The spleen is located in the left upper quadrant of the abdomen, adjacent to the stomach. Althoug the spleen is not essential to life, it has several important functions:

1. Destruction of old erythrocytes by macrophages. Because of hemolytic activity in the spleen, bilirubin is formed there and added to the bloodstream.

2. Filtration of microrganisms and other foreign material from the blood.

3. Activation of lymphocytes as it filters out antigens from the blood. Activated lymphocytes produce antibodies and engulf the antigens.

4. Storage of blood, especially platelets.

The spleen is an organ that is easily and frequently injured. A sharp blow or injury to the upper abdomen (as from the impact of a car's steering wheel) may cause rupture of the spleen. Massive hemorrhage can occur when the spleen is ruptured, and immediate surgical removal (splenectomy) may be necessary. After splenectomy, the liver, bone marrow, and lymph nodes take over the function of the spleen.