The spleen is an organ above the stomach and under the ribs on the human body's left side. It is about as big as a human's fist. The spleen is part of the lymphatic system, which fights infection and keeps body fluids in balance. The spleen contains white blood cells that fight germs, and also helps control the amount of blood in the body, and destroys old and damaged cells.
The primary function of the spleen is to recognize and dispose of red blood cells that are too old or not working properly. Blood flows into the spleen where the red blood cells go through a sort of quality control test. The splenic blood vessels enter and leave the gland at the hilum, which is on the inner surface. The blood vessels empty their contents directly into the splenic pulp, so that the blood comes into contact with the spleen substances, and is not separated from it by blood vessels, as in other organs. There is no ordinary capillary system, but instead, the blood comes into direct contact with the cells of the organ. The blood flows through the spleen and is collected in a system of venous sinuses which empty their blood into the branches which unite to form the splenic vein by which the blood is carried from the spleen to enter the portal circulation and be conveyed to the liver.
Damaged, fragile or abnormally shaped red blood cells will be detected and destroyed by the spleen. Useful parts of the cells such as iron are stored and recycled in new red blood cells.
The spleen can store blood for future use, as blood vessels in the spleen are capable of expanding and narrowing in response to bodily needs. When the vessels are expanded, the organ can actually hold up to a cup of reserve blood. If the body requires some extra blood short term – say if trauma causes blood loss – the spleen can respond by releasing it back into the system.
Ruptured spleens occur when the splenic tissue tears, leaking store blood into the body cavity. Ruptured spleens can result from trauma to the abdomen, and require immediate medical attention. Sometimes a splenectomy, or removal of the spleen is required to prevent further blood loss. A splenectomy can result in asplenia.
Asplenia, the total lack of splenic function, can be congenital or acquired from environmental factors. It can be require a permanent course of antibiotics.