Complex sentence: The spleen is an organ in the left upper quadrant of the abdomen that filters the blood by removing old or damaged blood cells and platelets, helps the immune system by destroying bacteria and other foreign substances by opsonization and phagocytosis, and producing antibodies.
Split into simpler sentences: The spleen is an organ in the left upper quadrant of the abdomen that filters blood by removing old or damaged blood cells and platelets. It also helps the immune system by destroying bacteria and other foreign substances by opsonization and phagocytosis, and by producing antibodies.