. . . "Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule.Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.Reasons for the procedureThe veins in a healthy kidney are free from obstruction, clots, or high blood pressure (hypertension)." .