ventilating the lungs

• ventilation


  = movement of air (caused by pressure changes in the thorax)
• • ribcage= provides semi-rigid case, pressure can be lowered and protection.
  • diaphragm= broad, dome sheet of muscle- floor of the thorax,
  • internal/external intercostal muscles found between ribs.
  • thorax= lined by plural membrane.
  • plural cavity= filled with thin layer of lubricating fluid so membrane slides over each other easily.
• inspiration

  = taking air in.

  • diaphragm contracts, flattening and lowering.
  • external intercostal muscles contract, moving ribs up and out.
  • volume of thorax increases and pressure decreases- so is now lower than pressure of atmosphere air so air is drawn in.
• expiration 


  = breathing out- passive process.

  • diaphragm relaxes- moves upwards to resting dome shape.
  • external intercostal muscles relax, moving ribs in and down.
  • decreases volume of thorax so greater than atmospheric pressure- air moves out.