KidneyStones.org

The urinary tract system is a group of organs of the body, which are responsible for the excretion of urine. In humans, the urinary system includes 2 kidneys, a pair of tube-like structures, called the ureters, which connect the kidneys to the bladder. The bladder is connected to the urethra, which delivers the urine to the outside of the body. The primary function of the urinary tract system is to remove substances from the blood, to form urine and help to regulate various metabolic processes.

(Click an organ above to see its description.)

Ureter

Function
The ureter is a thick-walled tube leading from each kidney, which carries urine to the bladder. Urine flows down partly by gravity, but mainly by a wave of contractions, called peristalsis, which pass several times per minute through the muscle layers of the urethral walls.

Structure
Each ureter is a tubular organ measuring about 25 centimeters (ten to twelve inches) in length beginning at the funnel-shaped renal pelvis. Within the wall of the ureter are three layers. The inner layer, or mucous coat, is continuous with the linings of the renal tubules above and the urinary bladder below. The middle layer, or the muscular coat, is composed of largely smooth muscle fibers. The outer layer, or the fibrous coat, is primarily composed of connective tissue. Each ureter enters the bladder through a tunnel in the bladder wall, which is angled to prevent the urine from running back into the ureter, known as reflux, when the bladder contracts.