Skip to content

Lung Disease & Respiratory Health Center

Font Size

How the Lungs and Respiratory System Work


The Act of Breathing




The alveoli are surrounded by a mesh of tiny blood vessels called capillaries. Here, oxygen from the inhaled air passes through the alveoli walls and into the blood.


As the cells use the oxygen, carbon dioxide is produced and absorbed into the blood. Your blood then carries the carbon dioxide back to your lungs, where it is removed from the body when you exhale.

The Diaphragm's Role in Breathing


When you breathe in, the diaphragm contracts downward, creating a vacuum that causes a rush of fresh air into the lungs.

The opposite occurs with exhalation, where the diaphragm relaxes upwards, pushing on the lungs, allowing them to deflate.

Clearing the Air



Mucus produced by cells in the trachea and bronchial tubes keeps air passages moist and aids in stopping dust, bacteria and viruses, allergy-causing substances, and other substances from entering the lungs.

Impurities that do reach the deeper parts of the lungs can often be moved up via mucous and coughed out or swallowed.

WebMD Medical Reference

Reviewed by Melinda Ratini, DO, MS on September 23, 2014

Today on WebMD

man coughing
You may not even know you have it.
blood clot
Signs of this potentially fatal complication.
man coughing
When a cold becomes bronchitis.
human lungs
Causes behind painful breathing, fluid buildup.

chest x-ray
Bronchitis Overview
Copd Myth Fact Quiz
Energy Boosting Foods

Pollen counts, treatment tips, and more.

It's nothing to sneeze at.

Loading ...

Sending your email...

This feature is temporarily unavailable. Please try again later.



woman coughing
Lung xray and caduceus