Ureters

Gross and histological perspective

The ureters are collapsible S-shaped channels, each about 25 cm in length. They are widest at the renal pelvis and narrow progressively as they enter the urinary bladder in the concavity of the true pelvis.

The lumen of each ureter is lined by a mucosal layer of urothelium (transitional epithelium), which accommodates the increase in pressure that accompanies increases in the volume of urine leaving the kidney; thereby aiding to minimize the risk of rupturing the ureters. These conduits have several in-folding caused by multiple layers of smooth muscle throughout the ureteral wall.

From a histological perspective, there are two muscular layers in the wall of the ureter: a longitudinal and a circular layer. In the lower segment of the ureters, another longitudinal layer can be found proximal to the bladder. Also interesting to note is that urine is propelled along the ureters by peristaltic motions initiated by pacemaker cells in the proximal renal pelvis. The whitish, non-pulsatile exterior along with the peristaltic waves helps to distinguish between ureters and blood vessels in vivo.

To test your knowledge about the histology of ureters, use the following study unit:

Course

The ureters leave the kidneys posterior to the renal vessels. Both ureters pass inferiorly over the abdominal surface of the psoas major, with the genitofemoral nerve behind it and the vessels of the gonads in front. As the right ureter travels towards the bladder, it travels posterior to the duodenum and further down it is crossed by branches of the superior mesenteric vessels.

How well do you think you know the urinary system? Test your knowledge and also learn in the process using Kenhub's urinary system quizzes and labeling diagrams!

The left ureter, however, travels laterally to the inferior mesenteric vessels and is subsequently crossed by its branches. Eventually, the vessels leave the psoas major as the common iliac arteries bifurcate to enter the true pelvis. The ureter pierces through the wall of the urinary bladder from lateral to medial and posterior to anterior. So, this entrance is oblique. It forms the orifice of the ureter in the urinary bladder at the ureterovesicular junction.

Blood supply

The ureters have an expansive anastomosing network of arterial supply and venous drainage along their length. The proximal end receives arterial supply from the ureteric branch of the renal artery.

Contributions from the ovarian artery (testicular artery in males) as well as a direct ureteric branch from the abdominal aorta supply the middle segment. The distal portion receives its arterial supply from ureteric branches from both the superior and inferior vesical arteries. They are drained by accompanying veins.

Innervation

Neuronal supply to the ureters comes from both divisions of the autonomic nervous system. Thoracolumbar outflow from T10-L1 provides sympathetic innervation via the:

• renal plexus and ganglia
• renal and upper ureteric branches from the intermesenteric plexus proximally
• middle ureteric branch of the intermesenteric plexus in the middle segment

The ureter receives parasympathetic supply from the superior hypogastric plexus, pelvic splanchnic nerves and the inferior hypogastric plexus. These innervations are not pertinent to the generation and maintenance of peristaltic action along the ureters; as this arises from pacemaker cells in the renal pelvis and calyces. However, both the sympathetic and parasympathetic divisions are capable of increasing ureteric peristalsis.

Lymphatic drainage

The lymphatic drainage of the proximal part of the ureters is similar to that of the kidneys, and therefore drains into the lateral caval nodes on the right, or lateral aortic nodes on the left. Distally, they drain to the internal and external iliac nodes. The middle segment drains to the common iliac and precaval/preaortic nodes. All lymph drained from the ureters eventually makes its way to the cisterna chyli and thoracic duct before returning to systemic circulation. To master the anatomy of the ureters, take a look at the following resources: