# Ureter

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{{Short description|Tubes used in the urinary system in most animals}}
{{good article}}
{{distinguish|urethra}}
{{Infobox anatomy
| Name        = Ureter
| Latin       = ureter
| Greek     = οὐρητήρ
| Image       = Urinary system.svg
| Caption     = The ureters (labeled 4) are tubes that carry [urine](/source/urine) and connect the [kidney](/source/kidney)s to the [bladder](/source/urinary_bladder).
| Width       = 
| Precursor   = [Ureteric bud](/source/Ureteric_bud)
| System      = [Urinary system](/source/Urinary_system)
| Artery      = [Superior vesical artery](/source/Superior_vesical_artery), [vaginal artery](/source/vaginal_artery), [ureteral branches of renal artery](/source/ureteral_branches_of_renal_artery)
| Vein        = 
| Nerve       = [Ureteric plexus](/source/Ureteric_plexus)
| Lymph       = 
}}
The '''ureters''' are tubes composed of [smooth muscle](/source/smooth_muscle) that transport [urine](/source/urine) from the [kidney](/source/kidney)s to the urinary [bladder](/source/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](/source/epithelium), and feature an extra layer of smooth muscle in the lower third to aid [peristalsis](/source/peristalsis).
The ureters can be affected by diseases including [urinary tract infections](/source/urinary_tract_infections) and [kidney stone](/source/kidney_stone)s. {{wt|en|Stenosis}} is the narrowing of a ureter, often caused by chronic inflammation. [Congenital abnormalities](/source/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 {{wt|en|uro-}} relating to [urinating](/source/urinating) and seen in written records since at least the time of [Hippocrates](/source/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](/source/medical_imaging) in the 20th century that techniques such as [X-ray](/source/X-ray), [CT](/source/CT_urogram), and [ultrasound](/source/urinary_tract_ultrasound) have been able to view the ureters. The ureters are also seen from the inside using a flexible camera, called [ureteroscopy](/source/ureteroscopy), which was first described in 1964.

==Structure==
[[File:Urinary system.svg|thumb|Structures that are near the ureters. 1. ''Human [urinary system](/source/urinary_system):'' 2. [Kidney](/source/Kidney), 3. [Renal pelvis](/source/Renal_pelvis), '''4'''. '''Ureter''', 5. [Urinary bladder](/source/Urinary_bladder), 6. [Urethra](/source/Urethra). (Left side with [frontal section](/source/Frontal_plane)), 7. [Adrenal gland](/source/Adrenal_gland)<br />''Vessels:''<br />8. [Renal artery](/source/Renal_artery) and [vein](/source/Renal_vein), 9. [Inferior vena cava](/source/Inferior_vena_cava), 10. [Abdominal aorta](/source/Abdominal_aorta), 11. [Common iliac artery](/source/Common_iliac_artery) and [vein](/source/Common_iliac_vein)<br />''With transparency:''<br />12. [Liver](/source/Liver), 13. [Large intestine](/source/Large_intestine), 14. [Pelvis](/source/Pelvis)]]
The ureters are tubular structures, approximately {{cvt|20–30|cm|0}} in adults,<ref name="Smiths2019" /> that pass from the [pelvis](/source/renal_pelvis) of each kidney into the bladder. From the renal pelvis, they descend on top of the [psoas major](/source/psoas_major) muscle to reach the [brim of the pelvis](/source/pelvic_brim). Here, they cross in front of the [common iliac arteries](/source/common_iliac_artery). 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.<ref name=Grays2016>{{Cite book|title=Gray's anatomy: the anatomical basis of clinical practice|editor=Standring, Susan|isbn=978-0-7020-5230-9|edition=41st|location=Philadelphia|oclc=920806541|year=2016|pages=1251–1254|section=Ureter}}</ref> The ureters are {{convert|1.5-6|mm|in|2|abbr=on}} in diameter<ref name="Smiths2019" /> and surrounded by a layer of [smooth muscle](/source/smooth_muscle) for {{convert|1-2|cm|in|1|abbr=on}} near their ends just before they enter the bladder.<ref name=Grays2016 /> 

<!--Vesicoureteric junction-->The ureters enter the bladder from its back surface, traveling {{cvt|1.5–2|cm|1}} before opening into the bladder at an angle on its outer back surface at the slit-like ''ureteric orifices''.<ref name=Grays2016 /><ref>{{Cite book|title=Gray's anatomy: the anatomical basis of clinical practice|editor=Standring, Susan|isbn=978-0-7020-5230-9|edition=41st|location=Philadelphia|oclc=920806541|year=2016|page=1259}}</ref> This location is also called the vesicoureteric junction.<ref>{{cite book |last1=Visveswaran |first1=kasi |title=Essentials of Nephrology, 2/e |date=2009 |publisher=BI Publications Pvt Ltd |isbn=978-81-7225-323-3 |page=61 |url=https://books.google.com/books?id=c4xAdJhIi6oC&q=vesicoureteric+junction+is+where+the+ureters+enter+the+bladder&pg=PA61 |language=en}}</ref> In the contracted bladder, they are about {{convert|25|mm|in|abbr=on|0}} apart and about the same distance from the [internal urethral orifice](/source/internal_urethral_orifice); in the distended bladder, these measurements may be increased to about {{convert|50|mm|in|abbr=on|0}}.<ref name=Grays2016 />

<!--Relations-->A number of structures pass by, above, and around the ureters on their path down from the kidneys to the bladder.<ref name=Grays2016 /> In its upper part, the ureter travels on the [psoas major muscle](/source/psoas_major_muscle) and sits just behind the [peritoneum](/source/peritoneum). As it passes down the muscle, it travels over the [genitofemoral nerve](/source/genitofemoral_nerve). The [inferior vena cava](/source/inferior_vena_cava) and the [abdominal aorta](/source/abdominal_aorta) sit to the midline of the right and left ureters, respectively.<ref name=Grays2016 /> In the lower part of the abdomen, the right ureter sits behind the lower [mesentery](/source/mesentery) and the [terminal ileum](/source/terminal_ileum), and the left ureter sits behind the [jejunum](/source/jejunum) and the [sigmoid colon](/source/sigmoid_colon).<ref name=Grays2016 /> As the ureters enter the pelvis, they are surrounded by connective tissue, and travel backward and outward, passing in front of the [internal iliac arteries](/source/internal_iliac_arteries) and [internal iliac veins](/source/internal_iliac_veins). They then travel inward and forward, crossing the [umbilical](/source/umbilical_arteries), [inferior vesical](/source/inferior_vesical_arteries), and [middle rectal arteries](/source/middle_rectal_arteries).<ref name=Grays2016 /> From here, in males, they cross under the vas deferens and in front of the [seminal vesicles](/source/seminal_vesicles) to enter the bladder near the trigone.<ref name=Grays2016 /> In females, the ureters pass behind the [ovaries](/source/ovaries) and then travel in the lower midline section of the [broad ligament of the uterus](/source/broad_ligament_of_the_uterus). For a short part, the [uterine arteries](/source/uterine_arteries) travel on top for a short ({{convert|2.5|cm|in|0|abbr=on}}) period. They then pass by the [cervix](/source/cervix), traveling inward towards the bladder.<ref name=Grays2016 /> 

===Blood and lymphatic supply===
The arteries which supply the ureter vary along its course. The upper third of the ureter, closest to the kidney, is supplied by the [renal arteries](/source/renal_artery).<ref name="Grays2016" /> The middle part of the ureter is supplied by the [common iliac arteries](/source/common_iliac_arteries), direct branches from the [abdominal aorta](/source/abdominal_aorta), and [gonadal arteries](/source/gonadal_artery);<ref name="Smiths2019" /> the gonadal arteries being the [testicular artery](/source/testicular_artery) in men and the [ovarian artery](/source/ovarian_artery) in women.<ref name="Grays2016" /> The lower third of the ureter, closest to the bladder, is supplied by branches from the [internal iliac arteries](/source/internal_iliac_artery), mainly the [superior](/source/Superior_vesical_artery) and [inferior vesical arteries](/source/inferior_vesical_arteries).<ref name="Smiths2019" /> The arterial supply can be variable, with arteries that contribute include the [middle rectal artery](/source/middle_rectal_artery), branches directly from the aorta,<ref name="Smiths2019" /> and, in women, the uterine and vaginal arteries.<ref name="Grays2016" />

The [arteries](/source/Artery) that supply the ureters end in a network of vessels within the [adventitia](/source/adventitia) of the ureters.<ref name="Smiths2019" /> There are many connections ({{wikt-lang|en|anastamoses}}) between the arteries of the ureter,<ref name=Grays2016 /> particularly in the adventitia,<ref name=CWUrology/> which means damage to a single vessel does not compromise the blood supply of the ureter.<ref name=Grays2016 /><ref name=CWUrology/> Venous drainage mostly parallels that of the arterial supply;<ref name=CWUrology>{{cite book |last= Wein |first= Alan J.  |title= Campbell-Walsh Urology |edition=10th |year= 2011|publisher= Elsevier |page= 31}}</ref><ref name=Grays2016 /> 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.<ref name="Smiths2019" />

Lymphatic drainage depends on the position of lymphatic vessels in the ureter.<ref name="Smiths2019" /> [Lymph](/source/Lymph) collects in submucosal, intramuscular and adventitial [lymphatic vessels](/source/lymphatic_vessels).<ref name=Grays2016 /> Those vessels closer to the kidney drain into renal collecting vessels, and from here into the [lateral aortic node](/source/Paraaortic_lymph_nodes)s near the gonadal vessels.<ref name="Grays2016" /> 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.<ref name="Smiths2019" /> In the lower ureter, lymph may drain into the [common iliac lymph node](/source/common_iliac_lymph_node)s, or lower down in the pelvis to the [common](/source/common_iliac_lymph_nodes), [external](/source/external_iliac_lymph_nodes), or [internal iliac lymph nodes](/source/internal_iliac_lymph_nodes).<ref name="Grays2016" />

===Nerve supply===
The ureters are richly supplied by nerves that form a network ({{wikt-lang|en|plexus}}) of nerves, the [ureteric plexus](/source/ureteric_plexus) that lies in the adventitia of the ureters.<ref name=Grays2016 /> This plexus is formed from a number of [nerve roots](/source/Nerve_root) 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 the [renal plexus](/source/renal_plexus) and [aortic plexus](/source/Abdominal_aortic_plexus), the middle part receives branches from the upper [hypogastric plexus](/source/Superior_hypogastric_plexus) and [nerve](/source/Superior_hypogastric_plexus), and the lower ureter receives branches from the lower hypogastric plexus and nerve.<ref name=Grays2016 /> The plexus is in the adventitia. These nerves travel in individual bundles and along small blood vessels to form the ureteric plexus.<ref name=Grays2016 /> Sensation supplied is sparse close to the kidneys and increases closer to the bladder.<ref name=Grays2016 />

Sensation to the ureters is provided by nerves that come from T11 – L2 segments of the [spinal cord](/source/spinal_cord).<ref name=Grays2016 /> When pain is caused, for example by spasm of the ureters or by a stone, the [pain may be referred](/source/referred_pain) to the [dermatome](/source/dermatome_(anatomy))s 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.<ref name=Grays2016 />

===Microanatomy===
[[File:2607 Ureter.jpg|thumb|[Microscopic cross-section](/source/Histology) of the ureter, showing the [epithelium](/source/epithelium) (purple cells) sitting next to the [lumen](/source/Lumen_(anatomy)). A large amount of muscle fibres can be seen surrounding the epithelium, and the [adventitia](/source/adventitia) sits beyond this.]]
The ureter is lined by [urothelium](/source/urothelium), a type of [transitional epithelium](/source/transitional_epithelium) that is capable of responding to stretches in the ureters. The transitional epithelium may appear as a layer of [column-shaped cells](/source/columnar_epithelia) when relaxed, and of [flatter cells](/source/squamous_epithelia) when distended. Below the epithelium sits the [lamina propria](/source/lamina_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.<ref>{{cite book|last=Lowe|first=Alan Stevens, James S.|title=Human histology|date=2005|publisher=Elsevier Mosby|location=Philadelphia & Toronto|isbn=0-3230-3663-5|edition=3rd|page=324}}</ref><ref name=Wheaters2014 /> The lower third of the ureter has a third muscular layer.<ref name=Wheaters2014 /> Beyond these layers sits an [adventitia](/source/adventitia) containing blood vessels, lymphatic vessels, and veins.<ref name=Wheaters2014>{{cite book |last1=Young |first1=Barbara |last2=O'Dowd |first2=Geraldine |last3=Woodford |first3=Phillip |title=Wheater's functional histology: a text and colour atlas.|publisher=Elsevier |location=Philadelphia |isbn=978-0-7020-4747-3 |edition=6th|page=314|date=2013-11-04 }}</ref>
{{clear}}

===Development===
{{See also|Development of the urinary system}}[[Image:Gray1116.png|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](/source/Gray's_Anatomy)'' 1918 edition.]]
The ureters develop from the [ureteric bud](/source/ureteric_bud)s, which are outpouchings from the [mesonephric duct](/source/mesonephric_duct). This is a duct, derived from [mesoderm](/source/mesoderm), found in the early [embryo](/source/embryo).<ref name=Langman2019>{{cite book |last1=Sadley |first1=TW |title=Langman's medical embryology |date=2019|location=Philadelphia|publisher=Wolters Kluwer |isbn=978-1-4963-8390-7 |edition=14th|section=Urinary system|pages=256–266}}</ref> 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.<ref name=Langman2019 />

The mesonephric duct is connected with the [cloaca](/source/Cloaca_(embryology)), which over the course of development splits into a [urogenital sinus](/source/urogenital_sinus) and the [anorectal canal](/source/anorectal_canal).<ref name=Langman2019 /> The urinary bladder forms from the urogenital sinus. Over time, as the bladder enlarges, it absorbs the surrounding parts of the primitive ureters.<ref name=Langman2019 /> Finally, the entry points of the ureters into the bladder move upwards, owing to the upward migration of the kidneys in the developing embryo.<ref name=Langman2019 />

==Function==
The ureters are a component of the [urinary system](/source/urinary_system). [Urine](/source/Urine), produced by the kidneys, travels along the ureters to the bladder. It does this through regular contractions called [peristalsis](/source/peristalsis).<ref name=Grays2016 />

<gallery>
File:Ultrasound_demonstration_of_ureteral_jet_effect_0301105703_1105300.gif|[Ultrasound](/source/Medical_ultrasound) showing a jet of urine entering the bladder (large black section) through the ureter
</gallery>

==Clinical significance==
===Ureteral stones===
[[File:Kidney stones.jpg|thumb|Kidney stones. One entire stone (the bigger one) and another one fragmented in small pieces after extracorporeal shock wave [lithotripsy](/source/Lithotripsy) ]]
A [kidney stone](/source/kidney_stone) can move from the [kidney](/source/kidney) and become lodged inside the ureter, which can block the flow of urine, as well as cause a sharp [cramp](/source/cramp) in the back, side, or lower [abdomen](/source/abdomen).<ref name=Moore2013 /> Pain often comes in waves lasting up to two hours, then subsides, called [renal colic](/source/renal_colic).<ref name=Davidsons2018Urolithiasis /> The affected kidney could then develop [hydronephrosis](/source/hydronephrosis), should a part of the kidney become [swollen](/source/Swelling_(medical)) due to blocked flow of urine.<ref name=Moore2013 /> 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,<ref name=Moore2013>{{cite book |last1=Moore |first1=Keith L. |last2=Dalley |first2=Arthur F. |last3=Agur |first3=A. M. R. |title=Clinically Oriented Anatomy |date=2013 |publisher=Lippincott Williams & Wilkins |isbn=978-1-4511-1945-9 |page=300 |url=https://books.google.com/books?id=-Le5bc5F0sYC&pg=PA300 |language=en}}</ref> however a [retrospective](/source/retrospective) [case study](/source/case_study), which is a [primary source](/source/primary_source), of where stones lodged based on [medical imaging](/source/medical_imaging) did not show many stones at the place where the iliac blood vessels cross.<ref>{{cite journal |last1=Ordon |first1=Michael |last2=Schuler |first2=Trevor D. |last3=Ghiculete |first3=Daniela |last4=Pace |first4=Kenneth T. |last5=Honey |first5=R. John D'A. |title=Third Place: Stones Lodge at Three Sites of Anatomic Narrowing in the Ureter: Clinical Fact or Fiction? |journal=Journal of Endourology |date=March 2013 |volume=27 |issue=3 |pages=270–276 |doi=10.1089/end.2012.0201|pmid=22984899 }}</ref>

Most stones are compounds containing [calcium](/source/calcium) such as [calcium oxalate](/source/calcium_oxalate) and [calcium phosphate](/source/calcium_phosphate). The first recommended investigation is a [CT scan of the abdomen](/source/Computed_tomography_of_the_abdomen_and_pelvis) because it can detect almost all stones. Management includes [analgesia](/source/analgesia), often with [nonsteroidal antiinflammatories](/source/NSAIDs).<ref name=Davidsons2018Urolithiasis /> Small stones (< 4mm) may pass themselves; larger stones may require [lithotripsy](/source/lithotripsy), and those with complications such as hydronephrosis or infection may require surgery to remove.<ref name=Davidsons2018Urolithiasis>{{cite book|title=Davidson's principles and practice of medicine|last1=Ralston |first1=Stuart H. |last2=Penman |first2=Ian D. |last3=Strachan |first3=Mark W. |last4=Hobson |first4=Richard P. (eds.)|date=2018 |publisher=Elsevier |isbn=978-0-7020-7028-0 |edition=23rd|pages=431–2|section=Urolithiasis}}</ref>

===Reflux===
[Vesicoureteral reflux](/source/Vesicoureteral_reflux) refers to the reflux of fluid from the bladder into the ureters.<ref name="Tullus2015">{{cite journal |last1=Tullus |first1=Kjell |title=Vesicoureteric reflux in children |journal=The Lancet |date=January 2015 |volume=385 |issue=9965 |pages=371–379 |doi=10.1016/S0140-6736(14)60383-4 |pmid=25164069 |s2cid=1733077 |url=https://macpeds.mcmaster.ca/documents/Vesicouretericrefluxinchildrenretrieved_2017.pdf |access-date=2020-07-06 |archive-date=2020-07-06 |archive-url=https://web.archive.org/web/20200706045755/https://macpeds.mcmaster.ca/documents/Vesicouretericrefluxinchildrenretrieved_2017.pdf }}</ref> This condition can be associated with [urinary tract infection](/source/urinary_tract_infection)s, particularly in children, and is present in up to 28–36% of children to some degree.<ref name="Tullus2015" /> A number of forms of medical imaging are available for diagnosis of the condition, with modalities including [doppler](/source/doppler_ultrasound) [urinary tract ultrasound](/source/urinary_tract_ultrasound). Factors that affect which of these are selected depends if a child is able to receive a [urinary catheter](/source/urinary_catheter), and whether a child is [toilet trained](/source/toilet_training).<ref name="Tullus2015" /> 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.&nbsp;coli](/source/Escherichia_coli)'') differ between US, EU and UK guidelines.<ref name="Tullus2015" />

Management is also variable, with differences between international guidelines on issues such as whether [prophylactic antibiotic](/source/prophylactic_antibiotic)s should be used, and whether surgery is recommended.<ref name="Tullus2015" /> One reason is most instances of vesicoureteral reflux improve by themselves.<ref name="Tullus2015" /> 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.<ref name="Tullus2015" />

===Anatomical and surgical abnormalities===
Blockage, or obstruction of the ureter can occur,<ref name="Davidsons2018A">{{cite book|last1=Ralston|first1=Stuart H.|title=Davidson's principles and practice of medicine|last2=Penman|first2=Ian D.|last3=Strachan|first3=Mark W.|last4=Hobson|first4=Richard P. (eds.)|date=2018|publisher=Elsevier|isbn=978-0-7020-7028-0|edition=23rd|pages=433–4|section=Diseases of the collecting system and ureters}}</ref> as a result of narrowing within the ureter, or compression or fibrosis of structures around the ureter.<ref name="Mayo2020" /> Narrowing can result of ureteric stones, masses associated with cancer, and other lesions such as [endometriosis](/source/endometriosis) [tuberculosis](/source/tuberculosis) and [schistosomiasis](/source/schistosomiasis).<ref name="Mayo2020">{{cite web |title=Ureteral obstruction - Symptoms and causes |url=https://www.mayoclinic.org/diseases-conditions/ureteral-obstruction/symptoms-causes/syc-20354676 |website=Mayo Clinic |access-date=6 July 2020 |language=en |date=2020}}</ref> Things outside the ureters such as [constipation](/source/constipation) and [retroperitoneal fibrosis](/source/retroperitoneal_fibrosis) can also compress them.<ref name="Mayo2020" /> Some [congenital abnormalities](/source/congenital_abnormalities) can also result in narrowing or the ureters. Congenital disorders of the ureter and [urinary tract](/source/urinary_tract) affect 10% of infants.<ref name="Davidsons2018A" /> These include partial or total duplication of the ureter (a [duplex ureter](/source/Duplicated_ureter)), or the formation of a second irregularly placed ({{wikt-lang|en|ectopic}}) ureter;<ref name="Davidsons2018A" /> or where the junction with the bladder is malformed or a [ureterocoele](/source/ureterocoele) develops (usually in that location).<ref name="Mayo2020" /> If the ureters have been resited as a result of surgery, for example due to a [kidney transplant](/source/kidney_transplant) or due to past surgery for vesicoureteric reflux, that site may also become narrowed.<ref name="Faenza1999">{{cite journal |last1=Faenza |first1=A. |last2=Nardo |first2=Bruno |last3=Catena |first3=Fausto |last4=Scolari |first4=Maria P. |last5=d'Arcangelo |first5=Giovanni Liviano |last6=Buscaroli |first6=Andrea |last7=Rossi |first7=Cristina |last8=Zompatori |first8=Maurizio |title=Ureteral stenosis after kidney transplantation |journal=Transplant International |date=1 October 1999 |volume=12 |issue=5 |pages=334–340 |doi=10.1007/s001470050236 |s2cid=71928271 |language=en |issn=1432-2277}}</ref><ref name=Smiths2019>{{cite book |last1=Arthur D. Smith (Editor), Glenn Preminger (Editor), Gopal H. Badlani (Editor), Louis R. Kavoussi (Editor)|title=Smith's textbook of endourology|year=2019 |publisher=John Wiley & Sons Ltd |isbn=978-1-119-24519-3 |edition=4th|chapter=38. Ureteral Anatomy|pages=455–464}}</ref>

A narrowed ureter may lead to ureteric enlargement ({{wt|en|dilation}}) and cause swelling of the kidneys ([hydronephrosis](/source/hydronephrosis)).<ref name=Davidsons2018A /> Associated symptoms may include recurrent infections, pain or [blood in the urine](/source/haematuria); and when tested, [kidney function](/source/kidney_function) might be seen to decrease.<ref name=Davidsons2018A /> These are considered situations when surgery is needed.<ref name=Davidsons2018A /> Medical imaging, including urinary tract ultrasound, [CT](/source/CT_urogram) or [nuclear medicine](/source/nuclear_medicine) imaging is conducted to investigate many causes.<ref name=Davidsons2018A /><ref name="Mayo2020" /> This may involve reinserting the ureters into a new place on the bladder (reimplantion), or widening of the ureter.<ref name=Davidsons2018A /> A [ureteric stent](/source/ureteric_stent) may be inserted to relieve an obstruction.<ref>{{cite journal |last1=Sali |first1=Gaurav Mohan |last2=Joshi |first2=Hrishikesh B |title=Ureteric stents: Overview of current clinical applications and economic implications |journal=International Journal of Urology |date=23 September 2019 |volume=27 |issue=1 |pages=7–15 |doi=10.1111/iju.14119|pmid=31549458 |doi-access=free }}</ref> If the cause cannot be removed, a [nephrostomy](/source/nephrostomy) may be required, which is the insertion of a tube connected to the renal pelvis which directly drains urine into a [stoma bag](/source/stoma_bag).<ref>{{cite journal |last1=R |first1=Martin|last2=Baker |first2=H |title=Nursing care and management of patients with a nephrostomy |journal=Nursing Times |date=14 October 2019|url=https://www.nursingtimes.net/clinical-archive/patient-safety/nursing-care-and-management-of-patients-with-a-nephrostomy-14-10-2019/ |language=en}}</ref>

===Cancer===
[Cancer](/source/Cancer) of the ureters is known as [ureteral cancer](/source/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;<ref name=Davidsons2018cancer>{{cite book|title=Davidson's principles and practice of medicine|last1=Ralston |first1=Stuart H. |last2=Penman |first2=Ian D. |last3=Strachan |first3=Mark W. |last4=Hobson |first4=Richard P. (eds.)|date=2018 |publisher=Elsevier |isbn=978-0-7020-7028-0 |edition=23rd|pages=435–6|section=Urothelial tumours}}</ref> other risk factors include [smoking](/source/smoking) and exposure to [dye](/source/dye)s such as [aromatic amine](/source/aromatic_amine)s and [aldehydes](/source/aldehydes).<ref name=Davidsons2018cancer/> When cancer is present, the most common symptom is blood in the urine; it may not cause symptoms, and a physical [medical examination](/source/medical_examination) may be otherwise normal, except in late disease.<ref name=Davidsons2018cancer /> Ureteral cancer is most often due to cancer of the cells lining the ureter, called [transitional cell carcinoma](/source/transitional_cell_carcinoma), although it can more rarely occur as a [squamous cell carcinoma](/source/squamous_cell_carcinoma) if the type of cells lining the urethra have changed due to chronic inflammation, such as due to stones or schistosomiasis.<ref name=Davidsons2018cancer />

Investigations performed usually include collecting a sample of urine for an inspection for malignant cells under a microscope, called [cytology](/source/cytology), as well as medical imaging by a CT urogram or [ultrasound](/source/ultrasound).<ref name=Davidsons2018cancer /> If a concerning lesion is seen, a flexible camera may be inserted into the ureters, called [ureteroscopy](/source/ureteroscopy), in order to view the lesion and take a [biopsy](/source/biopsy), and a [CT scan](/source/CT_scan) will be performed of other body parts (a [CT scan of the chest, abdomen and pelvis](/source/Full-body_CT_scan)) to look for additional {{wt|en|metastatic}} lesions.<ref name=Davidsons2018cancer /> After the cancer is [staged](/source/tumour_staging), treatment may involve [open surgery](/source/open_surgery) to remove the affected ureter and kidney if it is involved; or, if the lesion is small, it may be removed via ureteroscopy.<ref name=Davidsons2018cancer /> Prognosis can vary markedly depending on the [tumour grade](/source/tumour_grade), with a worse prognosis associated with an ulcerating lesion.<ref name=Davidsons2018cancer />

===Injury===
Injuries to the ureter can occur after penetrating abdominal injuries, and injuries at high speeds followed by an abrupt stop (such as a high speed car accident).<ref name=Stein2015>{{cite journal|last1=Stein |first1=D. M. |last2=Santucci |first2=R. A.|title=An update on urotrauma|journal=Current Opinion in Urology|volume=25|issue=4|pages=323–30|date=July 2015|pmid=26049876|doi=10.1097/MOU.0000000000000184|s2cid=26994715 }}</ref> The ureter can be injured during surgery to nearby structures.<ref name="Burks2014" /> It is injured in 2 per 10,000 cases of vaginal [hysterectomies](/source/Hysterectomy) and 13 per 10,000 cases of [abdominal hysterectomies](/source/Abdominal_hysterectomy),<ref name="Burks2014">{{cite journal|last1=Burks |first1=F. N. |last2=Santucci |first2=R. A.|title=Management of iatrogenic ureteral injury|journal=Therapeutic Advances in Urology|volume=6|issue=3|pages=115–24|date=June 2014 |pmid=24883109|pmc=4003841|doi=10.1177/1756287214526767}}</ref> usually near the [suspensory ligament of the ovary](/source/Suspensory_ligament_of_ovary) or near the [cardinal ligament](/source/cardinal_ligament), where the ureter runs close to the [blood vessels of the uterus](/source/Uterine_artery).<ref>{{cite web|url=http://emedicine.medscape.com/article/440933-overview#showall|title=Ureteral Trauma|last=Santucci|first=Richard A|publisher=Medscape|access-date=11 April 2012}}</ref>

===Imaging===
Several forms of medical imaging are used to view the ureters and urinary tract.<ref name=Davidsons2018Imaging>{{cite book|title=Davidson's principles and practice of medicine|last1=Ralston |first1=Stuart H. |last2=Penman |first2=Ian D. |last3=Strachan |first3=Mark W. |last4=Hobson |first4=Richard P. (eds.)|date=2018 |publisher=Elsevier |isbn=978-0-7020-7028-0 |edition=23rd|pages=389–390|section=Investigation of renal and urinary tract disease:Imaging}}</ref> Ultrasound may be able to show evidence of blockage because of hydronephrosis of the kidneys and renal pelvis.<ref name=Davidsons2018Imaging /> CT scans, including ones where [contrast media](/source/contrast_media) is injected [intravenous](/source/intravenous)ly to better show the ureters, and with contrast to better show lesions, and to differentiate benign from malignant lesions.<ref name=Davidsons2018Imaging /> Dye may also be injected directly into the ureters or renal tract; an [antegrade pyelogram](/source/Antegrade_pyelography) is when contrast is injected directly into the renal pelvis, and a [retrograde pyelogram](/source/retrograde_pyelogram) is where dye is injected into the urinary tract via a catheter, and flows backwards into the ureters.<ref name=Davidsons2018Imaging /> More invasive forms of imaging include ureteroscopy, which is the insertion of a flexible [endoscope](/source/endoscope) into the urinary tract to view the ureters.<ref name=":0">{{Cite web|date=2020|title=Ureteroscopy|url=https://www.kidney.org/atoz/content/kidneystones_ureteroscopy|access-date=2020-07-04|website=National Kidney Foundation|language=en-US}}</ref> Ureteroscopy is most commonly used for medium to large-sized stones when less invasive methods of removal cannot be used.<ref name=":0" />

==Other animals==
All [vertebrate](/source/vertebrate)s 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.<ref name=Kardon2019>{{cite book |last1=Kardong |first1=Kenneth |title=Vertebrates: comparative anatomy, function, evolution |date=2019 |publisher=McGraw-Hill |location=New York |isbn=978-1-260-09204-2 |edition=8th|chapter=The urogenital system|pages=546–552}}</ref> The structure specifically called the ureter is present in [amniote](/source/amniote)s, meaning [mammals](/source/mammals), [birds](/source/birds) and [reptiles](/source/reptiles).<ref name=Kardon2019 /> These animals possess an adult kidney derived from the [metanephros](/source/metanephros).<ref name=Kardon2019 /> The duct that connects the kidney to excrete urine in these animals is the ureter.<ref name=Kardon2019 /> In [placental mammals](/source/placental_mammals), it connects to the [urinary bladder](/source/urinary_bladder), whence urine leaves via the [urethra](/source/urethra).<ref name="Wake1992">{{cite book|author=Marvalee H. Wake|title=Hyman's Comparative Vertebrate Anatomy|url=https://books.google.com/books?id=VKlWjdOkiMwC&pg=PA583|access-date=6 May 2013|date=15 September 1992|publisher=University of Chicago Press|isbn=978-0-226-87013-7|page=583}}</ref> In [monotremes](/source/monotremes), urine flows from the ureters into the [cloaca](/source/cloaca).<ref>{{Cite book |last=Linzey |first=Donald W. |url=https://books.google.com/books?id=SOr4DwAAQBAJ&pg=PA305 |title=Vertebrate Biology: Systematics, Taxonomy, Natural History, and Conservation |date=2020-08-04 |publisher=JHU Press |isbn=978-1-4214-3734-7 |language=en}}</ref> The ureters are [ventral](/source/ventral) to the [vasa deferentia](/source/vasa_deferentia) in male placental mammals, but dorsal to the vasa deferentia in [marsupial](/source/marsupial)s.<ref>{{Cite book |last1=Withers |first1=Philip C. |url=https://books.google.com/books?id=pXB4DQAAQBAJ&pg=PT386 |title=Ecological and Environmental Physiology of Mammals |last2=Cooper |first2=Christine E. |last3=Maloney |first3=Shane K. |last4=Bozinovic |first4=Francisco |last5=Neto |first5=Ariovaldo P. Cruz |date=2016-11-10 |publisher=Oxford University Press |isbn=978-0-19-109268-8 |language=en}}</ref> In female marsupials, the ureters pass between the median and lateral [vaginae](/source/Vagina).<ref>{{Cite book |last=Miller |first=R. Eric |url=https://www.google.com/books/edition/Fowler_s_Zoo_and_Wild_Animal_Medicine_Vo/llBcBAAAQBAJ?hl=en&gbpv=1&pg=PA257&printsec=frontcover |title=Fowler's Zoo and Wild Animal Medicine, Volume 8 |last2=Fowler |first2=Murray E. |date=2014-06-02 |publisher=Elsevier Health Sciences |isbn=978-1-4557-7399-2 |language=en}}</ref>

==History==
The word "ureter" comes from the [Ancient Greek](/source/Ancient_Greek) noun {{Lang|grc|οὖρον}}, {{Transliteration|grc|ouron}}, meaning "urine", and the first use of the word is seen during the era of [Hippocrates](/source/Hippocrates) to refer to the [urethra](/source/urethra).<ref name="Marx2010">{{cite journal |last1=Marx |first1=Franz Josef |last2=Karenberg |first2=Axel |title=Uro-words making history: Ureter and urethra |journal=The Prostate |date=2010 |volume=70 |issue=9 |pages=952–958 |doi=10.1002/pros.21129|pmid=20166127 |s2cid=32778667 |doi-access=free }}</ref> The anatomical structure of the ureter was noted by 40&nbsp;AD. However, the terms "ureter" and "urethra" were variably used to refer to each other thereafter for more than a millennium.<ref name=Marx2010 /> It was only in the 1550s that anatomists such as [Bartolomeo Eustachi](/source/Bartolomeo_Eustachi) and [Jacques Dubois](/source/Jacques_Dubois) began to use the terms to specifically and consistently refer to what are in modern English called the ureter and the urethra.<ref name=Marx2010 /> Following this, in the 19th and 20th centuries, multiple terms relating to the structures such as [ureteritis](/source/ureteritis) and ureterography, were coined.<ref name=Marx2010 />
thumb|center|Ureters
Kidney stones have been identified and recorded about as long as written historical records exist.<ref name="Tefekli2013">{{cite journal |last1=Tefekli |first1=Ahmet |last2=Cezayirli |first2=Fatin |title=The History of Urinary Stones: In Parallel with Civilization |journal=The Scientific World Journal |date=2013 |volume=2013 |article-number=423964 |doi=10.1155/2013/423964|pmid=24348156 |pmc=3856162 |doi-access=free }}</ref> The urinary tract including the ureters, as well as their function to drain urine from the kidneys, has been described by [Galen](/source/Galen) in the second century AD.<ref name="Nahon2011">{{cite journal |last1=Nahon |first1=I |last2=Waddington |first2=G |last3=Dorey |first3=G |last4=Adams |first4=R |title=The history of urologic surgery: from reeds to robotics. |journal=Urologic Nursing |date=2011 |volume=31 |issue=3 |pages=173–80 |doi=10.7257/1053-816X.2011.31.3.173 |pmid=21805756}}</ref>

The first to examine the ureter through an internal approach, called ureteroscopy, rather than surgery was [Hampton Young](/source/Hampton_Young) in 1929.<ref name="Tefekli2013" /> This was improved on by [VF Marshall](/source/VF_Marshall) who is the first published use of a flexible endoscope based on [fiber optics](/source/fiber_optics), which occurred in 1964.<ref name="Tefekli2013" /> 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.<ref name="Tefekli2013" />

<!--Imaging-->The first [radiological imaging](/source/radiology) of the ureters was by [X-ray](/source/X-ray)s, 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.<ref name="RadiologyHistory2013">{{cite book |last1=Thomas |first1=Adrian M. K. |last2=Banerjee |first2=Arpan K. |title=The History of Radiology |date=2013 |publisher=OUP Oxford |isbn=978-0-19-166971-2 |language=en |chapter=Contrast media and the renal tract|chapter-url=https://books.google.com/books?id=y44bO1oCho8C&pg=PT93}}</ref> More useful images were able to be produced when [Edwin Hurry Fenwick](/source/Edwin_Hurry_Fenwick) in 1908 pioneered the use of tubes covered in {{wikt-lang|en|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).<ref name="RadiologyHistory2013" /> Unfortunately, much of the earlier retrograde pyelograms were complicated by significant damage to the kidneys as a result of contrast based on [silver](/source/silver) or [sodium iodide](/source/sodium_iodide).<ref name="RadiologyHistory2013" /> Hryntshalk in 1929 pioneered the development of the [intravenous urogram](/source/intravenous_urogram), in which contrast is injected into a vein and highlights the kidney and, when excreted, the urinary tract.<ref name="RadiologyHistory2013" /> Things improved with the development by [Moses Swick](/source/Moses_Swick) and [Leopold Lichtwitz](/source/Leopold_Lichtwitz) in the late 1920s of relatively nontoxic contrast media, with controversy surrounding publication as to who was the primary discoverer.<ref name="RadiologyHistory2013" /> Side-effects associated with imaging improved even more when [Tosten Almen](/source/Tosten_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.<ref name="RadiologyHistory2013" />

==References==
{{Reflist}}

{{Human systems and organs}}
{{Urinary system anatomy}}

{{Authority control}}

Category:Abdomen
Category:Urinary system
Category:Kidney

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Adapted from the Wikipedia article [Ureter](https://en.wikipedia.org/wiki/Ureter) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Ureter?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.