Air sacs and blood tubes

Open to everyone until Thursday, October 1

To keep it, print it while it is open.

Tiny balloon-like air sacs sit inside your lungs, wrapped in thin blood tubes. Oxygen slips out of the air sacs into the blood, and carbon dioxide slips the other way, out of the blood into the air sacs.

In the picture

Air sac wall: the thin surface that oxygen crosses
Blood tube along the sac: the channel that carries blood past the air
Blue dot entering the tube: oxygen leaving the air sac
Grey dot entering the sac: carbon dioxide leaving the blood

Examples

Air slowly escaping a balloon through its skin
Fizz rising out of a fizzy drink

Key takeaways

Oxygen goes from the air sacs into the blood, and carbon dioxide goes from the blood into the air sacs.
The walls of the air sacs and blood tubes are very thin, so gases can pass through them.