The spleen is located under the left side of the diaphragm, and has a smooth, convex surface that faces the diaphragm. The spleen is an organ that plays a very important role in the red blood cells and the immune system. The spleen metabolises haemoglobin from senescent erythrocytes. The globin part of haemoglobin is broken down into its constituent amino acids, and the haem part is metabolised into bilirubin, which is eliminated by the liver.

The splenic system stores and purifies erythrocytes, metabolises haemoglobin and recycles iron. The spleen also performs an essential function for the immune system by mounting a primary immune response to antigens in the blood and by synthesising antibodies. Endothelial cells, fibroblasts and splenocytes are essential components required for the normal functioning of the spleen cell system.