mechanisms of ventilation

• breathing = pulmonary ventilation
• inspiration

  • active process
  • diaphragm flattens as it contracts - increases height of chest cavity
  • external intercostal muscles contract to raise ribs - increases circumference of chest cavity
  • the volume of the thorax is larger meaning the air it is at a lower pressure than outside - air moves into lungs
• expiration

  • passive process - in healthy people
  • diaphragm relaxes and moves up
  • external intercostal muscles relax - rib cage drops
  • elastic fibres in the lungs recoil
  • volume of thorax and lungs decrease - inside pressure increases
  • air is forced out
• forced expiration

  • active process
  • contraction of abdominal wall muscles - increased abdominal pressure forces diaphragm up
  • rib cage is depressed with help from internal intercostal muscles and latissimus dorsi
  • air is forced out