organ [Gk, organon, instrument] , a structural part of a system of the body that is composed of tissues and cells that enable it to perform a particular function, such as the liver, spleen, digestive organs, reproductive organs, or organs of special sense. Each one of the paired organs can function independently of the other. The liver, pancreas, spleen, and brain may maintain normal or near-normal function with over 30% of the organ damaged, destroyed, or excised. Also called organon, organum.
