One of the functions is to remove nitrogenous wastes from the blood. Most nitrogenous wastes are produced in the liver. As in the piglet after birth, the fetal kidney is responsible for filtering waste products from the blood and excreting them to the outside environment.
Metabolic wastes are substances that are left over, after oxygen and nutrients have been supplied to a cell, and must be excreted. These are substances such as water, carbon dioxide, sodium chloride and soluble nitrogenous salts, which are excreted in urine, feces, and exhaled air.