The ureters are tubes composed of smooth muscle that transport urine from the kidneys to the urinary bladder.

They are lined with urothelial cells, a form of transitional epithelium, and feature an extra layer of smooth muscle in the lower third to aid in peristalsis.

The ureters can be affected by a number of diseases, including urinary tract infections and kidney stone.

The ureters are tubular structures, approximately 20–30 cm (8–12 in) in adults,[1] that pass from the pelvis of each kidney into the bladder.

[2] The ureters are 1.5–6 mm (0.06–0.24 in) in diameter[1] and surrounded by a layer of smooth muscle for 1–2 cm (0.4–0.8 in) near their ends just before they enter the bladder.

[2] From here, in males, they cross under the vas deferens and in front of the seminal vesicles to enter the bladder near the trigone.

[2] In females, the ureters pass behind the ovaries and then travel in the lower midline section of the broad ligament of the uterus.

These nerves travel in individual bundles and along small blood vessels to form the ureteric plexus.

The lamina propria is made up of loose connective tissue with many elastic fibers interspersed with blood vessels, veins and lymphatics.

[8] Over time, the buds elongate, moving into surrounding mesodermal tissue, dilate, and divide into left and right ureters.

Eventually, successive divisions from these buds form not only the ureters, but also the pelvis, major and minor calyces, and collecting ducts of the kidneys.

[8] The mesonephric duct is connected with the cloaca, which over the course of development splits into a urogenital sinus and the anorectal canal.

[12] Whether these investigations are performed at the first time a child has an illness, or later and depending on other factors (such as if the causal bacteria is E. coli) differ between US, EU and UK guidelines.

[14] Narrowing can result of ureteric stones, masses associated with cancer, and other lesions such as endometriosis tuberculosis and schistosomiasis.

[15][1] A narrowed ureter may lead to ureteric enlargement (dilation) and cause swelling of the kidneys (hydronephrosis).

[13] Associated symptoms may include recurrent infections, pain or blood in the urine; and when tested, kidney function might be seen to decrease.

[16] If the cause cannot be removed, a nephrostomy may be required, which is the insertion of a tube connected to the renal pelvis which directly drains urine into a stoma bag.

[18] Investigations performed usually include collecting a sample of urine for an inspection for malignant cells under a microscope, called cytology, as well as medical imaging by a CT urogram or ultrasound.

[22] More invasive forms of imaging include ureteroscopy, which is the insertion of a flexible endoscope into the urinary tract to view the ureters.

[24] The structure specifically called the ureter is present in amniotes, meaning mammals, birds and reptiles.

[29] It was only in the 1550s that anatomists such as Bartolomeo Eustachi and Jacques Dubois began to use the terms to specifically and consistently refer to what are in modern English called the ureter and the urethra.

[30] The urinary tract including the ureters, as well as their function to drain urine from the kidneys, has been described by Galen in the second century AD.

[30] This was improved on by VF Marshall who is the first published use of a flexible endoscope based on fiber optics, which occurred in 1964.

[30] The insertion of a drainage tube into the renal pelvis, bypassing the ureters and urinary tract, called nephrostomy, was first described in 1941.

[32] More useful images were able to be produced when Edwin Hurry Fenwick in 1908 pioneered the use of tubes covered in radioopaque material visible to X-rays inserted into the ureters, and in the early 20th century when contrasts were injected externally into the urinary tract (retrograde pyelograms).

[32] Unfortunately, much of the earlier retrograde pyelograms were complicated by significant damage to the kidneys as a result of contrast based on silver or sodium iodide.

[32] Hryntshalk in 1929 pioneered the development of the intravenous urogram, in which contrast is injected into a vein and highlights the kidney and, when excreted, the urinary tract.

[32] Things improved with the development by Moses Swick and Leopold Lichtwitz in the late 1920s of relatively nontoxic contrast media, with controversy surrounding publication as to who was the primary discoverer.