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apter 4 Ch Your Respiratory System and How It Works 왖 The air you breathe provides you with the oxygen you need. As you read, connect what you learn to your own life. Ask yourself, "How does oxygen help keep me healthy?" Your body needs nutrients and water to stay alive and healthy. You also need one more thing—oxygen. Without oxygen, you could only survive for a few minutes. Oxygen is a gas that is found in the air you breathe. Just as a fire cannot burn without oxygen, your cells cannot “burn” the fuel from the food you eat without oxygen. Your body needs oxygen to release the energy from the nutrients in your cells. Without oxygen, these nutrients would not release energy, and all the systems in your body would shut down. How does your body get oxygen? This is the job of the respiratory system. The main organs of the respiratory system are the mouth, nose, trachea [TRAY-kee-uh], and lungs. Let’s see how these organs work to bring oxygen to your cells. 92 NEL Nose Mouth Trachea Rib cage Lungs Diaphragm 왖 Your respiratory system brings oxygen to the cells in your body. You breathe in air through your nose or your mouth. Breathing in is called inhaling. The air travels down your throat to a tube called the trachea. The trachea is also called the windpipe. There is a flap over the trachea. This flap opens when you are breathing in so air can go down to your lungs. It closes if you are drinking or eating so that food or liquid does not go down the trachea. As you read, use your finger to trace the parts of the respiratory system on the diagram. The bottom of the trachea divides into two branches. Each branch goes into a lung. A lung is a spongy organ in your chest that sits inside your ribs. You have two lungs. The branch in each lung divides into smaller and smaller branches. At the end of these branches are tiny clusters of air sacs. It is here that the oxygen in the air is picked up and carried to all the cells in your body by your blood. Just below your lungs is a muscle called the diaphragm [DIE-uh-FRAHM]. This muscle moves up and down to help you breathe. NEL 93 Getting Rid of Wastes Your respiratory system has another job to do. Oxygen works with the nutrients in your cells to produce energy. Producing energy also produces water and carbon dioxide. 왖 Cells use oxygen and nutrients to produce energy. Water and carbon dioxide are also produced. Water is very important to the cells in your body. Sometimes, however, your cells don’t need all the water in your body. The water that is left over needs to be removed as waste. Some of the waste water is in the air you breathe out. This is why your breath is moist. 왘 What happens when you breathe on a mirror? What does this show you about your breath? Carbon dioxide [KAR-buhn die-AWK-side] is a gas. It is harmful to your body, so your body must remove it quickly. Your blood picks up the carbon dioxide and takes it to your lungs. You get rid of it when you breathe out. Breathing out is called exhaling. 94 NEL How You Breathe The diaphragm helps the air move in and out of your lungs. When you breathe in, the diaphragm contracts and moves down. Muscles are attached to the ribs. These muscles lift your rib cage so it expands. When the rib cage expands, air enters the lungs. When you breathe out, the diaphragm relaxes and moves up. The muscles attached to your ribs also relax. When the rib cage gets smaller, air leaves the lungs. Breathing in When you don't understand a word, you can often figure it out by reading the words around it. Read this paragraph. What do you think the word "contract" means? Breathing out Rib cage expands Rib cage gets smaller Diaphragm contracts and moves down Diaphragm relaxes and moves up 왖 Inhaling 왖 Exhaling 1. Why does your body need oxygen? How does your body get this oxygen? 2. List two ways in which the air you breathe in is different from the air you breathe out. 3. Describe how air gets into and out of your body. NEL 95