Structure & Function of Lungs at Rest

Updated April 17, 2017

The lungs perform a vital function of life. They are part of the respiratory system which also includes the nose, the epiglottis, the trachea, the bronchi and the diaphragm. The respiratory system is an intricate network of organs all working together to insure a constant flow of gases, oxygen and carbon dioxide, to keep the body functioning at rest or during exertion.


There are two lungs, one on the right side and a slightly smaller one, to make room for the heart, on the left side. Each lung is between 10 and 12 inches long and is full of blood vessels that carry carbon dioxide full blood in and oxygen rich blood out to the rest of the body. The lungs contain bronchial tubes, also called airways, that have alveoli (small air sacs) attached at the end of the tubes. Normal lungs contain over 300 million alveoli which are covered with tiny capillaries that also carry blood.

Oxygen In

The main function of the lungs is gas exchange. As you breathe in air through the nose or mouth the air travels through the epiglottis and down the trachea to the right and left bronchi (breathing tubes) that leads to the lungs. Each of these tubes branch into a group of smaller tubes called bronchioles which lead to the air sacs. In the capillaries inside these air sacs oxygen is infused into the blood. This oxygen rich blood then goes to the heart and is pumped throughout the body.

Carbon Dioxide Out

The blood in the capillaries arrives to the air sacs full of carbon dioxide, a waste gas. As the oxygen moves into the blood from the air, the carbon dioxide moves out of the blood into the air. This air is then pushed out of the body during exhalation.


The delicate lungs need to be protected against foreign bodies or irritants. The nose is the first line of protection filtering and trapping large particles. The smaller irritants that do get by the nose are then trapped in the airways by the thin layer of mucus known as sputum or phlegm. This mucus is constantly renewed as the old is swept along by the cilia (tiny hairs) toward the throat where it is then swallowed. Coughing is also a way the lungs protect themselves as it helps to expel infected mucus from the lungs faster than the cilia. These mechanisms of protection are necessary to keep the lungs performing their primary function of gas exchange.

Help of Muscles

Breathing cannot happen without the help of many muscles. Even at rest, the diaphragm, a large muscle that lies under the lungs, contracts as the lungs expand with air and relaxes as the air is exhaled from the lungs. The intercostal muscles, located between the ribs also play a major role in helping the lungs function in breathing during times of rest. Other muscles involved, including the abdominal muscles and neck muscles only aid in breathing during time of physical activity or exertion.

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About the Author

Stephanie Chandler is a freelance writer whose master's degree in biomedical science and over 15 years experience in the scientific and pharmaceutical professions provide her with the knowledge to contribute to health topics. Chandler has been writing for corporations and small businesses since 1991. In addition to writing scientific papers and procedures, her articles are published on and other websites.