Upper urinary system. X-ray of the upper urinary tract, which has been highlighted (white) by the injection of a contrast medium (urography). Spinal bones (vertebrae) run down centre, and either side are the two healthy kidneys (branched structures at upper left and upper right). From each kidney, a ureter drains urine down to the bladder (not seen). Urine contains urea, a waste product that the kidneys filter from the blood.