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Osseous Tissue & Skeletal Structure

  1. General

*Skeletal system => bones, cartilage, ligaments & connective tissues.

*Functions

Support

Store minerals & lipids

Blood cell production

Protection

Leverage

  1. Structure of Bone

*Bone is a supporting connective tissue

    1. Histological organization
    1. Four basic features
    1. matrix is very dense & contains deposits of Ca++ salts
    2. matrix contains osteocytes within lacunae
    3. Canaliculi extend between lacunae & blood vessels
    4. Outer surface covered by a periosteum
    1. The Matrix of Bone
    1. Calcium Phosphate => makes up about 2/3 the weight of bone
    2. collagen fibers => make up about 1/3 the weight of bone
    3. calcium phosphate => hard, inflexible & brittle => can withstand compression but may shatter when bent or twisted
    4. collagen => strong & flexible
    1. The cells in bone
    1. Osteocytes
    1. mature bone cells found in lacunae
    2. CAN NOT divide
    3. one osteocyte/lacunae
    4. canaliculi => cytoplasmic extensions of the osteocytes
    5. Function to recycle calcium salts in the matrix around them and participate in the repair of damaged bone.
    1. Osteoblasts
    1. precursor cells
    2. osteogenesis
    3. osteoid
    4. osteoblast become an osteocyte when completely surrounded by calcified matrix
    1. Osteoprogenitor cells
    1. mesencymal cells
    2. maintain population of osteoblasts
    3. important in fracture repair
    1. Osteoclasts
    1. giant cells derived from monocytes
    2. dissolve matrix & release stored minerals (osteolysis)
    1. Compact & Spongy Bone

*compact => dense & solid (walls)

*spongy => open network of struts & plates (internal layer)

*marrow => loose C.T. dominated by adipocytes (yellow) or a mixture of

mature & immature red and white blood cells (red).

*matrix same in compact & spongy bone; differ in arrangement of cells

    1. Compact Bone
    1. osteon => basic functional unit of mature compact bone

(Haversian System)

    1. osteocytes arranged in concentric layers around a central canal

(Haversian Canal) that contains one or more blood

vessels

    1. Perforating canals (canals of Volkman) extend perpendicular to the surface
    2. Distribution => cover surfaces of bone

thickness varies

    1. Function => thickest where stresses arrive from a limited range of directions
    1. Spongy Bone (Cancellous Bone)
    1. No osteons or blood vessels
    2. Matrix form struts & plates => Trabeculae
    3. Nutrients diffuse along canaliculi
    4. Distribution => present at expanded regions of long bones where they articulate with other skeletal elements
    5. Function => Found where bones are not heavily stressed or where stresses arrive from many directions
    1. Periosteum & Endosteum
    1. Periosteum

2) Endosteum

III) Bone Development & Growth

    1. Intramembranous Ossification (dermal ossification)
    1. Osteoblasts cluster together & secrete organic components of the matrix

Ossificatdion Center => location where ossification first

occurs

Some osteoblasts trapped => osteocytes

    1. bone grows outward from the ossification center in small struts
    2. bone assumes the structure of spongy bone => compact bone
    3. growth slows and the C.T. around bone is organized into the fibrous layer of the periosteum
    1. Endochondrial Ossification
    1. cartilage enlarges and chondrocytes near the center of the shaft increase in size
    2. cell enlarge, lacunae expand, matrix reduced to small struts and begin to calcify
    3. enlarged chondrocytes die and disentegrate
    4. blood vessels frow into perichondrium of the cartilaginous shaft
    5. cells develop into osteoblasts
    6. perichondrium becomes periosteum
    7. blood supply increases
    8. cartilaginous matrix breaks down and the osteoblasts replace it with spongy bone
    9. diaphysis filled with spongy bone
    10. osteoclasts erode central portion (marrow cavity)
    11. Increase in length and enlargement in diameter

C) Increasing the length of a developing bone

    1. Increasing diameter of a developing bone
    2. Blood and Nerve Supply
    1. Nutrient artery and vein
    2. metaphyseal vessels
    3. periosteal vessels
  1. The Dynamic Nature of Bone
    1. Effects of Exercise
    1. Effects of Hormones and Nutrients
    1. Skeleton as a Calcium Reserve

*Calcium concentration dependent on bones, kidneys & GI tract

*Negative feedback => Parathyroid and Calcitonin

    1. Fracture Repair
    1. Aging
  1. Anatomy of Skeletal Elements
    1. Classification of Bones
    1. Long bones
    2. Short bones
    3. Flat bones
    4. Irregular bones
    5. sesamoid bones
    6. sutural bones