Bones, cells and function

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
  • …