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Skeletal System (Gross classification of bones: (flat bones: found in…

- - - - lamina externa
      - lamina interna
- - - - mesenchyme is the embryonic connective tissue from which all other connective tissues
    - - development of bone tissue w/in the mesenchymal tissue w/out prior formation of flat bones
      - development of the ossification center
        
        a site where bones develops specific chemical messages cause Mesenchymal cells to aggregate and differentiate
        
        organic extracellular matrix secreted until bone surrounds cells
        
        osteogenic cells --> osteoblasts
      - Calcification
        
        calcium and other mineral salts are deposited and extracellular matrix becomes calcified
      - formation of trabaculae
        
        extracellular matrix develops into trabaculae that fuse with each other to form spongey bone
        
        blood vessels grow into the spaces
        
        connective tissue associated w/ blood vessels differentiates into red marrow
      - Development of the periosteum
        
        at the same time as the trabeculae is formed, the mesenchyme condenses at the periphery
        
        eventually a thin layer of compact bone replace the spongey bone- but spongey bone remains in the center
        
        majority of the new bone is remodeled as the bone is transformed into adult shape and size
    - - Development of the cartilage model
        
        specific chemical messages cause the mesenchymal cells to grow together in the shape of the future bone and develop into Chondroblasts
        
        chondroblasts secrete cartilage extracellular matrix producing the model
        
        a covering called perichondrium (dense irregular CT that surrounds the developing bone) develops around the model
      - Growth of the cartilage model:
        
        once the chrondroblasts are buried deep in cartilage they become chondrocytes
        
        Interstitial growth: chondrocytes dicide accompanied by more cartilage matrix
        
        Appositional growth: more matrix is also laid down at the periphery
        
        Matrix begins to calcify --> chondrocytes hypertrophy then die leaving lacunae which merge into small cavities
      - Development of the primary ossification center
        
        nutrient artery penetrates perichondrium and calcifying cartilage model through a nutrient foramen
        
        stimulates cells in perichondrium to differentiate into osteoblasts
        
        perichondrium starts forming bone then becomes periosteum
        
        near the middle of periosteal capillaries grow into the disintegrating calcified cartilage
        
        spongey bone is formed spreading from center to the ends
      - Development of the medullary cavity (marrow)
        
        Osteoclasts resorb some spongy bone leaving a cavity in the diaphysis
        
        wall of the diaphysis is eventually replaced by compact bone
      - Development of the secondary ossification centers:
        
        Branches of the epiphyseal artery enter around the time of birth
        
        develops similar to primary center
        
        spongy bone remains w/out formation of medullary cavity
      - Formation of articular cartilage and the epiphyseal growth plate
        
        hyaline cartilage cover the epiphyses
        
        Prior to adulthood hyaline cartilage remains in metaphysic
  - - - Cartilage cells are produced by mitosis on the epiphyseal side of plate
      - cartilage cells are destroyed and replaced by bone on the diaphysial side of plate
    - - Osteoclasts dissolve the calcified cartilage and osteoblasts invade the area laying down bone matrix
      - The activity of the epiphyseal plate is the way bone can increase in length
    - - Zone of resting cartilage
        
        Anchors growth plates to bone
      - Zone of proliferating cartilage
        
        rapid cell division (stacked coins)
      - Zone of hypertrophic cartilage
        
        cells enlarge and remain in columns
      - Zones of calcified cartilage
        
        thin zone- cells mostly dead since matrix calcified
        
        osteoclasts remove matrix
        
        osteoblasts and capillaries move in to create bone over calcified cartilage
    - - bone grow in thickness at the outer surface
        
        periosteal cells differentiate into osteoblasts and form bony ridges
        
        The bony ridges then tunnel around a periosteal blood vessel
        
        Concentric lamellae fill in the tunnel to form an osteon
    - - Nutrition: minerals and vitamins
      - Hormones: Insulin, Thyroid, estrogen, and testoreone
  - - - osteoclasts form a leak-proof seal around cell edges
        
        secrete enzymes and acids beneath themselves
        
        release calcium and phosphorus into interstitial fluid
      - Osteoblasts take over bone rebuilding
      - continual redistribution of bone matrix along lines of mechanical stress
    - - Parathyroid hormone (PTH) is secreted in Ca+2 level fall
        
        PTH gene is turned on and more PTH is secreted from gland
        
        Osteoclasts actively increased, kidney retains Ca+2 blood and produces calcitriol
      - Calcitonin hormone is secreted from parafollicular cells if thyroid if Ca +2 blood levels get too high
        
        Inhibits osteoclasts activity
        
        increase bone formation by osteoblasts
  - - - Fracture= break in bone
      - healing in bone is faster than in cartilage due to blood vessels in bone
        
        healing is still slow process due to vessel damage
      - Clinical treatment:
        
        Closed reduction = restores pieces to normal position by manipulation
        
        Open reduction = surgery
    - - Formation of fracture hematoma
        
        Damaged blood vessels produce clot in 6-8 hours = bone cells die
        
        Inflammation brings in phagocytic cells for clean up duty
        
        New capillaries grow into damaged area
      - Formation of fibrocartilagenous callus
        
        Fibroblast invade the pro callus and lay down collagen fibers
        
        Chondroblasts produce fibrocartilage to span the broken end of bone
      - Formation of bony callus
        
        Osteoblasts secrete spongy bone that joins 2 broken end of bone lasts 3-4 months
      - Bone remodeling
        
        Compact bone replaces the spongy in the bony callus
        
        Surface is remodeled back to normal shape
- - - - Cranial bones
        
        occipital, parietal, interparietal, and frontal
        
        from the caudal and dorsal walls
        
        horned animals have corneal process on frontal
        
        Temporal bones form lateral and ventral walls
        
        contain the middle and inner ears
        
        sphenoid bone
        
        supports the brain and pituitary gland
        
        ethmoid bone
        
        rostrally located
        
        has many openings for passage of olfactory nerves
      - facial bones
        
        orbit: eye socket
        
        composed of parts from frontal, lacrimal and zygomatic bones
        
        zygomatic arch
        
        frontal, zygomatic and temporal borders ventral and caudal parts of orbit
        
        Air passages through nasal areas
        
        dorsally: nasal bones
        
        laterally: maxillae and incisive
        
        ventrally: palatine processes of maxillae and incisive and palatine bone
        
        vomer bone
        
        divides right and left air passageways (septum)
        
        conchae (turbinates)
        
        arise from lateral walls of nasal cavity
        
        covered in highly vascular mucous membranes
        
        warm and humidify air
    - - Maxillae + Incisive + palatine
        
        make up the roof
        
        maxillae and incisive contain upper teeth; ruminants have no incisive teeth
  - - - Between adjacent vertebrae absorbs vertical shock
      - permit various movements of vertebral column
      - fibrocartilagenous rings with a pulpy center
    - - has many 2 parts
        
        Body: weight bearing (anterior part)
        
        Vertebral arch: contains vertebral foramen (posterior part)
        
        parts of vertebral arch: pedicles, laminae
    - - spinal canal is all vertebral foramen together
      - Intervertebral foramen are two vertebral notches together
    - - well-developed articular process
      - allows neck range of motion
      - atlas and axis:
        
        Atlas (C1) - ring of bone; superior facets for occipital condyles
        
        "yes"
        
        Axis (C2) - dens or odontoid process is body of atlas
        
        "No"
    - - well developed spinous processes and articular facets for rib
    - - large, flat transverse processes that project laterally
      - articular processes are more robust than thoracic but not as large as cervical
    - - fused
      - sacral formation: intervertebral foramina in dorsal and ventral rows
        
        allows spinal nerve passage
    - - tail
      - number varies w/ tail lengths
      - size of bone decreases toward distal end
- - - - not palpable in femur or humerus
    - - Usually contacts another bone
      - palpable
  - - - cavities: where the head of a bone fits
      - fovea: a small depression
      - notch: indentation at the edge of structure
        
        if articular, inside joint where ligaments attach
        
        if non articular, in the alar notch of the atlas
    - - fossa: large non-articular depression, basinlike
      - foramen: round or oval opening through bone
      - canal: tunnel through one or more bones