Air enters your body through your nose and mouth. From there, it goes through your trachea (which is also called the windpipe). The trachea is the hard tube that is in the front of your neck. See if you can feel yours.

At the end of your trachea, the air splits off into two bronchial tubes. There is one bronchial tube going into each lung in your body. The bronchial tubes split up into smaller and smaller tubes. At the end of these tubes, there are little sacs called alveoli. That's where the blood in your capillaries (tiny tubes carrying blood) meets the air and picks up the oxygen your body needs. At the same time, the blood gets rid of the harmful carbon dioxide that your cells produce.

Some people think the lungs are just big hollow bags, but in fact they are more like sponges. This increases the  amount of area inside the lungs that the blood can meet with the air.

Do you know that the surface area inside your lungs is big enough to cover the floor of your classroom? That's how much area your lungs need to get all of the oxygen into your body!

To work properly, your lungs have to be clean. Unfortunately, the air you breathe is not always that clean. That's why your lungs have a cleaning system. Dirt, germs, and other stuff get caught in the mucus that lines your nose, trachea and lungs. The glands that make the mucus are called mucus glands.

Next, little hairs called cilia act like tiny brooms to push the dirty mucus out of your lungs and into your throat. The cilia help prevent your lungs from getting sick from germs floating around in the air.

Without the cilia in our lungs, we would be sick all the time!!