The bronchioles end by entering the circular sacs called alveoli.

We breathe air into lungs elaborated with little sacs called alveoli.

These small airways end in sac-like structures called alveoli.

The bronchioles eventually end in clusters of microscopic air sacs called alveoli.

The lung contains many small bulbs, or sacs, called alveoli.

Tiny air sacs called alveoli and small tubes called bronchioles make up the inside of the lungs.

The bronchioles end in tiny balloon-like air sacs called alveoli.

In ciliates and Apicomplexa, it is formed from closely packed vesicles called alveoli.

At the end of the tubes are tiny air sacs called alveoli that deliver fresh air (oxygen) to the blood.

A lung is made up tubes that connect to millions of tiny air sacs called alveoli.