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. Infact, you have300,000,000 alveoliin each
hundred million in total - and your
body needs them all to get enough oxygen into your blood!