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Respiratory System You breathe about 20,000 times each day! What happens when you breathe? Air is drawn into your body with each breath. Your respiratory system works closely with your circulatory system to deliver oxygen to each part of your body. Carbon dioxide, which is a waste product, is removed as well. When you breathe in, air enters the respiratory system through the nose. The lining of the nose produces mucus, which moistens air and traps germs and dirt. The nose is also lined with hairs to remove dirt and dust from the air. Then the air travels to the throat and passes through the trachea or windpipe. A flap of tissue called the epiglottis covers the trachea to keep food and watering from entering. Place your fingers at the center of your neck where the neck and jaw meet and swallow hard. You can feel the movement of the epiglottis as it covers the windpipe when you swallow. The trachea branches off into two smaller tubes called bronchi which each lead to a lung through smaller and smaller branches called bronchioles. The air then enters the tiny air sacs called alveoli, where the blood gets rid of carbon dioxide and picks up oxygen. It’s Greek & Latin to Me: The prefix respir comes from Latin. It means breathe. Your lungs are the largest organs of the respiratory system. Which part of your lung model represented the lungs? That’s right, the balloons. How did you make the balloons expand? When you pulled down on the piece of balloon at the bottom of the cup, the balloons expanded. That piece of balloon on the bottom of the cup represents your diaphragm. The diaphragm and other muscles work to make your chest cavity larger. Put your hands on your ribs and take a big breath. Feel how your chest expands? When the chest cavity gets larger, air pressure inside the lungs is lower than air pressure outside the lungs and air rushes into the lungs. When the ribs move in and the diaphragm moves upward, the chest cavity becomes smaller and air is forced out. All of these actions take place without our thinking about it because breathing is an involuntary action controlled by the nervous system. Inside the lungs, the oxygen in the air passes across the thin membranes of the alveoli sacs in the lungs and into the oxygen-poor blood in the tiny capillaries that surround the sacs. The thin-walled capillaries are so narrow they hold red blood cells in a single line. The red blood cells contain hemoglobin, an iron-containing material that comes easily with oxygen or carbon dioxide. Hemoglobin acts like a transport system for oxygen and waste carbon dioxide. Oxygen-rich blood then flows back to the left atrium of the heart and is pumped throughout the body.