Editing Pancreas (section)

== Structure  ==
[[File:Pancreas and nearby organs.jpg|thumb|The pancreas (shown here in pink) sits behind the [[stomach]], with the body near the curvature of the [[duodenum]], and the tail stretching to touch the [[spleen]].]]

The pancreas is an organ that in humans lies in the [[abdomen]], stretching from behind the [[stomach]] to the left upper abdomen near the [[spleen]]. In adults, it is about {{convert|12|-|15|cm}} long, {{wt|en|lobulated}}, and salmon-coloured in appearance.{{sfn|Gray's|2016|pp=1179–1189}}

Anatomically, the pancreas is divided into a ''head'', ''neck'', ''body'', and ''tail''. The pancreas stretches from the inner curvature of the [[duodenum]], where the head surrounds two [[blood vessel]]s: the [[superior mesenteric artery]] and [[superior mesenteric vein|vein]]. The longest part of the pancreas, the body, stretches across behind the stomach, and the tail of the pancreas ends adjacent to the [[spleen]].{{sfn|Gray's|2016|pp=1179–1189}}

Two ducts, the [[main pancreatic duct]] and a smaller [[accessory pancreatic duct]] run through the body of the pancreas. The main pancreatic duct joins with the [[common bile duct]] forming a small ballooning called the [[ampulla of Vater]] (hepatopancreatic ampulla). This ampulla is surrounded by a muscle, the [[sphincter of Oddi]]. This ampulla opens into the descending part of the [[duodenum]]. The opening of the [[common bile duct]] into [[Pancreatic duct|main pancreatic duct]] is controlled by [[sphincter of Boyden]]. The [[accessory pancreatic duct]] opens into [[duodenum]] with separate openings located above the opening of the [[Pancreatic duct|main pancreatic duct]].{{sfn|Gray's|2016|pp=1179–1189}}

===Parts===
The head of the pancreas sits within the curvature of the duodenum, and wraps around the superior mesenteric artery and vein. To the right sits the descending part of the duodenum, and between these travel the [[superior pancreaticoduodenal artery|superior]] and [[inferior pancreaticoduodenal artery|inferior pancreaticoduodenal arteries]]. Behind rest the [[inferior vena cava]], and the [[common bile duct]]. In front sit the [[peritoneum|peritoneal membrane]] and the [[transverse colon]].{{sfn|Gray's|2016|pp=1179–1189}} A small [[uncinate process of pancreas|uncinate process]] emerges from below the head, situated behind the [[superior mesenteric vein]] and sometimes [[superior mesenteric artery|artery]].{{sfn|Gray's|2016|pp=1179–1189}}

The neck of the pancreas separates the head of the pancreas, located in the curvature of the duodenum, from the body. The neck is about {{convert|2|cm|abbr=on}} wide, and sits in front of where the [[portal vein]] is formed. The neck lies mostly behind the pylorus of the stomach, and is covered with peritoneum. The  [[anterior superior pancreaticoduodenal artery]] travels in front of the neck of the pancreas.{{sfn|Gray's|2016|pp=1179–1189}}

The body is the largest part of the pancreas, and mostly lies behind the stomach, tapering along its length. The peritoneum sits on top of the body of the pancreas, and the [[transverse colon]] in front of the peritoneum.{{sfn|Gray's|2016|pp=1179–1189}} Behind the pancreas are several blood vessels, including the [[aorta]], the [[splenic vein]], and the [[left renal vein]], as well as the beginning of the [[superior mesenteric artery]].{{sfn|Gray's|2016|pp=1179–1189}} Below the body of the pancreas sits some of the [[small intestine]], specifically the last part of the duodenum and the [[jejunum]] to which it connects, as well as the [[suspensory ligament of the duodenum]] which falls between these two. In front of the pancreas sits the transverse colon.{{sfn|Gray's|2008|pp=1183-1190}}

The pancreas narrows towards the tail, which sits near to the spleen.{{sfn|Gray's|2016|pp=1179–1189}} It is usually between {{convert|1.3|-|3.5|cm|abbr=on}} long, and sits between the layers of the [[splenorenal ligament|ligament between the spleen and the left kidney]]. The [[splenic artery]] and [[splenic vein|vein]], which also passes behind the body of the pancreas, pass behind the tail of the pancreas.{{sfn|Gray's|2016|pp=1179–1189}}

===Blood supply===
The pancreas has a rich blood supply, with vessels originating as branches of both the [[coeliac artery]] and [[superior mesenteric artery]].{{sfn|Gray's|2016|pp=1179–1189}} The [[splenic artery]], the largest branch of the celiac trunk, runs along the top of the pancreas, and supplies the left part of the body and the tail of the pancreas through its pancreatic branches, the largest of which is called the [[greater pancreatic artery]].{{sfn|Gray's|2016|pp=1179–1189}} The [[superior pancreaticoduodenal artery|superior]] and [[inferior pancreaticoduodenal arteries]] run along the back and front surfaces of the head of the pancreas adjacent to the duodenum. These supply the head of the pancreas. These vessels join together ({{wt|en|anastamose}}) in the middle.{{sfn|Gray's|2016|pp=1179–1189}}

The body and neck of the pancreas drain into the [[splenic vein]], which sits behind the pancreas.{{sfn|Gray's|2016|pp=1179–1189}} The head drains into, and wraps around, the [[superior mesenteric vein|superior mesenteric]] and [[portal vein]]s, via the [[pancreaticoduodenal vein]]s.{{sfn|Gray's|2016|pp=1179–1189}}

The pancreas drains into lymphatic vessels that travel alongside its [[artery|arteries]], and has a rich lymphatic supply.{{sfn|Gray's|2016|pp=1179–1189}} The [[lymphatic vessel]]s of the body and tail drain into [[splenic lymph nodes]], and eventually into [[Preaortic lymph nodes|lymph nodes that lie in front of the aorta]], between the coeliac and superior mesenteric arteries. The lymphatic vessels of the head and neck drain into intermediate lymphatic vessels around the pancreaticoduodenal, mesenteric and hepatic arteries, and from there into the lymph nodes that lie in front of the aorta.{{sfn|Gray's|2016|pp=1179–1189}}

===Microanatomy===
[[File:Langerhanssche Insel.jpg|thumb|This image shows a [[pancreatic islet]] when pancreatic tissue is stained and viewed under a microscope. Parts of the digestive ("exocrine") pancreas can be seen around the islet, more darkly. These contain hazy dark purple granules of inactive digestive enzymes ([[zymogen]]s).]]
[[File:Human pancreatic islet.jpg|thumb|A pancreatic islet that uses [[immunohistochemistry|fluorescent antibodies]] to show the location of different cell types in the pancreatic islet. Antibodies against glucagon, secreted by alpha cells, show their peripheral position. Antibodies against insulin, secreted by beta cells, show the more widespread and central position that these cells tend to have.{{sfn|Wheater's Histology|2013|pp=332-333}} ]]
The pancreas contains tissue with an [[endocrine]] and [[exocrine]] role, and this division is also visible when the pancreas is viewed under a microscope.{{sfn|Wheater's Histology|2013|pp=287-291}}

The majority of pancreatic [[Parenchyma|tissue]] has a digestive role. The cells with this role form clusters ([[acini]]) around small [[duct (anatomy)|ducts]], and are arranged in lobes that have thin [[fibrous tissue|fibrous]] walls. The cells of each acinus secrete inactive digestive enzymes called [[zymogen]]s into the small ''intercalated'' ducts which they surround. In each acinus, the cells are pyramid-shaped and situated around the intercalated ducts, with the [[Cell nucleus|nuclei]] resting on the [[basement membrane]], a large [[endoplasmic reticulum]], and a number of zymogen granules visible within the [[cytoplasm]]. The intercalated ducts drain into larger ''intralobular'' ducts within the lobule, and finally ''interlobular'' ducts. The ducts are lined by a single layer of [[columnar epithelium|column-shaped cells]]. There is more than one layer of cells as the diameter of the ducts increases.{{sfn|Wheater's Histology|2013|pp=287-291}}

The tissues with an [[endocrine]] role within the pancreas exist as clusters of cells called [[pancreatic islets]] (also called islets of [[Paul Langerhans|Langerhans]]) that are distributed throughout the pancreas.{{sfn|Wheater's Histology|2013|pp=332-333}} Pancreatic islets contain [[alpha cell]]s, [[beta cell]]s, and [[delta cell]]s, each of which releases a different hormone. These cells have characteristic positions, with alpha cells (secreting [[glucagon]]) tending to be situated around the periphery of the islet, and beta cells (secreting [[insulin]]) more numerous and found throughout the islet.{{sfn|Wheater's Histology|2013|pp=332-333}} [[Enterochromaffin cell]]s are also scattered throughout the islets.{{sfn|Wheater's Histology|2013|pp=332-333}} Islets are composed of up to 3,000 secretory cells, and contain several small arterioles to receive blood, and venules that allow the hormones secreted by the cells to enter the [[systemic circulation]].{{sfn|Wheater's Histology|2013|pp=332-333}}

===Variation===
The size of the pancreas varies considerably.{{sfn|Gray's|2016|pp=1179–1189}} Several [[anatomical variation]]s exist, relating to the embryological development of the two [[pancreatic bud]]s. The pancreas develops from these buds on either side of the duodenum. The [[pancreatic bud|ventral bud]] rotates to lie next to the [[pancreatic bud|dorsal bud]], eventually fusing. In about 10% of adults, an [[accessory pancreatic duct]] may be present if the main duct of the dorsal bud of the pancreas does not regress; this duct opens into the [[minor duodenal papilla]].<ref name=Langmans2019 /> If the two buds themselves, each having a duct, do not fuse, a pancreas may exist with two separate ducts, a condition known as a [[pancreas divisum]]. This condition has no physiologic consequence.<ref name="KanthMedscape">{{EMedicine|article|185307|Pancreatic Divisum}}</ref> If the ventral bud does not fully rotate, an [[annular pancreas]] may exist, where part or all of the duodenum is encircled by the pancreas. This may be associated with [[duodenal atresia]].<ref name="Noh2012">{{cite journal |last1=Noh |first1=TH |last2=Lee |first2=SE |last3=Park |first3=JM |title=Laparoscopic treatment of annular pancreas in adults: report of a case. |journal=Korean Journal of Hepato-biliary-pancreatic Surgery |date=February 2012 |volume=16 |issue=1 |pages=43–5 |doi=10.14701/kjhbps.2012.16.1.43 |pmid=26388905|pmc=4575014 }}</ref>

=== Gene and protein expression ===
{{Further |Bioinformatics#Gene and protein expression}}
10,000 protein coding genes (~50% of all human genes) are expressed in the normal human pancreas.<ref>{{Cite web|url=https://www.proteinatlas.org/humanproteome/pancreas|title=The human proteome in pancreas – The Human Protein Atlas|website=www.proteinatlas.org|access-date=2017-09-25}}</ref><ref>{{cite journal | vauthors = Uhlén M, Fagerberg L, Hallström BM, Lindskog C, Oksvold P, Mardinoglu A, Sivertsson Å, Kampf C, Sjöstedt E, Asplund A, Olsson I, Edlund K, Lundberg E, Navani S, Szigyarto CA, Odeberg J, Djureinovic D, Takanen JO, Hober S, Alm T, Edqvist PH, Berling H, Tegel H, Mulder J, Rockberg J, Nilsson P, Schwenk JM, Hamsten M, von Feilitzen K, Forsberg M, Persson L, Johansson F, Zwahlen M, von Heijne G, Nielsen J, Pontén F | display-authors = 6 | title = Proteomics. Tissue-based map of the human proteome | journal = Science | volume = 347 | issue = 6220 | page = 1260419 | date = January 2015 | pmid = 25613900 | doi = 10.1126/science.1260419 | s2cid = 802377 }}</ref> Less than 100 of these genes are specifically expressed in the pancreas. Similar to the [[salivary gland]]s, most pancreas-specific genes encode for secreted proteins. Corresponding pancreas-specific proteins are either expressed in the exocrine cellular compartment and have functions related to digestion or food uptake such as digestive [[chymotrypsinogen]] enzymes and pancreatic lipase [[Pancreatic lipase family|PNLIP]], or are expressed in the various cells of the endocrine [[pancreatic islets]] and have functions related to secreted hormones such as [[insulin]], [[glucagon]], [[somatostatin]] and [[pancreatic polypeptide]].<ref>{{cite journal | vauthors = Danielsson A, Pontén F, Fagerberg L, Hallström BM, Schwenk JM, Uhlén M, Korsgren O, Lindskog C | display-authors = 6 | title = The human pancreas proteome defined by transcriptomics and antibody-based profiling | journal = PLOS ONE | volume = 9 | issue = 12 | pages = e115421 | date = 2014-12-29 | pmid = 25546435 | pmc = 4278897 | doi = 10.1371/journal.pone.0115421 | bibcode = 2014PLoSO...9k5421D | doi-access = free }}</ref>