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Breathing involves two phases: breathing in and breathing out. If you have problems breathing, gas exchange may be impaired, which can be a serious health problem.
When you breathe in, or inhale, your diaphragm contracts and moves downward. This increases the space in your chest cavity, and your lungs expand into it. The muscles between your ribs also help enlarge the chest cavity. They contract to pull your rib cage both upward and outward when you inhale.
As your lungs expand, air is sucked in through your nose or mouth. The air travels down your windpipe and into your lungs. After passing through your bronchial tubes, the air travels to the alveoli, or air sacs.
Through the thin walls of the alveoli, oxygen from the air passes into your blood in the surrounding capillaries. At the same time, carbon dioxide moves from your blood into the air sacs. The oxygen in your blood is carried inside your red blood cells by a protein called hemoglobin .
The oxygen-rich blood from your lungs is carried to the left side of the heart through the pulmonary veins. The heart pumps the blood to the rest of the body, where oxygen in the red blood cells moves from blood vessels into your cells.
Your cells use oxygen to make energy so your body can work. During this process, your cells also make a waste gas called carbon dioxide. Carbon dioxide needs to be breathed out or it can damage your cells.
Carbon dioxide moves from the cells into the bloodstream, where it travels to the right side of your heart. The blood rich in carbon dioxide is then pumped from the heart through the pulmonary artery to the lungs, where it is breathed out.
For more information on blood flow, visit our How the Heart Works Health Topic.
When you breathe out, or exhale, your diaphragm and rib muscles relax, reducing the space in the chest cavity. As the chest cavity gets smaller, your lungs deflate, similar to releasing of air from a balloon. At the same time, carbon dioxide-rich air flows out of your lungs through the windpipe and then out of your nose or mouth.
Breathing out requires no effort from your body unless you have a lung disease or are doing physical activity. When you are physically active, your abdominal muscles contract and push your diaphragm against your lungs even more than usual. This rapidly pushes air out of your lungs.
Damage, infection, or inflammation in the lungs or airways or both, can lead to the following conditions.
Exposure to cigarette smoke, air pollutants, or other substances can damage the airways, causing disease of the airways or making a disease more severe.