Structure of the human gas exchange system

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Mammalian Lungs

  • supported and protected by the rib cage 
  • ensure efficient gas exchange between the air and the blood 
  • volume of oxygen inhaled must be large because mammals:
    • are large organisms 
    • need to maintain a high body temperature 
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The Lungs

  • a pair of lobed structures 
  • made up from tubules called bronchioles which end in tiny air sacs called alveoli 
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The Trachea

  • a flexible airway that is supported by rings of cartilage  
  • the cartliage prevents the trachea from collapsing 
  • the tracheal walls are made up of muscle, lined with epithelial and goblet cells 
  • the goblet cells produce mucus that traps dirt particles and bacteria from air breathed in. 
  • the cilia move the mucus, laden with dirt and microorganisms, up to the throat, where it passes down the oesophagus into the stomach 
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The Bronchi and Bronchioles


  • two divisions of the trachea, each leading to one lung 
  • similar structure to the trachea and produce mucus to trap dirt particles 
  • they also have cilia to move mucus towards the throat 


  • branching subdivisions of the bronchi 
  • their walls are made of muscle lined with epithelial cells
  • this them to constrict so they can control the air flow in and out of the alveoli 
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The Alveoli

  • miunte air sacs at the end of the bronchioles 
  • they contain collagen and elastic fibres and they are lined with epithelium 
  • the elastic fibres allow the alveloi to stretch as they fill with air 
  • they then spring back in order to expel the carbon dioxide rich air 
  • the alveolar membrane is the gas exchange surface 
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