During the development of a fetus (unborn infant still in the uterus), the spleen is one of the sites of formation of blood cells. This function is taken over by the bone marrow by the fifth month of pregnancy. The spleen, however, still has the ability to produce blood cells in the adult under certain conditions.

Anatomy and Physiology

• The spleen lies in the left upper part of the abdomen. It is about 6 by 3 inches (15 by 7.5 cm.) in size and weighs 3 to 6 oz. (90 to 180 gm) (Figure 1)
• The spleen lies beneath the left lower ribs and is attached by ligaments to the left kidney, colon, stomach and undersurface of the diaphragm. It may be injured by trauma that fractures the overlying ribs
• The spleen acts as a filter that removes old, abnormal or damaged blood cells and bacteria from the blood. It also has a role in immunity by creating antibodies to help battle infection
• The spleen is a source of antibodies and is important in the immune system of the body for fighting disease

Figure 1 - The spleen lies just to the left of the stomach and just below the diaphragm. Blood to the spleen goes through the splenic and short gastric arteries and drained by the splenic vein (not shown).