We remove undigested food from the body as stool and toxic products as urea and uric acid by urine time to time. Carbon dioxide, sweat, stool and urine are main excretory products of our body. When our body cells perform various types of bio chemical processes, certain waste products are released. These waste products are toxic and hence need to be removed from the body. The process of removal of waste produce in the cells of living organism is called excretion. The organs involved in excretion forms the excretory system. In humans, two kidneys, ureters, bladder and urethra forms the excretory system.

The removal of wastes substances present in the blood takes place in two kidneys. The waste dissolved in blood are removed as urine goes into the urinary bladder through tube like ureters. A muscular tube is attached with ureters. It is called urethra. Urethra opens outside the body through a pore which is called urinary opening. From the urinary bladder urine is passed through urethra and removed out by urinary opening.