Gases move by simple diffusion — always from high to low partial pressure. That same rule swaps gases in the lungs one way, and in the tissues the opposite way. Switch between them.
External respiration
Gas exchangefollow the gradient
Partial pressure (P) is the pressure one gas contributes in a mix. Each gas diffuses down its own gradient — independently of the others.
📷 Reference image
A real labeled figure to compare with the interactive above.
Gas Exchange — NIH NIAID, CC BY 4.0 (via Wikimedia Commons)
