Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve in case of hemorrhagic shock, especially in animals like horses (not in humans), while recycling iron. It synthesizes antibodies in its white pulp and removes, from blood and lymph node circulation, antibody-coated bacteria along with antibody-coated blood cells. Recently, it has been found to contain, in its reserve, half of the body''s monocytes, within the red pulp, that, upon moving to injured tissue (such as the heart), turns into dendritic cells and macrophages while aiding "wound healing", or the healing of lacerations.