The spleen is the largest organ of the lymphatic system, a pulpy-filled organ weighing about 80 grams. It is situated in the upper left abdomen at one end of the liver between the stomach and the diaphragm, where it is protected from injury by the rib cage. The spleen is unlike other lymphatic tissue. It is interposed in the stream because one of its functions involves breaking down and digesting old red blood , thus recycling the iron contained in their haemoglobin. In the unborn child the spleen also forms blood .
In addition it takes part in immunity forming lymphocytes and reticulum cells. A person can survive without a spleen but is more likely to catch certain infections, especially pneumonia. Lymph nodes enlarge in infections, and the spleen also does and can sometimes be felt under the rib cage. An enlarged spleen is therefore a typical symptom of an infectious disease, such as mononucleosis (glandular fever), probably caused by the Epstein-Barr virus. Leukemia, some kinds of anaemia and cirrhosis of the liver may also cause the spleen to become enlarged.