Kidney blood supply. Coloured angiogram showing the arteries supplying blood to the kidneys superimposed onto a male torso. The renal arteries, which supply the two kidneys, branch off the abdominal aorta (yellow), which runs down the centre of the picture. The kidneys filter excess water and soluble waste from the blood, producing urine. An angiogram is made by taking an X-ray after injecting the patient with an X- ray opaque contrast medium. The technique is used to look for diseased blood vessels or to check the functioning of organs associated with the vascular system.