What Happens Inside Your Lungs?

The warm, cleaner air passes from the upper respiratory system into the lower respiratory system: the lungs. The lungs are made up of thousands of bronchial tubes; small air passages leading to tiny air sacs called alveoli. Oxygen passes from the sacs into capillaries, blood vessels that carry it through the bloodstream to the body's many cells.

Traveling the opposite direction is carbon dioxide, a waste by-product of the energy created by your body's use of oxygen. The carbon dioxide is carried by the blood back into the air sacs where it is sent out of your body when you exhale.

If your lungs and respiratory system is weakened or damaged from lung disease, pollution or asthma, breathing can become difficult. If you have trouble breathing, your body might not get the oxygen you need to function properly.