The tube that carries urine from each kidney to the bladder is the ureter.
Humans normally have two ureters, one descending from each kidney. These narrow muscular tubes are typically about 20–30 centimeters long in adults. Their lining contains urothelial cells, while smooth muscle in their walls produces rhythmic contractions called peristalsis, pushing urine toward the bladder rather than relying only on gravity.
Each ureter begins at the renal pelvis, travels down through the abdomen and pelvis, and enters the back wall of the bladder at an angle. This angled entry helps limit the backflow of urine into the ureters when the bladder fills or contracts. Kidney stones can become lodged in the ureter and cause severe pain or obstruction.
The most common mix-up is the urethra. The ureters carry urine from the kidneys to the bladder; the urethra carries urine from the bladder out of the body. A bile duct belongs to the digestive system, and the vas deferens transports sperm in the male reproductive system.