Immune System

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To be immune means to be protected. So it makes sense that the body system that helps fight off sickness is called the immune system. The immune system is made up of a network of cells, tissues, and organs that work together to protect the body. White blood cells, also called leukocytes , are part of this defence system. There are two basic types of these germ-fighting cells: * phagocytes ( fah-guh-sytes), which chew up invading germs * lymphocytes ( lim-fuh-sytes), which allow the body to remember and recognize previous invaders Leukocytes are found in lots of places, including your spleen, an organ in your belly that filters blood and helps fight infections. Leukocytes also can be found in bone marrow, which is a thick, spongy jelly inside your bones. Your lymphatic ( lim-fah-tik) system is home to these germ-fighting cells, too. You've encountered your lymphatic system if you've ever had swollen "glands" on the sides of your neck, like when you have a sore throat. Although we call them "glands," they are actually lymph nodes ( limf nohdz), and they contain clusters of immune system cells. Normally, lymph nodes are small and round and you don't notice them. But when they're swollen, it means your immune system is at work. Lymph nodes work like filters to remove germs that could hurt you. Lymph nodes, and the tiny channels that connect them to each other, contain lymph, a clear fluid with leukocytes (white blood cells) in it. Beside your neck, where else do you have lymph nodes? Behind your knees, in your armpits, and in your groin — just to name a few. So you have this great system in place. Is it enough to keep you from getting sick? Well, everyone gets sick sometimes. But your immune system helps you get well again. And if you've had your shots, your body is extra-prepared to fight off serious illnesses that your immune system alone might not handle very well. If you get the shot that covers measles, for instance, it can protect...
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