Editing Duodenum (section)

==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 |url=https://linkinghub.elsevier.com/retrieve/pii/S1550413106000283 |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}}</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}}</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}}</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}}</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}}</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 |url=https://pubmed.ncbi.nlm.nih.gov/23684623/ |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]].