Gases move by simple diffusion. They always go from high to low partial pressure. In the lungs, this rule swaps gases one way. In the tissues, it swaps them the other way. Switch between them.
External respiration
Gas exchangefollow the gradient
Partial pressure (P) is the pressure one gas adds in a mix. Each gas moves down its own gradient. It does not depend on the other gases.
📷 Reference image
A real labeled figure to compare with the interactive above.
Gas Exchange — NIH NIAID, CC BY 4.0 (via Wikimedia Commons)
