Bones, cells and function

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Bones, cells and function

What is bone?

  • living tissue
  • support, muscle attachment
  • houses hameotpoeisis/marrow
  • protection (internal organs)
  • reservoir for calcium, phosphate (mineral for homeostasis, endocrine role)
  • strong, highly mineralised
  • continual turnover (remodelling)
  • blood diseases are associated with bone diseases

Bone consists of:

  • cells
  • matrix (25%) - all cells are made here, organic (95% type I collagen, 5% non-collagenous proteins, GAGs)
  • mineral (75%) - inorganic hydroxyapatite, gives hardness with calcium phosphate crystals

Types of bones

  • long bones e.g. femur, humerus (composed of epiphysis, metaphysis, diaphysis)
  • flat bones e.g. skull
  • short bones e.g. wrist, ankle
  • irregular bones e.g. maxilla

Cells of bones

  • osteoblasts
    • major cells
    • bone-forming cells
    • deposits bone matrix
    • deposits unmineralised substance
    • cuboidal morphology
    • post-mitotic
    • synthesise osteoid
    • gap junctions
    • do not divide
    • polarised - nucleus on one side of the cell
    • protein synthetic
    • RER, Golgi
  • osteocytes
    • terminally differentiated osteoblasts
    • osteoblasts become osteocytes after being engulfed
    • embedded in lacunae (holes which cells sit in)
    • 25 year life span
    • connected via canaliculi/gap junctions
    • communication
    • processes sent out through small canals
  • osteoclasts
    • bone-resorbing cells
    • degrade and dissolve mineral in bone
    • multinucleated
    • Howship's lacunae (pits created when osteoclasts resorb bone)
    • sealing zone/clean zone
    • ruffled border

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