Take a big breath in, hold it and breathe out. Now let's begin. You just use your respiratory system. It is a system in humans that is designed to extract oxygen from the air so we can use it in respiration around the body. And at the same time get rid of carbon dioxide gas into the air which is the waste product from respiration. Let's follow a molecule of oxygen gas as it travels through the respiratory system. As you inhale the molecule is drawn in through the mouth or the nose. It goes into the back of the throat where it enters a tube called the tracier. The tracier or windpipe has special rings of cartilage to keep it open at all times so you can breathe if you are lying down asleep or on a trampoline. The oxygen molecule now travels down the tracier and then will go into either the left or the right lung via a tube called the broncus. This broncus then splits into smaller tubes called bronchios. And finally the oxygen molecule will make its way into a tiny air sac called an alveolus. These alveoli are surrounded by tiny blood vessels called capillaries and the oxygen molecule now passes across from the air into the blood via a process called diffusion. At the same time a carbon dioxide molecule goes the other way coming out of the blood and into the alveoli as you exhale. As you exhale a carbon dioxide will take the journey back up the bronchios, a broncus, the tracier and out of the mouth. This happens to millions of molecules with each breath as you have about 300 million alveoli in each lung. On average you breathe like this 12 to 16 times a minute. Why not count yours after this video? Unlike your digestive system the respiratory system is a dead end. If something bad gets into your lungs it's very hard to get it back out. As usual the body has an answer to this. Look very closely at the cells lining the tracier and the bronchios. Some of them have tiny little hairs on them called cilia and in between these cells are other cells called goblet cells that are secreting mucous. Mucous tracier dirt dust and bacteria before it enters the lungs. This cilia then wafthis mucous up into the mouth where it can be swallowed to be killed by your stomach acid. There are many things that can go wrong with your lungs such as asthma, pneumonia and diseases associated with smoking such as emphysema and chronic bronchitis. However, if you have a problem a doctor may perform a bronchoscopy. This is when they put a tube with a light and a camera on it into your airways and look for signs of inflammation or bleeding. Take a big breath in, hold it and breathe out and relax.