Our bodies produce several kinds of wastes, including sweat, carbon dioxide gas, feces (stool or poop), and urine (pee). These wastes leave the body in different ways. Sweat is released through pores in the skin. Water vapor and carbon dioxide are exhaled from the lungs. And undigested food materials are formed into feces in the intestines and excreted from the body as solid waste in bowel movements.
Urine, which is produced by the kidneys, contains the byproducts of metabolism — salts, toxins, and water — that end up in the blood. The kidneys and urinary tract (which includes the kidneys, ureters, bladder, and urethra) filter and eliminate these waste substances from our blood. Without the kidneys, waste products and toxins would soon build up in the blood to dangerous levels.
The kidneys do a lot, but their most important job is to take waste out of the blood and make urine (pee). The urinary tract takes this waste out of the body when a person pees.