The Alveoli
 When
air enters your lungs, it goes through a maze of smaller and smaller
tubes until it reaches tiny sacs called alveoli. The sacs look
like bunches of grapes at the end of the bronchial tubes. The alveoli
are where the oxygen from the air enters your blood, and the carbon
dioxide from your body goes into the air. Alveoli are very tiny, but
you have a lot of them in your lungs. In fact, you have 300,000,000
alveoli in each lung. That's six hundred million in total - and your
body needs them all to get enough oxygen into your blood!
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