The ureters are tubes composed of smooth muscle that transport urine from the kidneys to the urinary bladder. In adult humans, the ureters are typically 20–30 centimeters long and 3–4 millimeters in diameter. 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 peristalsis.
The ureters can be affected by diseases including urinary tract infections and kidney stones. is the narrowing of a ureter, often caused by chronic inflammation. Congenital abnormalities can cause development of two ureters on the same side or abnormally placed ureters. Reflux of urine from the bladder into the ureters is common in children.
The ureters have been identified for at least two thousand years, with the word ureter stemming from the stem relating to urinating and seen in written records since at least the time of Hippocrates. It is, however, only since the 16th century that the term "ureter" has been consistently used to refer to the modern structure, and only since the development of medical imaging in the 20th century that techniques such as X-ray, CT, and ultrasound have been able to view the ureters. The ureters are also seen from the inside using a flexible camera, called ureteroscopy, which was first described in 1964.
Structure
thumb|Structures that are near the ureters. 1. Human [[urinary system: 2. Kidney, 3. Renal pelvis, 4. Ureter, 5. Urinary bladder, 6. Urethra. (Left side with frontal section), 7. Adrenal gland<br />Vessels:<br />8. Renal artery and vein, 9. Inferior vena cava, 10. Abdominal aorta, 11. Common iliac artery and vein<br />With transparency:<br />12. Liver, 13. Large intestine, 14. Pelvis]]
The ureters are tubular structures, approximately in adults, The ureters are in diameter This location is also called the vesicoureteric junction. In the contracted bladder, they are about apart and about the same distance from the internal urethral orifice; in the distended bladder, these measurements may be increased to about .
Development
thumb|right|300px|Image showing the bottom part of an embryo 4–5 weeks old. Here, the ureter (in orange) can be seen emerging from the bottom of the mesonephric duct (labelled "Wolffian duct"), connected to the primitive bladder. Image from [[Gray's Anatomy 1918 edition.]]
The ureters develop from the ureteric buds, which are outpouchings from the mesonephric duct. This is a duct, derived from mesoderm, found in the early embryo. 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. however a retrospective case study, which is a primary source, of where stones lodged based on medical imaging did not show many stones at the place where the iliac blood vessels cross.
Most stones are compounds containing calcium such as calcium oxalate and calcium phosphate. The first recommended investigation is a CT scan of the abdomen because it can detect almost all stones. Management includes analgesia, often with nonsteroidal antiinflammatories.
Reflux
Vesicoureteral reflux refers to the reflux of fluid from the bladder into the ureters. This condition can be associated with urinary tract infections, particularly in children, and is present in up to 28–36% of children to some degree. as a result of narrowing within the ureter, or compression or fibrosis of structures around the ureter. Things outside the ureters such as constipation and retroperitoneal fibrosis can also compress them.
A narrowed ureter may lead to ureteric enlargement () and cause swelling of the kidneys (hydronephrosis). 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.
Cancer
Cancer of the ureters is known as ureteral cancer. It is usually due to cancer of the urothelium, the cells that line the surface of the ureters. Urothelial cancer is more common after the age of 40, and more common in men than women; other risk factors include smoking and exposure to dyes such as aromatic amines and aldehydes. The ureter can be injured during surgery to nearby structures. usually near the suspensory ligament of the ovary or near the cardinal ligament, where the ureter runs close to the blood vessels of the uterus.
Imaging
Several forms of medical imaging are used to view the ureters and urinary tract. Ultrasound may be able to show evidence of blockage because of hydronephrosis of the kidneys and renal pelvis. Ureteroscopy is most commonly used for medium to large-sized stones when less invasive methods of removal cannot be used. The structure specifically called the ureter is present in amniotes, meaning mammals, birds and reptiles. In monotremes, urine flows from the ureters into the cloaca. The ureters are ventral to the vasa deferentia in male placental mammals, but dorsal to the vasa deferentia in marsupials. In female marsupials, the ureters pass between the median and lateral vaginae.
History
The word "ureter" comes from the Ancient Greek noun , , meaning "urine", and the first use of the word is seen during the era of Hippocrates to refer to the urethra. The anatomical structure of the ureter was noted by 40 AD. However, the terms "ureter" and "urethra" were variably used to refer to each other thereafter for more than a millennium. 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.
The first to examine the ureter through an internal approach, called ureteroscopy, rather than surgery was Hampton Young in 1929. More useful images were able to be produced when Edwin Hurry Fenwick in 1908 pioneered the use of tubes covered in 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).