system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 - How do lungs "collapse"?
gpt
Your lungs are inside a sealed "bag" in your chest. That's what makes them expand when your diaphragm pulls down and your ribs move outward...the outer surface of your lungs is basically stuck to the inside of your chest.

Except if you break the bag...then air gets in. Now, rather than your lungs expanding, the air bubble just gets bigger and your lungs get smaller. Your lungs don't really have any structure of their own, without the suction from the seal around them they collapse like wet sponges.