The ureters are two muscular tubes that are continuous superiorly with the funnel-shaped renal pelvis. The renal pelvis is formed by the condensation of two or three major calices, which in turn are formed by the condensation of several minor calyces in the kidney. The ureters are thick walled narrow structures, with an average 3mm width and a 25-30 cm length. Their function is to transport urine from the kidneys to the urinary bladder via the peristaltic contractions of the smooth muscles of the ureteral walls.
Course and relations
In the abdomen
In the abdomen, the ureter descends on the medial aspect of the psoas major muscle, posterior to the peritoneum. Anterior to the psoas major, it passes in front of the genitofemoral nerve and is crossed by the gonadal vessels. The ureter passes the pelvic brim at the area of the sacroiliac joints, and enters the pelvic cavity. There, it lies anterior to the end of the common iliac vessels or the origin of the external iliac vessels. The right ureter is lateral to the inferior vena cava and the left ureter is lateral to the aorta. The descending part of the duodenum tends to overlap the right ureter at its origin. The right ureter descends lateral to the inferior vena cava, and is crossed by the right colic and the ileocolic vessels as well. It passes posterior to the lower part of the mesentery and terminal ileum near the superior aperture of the pelvic cavity. The left ureter on the other hand, is crossed by the left gonadal and left colic vessels. In the posterior wall of the intersigmoid recess, it runs behind the loops of the jejunum and sigmoid colon and its mesentery.
In the pelvis
In the pelvis, the ureter descends lateral to the pelvic walls, along the anterior border of the greater sciatic notch. It then turns anteromedially, at the level of the ischial spine, to reach the base of the bladder. There, it pierces the lateral aspect of the bladder’s wall in an oblique manner, creating a one way valve. This valve prevents the backflow of urine. Throughout the ureter’s course, there are three constricted areas. The first is at the ureteropelvic joint, where the renal pelvis and proximal ureter meet. The second is at the pelvic brim, where the ureter crosses the common iliac vessels. And the third is at the point where the ureter enters the bladder’s wall. All of which are potential areas for kidney stones to become lodged.
The arterial blood supply of the ureters is provided by the adjacent vessels present throughout their course to reach the bladder. These arteries are the renal, gonadal, common iliac, internal iliac, vesical and uterine arteries. The venous drainage of the ureters follows that of their arteries. The ureteric innervation is provided by the lower three thoracic (T10-T12) segments, first lumbar (L1) segment, and the second to fourth sacral (S2-S4) segments of the spinal cord via branches from the renal and aortic plexuses, and the superior and inferior hypogastric plexuses that follow the blood vessels.