o Elastic Cartilage  Like hyaline  Most elastic fibers  Tolerate repeated bending  Epiglottis  External ear o Fibro cartilage  Cross between hyaline cart (chrondos) and dense reg conn tiss (thick coll fibers); high tensile strength  Resist high pressure stretch  Found in Menisici in knees, intervert disc, and pubic Growth o Appositional o Interstitial

Classification of Bones -

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Axial vs appendicular o Axial  Comprises the bones of the vertebral column  Protect internal organs o Appendicular  Consists of the 126 bones of the upper limbs and lower limbs and bones of the shoulder girdle and pelvic girdle that “append” the limbs to the axial skeleton  Support and facilitate movement By shape: o Long  Humerus  Support the weight of the body and facilitate movement  Medullary cavity (yellow bone marrow) o Short  Triquetral (wrist) carpal  Cube-shaped components of the wrist and ankle joints

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Flat  Sternum, cranial. Scapulae, ribs  Red bone marrow  Protect organs, such as the brain, heart, and lungs Irregular  Vertebra  Vary in shape and structure

Function of Bones -

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Support o Forces  Tension (pulling apart force)  Compression (weight of gravity)  Bending (twisting kind of bending) Protection Movement Storage of minerals, growth factors, fat Hematopoiesis

Bone Structure -

Gross anatomy o Texture  Compact (lamellar)  Solid bone  Outside  Made up of structural units called osteons  Spongy (cancellous)  Trabecular bone  Inside  Made of lattice of struts o Typical long bone structures  Diaphysis  Shaf  Covered by the periosteum  Epiphyses  End of the bones  Proximal epiphysis  Distal epiphysis  Covered with articular cartilage  Membranes o Short, irregular, flat bone structure  Compact over spongy; no marrow cavity o Hematopoietic tissue (Red marrow)

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Trabecular parts of long bones (esp. heads of femur, humerus in adult) and flat bones Microscopic anatomy o Cell types:  Osteogenic  Osteoblasts  Cells that help make the bone  adds  Osteocytes  Maintain bone tissue structure  Osteoclasts  Bone dissolving cells  Replaced by osteoblast  Bone resorption o Compact bone  Microscopic passageways; osteons (haversian systems)  Multiple lamellae per osteon; alternating collagen fiber orientation  Central canal; osteocytes between lamellae o Spongy bone  Trabeculae align with stress; no osteons Chemical composition o Organic  Cells and osteoid (ground substance & collagen fibers (proteins))  Collagen: tensile and bending strength o Inorganic  Hydroxyapatite crystals (mainly calcium phosphate)  40% hydroxyapatite is Ca+, total body Ca ~2.5 – 3 kg for normal 70 kg person

Development -

Ossification o Osteogenesis Forming the bony skeleton o Intramembranous ossification  Flat bone formation  Starting with membrane o Endochondral ossification  Long bone formation  Starting with cartilage  1. Start with hyaline cartilage  2. Cavitation of the hyaline cart within the cartilage model  3. Invasion of Internal cavities by the periosteal bud and spongy bone formation  4. Formation of the medullary cavity as ossification continues  5. Ossification of the epiphyses

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Postnatal bone growth o Length of long bones  Epiphyseal plate o Hormonal regulation  GH. Sex hormones  Growth spurt, epi plate closure

Bone Homeostasis: Remodeling and Repair -

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Remodeling o At periosteum and endosteum  Periosteum is outside of the bone  Endosteum is inside of the bone o Remodeling unit w/ osteoblasts, osteoclasts  Osteoblast: replace it with new bone  Osteoclast: dissolving bone o Osteocytes (stimulating by osteoblasts) secrete matrix o Control of remodeling  By hormones to regulate plasma [Ca]  PTH (parathyroid hormone) increases when [Ca] decreases, stimulates osteoclasts o Make more of PTH if our blood calcium is low o Calcium concentration in the blood  In response to mechanical stress  Bone strongest where stress acts  Long bone hollow ctr; shaf thickest at middle  Curved bones thickest where most likely to break  Spongy bone trabeculae line up along stress lines  Projection (tuberosity, crest…) where muscles attach Repair o Classification of fractures  Bone end positions: displaced or nondisplaced  Complete or incomplete  Orientation: linear (long axis) or transverse  Skin penetration: open (compound) or closed (simple)  By nature, location of break o Repair process

Homeostatic Imbalances of Bone -

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Osteomalachia o Failure to mineralize; weak bones o Rickets in children o Due to Ca deficiency, maybe secondary to vitamin D deficiency Osteoporosis

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o Resorption > formation; decrease bone density, mass o Elderly susceptible; vertebral, femoral neck fx o Estrogen, testosterone slow osteoclasts, stimulate blasts o Post-menopausal fall in estrogen Paget’s disease o Disorganized (Pagetic bone); spongy/compact too high o Elderly susceptible; affected bone weak

Hip Fractures -

300,000 hip fractures annually in US Majority related to osteoporosis and falls in older people Enormous public health implication and economic burden A top cause of immobilization in elderly Patients who have sustained a hip fracture o 2 year mortality rate of 36% o Immobility  increased bone resorption, predisposition to 2nd hip fractures o Many don’t regain prefracture level of mobility; lose independence, QOL o Risk of subsequent skeletal fracture up 2.5x o Risk of new hip fracture of 5x – 10x

Drug therapy For Osteoporosis -

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Ca, Vitamin D supplementation Bisphosphonates o Many have names ending -dronate  Actonel/risedronate o Reduce activity of osteoclasts o Reduce bone remodeling o Side effects  Osteonecrosis of jaw  Uncommon fractures PTH analogs o Forteo/teriparatide o 34 aa fragment of PTH...