How the Lungs Work What Breathing Does for the Body

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.

Breathing in

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 trachea, or windpipe, and into your lungs. After passing through your bronchial tubes, the air travels to the alveoli, or air sacs.

Gas exchange

Every time you breathe in, oxygen from the air you inhale passes through the thin walls of the alveoli into the surrounding capillaries, where red blood cells pick it up using a protein called hemoglobin. At the same time, carbon dioxide, the waste gas carried back to the lungs from the cells of the body, trades places with the oxygen, moving from the blood in the capillaries back into the alveoli.

Blood loaded up with oxygen-rich red blood cells travels to the left side of the heart through the pulmonary veins. The heart then pumps the oxygenated blood to the rest of the body, where it moves from your blood vessels to your cells. The cells need this oxygen to make the energy your body needs to work. When cells make that energy, they create the waste product carbon dioxide. That carbon dioxide has to be removed from the blood and the body, which is why it is pushed from the cells back to the blood.

The carbon dioxide, once in the bloodstream, travels back to the heart, where it enters the right side. From there, it travels through the pulmonary artery to the lungs, where it flows from the capillaries back into the alveoli in exchange for the incoming oxygen. From the alveoli, the carbon dioxide is breathed back out.

How the Heart Works includes information about blood flow and the heart’s role in these processes.

Breathing out

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 how air releases 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.

Conditions that affect the respiratory system

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, and can make a condition you already have more serious.