View source for Urinary system

{{short description|Anatomical system consisting of the kidneys, ureters, urinary bladder, and the urethra}}
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{{Infobox anatomy
| Name        = Urinary system
| Latin       = systema urinarium
| Image       = Urinary system.svg
| Caption     = 1. ''Human urinary system:'' 2. [[Kidney]], 3. [[Renal pelvis]], 4. [[Ureter]], 5. [[Urinary bladder]], 6. [[Urethra]]. (Left side with [[Frontal plane#Planes|frontal section]])<br />7. [[Adrenal gland]]<br />''Vessels:'' 8. [[Renal artery]] and [[Renal vein|vein]], 9. [[Inferior vena cava]], 10. [[Abdominal aorta]], 11. [[Common iliac artery]] and [[Common iliac vein|vein]]<br />''Translucent:'' 12. [[Liver]], 13. [[Large intestine]], 14. [[Pelvis]]
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| Image2      = Urinary System (Male).png
| Caption2    = Urinary system in the male. Urine flows from the [[kidney]]s via the [[ureters]] into the [[Urinary bladder|bladder]] where it is stored until it exits the body through the [[urethra]] (longer in males, shorter in females) during urination
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| System      =
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| Vein        =
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The '''urinary system''', also known as the '''urinary tract''' or '''renal system''', is a part of the [[excretory system]] of [[Vertebrate|vertebrates]]. In humans and [[Placentalia|placental mammals]], it consists of the [[kidneys]], [[ureters]], [[urinary bladder|bladder]], and the [[urethra]]. The purpose of the urinary system is to eliminate [[urine]] from the body, regulate blood volume and blood pressure, control levels of [[Electrolyte|electrolytes]] and [[Metabolite|metabolites]], and regulate [[Acid–base homeostasis|blood pH]].<ref name="NIH">{{cite web|title=The Urinary Tract & How It Works {{!}} NIDDK|url=https://www.niddk.nih.gov/health-information/urologic-diseases/urinary-tract-how-it-works|website=National Institute of Diabetes and Digestive and Kidney Diseases}}</ref> The kidneys have an extensive blood supply via the [[Renal artery|renal arteries]] which leave the kidneys via the [[renal vein]]. Each kidney consists of functional units called [[nephrons]]. Following [[filtration]] of blood and further processing, the [[Ureter|ureters]] carry urine from the kidneys into the [[urinary bladder]]. The [[urethra]] carries urine from the bladder through the [[penis]] or [[vulva]] during [[urination]]. The female and male urinary system are very similar, differing only in the length of the urethra.<ref>{{cite encyclopedia |url=https://www.medlineplus.gov/ency/imagepages/1122.htm |title=Female urinary tract |encyclopedia=MedLine Plus Medical Encyclopedia |date=16 September 2011 |first=David |last=C. Dugdale}}</ref>

800{{ndash}}2,000 milliliters (mL) of urine are normally produced every day in a healthy human. This amount varies according to fluid intake and kidney function.

==Structure== 
[[File:3DPX-002331 Urinary collecting system 3DFile.stl|thumb|3D model of urinary system]]
The urinary system refers to the structures that produce and excrete urine. In the human urinary system there are two kidneys that are located between the dorsal body wall and parietal peritoneum on both the left and right sides. 

The formation of urine begins within the functional unit of the kidney, the nephrons. Urine then flows through the nephrons, through a system of converging tubules called collecting ducts. These collecting ducts then join to form the [[Renal calyx|minor calyces]], followed by the major calyces that ultimately join the renal pelvis. Urine flows from the renal pelvis into the ureter, which transports urine into the urinary bladder. The anatomy of the human urinary bladder and urethra differs between males and females. In males, the urethra begins at the internal urethral orifice in the trigone of the bladder, and then becomes the prostatic, membranous, bulbar, and penile urethra. Urine exits the male urethra through the [[urinary meatus]] in the [[glans penis]]. The female urethra is much shorter, beginning at the bladder neck and terminating in the [[vulval vestibule]].

===Development===
{{Main|Development of the urinary system}}

===Microanatomy===
{{See also|Urothelium}}

Under microscopy, the urinary system is covered in a unique lining called [[urothelium]], a type of [[transitional epithelium]]. Unlike the [[epithelium|epithelial]] lining of most organs, transitional epithelium can flatten and distend. Urothelium covers most of the urinary system, including the renal pelvis, ureters, and bladder.

==Function==
The main functions of the urinary system and its components are to:
* Regulate [[blood volume]] and composition (e.g. [[sodium]], [[potassium]] and [[calcium]]) 
* Regulate [[blood pressure]].
* Regulate [[pH]] [[homeostasis]] of the blood. 
* Contributes to the production of red blood cells by the [[kidney]].
* Helps synthesize [[calcitriol]] (the active form of [[Vitamin D]]). 
* Stores waste products (mainly [[urea]] and [[uric acid]]) before it and other products are removed from the body.

===Urine formation===

Average urine production in adult humans is about 1{{ndash}}2 [[litres]] (L) per day, depending on state of hydration, activity level, environmental factors, weight, and the individual's health. Producing too much or too little urine requires medical attention. [[Polyuria]] is a condition of excessive urine production (> 2.5 L/day). Conditions involving low output of urine are [[oliguria]] (< 400 mL/day) and [[anuria]] (< 100 mL/day).

The first step in urine formation is the filtration of blood in the kidneys. In a healthy human, the kidney receives between 12 and 30% of [[cardiac output]], but it averages about 20% or about 1.25 L/min.

The basic structural and functional unit of the kidney is the [[nephron]]. Its chief function is to regulate the [[concentration]] of [[water]] and soluble substances like [[sodium salt|sodium]] by filtering the [[blood]], reabsorbing what is needed and excreting the rest as [[urine]].

In the first part of the nephron, [[Bowman's capsule]] filters blood from the [[circulatory system]] into the tubules. Hydrostatic and osmotic pressure gradients facilitate filtration across a semipermeable membrane. The filtrate includes water, small molecules, and ions that easily pass through the filtration membrane. However, larger molecules such as [[proteins]] and [[blood cell]]s are prevented from passing through the filtration membrane. The amount of filtrate produced every minute is called the [[glomerular filtration rate]] or GFR and amounts to 180 litres per day. About 99% of this filtrate is reabsorbed as it passes through the nephron and the remaining 1% becomes urine.

The urinary system is regulated by the [[endocrine system]] by [[hormone]]s such as [[antidiuretic hormone]], [[aldosterone]], and [[parathyroid hormone]].<ref>{{cite book | last = Maton | first = Anthea | author2 = Jean Hopkins | author3 = Charles William McLaughlin | author4 = Susan Johnson | author5 = Maryanna Quon Warner | author6 = David LaHart | author7 = Jill D. Wright | title = Human Biology and Health | publisher = Prentice Hall | year = 1993 | location = Englewood Cliffs, New Jersey, USA | url = https://archive.org/details/humanbiologyheal00scho | isbn = 0-13-981176-1 | url-access = registration }}</ref>

====Regulation of concentration and volume====

The urinary system is under influence of the [[circulatory system]], [[nervous system]], and [[endocrine system]].

[[Aldosterone]] plays a central role in regulating blood pressure through its effects on the kidney. It acts on the distal tubules and collecting ducts of the nephron and increases reabsorption of sodium from the glomerular filtrate. Reabsorption of sodium results in retention of water, which increases blood pressure and blood volume. Antidiuretic hormone (ADH), is a [[neurohypophysial hormone]] found in most [[mammals]]. Its two primary functions are to retain water in the body and [[vasoconstriction]]. Vasopressin regulates the body's [[Water retention (medicine)|retention of water]] by increasing water reabsorption in the collecting ducts of the kidney nephron.<ref name="isbn0-387-30348-0">{{cite book | vauthors = Caldwell HK, ((Young WS III)), Lajtha A, Lim R | title = Handbook of Neurochemistry and Molecular Neurobiology: Neuroactive Proteins and Peptides | edition = 3rd | publisher = Springer | location = Berlin | year = 2006 | chapter = Oxytocin and Vasopressin: Genetics and Behavioral Implications | chapter-url = http://refworks.springer.com/mrw/fileadmin/pdf/Neurochemistry/0387303480C25.PDF | pages = 573–607 | isbn = 0-387-30348-0 | archive-date = 2011-05-04 | access-date = 2013-03-06 | archive-url = https://web.archive.org/web/20110504131252/http://refworks.springer.com/mrw/fileadmin/pdf/Neurochemistry/0387303480C25.PDF }}</ref> Vasopressin increases water permeability of the kidney's collecting duct and distal convoluted tubule by inducing translocation of aquaporin-CD water channels in the kidney nephron collecting duct plasma membrane.<ref name="pmid7532304">{{cite journal |vauthors=Nielsen S, Chou CL, Marples D, Christensen EI, Kishore BK, Knepper MA | title = Vasopressin increases water permeability of kidney collecting duct by inducing translocation of aquaporin-CD water channels to plasma membrane | journal = Proc. Natl. Acad. Sci. U.S.A. | volume = 92 | issue = 4 | pages = 1013–7 |date=February 1995 | pmid = 7532304 | pmc = 42627 | doi = 10.1073/pnas.92.4.1013| bibcode = 1995PNAS...92.1013N | doi-access = free }}</ref>

===Urination===
{{main|Urination}}

Urination, also sometimes referred to as micturition, is the ejection of [[urine]] from the [[urinary bladder]] to the outside of the body. Urine is ejected through the [[urethra]] from the [[penis]] or [[vulva]] in [[Placentalia|placental mammals]] and through the [[cloaca]] in other [[vertebrate]]s. In healthy humans (and [[Urination#Animals|many other animals]]), the process of urination is under voluntary control. In infants, some elderly individuals, and those with neurological injury, urination may occur as an involuntary [[reflex]]. Physiologically, micturition involves coordination between the [[central nervous system|central]], [[autonomic nervous system|autonomic]], and [[somatic nervous system]]s. Brain centers that regulate urination include the [[pontine micturition center]], [[periaqueductal gray]], and the [[cerebral cortex]].

==Clinical significance==
{{Main|Urologic disease}} 
{{Further |Urinary tract infection}}

[[Urologic disease]] can involve congenital or acquired dysfunction of the urinary system. As an example, [[urinary tract obstruction]] is a urologic disease that can cause [[urinary retention]].

Diseases of the kidney tissue are normally treated by [[nephrologist]]s, while diseases of the urinary tract are treated by [[urologist]]s. [[Gynecology|Gynecologists]] may also treat female urinary incontinence.

Diseases of other bodily systems also have a direct effect on urogenital function.  For instance, it has been shown that [[protein]] released by the kidneys in [[diabetes mellitus]] sensitizes the kidney to the damaging effects of [[hypertension]].<ref>{{cite journal | last1 = Baba | first1 = T | last2 = Murabayashi | first2 = S | last3 = Tomiyama | first3 = T | last4 = Takebe | first4 = K | title = Uncontrolled hypertension is associated with a rapid progression of nephropathy in type 2 diabetic patients with proteinuria and preserved renal function | journal = The Tohoku Journal of Experimental Medicine | volume = 161 | issue = 4 | pages = 311–8 | year = 1990 | pmid = 2256104 | doi = 10.1620/tjem.161.311 | doi-access = free }}</ref>

[[Diabetes]] also can have a direct effect in [[urination]] due to [[peripheral neuropathy|peripheral neuropathies]], which occur in some individuals with poorly controlled blood sugar levels.<ref>{{cite web| url=http://www.patient.info/health/peripheral-neuropathy| title= Peripheral Neuropathy |publisher= Patient UK | access-date= 2014-03-20}}</ref>

[[Urinary incontinence]] can result from a weakening of the [[pelvic floor]] muscles caused by factors such as [[pregnancy]], [[childbirth]], [[ageing|aging]], and being [[overweight]]. Findings recent systematic reviews demonstrate that behavioral therapy generally results in improved urinary incontinence outcomes, especially for [[Stress incontinence|stress]] and [[Urge incontinence|urge]] UI, than medications alone.<ref>{{Cite journal|last1=Balk|first1=Ethan|last2=Adam|first2=Gaelen P.|last3=Kimmel|first3=Hannah|last4=Rofeberg|first4=Valerie|last5=Saeed|first5=Iman|last6=Jeppson|first6=Peter|last7=Trikalinos|first7=Thomas|date=2018-08-08|title=Nonsurgical Treatments for Urinary Incontinence in Women: A Systematic Review Update|url=https://effectivehealthcare.ahrq.gov/topics/urinary-incontinence-update/final-report-2018|doi=10.23970/ahrqepccer212|s2cid=80659370|doi-access=free|url-access=subscription}}{{Dead link|date=August 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{Cite journal|last1=Balk|first1=Ethan M.|last2=Rofeberg|first2=Valerie N.|last3=Adam|first3=Gaelen P.|last4=Kimmel|first4=Hannah J.|last5=Trikalinos|first5=Thomas A.|last6=Jeppson|first6=Peter C.|date=2019-04-02|title=Pharmacologic and Nonpharmacologic Treatments for Urinary Incontinence in Women: A Systematic Review and Network Meta-analysis of Clinical Outcomes|url=http://annals.org/article.aspx?doi=10.7326/M18-3227|journal=Annals of Internal Medicine|language=en|volume=170|issue=7|pages=465–479|doi=10.7326/M18-3227|pmid=30884526|s2cid=83458685|issn=0003-4819|url-access=subscription}}</ref> Pelvic floor exercises known as [[Kegel exercise]]s can help in this condition by strengthening the pelvic floor. There can also be underlying medical reasons for urinary incontinence which are often treatable. In children, the condition is called [[enuresis]].

Some cancers also target the urinary system, including [[bladder cancer]], [[kidney cancer]], [[ureteral cancer]], and [[urethral cancer]]. Due to the role and location of these organs, treatment is often complicated.{{cn|date=January 2018}}

==History==
[[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]] 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]] in 1929.<ref name="Tefekli2013" /> 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.<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 surgery|open surgical]] approaches within the urinary system employed during the preceding two millennia.<ref name="Tefekli2013" />

== See also ==
*[[Excretory system]]
*[[Major systems of the human body]]

== References ==

{{Reflist}}

== External links ==

{{Wikibooks|Human Physiology|The Urinary System}}
{{Wikibooks|Anatomy and Physiology of Animals|Urinary System}}

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