A person’s windpipe splits into two bronchi, one for each lung. The bronchi then divide into smaller bronchi, which split into bronchioles. These lead to tiny air sacs known as alveoli.

Cilia are small hairs which beat to push the mucus back up the trachea so it can be swallowed and destroyed in the stomach. Clean air then enters the two bronchi, one bronchus going to each lung.

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Bronchiole Each bronchus splits again and again into thousands of smaller tubes called bronchioles which take the air deeper into the lungs. Alveoli At the ends of bronchioles are tiny air sacs ...