Theureters are tubes composed ofsmooth muscle that transporturine from thekidneys to the urinarybladder. In an adult human, the ureters typically measure 20 to 30 centimeters in length and about 3 to 4 millimeters in diameter. They are lined with urothelial cells, a form of transitionalepithelium, and feature an extra layer of smooth muscle in the lower third to aid inperistalsis.The ureters can be affected by a number of diseases, includingurinary tract infections andkidney stone.Stenosis is when a ureter is narrowed, due to for example chronic inflammation.Congenital abnormalities that affect the ureters can include the development of two ureters on the same side or abnormally placed ureters. Additionally, reflux of urine from the bladder back up the ureters is a condition commonly seen in children.
The ureters have been identified for at least two thousand years, with the word "ureter" stemming from the stemuro- relating tourinating and seen in written records since at least the time ofHippocrates. It is, however, only since the 1500s that the term "ureter" has been consistently used to refer to the modern structure, and only since the development ofmedical imaging in the 1900s that techniques such asX-ray,CT, andultrasound have been able to view the ureters. The ureters are also seen from the inside using a flexible camera, calledureteroscopy, which was first described in 1964.
The ureters are tubular structures, approximately 20–30 cm (8–12 in) in adults,[1] that pass from thepelvis of each kidney into the bladder. From the renal pelvis, they descend on top of thepsoas major muscle to reach thebrim of the pelvis. Here, they cross in front of thecommon iliac arteries. They then pass down along the sides of the pelvis and finally curve forward and enter the bladder from its left and right sides at the back of the bladder.[2] The ureters are 1.5–6 mm (0.06–0.24 in) in diameter[1] and surrounded by a layer ofsmooth muscle for 1–2 cm (0.4–0.8 in) near their ends just before they enter the bladder.[2]
The ureters enter the bladder from its back surface, traveling 1.5–2 cm (0.6–0.8 in) before opening into the bladder at an angle on its outer back surface at the slit-likeureteric orifices.[2][3] This location is also called the vesicoureteric junction.[4] In the contracted bladder, they are about 25 mm (1 in) apart and about the same distance from theinternal urethral orifice; in the distended bladder, these measurements may be increased to about 50 mm (2 in).[2]
A number of structures pass by, above, and around the ureters on their path down from the kidneys to the bladder.[2] In its upper part, the ureter travels on thepsoas major muscle and sits just behind theperitoneum. As it passes down the muscle, it travels over thegenitofemoral nerve. Theinferior vena cava and theabdominal aorta sit to the midline of the right and left ureters, respectively.[2] In the lower part of the abdomen, the right ureter sits behind the lowermesentery and theterminal ileum, and the left ureter sits behind thejejunum and thesigmoid colon.[2] As the ureters enter the pelvis, they are surrounded by connective tissue, and travel backward and outward, passing in front of theinternal iliac arteries andinternal iliac veins. They then travel inward and forward, crossing theumbilical,inferior vesical, andmiddle rectal arteries.[2] From here, in males, they cross under the vas deferens and in front of theseminal vesicles to enter the bladder near the trigone.[2] In females, the ureters pass behind theovaries and then travel in the lower midline section of thebroad ligament of the uterus. For a short part, theuterine arteries travel on top for a short (2.5 cm (1 in)) period. They then pass by thecervix, traveling inward towards the bladder.[2]
Thearteries that supply the ureters end in a network of vessels within theadventitia of the ureters.[1] There are many connections (anastamoses) between the arteries of the ureter,[2] particularly in the adventitia,[5] which means damage to a single vessel does not compromise the blood supply of the ureter.[2][5] Venous drainage mostly parallels that of the arterial supply;[5][2] that is, it begins as a network of smaller veins in the adventitia; with the renal veins draining the upper ureters, and the vesicular and gonadal veins draining the lower ureters.[1]
Lymphatic drainage depends on the position of lymphatic vessels in the ureter.[1]Lymph collects in submucosal, intramuscular and adventitiallymphatic vessels.[2] Those vessels closer to the kidney drain into renal collecting vessels, and from here into thelateral aortic nodes near the gonadal vessels.[2] The middle part of the ureter drains into the right paracaval and interaortocaval nodes on the right, and the left paraaortic nodes on the left.[1] In the lower ureter, lymph may drain into thecommon iliac lymph nodes, or lower down in the pelvis to thecommon,external, orinternal iliac lymph nodes.[2]
The ureters are richly supplied by nerves that form a network (plexus) of nerves, theureteric plexus that lies in the adventitia of the ureters.[2] This plexus is formed from a number ofnerve roots directly (T9–12, L1, and S2-4), as well as branches from other nerve plexuses and nerves; specifically, the upper third of the ureter receives nerve branches from therenal plexus andaortic plexus, the middle part receives branches from the upperhypogastric plexus andnerve, and the lower ureter receives branches from the lower hypogastric plexus and nerve.[2] The plexus is in the adventitia. These nerves travel in individual bundles and along small blood vessels to form the ureteric plexus.[2] Sensation supplied is sparse close to the kidneys and increases closer to the bladder.[2]
Sensation to the ureters is provided by nerves that come from T11 – L2 segments of thespinal cord.[2] When pain is caused, for example by spasm of the ureters or by a stone, thepain may be referred to thedermatomes of T11 – L2, namely the back and sides of the abdomen, the scrotum (males) or labia majora (females) and upper part of the front of the thigh.[2]
Microscopic cross-section of the ureter, showing theepithelium (purple cells) sitting next to thelumen. A large amount of muscle fibres can be seen surrounding the epithelium, and theadventitia sits beyond this.
The ureter is lined byurothelium, a type oftransitional epithelium that is capable of responding to stretches in the ureters. The transitional epithelium may appear as a layer ofcolumn-shaped cells when relaxed, and offlatter cells when distended. Below the epithelium sits thelamina propria. The lamina propria is made up of loose connective tissue with many elastic fibers interspersed with blood vessels, veins and lymphatics. The ureter is surrounded by two muscular layers, an inner longitudinal layer of muscle, and an outer circular or spiral layer of muscle.[6][7] The lower third of the ureter has a third muscular layer.[7] Beyond these layers sits anadventitia containing blood vessels, lymphatic vessels, and veins.[7]
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 fromGray's Anatomy 1918 edition.
The ureters develop from theureteric buds, which are outpouchings from themesonephric duct. This is a duct, derived frommesoderm, found in the earlyembryo.[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 thecloaca, which over the course of development splits into aurogenital sinus and theanorectal canal.[8] The urinary bladder forms from the urogenital sinus. Over time, as the bladder enlarges, it absorbs the surrounding parts of the primitive ureters.[8] Finally, the entry points of the ureters into the bladder move upwards, owing to the upward migration of the kidneys in the developing embryo.[8]
The ureters are a component of theurinary system.Urine, produced by the kidneys, travels along the ureters to the bladder. It does this through regular contractions calledperistalsis.[2]
Ultrasound showing a jet of urine entering the bladder (large black section) through the ureter
A giant ureteral stone with dimensions of approximately 6 × 5 × 4 cm and weighing 61 grams extracted from the left ureter of a 19-year-old male
Akidney stone can move from thekidney and become lodged inside the ureter, which can block the flow of urine, as well as cause a sharpcramp in the back, side, or lowerabdomen.[9] Pain often comes in waves lasting up to two hours, then subsides, calledrenal colic.[10] The affected kidney could then develophydronephrosis, should a part of the kidney becomeswollen due to blocked flow of urine.[9] It is classically described that there are three sites in the ureter where a kidney stone will commonly become stuck:where the ureter meets the renal pelvis; where the iliac blood vessels cross the ureters; and where the ureters enter the urinary bladder,[9] however aretrospectivecase study, which is aprimary source, of where stones lodged based onmedical imaging did not show many stones at the place where the iliac blood vessels cross.[11]
Vesicoureteral reflux refers to the reflux of fluid from the bladder into the ureters.[12] This condition can be associated withurinary tract infections, particularly in children, and is present in up to 28–36% of children to some degree.[12] A number of forms of medical imaging are available for diagnosis of the condition, with modalities includingdopplerurinary tract ultrasound.Factors that affect which of these are selected depends if a child is able to receive aurinary catheter, and whether a child istoilet trained.[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 isE. coli) differ between US, EU and UK guidelines.[12]
Management is also variable, with differences between international guidelines on issues such as whetherprophylactic antibiotics should be used, and whether surgery is recommended.[12] One reason is most instances of vesicoureteral reflux improve by themselves.[12] If surgery is considered, it generally involves reattaching the ureters to a different spot on the bladder, and extending the part of the ureter that it is within the wall of the bladder, with the most common surgical option being Cohen's cross-trigonal reimplantation.[12]
Blockage, or obstruction of the ureter can occur,[13] as a result of narrowing within the ureter, or compression or fibrosis of structures around the ureter.[14] Narrowing can result of ureteric stones, masses associated with cancer, and other lesions such asendometriosistuberculosis andschistosomiasis.[14] Things outside the ureters such asconstipation andretroperitoneal fibrosis can also compress them.[14] Somecongenital abnormalities can also result in narrowing or the ureters. Congenital disorders of the ureter andurinary tract affect 10% of infants.[13] These include partial or total duplication of the ureter (aduplex ureter), or the formation of a second irregularly placed (ectopic) ureter;[13] or where the junction with the bladder is malformed or aureterocoele develops (usually in that location).[14] If the ureters have been resited as a result of surgery, for example due to akidney transplant or due to past surgery for vesicoureteric reflux, that site may also become narrowed.[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 orblood in the urine; and when tested,kidney function might be seen to decrease.[13] These are considered situations when surgery is needed.[13] Medical imaging, including urinary tract ultrasound,CT ornuclear medicine imaging is conducted to investigate many causes.[13][14] This may involve reinserting the ureters into a new place on the bladder (reimplantion), or widening of the ureter.[13] Aureteric stent may be inserted to relieve an obstruction.[16] If the cause cannot be removed, anephrostomy may be required, which is the insertion of a tube connected to the renal pelvis which directly drains urine into astoma bag.[17]
Cancer of the ureters is known asureteral 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;[18] other risk factors includesmoking and exposure todyes such asaromatic amines andaldehydes.[18] When cancer is present, the most common symptom is blood in the urine; it may not cause symptoms, and a physicalmedical examination may be otherwise normal, except in late disease.[18] Ureteral cancer is most often due to cancer of the cells lining the ureter, calledtransitional cell carcinoma, although it can more rarely occur as asquamous cell carcinoma if the type of cells lining the urethra have changed due to chronic inflammation, such as due to stones or schistosomiasis.[18]
Investigations performed usually include collecting a sample of urine for an inspection for malignant cells under a microscope, calledcytology, as well as medical imaging by a CT urogram orultrasound.[18] If a concerning lesion is seen, a flexible camera may be inserted into the ureters, calledureteroscopy, in order to view the lesion and take abiopsy, and aCT scan will be performed of other body parts (aCT scan of the chest, abdomen and pelvis) to look for additionalmetastatic lesions.[18] After the cancer isstaged, treatment may involveopen surgery to remove the affected ureter and kidney if it is involved; or, if the lesion is small, it may be removed via ureteroscopy.[18] Prognosis can vary markedly depending on thetumour grade, with a worse prognosis associated with an ulcerating lesion.[18]
Several forms of medical imaging are used to view the ureters and urinary tract.[22] Ultrasound may be able to show evidence of blockage because of hydronephrosis of the kidneys and renal pelvis.[22] CT scans, including ones wherecontrast media is injectedintravenously to better show the ureters, and with contrast to better show lesions, and to differentiate benign from malignant lesions.[22] Dye may also be injected directly into the ureters or renal tract; anantegrade pyelogram is when contrast is injected directly into the renal pelvis, and aretrograde pyelogram is where dye is injected into the urinary tract via a catheter, and flows backwards into the ureters.[22] More invasive forms of imaging include ureteroscopy, which is the insertion of a flexibleendoscope into the urinary tract to view the ureters.[23] Ureteroscopy is most commonly used for medium to large-sized stones when less invasive methods of removal cannot be used.[23]
Allvertebrates have two kidneys located behind the abdomen that produce urine, and have a way of excreting it, so that waste products within the urine can be removed from the body.[24] The structure specifically called the ureter is present inamniotes, meaningmammals,birds andreptiles.[24] These animals possess an adult kidney derived from themetanephros.[24] The duct that connects the kidney to excrete urine in these animals is the ureter.[24] Inplacental mammals, it connects to theurinary bladder, whence urine leaves via theurethra.[25] Inmonotremes, urine flows from the ureters into thecloaca.[26] The ureters areventral to thevasa deferentia in male placental mammals, but dorsal to the vasa deferentia inmarsupials.[27] In female marsupials, the ureters pass between the median and lateralvaginae.[28]
The word "ureter" comes from theAncient Greek nounοὖρον,ouron, meaning "urine", and the first use of the word is seen during the era ofHippocrates to refer to theurethra.[29] 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.[29] It was only in the 1550s that anatomists such asBartolomeo Eustachi andJacques Dubois began to use the terms to specifically and consistently refer to what are in modern English called the ureter and the urethra.[29] Following this, in the 19th and 20th centuries, multiple terms relating to the structures such asureteritis and ureterography, were coined.[29]
Ureters
Kidney stones have been identified and recorded about as long as written historical records exist.[30] The urinary tract including the ureters, as well as their function to drain urine from the kidneys, has been described byGalen in the second century AD.[31]
The first to examine the ureter through an internal approach, called ureteroscopy, rather than surgery wasHampton Young in 1929.[30] This was improved on byVF Marshall who is the first published use of a flexible endoscope based onfiber 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. Such an approach differed greatly from the open surgical approaches within the urinary system employed during the preceding two millennia.[30]
The firstradiological imaging of the ureters was byX-rays, although this was made more difficult by the thick abdomen, which the low power of the original X-rays could not penetrate enough to produce clear images.[32] More useful images were able to be produced whenEdwin Hurry Fenwick in 1908 pioneered the use of tubes covered inradioopaque 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 onsilver orsodium iodide.[32] Hryntshalk in 1929 pioneered the development of theintravenous 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 byMoses Swick andLeopold Lichtwitz in the late 1920s of relatively nontoxic contrast media, with controversy surrounding publication as to who was the primary discoverer.[32] Side-effects associated with imaging improved even more whenTosten Almen published a ground-breaking thesis in 1969 based on the less toxic low-osmolar contrast media, developed based on swimming experiences in lakes with different salinity.[32]
^abcdefghijArthur D. Smith (Editor), Glenn Preminger (Editor), Gopal H. Badlani (Editor), Louis R. Kavoussi (Editor) (2019). "38. Ureteral Anatomy".Smith's textbook of endourology (4th ed.). John Wiley & Sons Ltd. pp. 455–464.ISBN9781119245193.{{cite book}}:|last1= has generic name (help)CS1 maint: multiple names: authors list (link)
^abcWein, Alan J. (2011).Campbell-Walsh Urology (10th ed.). Elsevier. p. 31.
^Lowe, Alan Stevens, James S. (2005).Human histology (3rd ed.). Philadelphia & Toronto: Elsevier Mosby. p. 324.ISBN0-3230-3663-5.{{cite book}}: CS1 maint: multiple names: authors list (link)
^abcYoung, Barbara; O'Dowd, Geraldine; Woodford, Phillip (2013-11-04).Wheater's functional histology: a text and colour atlas (6th ed.). Philadelphia: Elsevier. p. 314.ISBN9780702047473.
^abcdeSadley, TW (2019). "Urinary system".Langman's medical embryology (14th ed.). Philadelphia: Wolters Kluwer. pp. 256–266.ISBN9781496383907.
^abcRalston, Stuart H.; Penman, Ian D.; Strachan, Mark W.; Hobson, Richard P. (eds.) (2018). "Urolithiasis".Davidson's principles and practice of medicine (23rd ed.). Elsevier. pp. 431–2.ISBN978-0-7020-7028-0.{{cite book}}:|first4= has generic name (help)
^Ordon, Michael; Schuler, Trevor D.; Ghiculete, Daniela; Pace, Kenneth T.; Honey, R. John D'A. (March 2013). "Third Place: Stones Lodge at Three Sites of Anatomic Narrowing in the Ureter: Clinical Fact or Fiction?".Journal of Endourology.27 (3):270–276.doi:10.1089/end.2012.0201.PMID22984899.
^abcdefghRalston, Stuart H.; Penman, Ian D.; Strachan, Mark W.; Hobson, Richard P. (eds.) (2018). "Diseases of the collecting system and ureters".Davidson's principles and practice of medicine (23rd ed.). Elsevier. pp. 433–4.ISBN978-0-7020-7028-0.{{cite book}}:|first4= has generic name (help)
^abcdefghRalston, Stuart H.; Penman, Ian D.; Strachan, Mark W.; Hobson, Richard P. (eds.) (2018). "Urothelial tumours".Davidson's principles and practice of medicine (23rd ed.). Elsevier. pp. 435–6.ISBN978-0-7020-7028-0.{{cite book}}:|first4= has generic name (help)
^Santucci, Richard A."Ureteral Trauma". Medscape. Retrieved11 April 2012.
^abcdRalston, Stuart H.; Penman, Ian D.; Strachan, Mark W.; Hobson, Richard P. (eds.) (2018). "Investigation of renal and urinary tract disease:Imaging".Davidson's principles and practice of medicine (23rd ed.). Elsevier. pp. 389–390.ISBN978-0-7020-7028-0.{{cite book}}:|first4= has generic name (help)
^Nahon, I; Waddington, G; Dorey, G; Adams, R (2011). "The history of urologic surgery: from reeds to robotics".Urologic Nursing.31 (3):173–80.doi:10.7257/1053-816X.2011.31.3.173.PMID21805756.
