Features of human gas exchange system

• Cartilage

  • Found: Trachea and bronchus
  • Provides strength to trachea and bronchus
  • Holds the airway open - prevents collapse of airway when air pressure falls
• Surfactant

  • Found: Coats surface of lungs
  • Phospholipid layer which maintains moisture but reduces surface tension to stop alveoli collapsing when air pressure falls
• Smooth muscle

  • Found: Lining trachea - bronchioles
  • Can contract to constrict (narrow) the airways
• Goblet Cells

  • Found: Lining trachea - bronchioles
  • Secrete mucus which traps particles of dust and bacteria which are breathed into the lungs
• Ciliated epithelial cells

  • Found: Lining trachea - bronchioles
  • Beat regularly to move mucus up the airways towards the mouth to be removed.
  • Helps keep the airways clear and prevent infections
  • Contain lots of mitochondria to provide energy required to move cilia
• Elastin (protein)

  • Found: Lining of all airways and alveoli
  • Allows lung tissue to stretch when breathing in and filling up the lungs, recoil when breathing out to help force air out of the lungs
  • Allows alveoli to return to original shape after exhaling
• Squamous epithelium

  • Found: Lining alveoli
  • Gives a short diffusion distance pathway for oxygen and carbon dioxide in the alveoli, cell layer only 0.05-0.3 micrometres wide