The lung is an organ. It gives blood oxygen from the air, and takes away carbon dioxide. Most vertebrates have two lungs.

In animals, the lungs are the area where gas exchange takes place. Without gas exchange, oxygen would not pass into the blood from the lungs, so the body cells would not be able to receive the oxygen needed for respiration (breathing), which is something we all need to do all the time.

Here’s how respiration happens.

• The first step in this process is breathing in air, or inhaling.
• The second step is gas exchange in the lungs, where oxygen is sent into into the blood and the carbon dioxide comes out of the blood.
• The third step is a process where the cells take in the oxygen, use it to produce the energy they need, and give back carbon dioxide in place of the oxygen.
• Finally, the carbon dioxide is exhaled from the lungs out of our bodies.

The alveoli are moist to allow oxygen to move from the lung through the alveoli into blood vessels and red blood cells. Carbon dioxide passes from the blood into the alveoli. The oxygen-filled blood goes back to the heart, and the carbon dioxide in the alveoli is pushed out of the lungs and into the air we breathe out.

 

(edited from source: one, two)