In a normal urinary tract, the ureters are two thin tubes in the abdomen, one each connecting a kidney to the bladder. These enable the removal of urine from the body. When a duplex collecting system is present, two ureters (one draining the upper part of a kidney-the other draining the lower half) connect each kidney to the bladder. Often a ballooning of the ureter (ureterocele) occurs in the ureter draining the top half of the kidney, close to the bladder which with its lower bladder position may cause urinary reflux (backflow of urine from the bladder towards the kidney-vesicoureteral reflux-VUR, and hydronephrosis-swelling of the kidney). Learn more about Duplex Collecting System.