------------------
16. The following occurs during the process of inhalation:
a) The external intercostal muscles contract, moving the ribcage upwards and outwards.
b) At the same time, the diaphragm also contracts, moving downward as it becomes flatter.
c) Both the previous 2 steps increase the volume of the thorax or chest, causing the pressure within the thorax to decrease.
d) When the pressure in the thorax decreases below that of the surrounding air, air flows into the lungs from outside the body (This would be like diffusion, from high concentration to low concentration.). Air continues to enter the lungs until an equilibrium (equal pressures) between the internal and external environments is reached.
e) Since there is a high concentration of oxygen in the alveoli and less in the blood, oxygen diffuses into the blood.
------------------