Every breath you take ends up in tiny bubbles deep in your lungs. Their super thin walls let oxygen into your blood and carbon dioxide out.
Drag to turn it around. Use the buttons to zoom in and try things from the lessons.
The 3D model can't load right now. Check your internet connection, or try a different web browser.
Air goes down your windpipe and into smaller and smaller tubes, like the branches of an upside down tree. At the very ends are bunches of tiny air sacs called alveoli.
The walls of the air sacs are made of very flat, thin cells. Other cells make a soapy liquid that stops the sacs from sticking shut.
Your lungs have about 480 million air sacs!
Each air sac is wrapped in tiny blood tubes. The walls between the air and the blood are far thinner than a sheet of paper.
Scroll up to the 3D model and press Breathe in, then Swap gases.
Red blood cells pick up the oxygen and carry it all over your body. Running and playing makes you breathe faster to get more oxygen.
Home activity: Put your hands on your ribs and take a slow, deep breath. Feel your chest get bigger as millions of air sacs fill up!
Clean air keeps air sacs healthy. Smoke can hurt them.