What is the anatomical course of the ureter, including its length, relations, and natural constrictions?

Anatomical Course of the Ureter

The ureter is a muscular tube approximately 25-30 cm in length that transports urine from the renal pelvis to the urinary bladder through coordinated peristaltic contractions. 1, 2

Origin and Termination

• The ureter originates at the ureteropelvic junction (UPJ), where the renal pelvis transitions into the tubular ureter at the level of the renal hilum. 3
• It terminates at the ureterovesical junction (UVJ), where it enters the bladder wall obliquely to create an anti-reflux mechanism. 1

Anatomical Divisions and Course

Abdominal Ureter

• Descends retroperitoneally along the anterior surface of the psoas major muscle, running parallel to the tips of the lumbar transverse processes. 4
• Crosses anterior to the common iliac artery bifurcation at approximately the level of the sacroiliac joint (L5-S1). 4
• Lies posterior to the gonadal vessels (ovarian or testicular arteries and veins) throughout its abdominal course. 4

Pelvic Ureter

• Enters the pelvis by crossing over the bifurcation of the common iliac artery, then courses along the lateral pelvic wall. 5
• In males: runs lateral to the vas deferens before passing posterior to it near the bladder.
• In females: passes beneath the uterine artery ("water under the bridge") approximately 1.5-2 cm lateral to the cervix, making it vulnerable during hysterectomy.
• Curves anteromedially as it approaches the bladder base. 1

Intramural Ureter

• Penetrates the bladder wall obliquely for approximately 1.5-2 cm, creating a flap-valve mechanism that prevents vesicoureteral reflux during bladder filling. 1
• Opens at the ureteral orifice in the trigone of the bladder. 3

Three Natural Constrictions (Critical for Stone Impaction)

The ureter has three physiologic narrowings where kidney stones most commonly lodge:

1. Ureteropelvic junction (UPJ): where the renal pelvis transitions to ureter—the most proximal and often narrowest point. 5
2. Pelvic brim: where the ureter crosses the iliac vessels at the pelvic inlet. 5
3. Ureterovesical junction (UVJ): where the ureter enters the bladder wall—the most distal constriction and most common site of stone impaction. 5

Structural Composition

• Inner layer: multilayered water-impermeable urothelium (transitional epithelium) that allows distension without urine leakage. 2, 3
• Middle layer: smooth muscle arranged in inner longitudinal and outer circular layers (with an additional outer longitudinal layer in the distal third) that generates peristaltic waves. 2, 3
• Outer layer: adventitial connective tissue containing blood vessels, lymphatics, and nerves. 3

Functional Peristalsis

• Pacemaker cells in the renal pelvis initiate electrical impulses that propagate distally at 2-6 contractions per minute, creating coordinated peristaltic waves that propel urine boluses toward the bladder. 6, 7
• The ureter functions as a functional syncytium, with electrical impulses passing from cell to cell to coordinate contraction. 7
• Peristalsis is primarily myogenic (intrinsic to smooth muscle), with neurogenic input playing only a modulatory role. 7

Clinical Relevance

• Understanding the posterior position of the ureter relative to renal vessels is crucial for surgical exploration and imaging interpretation, particularly in trauma cases where ureteral injury must be identified. 4
• The three natural constrictions are the most common sites of ureteral obstruction from stones, requiring knowledge of these locations for diagnostic imaging and intervention planning. 5
• The oblique intramural course creates a one-way valve that normally prevents reflux but can be disrupted by trauma, congenital anomalies, or surgical injury. 1, 3