spleen

a roughly ovoid (egg-shaped) organ, coloured a deep purple, that is situated on the left of the body, behind and below the stomach. It is surrounded by a peritoneal MEMBRANE and contains a mass of lymphoid tissue. MACROPHAGES in the spleen destroy microorganisms by PHAGOCYTOSIS . The spleen produces LYMPHOCYTES , LEUCOCYTES , PLASMA cells and blood PLATELETS . It also stores red blood cells ( ERYTHROCYTES ) for use in emergencies. Release of red blood cells is facilitated by smooth MUSCLE under the control of the SYMPATHETIC NERVOUS SYSTEM , and when this occurs, the familiar pain called STITCH may be experienced. The spleen removes worn-out red blood cells, conserving the iron for further production in the BONE MARROW . Although the spleen performs many functions, it can be removed without detriment and as a result there is an increase in size of the lymphatic GLANDS .