The excretory system is a biological system that removes excess, unnecessary or dangerous materials from an organism. It is responsible for the elimination of oxygen waste products of metabolism as well as other nitrogeneous materials. Since the normal operation of most biological systems creates waste, the excretory system is not necessarily distinct from other systems. Instead, it often represents the various excretory processes of several different systems
The elimination of nitrogenous waste products from the body to regulate the composition of the body fluids and tissues is called excretion. In human and other vertebrates, kidneys are the primary or major excretory organs since they eliminate the principal metabolic wastes, namely nitrogenous materials. The the kidneys or other organs which participate in the removal of nitrogenous waste materials i the form of urine collectively form the excretory or urinary system. Some other organs such as lungs, liver, intestine and skin, also remove certain metabolic wastes besides their normal functions. They are lnown as accessory or additional excretory organs.