Breathing ~ The Human Lungs

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  • Air is constantly moved in and out of the lungs 
  • Known as ventilation 
  • Pressure changes and that is what leads to inspiration and expiration
  • Breathing in oxygen and breathing out carbon dioxide maintains a steep diffusion gradient



  • Breathing in 
  • Active process
  • External intercostal muscles contract 
  • Internal intercostal muscles relax
  • Ribs are pulled upwards and outwards, increasing the volume of the thorax
  • Diaphragm muscles contract and flatten, increasing the volume of the thorax
  • The increased volume in the thorax means the pressure in the lungs is reduced


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