ventilation and lung capacities

• Bell jar model: when rubber sheet is pulled down, volume increases, air pressure decreases below atmospheric pressure
• Inhalation:

  • diaphragm contracts and lowers
  • external intercostal muscles contract
  • ribs move up and outwards
  • thorax volume increases
  • thorax pressure decreases
  • internal intercostal muscles relax
  • air moves in a pressure gradient and lungs inflate
• Exhalation: (passive process)

  • diaphragm relaxes, moves upwards
  • external intercostal muscles relax
  • ribs move down and inwards`
  • thorax volume decreases
  • thorax pressure increases
  • air moves down a pressure gradient and lungs deflate
• forced exhalation: an active process because internal intercostal and abdominal muscles contract which requires energy
• energy fibres recoiling in alveoli help to release in exhalation