Gas Exchange

• Lungs


  • Air passes into the lungs through a tube called the trachea
  • Trachea contains rings of cartilage to prevent it from collapsing when we inhale
  • Trachea splits into two smaller tubes called bronchioles
  • Bronchioles subdivide into many smaller tubes
  • Bronchioles end in tiny air sacs called alveoli
  • Lungs contain a huge number of alveoli
• Alveoli


  The sites of gas exchange where gases diffuse in and out of the bloodstream
• Alveoli


  • Have a huge surface area
  • Have very thin walls so the diffusion path is very short
  • Have a very good blood supply so oxygen is rapidly removed and the concentration gradient is steep
• Oxygen in the air


  Diffuses into the bloodstream
• Carbon dioxide in the bloodstream

  Diffuses out of the bloodstream into the air
• Breathing


  Brings fresh oxygen into the alveoli and takes away carbon dioxide, increasing the concentration gradients and the rate of diffusion