lungs
Finally, the air makes it to your lungs! You have two lungs: one on the right side of your body, and one on the left side. Your lungs are protected by your ribcage. If you watch your chest as you breathe, you can see how your lungs get bigger as you breathe in, and smaller as you breathe out. This happens because your lungs are lined with elastic tissues, called pleura, which help them inflate and deflate without losing shape.
The bottom of the trachea connects to the lungs with two small air tubes called bronchi. These tubes break into smaller and smaller tubes called bronchioles. Bronchioles are as thin as a strand of hair, and end in tiny air sacs called alveoli. There are hundreds of millions of alveoli in our lungs--enough to cover an entire tennis court! Inside the alveoli, oxygen is exchanged for carbon dioxide, which travels back up through the bronchioles, bronchi, and trachea, and out the nose or mouth.
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