This illustration shows the anterior view of the urinary system with an outlet obstruction affecting the left kidney and ureter. An outlet obstruction is caused by a blockage at the base of the bladder, preventing urine from draining properly to the urethra. Hydronephrosis of the left kidney and hydroureter of the left ureter are a result of this outlet obstruction. Hydronephrosis is the swelling of the kidney due to a buildup of urine. Hydroureter is the swelling of the ureter due to a blockage that is preventing urine from draining to the bladder.