Editing Gallbladder (section)

==Structure==
The human gallbladder is a hollow grey-blue [[Organ (anatomy)|organ]] that sits in a shallow depression below the right lobe of the [[liver]].{{sfn|Gray's Anatomy|2008|p=1187-81}} In adults, the gallbladder measures approximately {{convert|7|to|10|cm|abbr=off}} in length and {{convert|4|cm|in}} in diameter when fully distended.<ref name="meilstrup">{{cite book |author=Jon W. Meilstrup |title=Imaging Atlas of the Normal Gallbladder and Its Variants |publisher=CRC Press |location=Boca Raton |year=1994 |page=4 |isbn=978-0-8493-4788-7 }}</ref> The gallbladder has a capacity of about {{convert|50|ml|impoz|abbr=off}}.{{sfn|Gray's Anatomy|2008|p=1187-81}}

The gallbladder is shaped like a pear, with its tip opening into the [[cystic duct]].<ref name="Nagral2005">{{cite journal|last1=Nagral|first1=Sanjay|title=Anatomy relevant to cholecystectomy|journal=Journal of Minimal Access Surgery|date=2005|volume=1|issue=2|pages=53–8|doi=10.4103/0972-9941.16527|pmid=21206646|pmc=3004105 |doi-access=free }}</ref> The gallbladder is divided into three sections: the ''fundus'', ''body'', and ''neck''. The ''fundus'' is the rounded base, angled so that it faces the [[abdominal wall]]. The ''body'' lies in a depression in the surface of the lower liver. The ''neck'' tapers and is continuous with the [[cystic duct]], part of the [[biliary tree]].{{sfn|Gray's Anatomy|2008|p=1187-81}} The gallbladder fossa, against which the fundus and body of the gallbladder lie, is found beneath the junction of [[hepatic segments]] IVB and V.<ref>Shakelford's Surgery of Alimentary Tract, ed.7. 2013</ref> The cystic duct unites with the [[common hepatic duct]] to become the [[common bile duct]]. At the junction of the neck of the gallbladder and the cystic duct, there is an out-pouching of the gallbladder wall forming a mucosal fold known as "[[Henri Albert Hartmann|Hartmann]]'s pouch".{{sfn|Gray's Anatomy|2008|p=1187-81}}

Lymphatic drainage of the gallbladder follows the cystic node, which is located between the cystic duct and the common hepatic duct. Lymphatics from the lower part of the organ drain into lower [[hepatic lymph nodes]]. All the lymph finally drains into [[celiac lymph nodes]].

===Microanatomy===
[[File:Gallbladder - intermed mag.jpg|thumb|[[Micrograph]] of a normal gallbladder wall. [[H&E stain]].]]
The gallbladder wall is composed of a number of layers. The innermost surface of the gallbladder wall is lined by a single layer of [[columnar epithelia|columnar cells]] with a [[brush border]] of [[microvilli]], very similar to intestinal absorptive cells.{{sfn|Gray's Anatomy|2008|p=1187-81}} Underneath the epithelium is an underlying [[lamina propria]], a [[muscular layer]], an outer perimuscular layer and [[serosa]]. Unlike elsewhere in the intestinal tract, the gallbladder does not have a [[muscularis mucosae]], and the muscular fibres are not arranged in distinct layers.<ref name=WHEATERS>{{cite book| first2=Philip J. | last2=Deakin (drawings) | first1=Barbara | last1=Young | title=Wheater's functional histology: a text and colour atlas | url=https://archive.org/details/wheatersfunction00youn | url-access=limited | year=2006 | publisher=Churchill Livingstone/Elsevier | location=[Edinburgh?] | isbn=978-0-443-06850-8 | edition=5th | page=[https://archive.org/details/wheatersfunction00youn/page/n671 298] | display-authors=1}}</ref>

The [[mucous membrane|mucosa]], the inner portion of the gallbladder wall, consists of a [[epithelium|lining]] of a [[Simple columnar epithelium|single layer of columnar]] cells, with cells possessing small hair-like attachments called [[microvilli]].{{sfn|Gray's Anatomy|2008|p=1187-81}} This sits on a thin layer of connective tissue, the [[lamina propria]].<ref name=WHEATERS /> The mucosa is curved and collected into tiny outpouchings called ''rugae''.{{sfn|Gray's Anatomy|2008|p=1187-81}}

A muscular layer sits beneath the mucosa. This is formed by [[smooth muscle]], with fibres that lie in longitudinal, oblique and transverse directions, and are not arranged in separate layers. The muscle fibres here contract to expel bile from the gallbladder.<ref name=WHEATERS /> A distinctive feature of the gallbladder is the presence of ''Rokitansky–Aschoff sinuses'', deep outpouchings of the mucosa that can extend through the muscular layer, and which indicate [[adenomyomatosis]].<ref name="ross">{{cite book|title=Histology: A Text and Atlas|url=https://archive.org/details/histologytextatl00ross_530|url-access=limited|publisher=Lippincott Williams & Wilkins|last1=Ross|first1=M.|last2=Pawlina|first2=W.|year=2011|isbn=978-0-7817-7200-6|page=[https://archive.org/details/histologytextatl00ross_530/page/n665 646]|edition=6th}}</ref> The muscular layer is surrounded by a layer of connective and [[adipose tissue|fat]] tissue.{{sfn|Gray's Anatomy|2008|p=1187-81}}

The outer layer of the fundus of gallbladder, and the surfaces not in contact with the liver, are covered by a thick [[serosa]], which is exposed to the [[peritoneum]].{{sfn|Gray's Anatomy|2008|p=1187-81}} The serosa contains blood vessels and lymphatics.<ref name=WHEATERS /> The surfaces in contact with the liver are covered in [[connective tissue]].{{sfn|Gray's Anatomy|2008|p=1187-81}}

===Variation===
[[File:Gallbladder and common bile duct ultrasound.jpg|thumb|left|[[Abdominal ultrasonography]] showing gallbladder and common bile duct]]
The gallbladder varies in size, shape, and position among different people.{{sfn|Gray's Anatomy|2008|p=1187-81}} Rarely, two or even three gallbladders may coexist, either as separate bladders draining into the cystic duct, or sharing a common branch that drains into the cystic duct. Additionally, the gallbladder may fail to form at all. Gallbladders with two lobes separated by a [[septum]] may also exist. These abnormalities are not likely to affect function and are generally asymptomatic.<ref>{{cite journal|last=Leeuw|first=Th.G.|author2=Verbeek, P.C.M. |author3=Rauws, E.A.J. |author4= Gouma, D.J. |title=A double or bilobar gallbladder as a cause of severe complications after (laparoscopic) cholecystectomy|journal=Surgical Endoscopy|date=September 1995|volume=9|issue=9|doi=10.1007/BF00188459 |pmid=7482221|pages=998–1000|s2cid=2581053}}</ref>

The location of the gallbladder in relation to the liver may also vary, with documented variants including gallbladders found within,<ref>{{cite journal|last1=Segura-Sampedro |first1=JJ |last2=Navarro-Sánchez |first2=A |last3=Ashrafian |first3=H |last4=Martínez-Isla |first4=A |title=Laparoscopic approach to the intrahepatic gallbladder. A case report. |journal=Revista Espanola de Enfermedades Digestivas |date=February 2015 |volume=107 |issue=2 |pages=122–3 |pmid=25659400 |url=http://www.grupoaran.com/mrmUpdate/lecturaPDFfromXML.asp?IdArt=4621099&TO=RVN&Eng=1 |url-status=dead |archive-url=https://web.archive.org/web/20160304040204/http://www.grupoaran.com/mrmUpdate/lecturaPDFfromXML.asp?IdArt=4621099&TO=RVN&Eng=1 |archive-date=March 4, 2016 |df=mdy }}</ref> above, on the left side of, behind, and detached or suspended from the liver. Such variants are very rare: from 1886 to 1998, only 110 cases of left-lying liver, or less than one per year, were reported in scientific literature.<ref>{{cite journal|last=Dhulkotia|first=A|author2=Kumar, S |author3=Kabra, V |author4= Shukla, HS |title=Aberrant gallbladder situated beneath the left lobe of liver|journal=HPB|date=March 1, 2002|volume=4|issue=1|pages=39–42|doi=10.1080/136518202753598726|pmid=18333151|pmc=2023911}}</ref><ref>{{cite journal|last1=Naganuma|first1=S.|last2=Ishida |first2=H. |last3=Konno |first3=K. |last4=Hamashima |first4=Y. |last5=Hoshino |first5=T. |last6=Naganuma |first6=H. |last7=Komatsuda |first7=T. |last8=Ohyama |first8=Y. |last9=Yamada |first9=N. |last10=Ishida |first10=J. |last11=Masamune |first11=O.|title=Sonographic findings of anomalous position of the gallbladder|journal=Abdominal Imaging|date=March 6, 2014|volume=23|issue=1|pages=67–72|doi=10.1007/s002619900287|pmid=9437066|s2cid=30176379}}</ref>{{sfn|Gray's Anatomy|2008|p=1187-81}}

An [[anatomical variation]] can occur, known as a [[Phrygian cap (anatomy)|Phrygian cap]], which is an innocuous fold in the fundus, named after its resemblance to the [[Phrygian cap]].<ref name="pmid1950867">{{cite journal | author=Meilstrup JW | author2=Hopper KD | author3=Thieme GA | title=Imaging of gallbladder variants | journal=AJR Am J Roentgenol | volume=157 | issue=6 | pages=1205–8 | date=December 1991 | pmid=1950867 | doi= 10.2214/ajr.157.6.1950867 | url=http://www.ajronline.org/cgi/pmidlookup?view=long&pmid=1950867| url-access=subscription }}</ref>

===Development===
The gallbladder develops from an [[endoderm]]al outpouching of the embryonic gut tube.<ref name= LARSEN2009 /> Early in development, the human embryo has three [[germ layer]]s and abuts an embryonic [[yolk sac]]. During the second week of [[human embryogenesis|embryogenesis]], as the embryo grows, it begins to surround and envelop portions of this sac. The enveloped portions form the basis for the adult gastrointestinal tract. Sections of this [[foregut]] begin to differentiate into the organs of the gastrointestinal tract, such as the [[esophagus]], [[stomach]], and [[intestine]]s.<ref name= LARSEN2009 />

During the fourth week of embryological development, the stomach rotates. The stomach, originally lying in the midline of the embryo, rotates so that its body is on the left. This rotation also affects the part of the gastrointestinal tube immediately below the stomach, which will go on to become the [[duodenum]]. By the end of the fourth week, the developing duodenum begins to spout a small outpouching on its right side, the [[hepatic diverticulum]], which will go on to become the [[hepatobiliary system|biliary tree]]. Just below this is a second outpouching, known as the ''cystic diverticulum'', that will eventually develop into the gallbladder.<ref name=LARSEN2009>{{cite book|first=Gary C. |last=Schoenwolf |display-authors=etal|title=Larsen's human embryology|year=2009|publisher=Churchill Livingstone/Elsevier|location=Philadelphia|isbn=978-0-443-06811-9|chapter=Development of the Gastrointestinal Tract|edition=4th}}</ref>