The ureter is a narrow, muscular tube connecting the kidney to the urinary bladder. Its primary function is to transport urine from the kidney, where it is produced, down to the bladder for storage. This transport is achieved through rhythmic, wave-like muscular contractions called peristalsis. The physical dimensions of this tube are highly relevant to its function and have significant implications for urinary tract health.
The Standard Dimensions of the Ureter
In an adult, the ureter is a relatively long structure, typically measuring between 25 to 30 centimeters (about 10 to 12 inches) from the kidney to the bladder. This length allows the tube to travel from the abdominal cavity, down the posterior body wall, and into the pelvis. The diameter, or width, of the ureter is surprisingly small, generally maintaining an inner measurement of only about 3 to 4 millimeters.
These dimensions represent the average size in a healthy individual and are not uniform across the entire length of the tube. The smooth muscle in the ureter wall enables it to distend slightly as urine passes through, but its resting caliber remains quite narrow.
Anatomical Constrictions and Critical Narrowing Points
The ureter is not uniformly wide; it features three specific, naturally occurring points of narrowing, or constrictions, that are narrower than the rest of the tube. These anatomical sites are significant because they are the most common locations where solid material, such as a kidney stone, may become lodged.
The first constriction occurs at the ureteropelvic junction (UPJ), where the kidney’s collecting basin, the renal pelvis, funnels down to become the ureter itself. The second narrowing happens where the ureter crosses the pelvic brim, passing over the common iliac artery and vein. The final and often narrowest constriction is found at the ureterovesical junction (UVJ), where the ureter enters and passes obliquely through the wall of the bladder.
This oblique entry at the UVJ is a purposeful design feature, creating a functional valve that prevents urine from flowing backward into the kidney when the bladder fills and contracts. These naturally tight spots are crucial determinants of whether a solid object can successfully pass through the urinary tract.
Clinical Relevance of Ureter Width
The small width of the ureter, especially at its three constricted points, dictates much of the clinical management for kidney stones. The chance of a stone passing without surgical intervention is directly related to its width compared to the ureter’s resting diameter. Stones 4 millimeters or less have a high likelihood of passing spontaneously, with success rates often reported above 80%.
The passage rate drops sharply as the stone size increases beyond the ureter’s average width. For a stone measuring 5 millimeters wide, the probability of spontaneous passage falls to around 65%. Stones wider than 6 or 7 millimeters are far less likely to pass on their own and typically require medical procedures to remove or fragment them.
When a stone becomes stuck at one of the narrowings, it causes a blockage that prevents urine from draining from the kidney. This leads to hydronephrosis, which is the swelling and distention of the kidney’s urine-collecting system due to the buildup of pressure behind the obstruction. Treatment protocols often use this size threshold to decide between conservative management, such as watchful waiting, and active intervention, such as the placement of a stent or surgical removal.