The spleen's an organ found in all vertebrate animals. In humans, the spleen's located in the abdomen of the body, where it's three primary functions: 1) Removal and destruction of old, aged red blood cells, 2) Synthesis of antibodies in the white pulp, and 3) Removal of antibody-coated bacteria and antibody-coated blood cells from the circulation . It's one of the centers of activity of the reticuloendothelial system (part of the immune system). Its absence leads to a predisposition to certain… (More on Spleen)