Waiting to Exhale

When it's time to exhale (breathe out), everything happens in reverse: now it's the diaphragm's turn to say, "Move it!" Your diaphragm relaxes and moves up, pushing air out of the lungs. Your rib muscles become relaxed, and your ribs move in again, creating a smaller space in your chest.

By now your cells have used the oxygen they need, and your blood is carrying carbon dioxide and other wastes that must leave your body. The blood comes back through the capillaries and the wastes enter the alveoli. Then you breathe them out in the reverse order of how they came in: the air goes through the bronchioles, out the bronchi, out the trachea, and finally out through your mouth or nose.

The air that you breathe out not only contains wastes and carbon dioxide, but it's warm, too! As air travels through your body, it picks up heat along the way. You can feel this heat by putting your hand in front of your mouth or nose as you breathe out. What is the temperature of the air that comes out of your mouth or nose?

With all this movement, you might be wondering why things don't get stuck as the lungs fill and empty! Luckily, your lungs are covered by two really slick special layers called pleural membranes (say: ploo-ral mem-branes). These membranes are separated by a fluid that allows them to slide around easily while you inhale and exhale.

Time for Talk

Your lungs are important for breathing . . . and also for talking! Above the trachea (windpipe) is the larynx (say: larr-inks), which is sometimes called the voice box. Across the voice box are two tiny ridges called vocal cords, which open and close to make sounds. When you exhale air from the lungs, it comes through the trachea and larynx and reaches the vocal cords. If the vocal cords are closed and the air flows between them, the vocal cords vibrate and a sound is made.

The amount of air you blow out from your lungs determines how loud a sound will be and how long you can make the sound. Try inhaling very deeply and saying the names of all the kids in your class - how far can you get without taking the next breath? The next time you're outside, try shouting and see what happens - shouting requires lots of air, so you'll need to breathe in more frequently than you would if you were only saying the words. Experiment with different sounds and the air it takes to make them: when you giggle, you let out your breath in short bits, but when you burp, you let swallowed air in your stomach out in one long one! When you hiccup, it's because the diaphragm moves in a funny way that causes you to breathe in air suddenly, and that air hits your vocal cords when you're not ready.