The excretory system is a passive biological system that removes excess, unnecessary materials from the body fluids of an organism, to help maintain internal chemical homeostasis and prevent damage to the body. Several parts of the body are involved in this process, such as sweat glands, the liver, the lungs and the kidney system. Every human has two kidneys. Removal of nitrogenous waste from the body due to its metabolic activities is called excretion. Excretion is a process by which metabolic waste is eliminated from an organism. Accumulation of these wastes beyond a level inside the body is harmful to the body. The excretory organs remove these wastes. This process of removal of metabolic waste from the body is known as excretion.