The spleen is a fist-sized organ located under the ribcage. It serves as a blood reservoir capable of retaining up to 3 gallons of blood. The spleen also filters out unwanted materials such as bacteria and viruses from the blood. It destroys red blood cells that are too old, damaged or abnormal to function correctly, thereby enabling the immune system to provide defense against infections and diseases.
In traditional Chinese physiology, the spleen plays a central part in the health and vitality of the body, taking a lead role in the assimilation of nutrients and maintenance of physical strength. It turns digested food from the stomach into usable nutrients and qi. Entire schools of medicine were formed around this organ; the premise was that all aspects of vitality depend on the entire body receiving proper nutrition from the healthy functioning of this essential organ.