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Anatomy and function of the ureters.
Hi everyone! It’s Matt from Kenhub, and in this tutorial, we will discuss the ureters. The ureters are a pair of muscular, tubular structures responsible for taking urine from the kidneys to the urinary bladder for storage, prior to excretion. They 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. The lumen of each ureter is lined by a mucosal layer of transitional epithelium that accommodates the increase in pressure when the volume of urine leaving the kidney increases minimizing the risk of rupturing the ureters. These conduits have several infoldings caused by multiple layers of smooth muscle through the ureteral wall.
From a histological perspective, there are 2 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. It’s interesting to note that urine is propelled along the ureters by peristaltic motions initiated by pacemaker cells in the proximal renal pelvis. So, in vivo, you can tell the difference between the ureters and blood vessels because the ureters have a whitish non-pulsatile exterior with peristaltic waves.
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 gonad 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. 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 and the urinary bladder at the ureteral vesicular junction.
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 seen here highlighted in green. Contributions from the ovarian artery in females, testicular artery in males as well as the direct ureteric branch from the abdominal aorta supply the middle segment. The distal portion receives its arterial supply from the ureteric branches from both the superior and inferior vesicle arteries. They are drained by accompanying veins.
Urinal supply to the ureters comes from both divisions of the autonomic nervous system. T10-L1 provides sympathetic innervation via the renal plexus and ganglia, renal and upper ureteric branches from the intermesenteric plexus proximally and the middle ureteric branch of the intermesenteric plexus in the middle segment.
In the true pelvis, the ureter receives parasympathetic supply from the pelvic splanchnic nerves which are seen here highlighted in green on this image of the female pelvis, and from 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 calices as mentioned earlier. However, both the sympathetic and parasympathetic divisions are capable of increasing ureteric peristalsis.
The lymphatic drainage of the ureters is similar to that of the kidneys. Most of the nodes are named relative to the segment of the aorta they travel adjacent to. Distally, they drain to the internal and external iliac nodes. The middle segment drains to the common iliac and precaval nodes. Proximally, they drain to the lumbar (lateral aortic) and precaval nodes. From there, lymphatic fluid travels to the cisterna chyli and thoracic duct before returning to systemic circulation.