The largest single mass of lymphoid tissue in the body. The spleen is a soft, purple, highly vascular organ located in the upper left region of your abdomen. It lies just behind and partly lateral to the stomach and just under the diaphragm. It is shaped like a very small smooth rounded catcher's mitt with notches at its upper anterior edge.
When you get mono (mononucleosis) malaria or blood poisoning, the spleen can swell, and once swollen it is in danger of rupturing. If the spleen ruptures, it will bleed profusely and cause shock, so be careful and protective of your body during a recovery from one of these ailments. During this time, you should avoid contact sports such as football where one good bump could cause a ruptured spleen.