is also called the windpipe.

This occurs whenever air cannot flow freely through the back of the mouth and the nose.

is a disorder that causes the small bronchial tubes to become narrow from time to time making it hard to breathe; it is often triggered by allergies and air pollution.

is a lung infection caused by viruses or bacteria that causes the lungs to fill with fluid making it difficult for the lungs to fill properly with air.

are tiny air sacs at the end of the bronchioles where the exchange of oxygen and carbon dioxide take place.

 Tiny blood vessels that surround the alveoli are called