The spleen has a function in the manufacture and breakdown of blood cells, the latter function being the more important. Aging and malformed blood cells are removed from the bloodstream by the spleen and cleared away. In an illness that produces large numbers of malformed blood cells, the spleen becomes overactive. Such disorders include haemolytic anaemia for red blood cells and leukaemia and Hodgkin’s disease for white blood cells. Overactivity causes the spleen to swell. The swelling can be clearly felt on physical examination, and also causes abdominal pain by exerting pressure on other organs in the abdomen. The spleen is also able to manufacture blood cells, although generally this facility is not used. If the bone marrow is no longer able to produce enough blood cells as a result of aplastic anaemia, leukaemia or multiple myeloma, the spleen can produce extra cells, an activity which can again cause it to swell. The spleen always contains large quantities of blood because of its role in blood breakdown; thus if the organ is ruptured, in a car accident for example, there can be massive haemorrhage with risk of shock. Despite the importance of the spleen’s function in the breakdown of blood, it is The spleen is in the rear of the upper part of the left-hand abdominal cavity and is protected. By the rib cage.