How your lungs work

Why do you breathe?

Every part of your body needs oxygen to survive. On this page, we explain why you breathe, and the muscles used while breathing.

Why do we breathe?

Everyday functions of the body like digesting your food, moving your muscles or even just thinking, need oxygen. When these processes happen, a gas called carbon dioxide is produced as a waste product. The job of your lungs is to provide your body with oxygen and to get rid of the waste gas, carbon dioxide.

Your brain constantly gets signals from your body which detect the amount of oxygen and carbon dioxide in your blood.

Your brain will send signals to the muscles involved in breathing and adjust your breathing rate depending on how active you are.

When you’re active, your breathing can increase up to about 40-60 times a minute to cope with the extra demand. The delivery of oxygen to your muscles also speeds up, so they can do their job efficiently. The increase in your breathing also makes sure there’s no build-up of carbon dioxide in your bloodstream.

What muscles do you use to breathe?

Your main breathing muscle is the diaphragm. This divides your chest from your abdomen.

Your diaphragm contracts when you breathe in, pulling the lungs down, stretching and expanding them. It then relaxes back into a dome position when you breathe out, reducing the amount of air in your lungs.

When you exercise, your abdominal muscles are used to push air out of the lungs when you breathe out. This is called forced expiration.

There are also muscles in between the ribs, which keep the ribcage stiff and help with breathing. These are called intercostal muscles.

Breathing control

Breathing in:

Healthy lung tissue is springy and elastic, so your muscles need to work to expand your chest and draw air into your lungs.

Signals from the respiratory centre in your brain travel down nerves to your diaphragm and other muscles. The diaphragm is pulled flat, pushing out the lower ribcage and abdomen. At the same time, the muscles between your ribs pull your rib cage up and out. This expands the chest and draws air into the lungs.

Air is pulled into your nose or mouth, and into your windpipe. This divides into airways supplying the left and right lungs.

The air passes down the airways, which divide another 15 to 25 times, and finally into thousands of smaller airways until the air reaches the air sacs.

Breathing out:

At rest, breathing out is mostly a passive process. The muscles you use to breathe in now relax and your elastic lungs push air out. When you exercise and your body needs to move air more quickly, your abdominal muscles provide the main drive for exhaling. The intercostal muscles also help.

The system works so that you breathe in and out comfortably at rest where the least effort is required to move air – and you’re probably not conscious of your breathing. When you exercise, you need to move more air. To do this you can take bigger breaths or breathe more quickly – usually both.

Although breathing is usually automatic, you can control it if you want to - when you talk or sing for example.

Read next: Oxygen and blood

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