Introduction
The ureters are bilateral thin tubular structures with a 3 to 4 mm diameter that connect the kidneys to the urinary bladder (see Image. Posterior Thoracolumbar Surface Anatomy). These muscular tubes transport urine from the renal pelvis to the bladder. The ureter’s muscular layers are responsible for the peristaltic activity that moves urine from the kidneys to the bladder.
Embryologically, the ureter originates from the ureteric bud—a protrusion of the mesonephric duct that forms part of the embryo’s primitive genitourinary system.[1] The ureters begin at the kidneys’ ureteropelvic junction (UPJ), which lies posterior to the renal vein and artery in the hilum.[2] The ureters then travel inferiorly inside the retroperitoneal space. These structures pass anterior to the psoas muscle, enter the bony pelvis at the iliac bifurcation, follow the posterolateral pelvic wall, and enter the bladder posterolaterally via the trigone.
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The ureters narrow at 2 points along their path: the UPJ and the ureterovesical junction (UVJ). These constrictions are clinically significant, as they are areas where renal calculi can potentially lodge and obstruct urinary flow.[3][4][3]
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The UPJ is roughly at the L2 level, where the renal pelvis funnels down inferiorly and transitions into the ureter. This site is commonly involved in proximal ureteral developmental anomalies.
The level of the iliac bifurcation is where the ureters cross over the iliac vessels and may be found within the cleft formed by the external and internal iliac arteries. The ureters are fixed at this location. The ureters then enter to pelvic brim, entering at an acute angle.[5][6][7] While not anatomically constricted, longer stones may have difficulty passing the sharp angulation as the ureter plunges suddenly posteriorly into the pelvis. It is also the point above which rigid ureteroscopy is usually discouraged. The ureter is fixed at this position, so it provides one of the few known locations where the ureter can always be found during open surgery.
The UVJ is where each of the ureters enters the bladder. This site has an antireflux mechanism for preventing retrograde urine flow from the bladder to the ureter and kidneys.
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The ureter’s blood supply is segmental. The ureteral portion closest to the kidneys receives blood directly from the renal arteries. Abdominal aortic branches and the common iliac and gonadal arteries supply the middle part. The ureters’ most distal segment receives circulation from internal iliac artery branches.
The T12 to L2 roots create a ureteric plexus and innervate the ureters. Ureteral pain typically refers to T12-L2 dermatomes.
The ureters lack reliable anatomical landmarks to mark their location besides the 3 physiologic constrictions. Colorectal and gynecologic procedures, particularly laparoscopic hysterectomies, are highly likely to damage these structures.[8]
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