Mechanics of breathing 4.2

4.2

pressure in inspiration

pressure of air in lungs must be less then atmospheric pressure outside body

how is pressure changed in inspiration

pressure in lungs decreases by increasing volume of lungs
diaphragm and intercostal muscles contract
diaphragm is flatter and ribs move up and out
pleura adheres lungs to chest cavity expanding them

what happens at the end of inspiration

air flows in through nose and trachea until the pressure is equal

difference between quiet and heavy inspiration

in quiet breathing the diaphragm is mainly responsible, in heavier breathing the ribcage becomes more important

pressure in expiration

air pressure in lungs is greater then air pressure outside body

how is pressure changed in expiration

diaphragm and intercostal muscles relax
ribcage moves downwards

what happens at the end of expiration

air flows out through trachea and nose until pressures are equal

difference between quiet and heavy expiration

with quiet breathing expiration is a passive process
intercostal muscles contract to lower ribcage in heavier breathing