A key point to remember when thinking about ventilation is that air moves from
high pressure to low pressure. Pressure is directly related to volume. So when
volume increases pressure and decreases and vice versa.
During inhalation air moves in. For this to occur the pressure inside the lungs
needs to be lower than outside.
To ensure the pressure in the lungs is lower, the diaphragm contracts and
flattens and therefore increases the volume in the lungs. Also the intercostal
muscles, the muscles that surround the rib cage contract, this move the ribs
up and out, therefore allowing the lungs to increase in volume even more.
During exhalation air moves out of the body. For this to occur the pressure
inside the lungs has to be greater than outside To ensure the pressure in the
lungs is lower, the diaphragm relaxes and moves upwards back into its original
shape, the intercostal muscles also relax letting the ribs move down. Overall
this makes the volume in lungs decrease and therefore the pressure increases
so air moves out.
|Diaphragm||Contracts causing it to flatten||Relaxes causing it to move back to its original shape|
|Intercostal Muscles||Contract causing the ribs to move up and out||Relaxes causing the ribs to move down and in|
|Volume of ribcage||increases||decreases|
|Pressure inside the chest||decreases||increases|
|Movement of air||Air move in to the lungs||Air moves out of the lungs|