Kidneys and duplicated ureter. Coloured computed tomography (CT) scan of human kidneys, separated by the backbone. The kidney at right has a duplicated ureter. This is a congenital condition where two ureters are present, both draining a single kidney. The kidneys (of which there are two) perform a vital role in cleaning the blood. They filter waste products such as urea (a nitrogenous waste) and excrete the urea in the form of urine. A contrast medium has been used to highlight the production and excretion of urine.