Rocket and Raven play a trading game. Rocket hands over a red card and gets a blue card back.
"Trade complete!" Rocket says.
Raven holds up the cards. "What do you notice? Something goes in and something comes out."
Nova blinks. "Your lungs trade too," she says. "Think about what your cells need, and what they make."
You have two lungs. They are spongy and pinkish-gray.
They sit in your chest, one on each side of your heart.
The right lung has three sections. The left lung has two.
The left lung is a bit smaller. Your heart takes up some space on that side.
Your ribs make a strong cage around your lungs and heart.
Your lungs have millions of tiny air sacs.
Each air sac is wrapped in capillaries, the tiny blood vessels from last week.
Oxygen moves from the air sac into the blood.
At the same time, carbon dioxide moves from the blood into the air sac.
Then you breathe the carbon dioxide out. This trade is called gas exchange.
| Gas | Where it goes in the lungs | Why |
|---|---|---|
| oxygen | From the air sacs into the blood | Cells need it to make energy |
| carbon dioxide | From the blood into the air sacs | Cells make it as waste when they work |
Remember the right side of your heart? It pumps blood to the lungs.
In the lungs, the blood drops off carbon dioxide and picks up oxygen.
Then the blood goes back to the left side of the heart.
The left side pumps that oxygen-rich blood out to your whole body.
Terrific trading! Tomorrow we meet the muscle that powers every breath.