The ureters are paired, muscular tubular structures that transport urine from the renal pelves of the kidneys down to the urinary bladder. Each tube measures roughly 25 to 30 centimeters in length in an adult. Once urine leaves the renal pelvis at the ureteropelvic junction, the ureter descends retroperitoneally along the posterior abdominal wall, crossing over the psoas major muscle and the common iliac vessels to enter the lesser pelvis before finally piercing the posterior wall of the bladder.
The wall of the ureter consists of three distinct tissue layers designed to handle fluid transport and withstand stretching:
Urine movement through the ureters is not a passive trickle; it relies heavily on active physiological mechanisms. Smooth muscle pacemaker cells in the renal pelvis initiate rhythmic contractions known as peristalsis. These waves occur about one to five times per minute, forcing urine down the lumen regardless of body position. Gravity and hydrostatic pressure also assist when a person is upright, but peristalsis remains the primary driver of ureteral flow.
The ureter features three natural narrow points along its course where kidney stones (renal calculi) are most likely to lodge:
When a calculus becomes trapped at one of these sites, it causes severe loin-to-groin pain known as renal colic, often accompanied by hematuria due to mucosal trauma.
Blood supply to the ureters is segmental, arriving via branches from nearby vessels including the renal, gonadal, and internal iliac arteries. These vessels form an anastomotic network within the adventitia. Venous drainage generally mirrors the arterial supply, emptying into renal, gonadal, and internal iliac veins. Autonomic nerve fibers from the renal, aortic, and hypogastric plexuses innervate the ureter, transmitting visceral pain afferents back to the T11 through L2 spinal cord segments during obstruction.