When you inhale (breathe in) through your nose or your mouth, you bring oxygen into the lungs. When you breathe out, you exhale carbon dioxide and other waste that your body no longer needs.

Your lungs are made of lots of tiny tubes which lead to even tinier air sacs called alveoli. These little sacs fill up with air like balloons when you inhale.

The oxygen in the air is filtered through the thin walls of the alveoli and is carried into the bloodstream through small blood vessels called capillaries. Waste such as carbon dioxide is carried out of the body in the same manner, only it is headed in the opposite direction: from the blood through the cappilaries and the alveoli and finally breathed out!