The tube that connects each kidney to the bladder is called a ureter. You have two of them, one running from each kidney, and their sole job is to carry urine downward into the bladder for storage. They’re thin, muscular tubes about 26 centimeters (roughly 10 inches) long in the average adult, with a diameter of just 3 to 4 millimeters.
How the Ureter Moves Urine
Urine doesn’t simply drip from the kidneys into the bladder by gravity. The ureter wall contains layers of muscle fibers that contract in coordinated waves, much like the way your esophagus pushes food toward your stomach. These rhythmic squeezes, called peristalsis, are triggered by built-in pacemaker cells near the top of each ureter. The contractions travel at roughly 1.5 to 3.5 centimeters per second, steadily pushing small boluses of urine downward regardless of whether you’re standing, sitting, or lying flat.
Where the Ureter Connects at Each End
The upper end of the ureter joins the kidney at a point called the ureteropelvic junction (UPJ). This is where the kidney’s internal collection system, a funnel-shaped area called the renal pelvis, narrows into the tube itself. At the bottom end, the ureter enters the bladder wall at the ureterovesical junction (UVJ). This lower connection is designed as a one-way valve: when the bladder fills and pressure rises, the angle at which the ureter passes through the bladder wall pinches shut, preventing urine from washing back up toward the kidney.
Why Kidney Stones Get Stuck in the Ureter
Because the ureter is so narrow, it’s the most common place for a kidney stone to become lodged on its way out of the body. Three spots along its length are especially tight: the ureteropelvic junction at the top, the point where the ureter crosses over the pelvic bone in the middle, and the ureterovesical junction at the bottom where it enters the bladder. A stone trapped at any of these points can block urine flow, causing the intense, wave-like flank pain most people associate with “passing a kidney stone.”
Urinary stone disease affects roughly 1% of privately insured adults under 65 each year and about 4% of adults 65 and older, according to a 2024 report from the National Institute of Diabetes and Digestive and Kidney Diseases. Not all of those stones end up stuck in the ureter, but it’s the bottleneck where problems most often arise.
What Happens When a Ureter Is Blocked
When something blocks a ureter, whether a stone, scar tissue, or external pressure, urine backs up into the kidney. This causes the kidney to swell, a condition called hydronephrosis. Short-term blockages are painful but usually resolve without lasting damage. A prolonged blockage, if left untreated for weeks, can permanently reduce kidney function on that side.
If the blockage also traps bacteria, the combination of infection and obstruction can become a medical emergency. In these situations, doctors may place a ureteral stent, a thin, flexible tube threaded through the ureter to hold it open and restore drainage. Stents can also be placed after stone treatment to help fragments pass and prevent swelling from closing off the ureter during healing. Standard plastic stents are temporary, while metallic versions used in certain cases can remain in place for up to one to three years.
How the Ureter Differs From the Urethra
The ureter and the urethra are easy to confuse because their names are so similar, but they do completely different jobs. The ureters (you have two) connect the kidneys to the bladder. The urethra (you have one) connects the bladder to the outside of the body and is the tube through which you actually urinate. In short: ureters deliver urine to the bladder, and the urethra lets urine leave the body.