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How Your Lungs Work

The lungs’ job is to get air into and out of the body. Inside the lungs, air moves through a network of branching airways (tubes). These are made of stretchy tissue. Each airway is wrapped with bands of muscle that help control the width of the tube. The airways branch out and get smaller as they go deeper into the lungs. The smallest airways end in clusters of tiny balloon-like air sacs (alveoli). These clusters are surrounded by blood vessels.

Front view of male head and torso showing respiratory system.

When you breathe

  • When you breathe in (inhale), air enters the lungs. It travels down through the airways until it reaches the air sacs.

  • When you breathe out (exhale), air travels up through the airways and out of the lungs.

The air you inhale contains oxygen, a gas your body needs. When this air reaches the air sacs, oxygen passes into the blood vessels. Oxygen-rich blood then leaves the lungs and travels to all parts of the body. As the body uses oxygen, a waste gas (carbon dioxide) is made. The blood carries this back to the lungs. Carbon dioxide leaves the body with the air you exhale.

Bronchiole and alveolar sac with blood supply.

To keep the lungs clean

The cells in the lining of the airways make a sticky secretion called mucus. The mucus traps dust, smoke, and other particles in the air you breathe. The cells have tiny hairs called cilia. They sweep mucus up the airways to the throat. There it’s coughed out or exhaled.

Cells with cilia and mucus on top. Arrow shows mucus being swept along.

To learn more


  • National Cancer Institute Smoking Quitline: 877-44U-QUIT (877-448-7848)

© 2000-2022 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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