Ureters

Ureters are retroperitoneal tubes on either side of the vertebral column that transport urine from each kidney to the urinary bladder.

They have thick walls and are 25–30 cm long. They have a diameter of 10 mm at the renal pelvis, which narrows to 1 mm as the ureter obliquely enters the posterior bladder wall at the ureteric orifices.

The slit-like shape of the ureteric orifices prevents urine backflow toward the kidneys when the urinary bladder contracts.

Histologically, each ureter comprises three layers — the mucosa, muscularis, and adventitia.

The innermost layer, the mucosa, is composed of transitional epithelium continuous with the mucosae of the kidney pelvis and the bladder.

It allows the ureters to stretch and adjust according to the volume of urine flow.

Next, the muscularis layer is made of smooth muscle. The inner layer has longitudinal fibers, while the outer fibers are circularly arranged.

It undergoes rhythmic peristalsis, enabling the unidirectional propulsion of urine into the bladder.

Finally, the outermost adventitia is composed of connective tissue that securely positions and shields the ureters from potential damage.