Editing Bladder (section)

==Structure==
{{Further|Urination#Anatomy of the bladder and outlet}}
[[File:Position of the urinary bladder 1.png|thumb|Male and female urinary bladders in lateral cross-section]]

In humans, the bladder is a hollow muscular organ situated at the base of the [[pelvis]]. <!-- Shape -->In [[gross anatomy]], the bladder can be divided into a broad {{wt|en|fundus}} (base), a body, an apex, and a neck.<ref name="Netter" /> The apex (also called the vertex) is directed forward toward the upper part of the [[pubic symphysis]], and from there the [[median umbilical ligament]] continues upward on the back of the anterior abdominal wall to the [[Navel|umbilicus]]. The [[peritoneum]] is carried by it from the apex on to the [[abdominal wall]] to form the [[middle umbilical fold]]. The neck of the bladder is the area at the base of the [[trigone of the urinary bladder|trigone]] that surrounds the [[internal urethral orifice]] that leads to the urethra.<ref name="Netter">{{cite book|last1= Netter|first1= Frank H.|title= Atlas of Human Anatomy Including Student Consult Interactive Ancillaries and Guides|date= 2014|publisher= W B Saunders Co|location= Philadelphia, Penn.|isbn= 978-14557-0418-7|pages= 346–8|edition= 6th}}</ref> In males, the neck of the urinary bladder is next to the [[prostate gland]].

<!-- Openings -->The bladder has three openings. The two [[ureter]]s enter the bladder at [[Ureter#Structure|ureteric orifices]], and the [[urethra]] enters at the [[Trigone of the urinary bladder|trigone of the bladder]]. These ureteric openings have mucosal flaps in front of them that act as valves in preventing the backflow of urine into the ureters,<ref name="SEER">{{cite web|title= SEER Training:Urinary Bladder|url= https://training.seer.cancer.gov/anatomy/urinary/components/bladder.html|website= training.seer.cancer.gov|language= en}}</ref> known as [[vesicoureteral reflux]]. Between the two ureteric openings is a raised area of tissue called the interureteric crest.<ref name="Netter" /> This makes the upper boundary of the trigone. The trigone is an area of [[smooth muscle]] that forms the floor of the bladder above the urethra.<ref name="Viana">{{cite journal | vauthors = Viana R, Batourina E, Huang H, Dressler GR, Kobayashi A, Behringer RR, Shapiro E, Hensle T, Lambert S, Mendelsohn C | title = The development of the bladder trigone, the center of the anti-reflux mechanism | journal = Development | volume = 134 | issue = 20 | pages = 3763–9 | date = October 2007 | pmid = 17881488 | doi = 10.1242/dev.011270| doi-access = free }}</ref> It is an area of smooth tissue for the easy flow of urine into and from this part of the bladder - in contrast to the irregular surface formed by the rugae.

<!-- Walls -->The walls of the bladder have a series of ridges, thick mucosal folds known as [[rugae]] that allow for the expansion of the bladder. The [[detrusor muscle]] is the muscular layer of the wall made of [[smooth muscle]] [[muscle fibers|fibers]] arranged in spiral, longitudinal, and circular bundles.<ref name="Wheaters2013" /> The detrusor muscle is able to change its length. It can also contract for a long time whilst [[urination|voiding]], and it stays relaxed whilst the bladder is filling.<ref name="Andersson">{{cite journal | vauthors = Andersson KE, Arner A | title = Urinary bladder contraction and relaxation: physiology and pathophysiology | journal = Physiol. Rev. | volume = 84 | issue = 3 | pages = 935–86 | date = July 2004 | pmid = 15269341 | doi = 10.1152/physrev.00038.2003 | citeseerx = 10.1.1.324.7009 }}</ref> The wall of the urinary bladder is normally 3–5&nbsp;mm thick.<ref name="Patel2010" /> When well distended, the wall is normally less than 3&nbsp;mm.

=== Nearby structures ===
[[File:Prostatelead.jpg|thumb|240px|Bladder location and associated structures in the male]]

In males, the [[Prostate|prostate gland]] lies outside the opening for the urethra. The middle lobe of the prostate causes an elevation in the mucous membrane behind the internal urethral orifice called the uvula of urinary bladder. The uvula can enlarge when the prostate becomes enlarged.

The bladder is located below the [[peritoneal cavity]] near the [[pelvic floor]] and behind the [[pubic symphysis]]. In males, it lies in front of the rectum, separated by the [[rectovesical pouch]], and is supported by fibres of the [[levator ani]] and of the prostate gland. In females, it lies in front of the [[uterus]], separated by the [[vesicouterine pouch]], and is supported by the elevator ani and the upper part of the [[vagina]].<ref name=Patel2010>[https://books.google.com/books?id=Z4t3dnDR1e8C&pg=PA12 Page 12] in: {{cite book|title= Imaging and Urodynamics of the Lower Urinary Tract|author= Uday Patel|publisher= Springer Science & Business Media|year= 2010|isbn= 9781848828360}}</ref>

===Blood and lymph supply===
The bladder receives blood by the [[vesical arteries]] and drained into a network of [[vesical veins]].<ref name="Grays2016" /> The [[superior vesical artery]] supplies blood to the upper part of the bladder. The lower part of the bladder is supplied by the [[inferior vesical artery]], both of which are branches of the [[internal iliac arteries]].<ref name="Grays2016" /> In females, the [[uterine arteries|uterine]] and [[vaginal arteries]] provide additional blood supply.<ref name="Grays2016" /> Venous drainage begins in a network of small vessels on the lower {{wt|en|lateral}} surfaces of the bladder, which coalesce and travel with the lateral ligaments of the bladder into the [[internal iliac vein]]s.<ref name="Grays2016" />

The [[lymphatic system|lymph]] drained from the bladder begins in a series of networks throughout the mucosal, muscular and serosal layers. These then form three sets of vessels: one set near the trigone draining the bottom of the bladder; one set draining the top of the bladder; and another set draining the outer undersurface of the bladder. The majority of these vessels drain into the [[external iliac lymph nodes]].<ref name="Grays2016" />

=== Nerve supply ===
The bladder receives both sensory and motor supply from [[sympathetic nervous system|sympathetic]] and the [[parasympathetic nervous system]]s.<ref name="Grays2016" /> The motor supply from both sympathetic fibers, most of which arise from the [[superior hypogastric plexus|superior]] and [[inferior hypogastric plexus]]es and nerves, and from parasympathetic fibers, which come from the [[pelvic splanchnic nerves]].<ref name="Moore227">{{cite book|last= Moore|first= Keith|title= Essential Clinical Anatomy, Third Edition|year= 2007|publisher= Lippincott Williams & Wilkins|isbn= 978-0-7817-6274-8|pages= 227–228|author2= Anne Agur }}</ref>

Sensation from the bladder, relating to distension or to irritation (such as by infection or a stone) is transmitted primarily through the parasympathetic nervous system.<ref name="Grays2016" /> These travel via [[sacral nerves]] to [[sacral nerve roots|S2-4]].<ref name=Ganong2019 /> From here, sensation travels to the [[human brain|brain]] via the [[dorsal columns]] in the [[spinal cord]].<ref name=Grays2016 />

===Microanatomy===
When [[Histology|viewed under a microscope]], the bladder can be seen to have an inner lining (called [[epithelium]]), three layers of muscle fibres, and an outer [[adventitia]].<ref name=Wheaters2013 >{{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 |date=2013|isbn=9780702047473 |edition=6th|chapter=Urinary system|pages=315–7}}</ref>

The inner wall of the bladder is called [[urothelium]], a type of [[transitional epithelium]] formed by three to six layers of cells; the cells may become more cuboidal or flatter depending on whether the bladder is empty or full.<ref name=Wheaters2013 /> Additionally, these are lined with a [[mucous membrane]] consisting of a surface [[glycocalyx]] that protects the cells beneath it from urine.<ref name="Urothelium">{{cite journal |last1=Stromberga |first1=Z |last2=Chess-Williams |first2=R |last3=Moro |first3=C |title=Histamine modulation of urinary bladder urothelium, lamina propria and detrusor contractile activity via H1 and H2 receptors. |journal=Scientific Reports |date=7 March 2019 |volume=9 |issue=1 |pages=3899 |doi=10.1038/s41598-019-40384-1 |pmid=30846750|pmc=6405771 |bibcode=2019NatSR...9.3899S }}</ref> The epithelium lies on a thin [[basement membrane]], and a [[lamina propria]].<ref name=Wheaters2013 /> The mucosal lining also offers a urothelial barrier against the passing of infections.<ref name="Janssen">{{cite journal|last1= Janssen|first1= DA|title= The distribution and function of chondroitin sulfate and other sulfated glycosaminoglycans in the human bladder and their contribution to the protective bladder barrier.|journal= The Journal of Urology|date= January 2013|volume= 189|issue= 1|pages= 336–42|pmid= 23174248|doi=10.1016/j.juro.2012.09.022}}</ref>

These layers are surrounded by three layers of muscle fibres arranged as an inner layer of fibres orientated longitudinally, a middle layer of circular fibres, and an outermost layer of longitudinal fibres; these form the detrusor muscle, which can be seen with the naked eye.<ref name=Wheaters2013 />

The outside of the bladder is protected by a [[serous membrane]] called [[adventitia]].<ref name=Wheaters2013/><ref name=Fry2016rev>{{cite journal|last1= Fry|first1= CH|last2= Vahabi|first2= B|title= The Role of the Mucosa in Normal and Abnormal Bladder Function.|journal= Basic & Clinical Pharmacology & Toxicology|date= October 2016|volume= 119|issue= Suppl 3|pages= 57–62|doi= 10.1111/bcpt.12626|pmid= 27228303|pmc=5555362}}</ref>

<gallery>
File:Gray1141.png|Vertical section of bladder wall
File:Urinary bladder.JPG|Layers of the bladder wall and cross-section of the detrusor muscle
File:2605 The Bladder.jpg|Anatomy of the male bladder, showing transitional epithelium and part of the wall in a histological cut-out
</gallery>

===Development===
{{Further|Development of the urinary system}}
In the developing [[embryo]], at the hind end lies a [[Cloaca (embryology)|cloaca]]. This, over the fourth to the seventh week, divides into a [[urogenital sinus]] and the beginnings of the [[anal canal]], with a wall forming between these two inpouchings called the [[urorectal septum]].<ref name=Langman2019>{{cite book |last1=Sadley |first1=TW |title=Langman's medical embryology |date=2019|location=Philadelphia|publisher=Wolters Kluwer |isbn=9781496383907 |edition=14th|section=Bladder and urethra|pages=263–66}}</ref> The urogenital sinus divides into three parts, with the upper and largest part becoming the bladder; the middle part becoming the [[urethra]], and the lower part changes depending on the biological sex of the embryo.<ref name=Langman2019 />

The human bladder derives from the [[urogenital sinus]], and it is initially continuous with the [[allantois]]. The upper and lower parts of the bladder develop separately and join around the middle part of [[prenatal development|development]].<ref name="Viana"/> At this time the ureters move from the [[mesonephric duct]]s to the trigone.<ref name="Viana"/> In males, the base of the bladder lies between the rectum and the pubic symphysis. It is superior to the [[prostate]], and separated from the [[rectum]] by the [[recto-vesical pouch]]. In females, the bladder sits inferior to the uterus and anterior to the vagina; thus its maximum capacity is lower than in males. It is separated from the [[uterus]] by the [[vesico-uterine pouch]]. In [[infants]] and young children the urinary bladder is in the [[abdomen]] even when empty.<ref>{{cite book |author1= Moore, Keith L. |author2= Dalley, Arthur F |title= Clinically Oriented Anatomy|url= https://archive.org/details/clinicallyorient00moor_1 |url-access= registration |edition= 5th |year= 2006 |publisher= Lippincott Williams & Wilkins |isbn= 9780781736398 }}</ref>