The spleen, a spongy, soft organ about as big as a person's fist, is located in the upper left part of the abdomen, just under the rib cage. The splenic artery brings blood to the spleen from the heart. Blood leaves the spleen through the splenic vein, which drains into a larger vein (the portal vein) that carries the blood to the liver. The spleen has a covering of fibrous tissue (the splenic capsule) that supports its blood vessels and lymphatic vessels.
The spleen is made up of two basic types of tissue, each with different functions:
The white pulp is part of the infection-fighting (immune) system. It produces white blood cells called lymphocytes, which in turn produce antibodies (specialized proteins that protect against invasion by foreign substances).
The red pulp filters the blood, removing unwanted material. The red pulp contains other white blood cells called phagocytes that ingest microorganisms, such as bacteria, fungi, and viruses. It also monitors red blood cells, destroying those that are abnormal or too old or damaged to function properly. In addition, the red pulp serves as a reservoir for different elements of the blood, especially white blood cells and platelets (cell-like particles involved in clotting). However, releasing these elements is a minor function of the red pulp.
People can live without a spleen. Sometimes the spleen must be removed surgically (splenectomy) if there was severe damage from an injury (see Abdominal Injuries: Spleen Injury), for example, due to a car crash. When the spleen is removed, the body loses some of its ability to produce protective antibodies and to remove unwanted microorganisms from the blood. As a result, the body's ability to fight infections is impaired. People who do not have a spleen are at particularly high risk of infections because of the spleen's role in fighting certain kinds of bacteria, such as Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae. Because of this risk, people receive vaccinations to help protect them from infection with these organisms. People should also be sure they receive the influenza vaccine every year, as is now recommended for all people. Some people take antibiotics to prevent infections, particularly when they have another disorder (such as sickle cell disease or cancer) that increases the risk of developing life-threatening infections.
Despite these problems, however, the spleen is not critical to survival. Other organs (primarily the liver) compensate for the loss by increasing their infection-fighting ability and by monitoring for and removing red blood cells that are abnormal, too old, or damaged.
Last full review/revision August 2012 by Harry S. Jacob, MD