Ureters

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The ureters are bilateral, muscular, tubular structures, responsible for taking urine from one kidney to the urinary bladder for storage, prior to excretion. 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 transitional epithelium (urothelium), which allows the increase in pressure that accompanies increases in the volume of urine leaving the kidney. This helps to minimize any risk of rupturing the ureters. A thick fibroelastic lamina propria lies underneath the epithelium. The mucosa of the ureters executes a protective function in general.

The remainder of the ureteral wall is composed of multiple layers of smooth muscle and connective tissue. There are two muscular layers in the wall of the ureter: an inner longitudinal and a middle circular layer. In the lower third segment of the ureters, another outer longitudinal layer can be found proximal to the bladder. As the ureter is usually embedded within the retroperitoneal adipose tissue, this also forms the adventitia (outer layer) of the ureter.

Urine is propelled along the ureters through peristalsis initiated by pacemaker cells in the proximal renal pelvis. The whitish, non-pulsatile exterior along with the peristaltic waves aids in the differentiation of ureters and blood vessels in vivo.

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