View source for Duodenum

{{Short description|First section of the small intestine}}
{{for|the song|Duodenum (song)}}
{{Infobox anatomy
| Name        = Duodenum
| Latin       = duodenum
| Image       = Tractus intestinalis duodenum.svg
| Caption     = Image of the [[Human gastrointestinal tract|gastrointestinal tract]], with the duodenum highlighted.
| Width       =
| Image2      = Duodenumanatomy.jpg
| Caption2    = Diagram of the human duodenum with major parts labelled
| Precursor   = [[Foregut]] (1st and 2nd parts), [[midgut]] (3rd and 4th part)
| System      = [[Digestion|Digestive system]]
| PartOf      = [[Small intestine]]
| Pronunciation = {{IPAc-en|ˌ|dj|uː|ə|ˈ|d|iː|n|ə|m}}, {{IPAc-en|usalso|dj|u|ˈ|ɒ|d|ɪ|n|ə|m}}<ref>{{cite EPD|18}}</ref>
| Artery      = [[Inferior pancreaticoduodenal artery]], [[superior pancreaticoduodenal artery]]
| Vein        = [[Pancreaticoduodenal veins]]
| Nerve       = [[Celiac ganglia]], [[vagus]]<ref>{{cite book| title= Essentials of Human Physiology| first= Thomas M. |last= Nosek| chapter=Section 6/6ch2/s6ch2_30 |chapter-url=http://humanphysiology.tuars.com/program/section6/6ch2/s6ch2_30.htm |archive-url=https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section6/6ch2/s6ch2_30.htm|archive-date=2016-03-24}}</ref>
| Lymph       =
}}
{{Gastrointestinal tract sidebar}}
The '''duodenum''' is the first section of the [[small intestine]]<ref name="National Cancer Institute">{{cite web | title=NCI Dictionary of Cancer Terms | website=National Cancer Institute | url=https://www.cancer.gov/publications/dictionaries/cancer-terms | access-date=2022-06-07 | quote=The first part of the small intestine. It connects to the stomach. The duodenum helps to further digest food coming from the stomach. It absorbs nutrients (vitamins, minerals, carbohydrates, fats, proteins) and water from food so they can be used by the body.}}</ref> in most [[vertebrates]], including [[mammals]], [[reptiles]], and [[birds]]. In mammals, it may be the principal site for [[iron]] absorption.
The duodenum precedes the [[jejunum]] and [[ileum]] and is the shortest part of the small intestine.

In humans, the duodenum is a hollow jointed tube about {{convert|25–38|cm|4=0|abbr=off}} long connecting the [[stomach]] to the jejunum, the middle part of the small intestine.<ref name="MedlinePlus">{{cite web | title=Duodenum: MedlinePlus Medical Encyclopedia | website=MedlinePlus | url=https://medlineplus.gov/ency/article/002347.htm | access-date=2022-06-07 | quote=It is located between the stomach and the middle part of the small intestine. After foods mix with stomach acid, they move into the duodenum, where they mix with bile from the gallbladder and digestive juices from the pancreas.}}</ref><ref name="Nolan 2002 pp. 247–259">{{cite book | last=Nolan | first=D. J. | title=Radiological Imaging of the Small Intestine | chapter=Radiology of the Duodenum | series=Medical Radiology | publisher=Springer Berlin Heidelberg | publication-place=Berlin, Heidelberg | year=2002 | isbn=978-3-642-62993-8 | issn=0942-5373 | doi=10.1007/978-3-642-56231-0_6 | pages=247–259 | quote=duodenum is a C-shaped hollow organ forming an incomplete circle around the head of the pancreas. ...it is normally examined as part of the upper gastrointestinal tract. | chapter-url=https://link.springer.com/chapter/10.1007/978-3-642-56231-0_6}}</ref> It begins with the [[duodenal bulb]], and ends at the [[duodenojejunal flexure]] marked by the  [[suspensory muscle of duodenum]].<ref>{{cite journal |author=van Gijn J |title=Treitz and his ligament. |journal=Ned. Tijdschr. Geneeskd. |volume=155 |issue=8 |year=2011 |pmid=21557825 |author2=Gijselhart JP |pages=A2879}}</ref> The duodenum can be divided into four parts: the first (superior), the second (descending), the third (transverse) and the fourth (ascending) parts.<ref name="Nolan 2002 pp. 247–259"/>

==Overview==
The duodenum is the first section of the [[small intestine]] in most [[higher vertebrates]], including [[mammals]], [[reptiles]], and [[birds]]. In [[fish]], the divisions of the small intestine are not as clear, and the terms ''anterior intestine'' or ''proximal intestine'' may be used instead of duodenum.<ref name="fish_feeding_book">
{{cite book |last=Guillaume |first=Jean |url=https://books.google.com/books?id=As0flTZo_EAC&q=fish+cytology+jejunum+duodenum&pg=PA31 |title=Nutrition and Feeding of Fish and Crustaceans |author2=Praxis Publishing |author3=Sadasivam Kaushik |author4=Pierre Bergot |author5=Robert Metailler |publisher=Springer |year=2001 |isbn=978-1-85233-241-9 |page=31 |access-date=2009-01-09}}
</ref> In mammals the duodenum may be the principal site for [[iron]] absorption.<ref>{{cite journal |author=Latunde-Dada GO |author2=Van der Westhuizen J |author3=Vulpe CD |last4=Anderson |first4=G.J. |last5=Simpson |first5=R.J. |last6=McKie |first6=A.T. |display-authors=3 |year=2002 |title=Molecular and functional roles of duodenal cytochrome B (Dcytb) in iron metabolism |journal=Blood Cells Mol. Dis. |volume=29 |issue=3 |pages=356–60 |doi=10.1006/bcmd.2002.0574 |pmid=12547225}}</ref>

In humans, the duodenum is a C-shaped hollow jointed tube, {{convert|25–38|cm|4=0|abbr=off}} in length, lying adjacent to the [[stomach]] (and connecting it to the small intestine). It is divided anatomically into four sections. The first part lies within the [[peritoneum]] but its other parts are [[retroperitoneal]].<ref name="GRAYS2005" />{{rp|273}}

===Parts===
The ''first'' or ''superior part'' of the duodenum is a continuation from the [[pylorus]] to the transpyloric plane. It is superior (above) to the rest of the segments, at the [[vertebral]] level of [[lumbar vertebrae|L1]]. The [[duodenal bulb]], about {{Convert|2|cm|in|abbr=on|frac=4}} long, is the first part of the duodenum and is slightly dilated. The duodenal bulb is a remnant of the mesoduodenum, a [[mesentery]] that suspends the organ from the posterior abdominal wall in fetal life.<ref>{{cite book|last=Singh|first=Inderbir|author2=GP Pal|title=Human Embryology|publisher=Macmillan Publishers India|location=Delhi|date=2012|edition=9|page=163|chapter=13|isbn=978-93-5059-122-2}}</ref> The first part of the duodenum is mobile, and connected to the liver by the [[hepatoduodenal ligament]] of the [[lesser omentum]]. The first part of the duodenum ends at the corner, the ''superior duodenal flexure''.<ref name="GRAYS2005">{{cite book|last=Drake|first=Richard L.|title=Gray's anatomy for students|year=2005|publisher=Elsevier/Churchill Livingstone|location=Philadelphia|isbn=978-0-8089-2306-0|author2=Vogl, Wayne |author3=Tibbitts, Adam W.M. Mitchell  |author4=illustrations by Richard |author5= Richardson, Paul }}</ref>{{rp|273}}

<!-- Only the first 2 cm of the superior part is mobile (covered by [[peritoneum]]) – the [[Anatomical terms of location#Proximal and distal|distal]] 3&nbsp;cm of the first part along with the rest of the duodenum is retroperitoneal (immobile). unsourced-->Relations:{{citation needed|date=December 2013}}
* Anterior
** [[Gallbladder]]
** [[Quadrate lobe of liver]]
* Posterior
** [[Bile duct]]
** [[Gastroduodenal artery]]
** [[Portal vein]]
** [[Inferior vena cava]]
** [[Head of pancreas]]
* Superior
** [[Neck of gallbladder]]
** [[Hepatoduodenal ligament]] ([[lesser omentum]])
* Inferior
** [[Neck of pancreas]]
** [[Greater omentum]]
** [[Head of pancreas]]
The ''second'' or ''descending part'' of the duodenum begins at the superior duodenal flexure. It goes [[Anatomical terms of location#Superior and inferior|inferior]] to the lower border of vertebral body L3, before making a sharp turn [[Lateral and medial|medial]]ly into the ''inferior duodenal flexure'', the end of the descending part.<ref name="GRAYS2005" />{{rp|274}}

The [[pancreatic duct]] and [[common bile duct]] enter the descending duodenum, through the [[major duodenal papilla]]. The second part of the duodenum also contains the minor duodenal papilla, the entrance for the [[accessory pancreatic duct]]. The junction between the embryological [[foregut]] and [[midgut]] lies just below the major duodenal papilla.<ref name="GRAYS2005" />{{rp|274}}

The ''third'', ''horizontal'' or ''inferior part'' of the duodenum is 10~12&nbsp;cm in length. It begins at the ''inferior duodenal flexure'' and passes transversely to the left, passing in front of the [[inferior vena cava]], [[abdominal aorta]] and the [[vertebral column]]. The [[superior mesenteric artery]] and [[superior mesenteric vein|vein]] are [[anterior]] to the third part of the duodenum.<ref name="GRAYS2005" />{{rp|274}} This part may be compressed between the aorta and SMA causing [[superior mesenteric artery syndrome]].

The ''fourth'' or ''ascending part'' of the duodenum passes upward, joining with the [[jejunum]] at the [[duodenojejunal flexure]]. The fourth part of the duodenum is at the vertebral level L3, and may pass directly on top, or slightly to the left, of the [[aorta]].<ref name="GRAYS2005" />{{rp|274}}

===Blood supply===
The first (superior) part of the duodenum, right after the [[pylorus]] of the stomach, is not supplied by the arcades. Instead, it is supplied by the [[supraduodenal artery]] and posterior superior pancreaticoduodenal artery, along with some branches of the [[right gastroepiploic artery]] and the anterior superior pancreaticoduodenal artery. In many people part of the first centimeter of the duodenum is also supplied by branches of the [[right gastric artery]].<ref name=":4">{{Cite journal |last1=Androulakis |first1=John |last2=Colborn |first2=Gene L. |last3=Skandalakis |first3=Panagiotis N. |last4=Skandalakis |first4=Lee J. |last5=Skandalakis |first5=John E. |date=2000-02-01 |title=Embryologic and Anatomic Basis of Duodenal Surgery |url=https://linkinghub.elsevier.com/retrieve/pii/S0039610905704011 |journal=Surgical Clinics of North America |volume=80 |issue=1 |pages=171–199 |doi=10.1016/S0039-6109(05)70401-1 |issn=0039-6109|url-access=subscription }}</ref>

The remaining three parts (descending, horizontal, and ascending) of the duodenum are supplied by two arcades (rings) of arteries, one anterior (in front) of the duodenum and pancreas and one posterior to (behind) them. Each arcade is made of two [[Anastomosis|anastomosed]] (connected) arteries. The superior artery of each arcade comes from the [[superior pancreaticoduodenal artery]], which arises from the [[celiac artery]] via the [[gastroduodenal artery]]. The inferior artery of each arcade comes from the [[inferior pancreaticoduodenal artery]], a branch of the [[superior mesenteric artery]]. The anterior arcade is formed by the anterior superior pancreaticoduodenal artery and the anterior inferior pancreaticoduodenal artery; the posterior arcade is formed by the posterior superior pancreaticoduodenal artery and the posterior inferior pancreaticoduodenal artery.<ref name=":4" /><ref>{{Citation |last1=Aasen |first1=S. |title=Stomach Duodenum Normal Anatomy, Function and Congenital Anomalies |date=2013 |work=Abdominal Imaging |pages=367–382 |editor-last=Hamm |editor-first=Bernd |url=https://link.springer.com/referenceworkentry/10.1007/978-3-642-13327-5_17 |access-date=2025-03-09 |place=Berlin, Heidelberg |publisher=Springer |language=en |doi=10.1007/978-3-642-13327-5_17 |isbn=978-3-642-13327-5 |last2=Lundin |first2=K. E. A. |editor2-last=Ros |editor2-first=Pablo R.|url-access=subscription }}</ref>

Vessels from the arcades supply the [[Muscular layer|muscularis externa]] (muscular layer) before forming a [[plexus]] (network of blood vessels) in the [[submucosa]] (a layer of connective tissue) called the [[submucosal plexus]]. Vessels continue from the submucosal plexus through the [[muscularis mucosae]] (another thin muscular layer) before forming another plexus under the [[epithelium]] of the [[Intestinal villus|villi]], the layer where nutrients are absorbed. These vessels entering the duodenum from the arcades are sometimes called [[Vasa recta (intestines)|vasae rectae]] or arteriae rectae.<ref name=":4" />

The venous drainage of the duodenum mainly follows the arteries, ultimately draining into the [[Hepatic portal system|portal system]]. The venous arcades are usually superficial to the arterial arcades. The anterior superior pancreaticoduodenal vein drains into the [[right gastroepiploic vein]], as do the veins of the lower first part of the duodenum and the pylorus (subpyloric veins). The upper first part of the duodenum is drained by suprapyloric veins, which can drain into the [[portal vein]] or the posterior superior pancreaticoduodenal vein, which drains into the portal vein. The inferior veins of the arcades drain into the [[Superior mesenteric vein|superior mesenteric]], [[Inferior mesenteric vein|inferior mesenteric]], [[Splenic vein|splenic]], or first [[Jejunal veins|jejunal vein]].<ref name=":4" />

Embryologically, the duodenum arises from both the [[foregut]] and [[midgut]], constituting the boundary between the two. However, the "midgut" is defined surgically as the parts of the intestine supplied by the superior mesenteric artery. Since the duodenum is supplied both by the [[celiac artery]] and the superior mesenteric artery, these two definitions are similar but not exactly the same.<ref name=":4" />

===Lymphatic drainage===
The [[Lymph vessel|lymphatic vessels]] follow the arteries in a retrograde fashion. The anterior lymphatic vessels drain into the pancreatoduodenal [[lymph node]]s located along the superior and inferior pancreatoduodenal arteries and then into the pyloric lymph nodes (along the gastroduodenal artery). The posterior lymphatic vessels pass posterior to the head of the pancreas and drain into the superior mesenteric lymph nodes. Efferent lymphatic vessels from the duodenal lymph nodes ultimately pass into the celiac lymph nodes.

===Histology===
Under [[microscopy]], the duodenum has a [[Intestinal villus|villous]] [[mucosa]]. This is distinct from the mucosa of the [[pylorus]], which directly joins the duodenum. Like other structures of the [[Gastrointestinal wall|gastrointestinal tract]], the duodenum has a [[mucosa]], [[submucosa]], [[muscularis externa]], and [[adventitia]]. Glands line the duodenum, known as [[Brunner's gland]]s, which secrete [[mucus]] and [[bicarbonate]] in order to neutralise stomach acids. These are distinct glands not found in the ileum or jejunum, the other parts of the small intestine.<ref name="WHEATERS2006">{{cite book|last=Deakin|first=Barbara Young  |display-authors=etal |title=Wheater's functional histology: a text and colour atlas|year=2006|publisher=Churchill Livingstone/Elsevier|location=[Edinburgh?]|isbn=978-0-443-06850-8|edition=5th}}</ref>{{rp|274–275}}
<gallery>
 File:Dogduodenum100x3.jpg|Dog duodenum 100X
 Image:Small bowel duodenum with amyloid deposition congo red 10X.jpg|Duodenum with amyloid deposition in lamina propria
 Image:Gray1058.png|Section of duodenum of cat. X 60
 Image:Giardiasis duodenum low.jpg |[[Micrograph]] showing [[giardiasis]] on a duodenal biopsy ([[H&E stain]])
 Image:Microvilli-Duodenum.JPG|Duodenum with brush border ([[microvilli|microvillus]])
</gallery>

===Variation===
The duodenum's close anatomical association with the pancreas creates differences in function based on the position and orientation of the organs. The congenital abnormality, annular pancreas, causes a portion of the pancreas to encircle the duodenum. In an extramural annular pancreas, the pancreatic duct encircles the duodenum which results in gastrointestinal obstruction. An intramural annular pancreas is characterized by pancreatic tissue that is fused with the duodenal wall, causing duodenal ulceration.<ref>{{Cite journal |last1=Borghei |first1=Peyman |last2=Sokhandon |first2=Farnoosh |last3=Shirkhoda |first3=Ali |last4=Morgan |first4=Desiree E. |date=January 2013 |title=Anomalies, Anatomic Variants, and Sources of Diagnostic Pitfalls in Pancreatic Imaging |url=http://pubs.rsna.org/doi/10.1148/radiol.12112469 |journal=Radiology |language=en |volume=266 |issue=1 |pages=28–36 |doi=10.1148/radiol.12112469 |pmid=23264525 |issn=0033-8419|url-access=subscription }}</ref>{{expand section|date=December 2013}}

===Gene and protein expression===
{{Further |Bioinformatics#Gene and protein expression}}
About 20,000 protein coding genes are expressed in human cells and 70% of these genes are expressed in the normal duodenum.<ref>{{Cite web|url=https://www.proteinatlas.org/humanproteome/duodenum|title=The human proteome in duodenum - The Human Protein Atlas|website=www.proteinatlas.org|access-date=2017-09-26}}</ref><ref>{{Cite journal|last1=Uhlén|first1=Mathias|last2=Fagerberg|first2=Linn|last3=Hallström|first3=Björn M.|last4=Lindskog|first4=Cecilia|last5=Oksvold|first5=Per|last6=Mardinoglu|first6=Adil|last7=Sivertsson|first7=Åsa|last8=Kampf|first8=Caroline|last9=Sjöstedt|first9=Evelina|date=2015-01-23|title=Tissue-based map of the human proteome|journal=Science|language=en|volume=347|issue=6220|article-number=1260419|doi=10.1126/science.1260419|issn=0036-8075|pmid=25613900|s2cid=802377}}</ref> Some 300 of these genes are more specifically expressed in the duodenum with very few genes expressed only in the duodenum. The corresponding specific proteins are expressed in the duodenal mucosa, and many of these are also expressed in the small intestine, such as [[alanine aminopeptidase]], a digestive enzyme, [[angiotensin-converting enzyme]], involved in controlling [[blood pressure]], and [[RBP2]], a protein involved in the uptake of [[vitamin A]].<ref>{{Cite journal|last1=Gremel|first1=Gabriela|last2=Wanders|first2=Alkwin|last3=Cedernaes|first3=Jonathan|last4=Fagerberg|first4=Linn|last5=Hallström|first5=Björn|last6=Edlund|first6=Karolina|last7=Sjöstedt|first7=Evelina|last8=Uhlén|first8=Mathias|last9=Pontén|first9=Fredrik|date=2015-01-01|title=The human gastrointestinal tract-specific transcriptome and proteome as defined by RNA sequencing and antibody-based profiling|journal=Journal of Gastroenterology|language=en|volume=50|issue=1|pages=46–57|doi=10.1007/s00535-014-0958-7|pmid=24789573|s2cid=21302849|issn=0944-1174}}</ref>

==Function==
The duodenum is largely responsible for the breakdown of food in the small intestine, using [[enzymes]]. The duodenum also regulates the rate of emptying of the stomach via hormonal pathways. [[Secretin]] and [[cholecystokinin]] are released from cells in the duodenal [[epithelium]] in response to acidic and fatty stimuli present there when the [[pylorus]] opens and emits gastric [[chyme]] into the duodenum for further digestion. These cause the [[liver]] and [[gallbladder]] to release [[bile]], and the [[pancreas]] to release bicarbonate and digestive enzymes such as [[trypsin]], [[lipase]] and [[amylase]] into the duodenum as they are needed.<ref>{{Cite journal |last1=Chandra |first1=Rashmi |last2=Liddle |first2=Rodger A. |date=September 2014 |title=Recent advances in the regulation of pancreatic secretion |journal=Current Opinion in Gastroenterology |language=en-US |volume=30 |issue=5 |pages=490–494 |doi=10.1097/MOG.0000000000000099 |issn=0267-1379 |pmc=4229368 |pmid=25003603}}</ref>

The duodenum is a critical contributor to the regulation of food intake<ref>{{Cite journal |last1=Woodward |first1=Orla R. M. |last2=Gribble |first2=Fiona M. |last3=Reimann |first3=Frank |last4=Lewis |first4=Jo E. |date=2022 |title=Gut peptide regulation of food intake – evidence for the modulation of hedonic feeding |journal=The Journal of Physiology |language=en |volume=600 |issue=5 |pages=1053–1078 |doi=10.1113/JP280581 |pmid=34152020 |issn=1469-7793|doi-access=free }}</ref> and glycemic control.<ref>{{Cite journal |last=Drucker |first=Daniel J. |date=2006-03-01 |title=The biology of incretin hormones |journal=Cell Metabolism |language=English |volume=3 |issue=3 |pages=153–165 |doi=10.1016/j.cmet.2006.01.004 |issn=1550-4131 |pmid=16517403|doi-access=free }}</ref> As the first part of the small intestine, the duodenum is the initial site of nutrient absorption in the gastrointestinal tract. The duodenum senses nutrient intake and composition, and signals to the liver, pancreas, adipose tissue and brain<ref>{{Cite journal |last1=Bany Bakar |first1=Rula |last2=Reimann |first2=Frank |last3=Gribble |first3=Fiona M. |date=December 2023 |title=The intestine as an endocrine organ and the role of gut hormones in metabolic regulation |url=https://www.nature.com/articles/s41575-023-00830-y |journal=Nature Reviews Gastroenterology & Hepatology |language=en |volume=20 |issue=12 |pages=784–796 |doi=10.1038/s41575-023-00830-y |pmid=37626258 |issn=1759-5053|url-access=subscription }}</ref> through the direct and indirect<ref name=":0">{{Cite journal |last1=Hansen |first1=Lene |last2=Holst |first2=Jens J |date=2002-12-31 |title=The effects of duodenal peptides on glucagon-like peptide-1 secretion from the ileum: A duodeno–ileal loop? |url=https://linkinghub.elsevier.com/retrieve/pii/S016701150200157X |journal=Regulatory Peptides |volume=110 |issue=1 |pages=39–45 |doi=10.1016/S0167-0115(02)00157-X |pmid=12468108 |issn=0167-0115|url-access=subscription }}</ref> release of several key hormones and signaling molecules, including the [[incretin]] peptides [[Glucose-dependent insulinotropic polypeptide]] (GIP) and [[Glucagon-like peptide-1]] (GLP-1),<ref name=":0" /> as well as [[Cholecystokinin]] (CCK) and [[Secretin]].  The duodenum also signals to the brain directly via vagal afferents enabling neural control over food intake and glycemia.<ref>{{Cite journal |last1=Thorens |first1=Bernard |last2=Larsen |first2=Philip Just |date=July 2004 |title=Gut-derived signaling molecules and vagal afferents in the control of glucose and energy homeostasis |url=https://journals.lww.com/co-clinicalnutrition/abstract/2004/07000/gut_derived_signaling_molecules_and_vagal.18.aspx |journal=Current Opinion in Clinical Nutrition & Metabolic Care |language=en-US |volume=7 |issue=4 |pages=471–478 |doi=10.1097/01.mco.0000134368.91900.84 |pmid=15192452 |issn=1363-1950|url-access=subscription }}</ref>  Intestinal secretion of GIP and GLP-1 stimulates glucose-dependent insulin secretion from pancreatic beta-cells, known as the incretin effect.<ref>{{Cite journal |last1=Nauck |first1=Michael A. |last2=Meier |first2=Juris J. |date=February 2018 |title=Incretin hormones: Their role in health and disease |url=https://dom-pubs.pericles-prod.literatumonline.com/doi/10.1111/dom.13129 |journal=Diabetes, Obesity and Metabolism |volume=20 |issue=S1 |pages=5–21 |doi=10.1111/dom.13129 |pmid=29364588 |issn=1462-8902|url-access=subscription }}</ref> Incretin peptides, principally GLP-1 and GIP, regulate islet hormone secretion, glucose concentrations, lipid metabolism, gut motility, appetite and body weight, and immune function.<ref>{{Cite journal |last1=Campbell |first1=Jonathan E. |last2=Drucker |first2=Daniel J. |date=2013-06-04 |title=Pharmacology, physiology, and mechanisms of incretin hormone action |journal=Cell Metabolism |volume=17 |issue=6 |pages=819–837 |doi=10.1016/j.cmet.2013.04.008 |issn=1932-7420 |pmid=23684623}}</ref>

The villi of the duodenum have a leafy-looking appearance, which is a histologically identifiable structure. [[Brunner's glands]], which secrete [[mucus]], are only found in the duodenum. The duodenum wall consists of a very thin layer of cells that form the [[muscularis mucosae]].

==Clinical significance==
===Ulceration===
{{Main|Peptic ulcer disease}}

Ulcers of the duodenum commonly occur because of infection by the bacteria ''[[Helicobacter pylori]]''. These bacteria, through a number of mechanisms, erode the protective mucosa of the duodenum, predisposing it to damage from gastric acids. The first part of the duodenum is the most common location of ulcers since it is where the acidic chyme meets the duodenal mucosa before mixing with the alkaline secretions of the duodenum.<ref>{{cite book|last=Smith|first=Margaret E|title=The Digestive System}}</ref> Duodenal ulcers may cause recurrent abdominal pain and [[dyspepsia]], and are often investigated using a [[urea breath test]] to test for the bacteria, and [[endoscopy]] to confirm ulceration and take a [[biopsy]]. If managed, these are often managed through [[antibiotic]]s that aim to eradicate the bacteria, and [[proton-pump inhibitors]] and [[antacid]]s to reduce the gastric acidity.<ref name="DAVIDSONS2010">{{cite book |editor1-first=Nicki R. |editor1-last=Colledge |editor2-first=Brian R. |editor2-last=Walker |editor3-first=Stuart H. |editor3-last=Ralston |title=Davidson's principles and practice of medicine.|year=2010|publisher=Churchill Livingstone/Elsevier|location=Edinburgh|isbn=978-0-7020-3085-7|pages=871–874|edition=21st}}</ref>

===Celiac disease===
The [[British Society of Gastroenterology]] guidelines specify that a duodenal biopsy is required for the diagnosis of adult [[celiac disease]]. The biopsy is ideally performed at a moment when the patient is on a gluten-containing diet.<ref>{{cite journal|last1=Ludvigsson|first1=J. F.|last2=Bai|first2=J. C.|last3=Biagi|first3=F.|last4=Card|first4=T. R.|last5=Ciacci|first5=C.|last6=Ciclitira|first6=P. J.|last7=Green|first7=P. H. R.|last8=Hadjivassiliou|first8=M.|last9=Holdoway|first9=A.|last10=van Heel|first10=D. A.|last11=Kaukinen|first11=K.|last12=Leffler|first12=D. A.|last13=Leonard|first13=J. N.|last14=Lundin|first14=K. E. A.|last15=McGough|first15=N.|last16=Davidson|first16=M.|last17=Murray|first17=J. A.|last18=Swift|first18=G. L.|last19=Walker|first19=M. M.|last20=Zingone|first20=F.|last21=Sanders|first21=D. S.|title=Diagnosis and management of adult coeliac disease: Guidelines from the British Society of Gastroenterology|journal=Gut|volume=63|issue=8|year=2014|pages=1210–1228|issn=0017-5749|doi=10.1136/gutjnl-2013-306578|pmid=24917550|pmc=4112432}}</ref>

===Cancer===
Duodenal cancer is a cancer in the first section of the small intestine. Cancer of the duodenum is relatively rare compared to [[stomach cancer]] and [[colorectal cancer]]; malignant tumors in the duodenum constitute only around 0.3% of all the gastrointestinal tract tumors but around half of cancerous tissues that develop in the small intestine.<ref>{{cite book |last1=Fagniez |first1=Pierre-Louis |last2=Rotman |first2=Nelly |title= Malignant tumors of the duodenum |year=2001 |publisher=Zuckschwerdt |url=https://www.ncbi.nlm.nih.gov/books/NBK6953/}}</ref> Its histology is often observed to be [[adenocarcinoma]], meaning that the cancerous tissue arises from glandular cells in the [[epithelial tissue]] lining the duodenum.<ref>{{cite web |title=Definition of adenocarcinoma - NCI Dictionnary of Cancer Terms |url=https://www.cancer.gov/publications/dictionaries/cancer-terms/def/adenocarcinoma |access-date=12 July 2024 |website=National Cancer Institute}}</ref>

=== Obesity and diabetes ===
A [[western diet]] induces duodenal mucosal hyperplasia and dysfunction that underlie insulin resistance, type 2 diabetes and obesity.<ref name=":1">{{Cite journal |last1=Aliluev |first1=Alexandra |last2=Tritschler |first2=Sophie |last3=Sterr |first3=Michael |last4=Oppenländer |first4=Lena |last5=Hinterdobler |first5=Julia |last6=Greisle |first6=Tobias |last7=Irmler |first7=Martin |last8=Beckers |first8=Johannes |last9=Sun |first9=Na |last10=Walch |first10=Axel |last11=Stemmer |first11=Kerstin |last12=Kindt |first12=Alida |last13=Krumsiek |first13=Jan |last14=Tschöp |first14=Matthias H. |last15=Luecken |first15=Malte D. |date=2021-09-22 |title=Diet-induced alteration of intestinal stem cell function underlies obesity and prediabetes in mice |journal=Nature Metabolism |language=en |volume=3 |issue=9 |pages=1202–1216 |doi=10.1038/s42255-021-00458-9 |issn=2522-5812 |pmc=8458097 |pmid=34552271}}</ref><ref>{{Cite journal |last1=Clara |first1=Rosmarie |last2=Schumacher |first2=Manuel |last3=Ramachandran |first3=Deepti |last4=Fedele |first4=Shahana |last5=Krieger |first5=Jean-Philippe |last6=Langhans |first6=Wolfgang |last7=Mansouri |first7=Abdelhak |date=January 2017 |title=Metabolic Adaptation of the Small Intestine to Short- and Medium-Term High-Fat Diet Exposure: INTESTINAL METABOLIC ADAPTATION TO HFD |url=https://onlinelibrary.wiley.com/doi/10.1002/jcp.25402 |journal=Journal of Cellular Physiology |language=en |volume=232 |issue=1 |pages=167–175 |doi=10.1002/jcp.25402|pmid=27061934 |url-access=subscription }}</ref> Diet-induced duodenal mucosal hyperplasia consists of increased mucosal mass,<ref>{{Cite journal |last1=Hvid |first1=Henning |last2=Jensen |first2=Stina Rikke |last3=Witgen |first3=Brent M. |last4=Fledelius |first4=Christian |last5=Damgaard |first5=Jesper |last6=Pyke |first6=Charles |last7=Rasmussen |first7=Thomas Bovbjerg |date=2016 |title=Diabetic Phenotype in the Small Intestine of Zucker Diabetic Fatty Rats |url=https://karger.com/DIG/article/doi/10.1159/000453107 |journal=Digestion |language=en |volume=94 |issue=4 |pages=199–214 |doi=10.1159/000453107 |pmid=27931035 |issn=0012-2823|url-access=subscription }}</ref> increased villus length,<ref name=":1" /><ref name=":2">{{Cite journal |last1=Taylor |first1=Samuel R. |last2=Ramsamooj |first2=Shakti |last3=Liang |first3=Roger J. |last4=Katti |first4=Alyna |last5=Pozovskiy |first5=Rita |last6=Vasan |first6=Neil |last7=Hwang |first7=Seo-Kyoung |last8=Nahiyaan |first8=Navid |last9=Francoeur |first9=Nancy J. |last10=Schatoff |first10=Emma M. |last11=Johnson |first11=Jared L. |last12=Shah |first12=Manish A. |last13=Dannenberg |first13=Andrew J. |last14=Sebra |first14=Robert P. |last15=Dow |first15=Lukas E. |date=2021-09-09 |title=Dietary fructose improves intestinal cell survival and nutrient absorption |journal=Nature |language=en |volume=597 |issue=7875 |pages=263–267 |doi=10.1038/s41586-021-03827-2 |issn=0028-0836 |pmc=8686685 |pmid=34408323}}</ref><ref>{{Cite journal |last=Dailey |first=Megan J. |date=September 2014 |title=Nutrient-induced intestinal adaption and its effect in obesity |journal=Physiology & Behavior |language=en |volume=136 |pages=74–78 |doi=10.1016/j.physbeh.2014.03.026 |pmc=4182169 |pmid=24704111}}</ref><ref>{{Cite journal |last1=Sagher |first1=F. A. |last2=Dodge |first2=J. A. |last3=Johnston |first3=C. F. |last4=Shaw |first4=C. |last5=Buchanan |first5=K. D. |last6=Carr |first6=K. E. |year=1991 |title=Rat small intestinal morphology and tissue regulatory peptides: effects of high dietary fat |url=https://www.cambridge.org/core/product/identifier/S0007114591000077/type/journal_article |journal=British Journal of Nutrition |language=en |volume=65 |issue=1 |pages=21–28 |doi=10.1079/BJN19910062 |pmid=1705145 |issn=0007-1145}}</ref> decreased crypt density,<ref name=":1" /> proliferation of enteroendocrine cells,<ref name=":3">{{Cite journal |last1=Gniuli |first1=D. |last2=Calcagno |first2=A. |last3=Dalla Libera |first3=L. |last4=Calvani |first4=R. |last5=Leccesi |first5=L. |last6=Caristo |first6=M. E. |last7=Vettor |first7=R. |last8=Castagneto |first8=M. |last9=Ghirlanda |first9=G. |last10=Mingrone |first10=G. |date=October 2010 |title=High-fat feeding stimulates endocrine, glucose-dependent insulinotropic polypeptide (GIP)-expressing cell hyperplasia in the duodenum of Wistar rats |url=http://link.springer.com/10.1007/s00125-010-1830-9 |journal=Diabetologia |language=en |volume=53 |issue=10 |pages=2233–2240 |doi=10.1007/s00125-010-1830-9 |pmid=20585935 |issn=0012-186X}}</ref> increased enterocyte mass,<ref>{{Cite journal |last1=Verdam |first1=Froukje J. |last2=Greve |first2=Jan Willem M. |last3=Roosta |first3=Sedigheh |last4=van Eijk |first4=Hans |last5=Bouvy |first5=Nicole |last6=Buurman |first6=Wim A. |last7=Rensen |first7=Sander S. |date=2011-02-01 |title=Small Intestinal Alterations in Severely Obese Hyperglycemic Subjects |url=https://academic.oup.com/jcem/article/96/2/E379/2709569 |journal=The Journal of Clinical Endocrinology & Metabolism |language=en |volume=96 |issue=2 |pages=E379–E383 |doi=10.1210/jc.2010-1333 |pmid=21084402 |issn=0021-972X}}</ref> and an accumulation of lipid droplets in the mucosa.<ref>{{Cite journal |last1=Sferra |first1=Roberta |last2=Pompili |first2=Simona |last3=Cappariello |first3=Alfredo |last4=Gaudio |first4=Eugenio |last5=Latella |first5=Giovanni |last6=Vetuschi |first6=Antonella |date=2021-07-06 |title=Prolonged Chronic Consumption of a High Fat with Sucrose Diet Alters the Morphology of the Small Intestine |journal=International Journal of Molecular Sciences |language=en |volume=22 |issue=14 |page=7280 |doi=10.3390/ijms22147280 |doi-access=free |issn=1422-0067 |pmc=8303301 |pmid=34298894}}</ref><ref>{{Cite journal |last1=D'Aquila |first1=Theresa |last2=Zembroski |first2=Alyssa S. |last3=Buhman |first3=Kimberly K. |date=2019-03-05 |title=Diet Induced Obesity Alters Intestinal Cytoplasmic Lipid Droplet Morphology and Proteome in the Postprandial Response to Dietary Fat |journal=Frontiers in Physiology |volume=10 |page=180 |doi=10.3389/fphys.2019.00180 |doi-access=free |issn=1664-042X |pmc=6413465 |pmid=30890954}}</ref> Diet induced duodenal dysfunction  includes increased duodenal nutrient absorption,<ref name=":2" /><ref>{{Cite journal |last1=Dyer |first1=J. |last2=Wood |first2=I. S. |last3=Palejwala |first3=A. |last4=Ellis |first4=A. |last5=Shirazi-Beechey |first5=S. P. |date=2002-02-01 |title=Expression of monosaccharide transporters in intestine of diabetic humans |url=https://www.physiology.org/doi/10.1152/ajpgi.00310.2001 |journal=American Journal of Physiology. Gastrointestinal and Liver Physiology |language=en |volume=282 |issue=2 |pages=G241–G248 |doi=10.1152/ajpgi.00310.2001 |issn=0193-1857|url-access=subscription }}</ref><ref>{{Cite journal |last1=Fiorentino |first1=Teresa Vanessa |last2=Suraci |first2=Evelina |last3=Arcidiacono |first3=Gaetano Paride |last4=Cimellaro |first4=Antonio |last5=Mignogna |first5=Chiara |last6=Presta |first6=Ivan |last7=Andreozzi |first7=Francesco |last8=Hribal |first8=Marta Letizia |last9=Perticone |first9=Francesco |last10=Donato |first10=Giuseppe |last11=Luzza |first11=Francesco |last12=Sesti |first12=Giorgio |date=2017-11-01 |title=Duodenal Sodium/Glucose Cotransporter 1 Expression Under Fasting Conditions Is Associated With Postload Hyperglycemia |url=https://academic.oup.com/jcem/article/102/11/3979/4117420 |journal=The Journal of Clinical Endocrinology & Metabolism |language=en |volume=102 |issue=11 |pages=3979–3989 |doi=10.1210/jc.2017-00348 |issn=0021-972X|url-access=subscription }}</ref><ref>{{Cite journal |last1=Fiorentino |first1=Teresa Vanessa |last2=De Vito |first2=Francesca |last3=Suraci |first3=Evelina |last4=Marasco |first4=Raffaella |last5=Hribal |first5=Marta Letizia |last6=Luzza |first6=Francesco |last7=Sesti |first7=Giorgio |date=March 2023 |title=Obesity and overweight are linked to increased sodium-glucose cotransporter 1 and glucose transporter 5 levels in duodenum |url=https://onlinelibrary.wiley.com/doi/10.1002/oby.23653 |journal=Obesity |language=en |volume=31 |issue=3 |pages=724–731 |doi=10.1002/oby.23653 |issn=1930-7381|url-access=subscription }}</ref> altered duodenal hormone secretion,<ref name=":1" /><ref name=":3" /> and altered intestinal vagal afferent neuronal function.<ref>{{Cite journal |last1=de Lartigue |first1=Guillaume |last2=Barbier de la Serre |first2=Claire |last3=Espero |first3=Elvis |last4=Lee |first4=Jennifer |last5=Raybould |first5=Helen E. |date=2012-03-07 |editor-last=Gaetani |editor-first=Silvana |title=Leptin Resistance in Vagal Afferent Neurons Inhibits Cholecystokinin Signaling and Satiation in Diet Induced Obese Rats |journal=PLOS ONE |language=en |volume=7 |issue=3 |article-number=e32967 |doi=10.1371/journal.pone.0032967 |doi-access=free |issn=1932-6203 |pmc=3296757 |pmid=22412960}}</ref>

=== Inflammation ===
Inflammation of the duodenum is referred to as [[duodenitis]]. There are multiple known causes.<ref name="pmid16679353">{{cite journal |vauthors=Serra S, Jani PA |title=An approach to duodenal biopsies |journal=J. Clin. Pathol. |volume=59 |issue=11 |pages=1133–50 |year=2006 |pmid=16679353 |pmc=1860495 |doi=10.1136/jcp.2005.031260 }}</ref> Celiac disease and inflammatory bowel disease are two of the known causes.<ref>{{Cite journal |last1=Alper |first1=Arik |last2=Hardee |first2=Steven |last3=Rojas-velasquez |first3=Danilo |last4=Escalera |first4=Sandra |last5=Morotti |first5=Raffaella A |last6=Pashankar |first6=Dinesh S. |date=February 2016 |title=Prevalence, clinical, endoscopic and pathological features of duodenitis in children |journal=Journal of Pediatric Gastroenterology and Nutrition |volume=62 |issue=2 |pages=314–316 |doi=10.1097/MPG.0000000000000942 |issn=0277-2116 |pmc=4724230 |pmid=26252915}}</ref>

==Etymology==
The name ''duodenum'' is [[Medieval Latin]], short for ''intestīnum duodēnum digitōrum'', meaning "intestine of twelve finger-widths (in length)", genitive{{citation needed|date=February 2025}} of ''duodēnī'', "twelve each", (related to ''duodecim'' "twelve"). Coined by Gerard of Cremona (d. 1187) in his Latin translation of "Canon Avicennae", "اثنا عشر" itself a loan-translation of Greek dodekadaktylon (δωδεκάδάκτυλον), literally "twelve fingers long". The intestine part was so called by the Greek physician [[Herophilus]] (c. 335–280 BCE) for its length, about equal to the breadth of 12 fingers.<ref>{{cite web|title=duodenum - Origin and meaning of duodenum by Online Etymology Dictionary|url=https://www.etymonline.com/word/duodenum|website=www.etymonline.com}}</ref>

Many languages use [[calque]]s for this word. For example, [[German language|German]] {{lang|de|Zwölffingerdarm}}, [[Dutch language|Dutch]] {{lang|nl|Twaalfvingerige darm}}, [[Turkish language|Turkish]] {{lang|tr|Oniki parmak bağırsağı}}, and  [[Mandarin Chinese]] {{lang|zh|十二指肠}} ''shí'èr zhǐ cháng''.

==Additional images==
<gallery>
 File:Blausen 0817 SmallIntestine Anatomy.png|Sections of the small intestine
 Image:Gray533.png|The celiac artery and its branches; the stomach has been raised and the peritoneum removed
 Image:Gray1041.png |Superior and inferior duodenal fossæ
 Image:Gray1042.png|Duodenojejunal fossa
 Image:Gray1099.png|The pancreas and duodenum from behind
 Image:Gray1097.png|Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas
 Image:Gray1100.png|The pancreatic duct
 Image:Illu pancrease.jpg|Region of pancreas
 File:Slide3ii.JPG|Duodenum
File:Slide2ffff.JPG|Duodenum
File:Slide7ffff.JPG|Duodenum
</gallery>

==See also==
{{Anatomy-terms}}
{{Commons category|Duodenum}}
* [[Pancreas]]
* [[Choledochoduodenostomy]] - a surgical procedure to create a connection between the common bile duct (CBD) and an alternative portion of the duodenum.

==References==
{{Reflist}}

==External links==
{{Wiktionary}}
* [https://www.proteinatlas.org/humanproteome/duodenum Duodenum] at the [https://www.proteinatlas.org Human Protein Atlas]
* {{NormanAnatomy|Duodenum}}
{{Digestive tract}}

{{Authority control}}

[[Category:Digestive system]]
[[Category:Small intestine]]