The excretion of toxic waste mainly occurs through the lungs, skin, and kidneys. The kidneys are two bean-shaped organs, roughly the size of a fist, located in the lumbar area that filter over 200 liters of blood per day. Inside each kidney, there are approximately a million structures called nephrons that filter the blood. These nephrons eliminate waste products and excess water through urine. The urine flows through tubes called ureters to the bladder, where it is stored before excretion.