How do the lungs work?

The lungs are the main organ in your respiratory (breathing) system. The main job of the respiratory system is to move oxygen from the air into the blood, and to move carbon dioxide from the blood back into the air. But the respiratory system consists of more than just the lungs; it also includes areas of your brain that control your breathing. Some of these areas give you voluntary control over breathing (allowing you to hold your breath, for example) while other areas involve involuntary or automatic control (allowing you to not have to think about your breathing all the time, for example).

The lungs look like big pink sponges and are located on the right and left sides of your chest. On the outside, the lungs are protected by the rib cage; on the inside, they are connected to your mouth and nose through the windpipe (trachea) and its branches (bronchi), and also connected to your heart through pulmonary arteries (bringing blood from the heart to the lungs) and the pulmonary veins (bringing blood back to the heart). The diaphragm, the dome-shaped main muscle of breathing, sits below the lungs and separates them from the abdominal contents (stomach, intestines, etc.). The motions of the diaphragm and the rib cage help move air in and out of the lungs.

The surrounding air that we inhale is made up mostly of two gases: nitrogen, which accounts for approximately 79%, and oxygen, which accounts for approximately 21%. The amount of carbon dioxide in inhaled air is generally very tiny (much less than 1%); on the other hand, exhaled air contains more carbon dioxide because the lungs help rid your body of this byproduct of normal cellular function.

Every time you breathe in through your mouth or nose, air moves down into your lungs. The air travels from your mouth or nose into your trachea and then through smaller and smaller branching passageways, called bronchi and bronchioles, until it reaches tiny air sacs known as alveoli, the smallest lung units that include thin-walled air sacs directly linked with a network of small blood vessels (capillaries) where gas exchange occurs.

The oxygen in the inhaled air moves across the thin walls of the alveoli into the blood that is flowing by in tiny blood vessels called capillaries. You can think of the blood that moves through the lungs as a constantly flowing stream, driven by the pumping of your heart and carrying the oxygen to all the places in your body that need it.