The spleen and its functions: 

Dear brothers, one might make a stop at a sandwich vendor on whose menu he sells sandwiches of spleen, so this person buys it and might loves it. 
Dear brothers, what is the spleen? It is a wonderful organ, in the abdomen, that causes changes in the blood. It is indeed a very important organ in the human body. Deficiency or hyperactivity of this vital organ makes life unbearable if not impossible.
 In fact, this wonderful part of the body, the spleen, which is a kind of apparatus, organ, gland, or whatever, is not more than 200 g’s in weight. It is a dark red body that receives blood through a lot of big blood vessels, an artery and a vein. From inside, it has barriers, and it is divided into compartments. It is surrounded with special muscles, which contract in order to empty it from the extra blood.
 This organ produces a great deal of white cells, which constitute the army that defends the human body. By the way, the AIDS, which has caused a lot of worry to the whole world, is a virus that causes destruction to this army and as a result it weakens the immunity of the body and allows the weakest germs to overcome it.
 The spleen is considered as a graveyard for the dead red blood cells. As soon as the dead red blood cells reach the spleen, the latter produces a substance that breaks down these cells into their original components: iron is released and taken to the factories of red blood cells in the marrow of the bones; and hemoglobin is also released and taken to the liver to produce bile which is important to the process of digestion. 
 Is this not an economic planning?! Is this not Divine Guidance to teach us that wastefulness clashes with human perfection?!
 The fourth thing: The spleen is a factory for manufacturing red blood cells, but it is an auxiliary factory. In other words, if the factories in the marrow of bones fail to work, this factory begins to make red blood cells in order to maintain human life.
 A fifth thing: The spleen is also an auxiliary store of red blood cells, which it sends to the body when necessary.
 If the spleen becomes hyperactive, it destroys the red blood cells and causes death or a special kind of anemia. If there it becomes under-active, the person’s system of immunity weakens; and this causes a lot of diseases and illnesses from which the human race are suffering nowadays.
 In brief, this magnificent organ, the spleen, which you sometimes buy at the sandwich vendor to eat in a snack, is a whole unique world in every sense of the word. In this context, Allah’s Messenger, (PBUH), says,

“Two dead things and two bloods have been made permissible for you (to eat). The two dead things are fishes and locusts, and the two bloods are the liver and the spleen.”

[Ibn Majah]