Gastrointestinal tract 69720 223125079 2008-07-02T18:04:37Z Bigbluefish 457199 fix self {{redirect2|Gut|Guts|Gut}} {{redirect|Entrails|reading entrails|Extispicy}} {{Digestive system diagram}} <!--To edit, search for Template:Digestive system diagram the image is: Image:Digestive system diagram en.svg--> The '''digestive tract''' (also known as the '''alimentary canal''') is the system of [[Organ (anatomy)|organ]]s within [[multicellular animal]]s that takes in [[food]], [[digestion|digests]] it to extract energy and [[nutrient]]s, and expels the remaining waste. The major functions of the GI tract are [[ingestion]], [[digestion]], absorption, and [[defecation]]. The GI tract differs substantially from animal to animal. Some animals have multi-chambered stomachs, while some animals' stomachs contain a single chamber. In a normal [[human]] adult male, the GI tract is approximately 6.5 [[meter]]s (20 [[foot (unit of length)|feet]]) long and consists of the upper and lower GI tracts. The tract may also be divided into [[foregut]], [[midgut]], and [[hindgut]], reflecting the [[embryology|embryological]] origin of each segment of the tract.<ref>{{cite book | last = Maton | first = Anthea | authorlink = | coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright | title = Human Biology and Health | publisher = Prentice Hall | date = 1993 | location = Englewood Cliffs, New Jersey, USA | pages = | url = | doi = | id = | isbn = 0-13-981176-1}}</ref> ==Upper gastrointestinal tract== The upper GI tract consists of the [[mouth (human)|mouth]], [[pharynx]], [[esophagus]], and [[stomach]]. * The mouth contains the [[buccal mucosa]], which contains the openings of the [[salivary gland]]s; the [[tongue]]; and the [[tooth]]. * Behind the mouth lies the [[pharynx]], which leads to a hollow muscular tube, the [[esophagus]]. * [[Peristalsis]] takes place, which is the contraction of muscles to propel the food down the esophagus which extends through the chest and pierces the [[diaphragm]] to reach the stomach. ==Lower gastrointestinal tract== The lower GI tract comprises the intestines and anus. *Bowel or [[intestine]] **[[Small intestine]], which has three parts: ***[[Duodenum]] ***[[Jejunum]] ***[[Ileum]] **[[Large intestine]], which has three parts: ***[[Cecum]] (the [[vermiform appendix]] is attached to the cecum). ***[[Colon (anatomy)|Colon]] ([[ascending colon]], [[transverse colon]], [[descending colon]] and [[sigmoid flexure]]) ***[[Rectum]] *[[Anus]] ==Accessory organs== Accessory organs to the alimentary canal include the liver, gallbladder, and pancreas. The [[liver]] secretes [[bile]] into the small intestine via the [[biliary system]], employing the [[gallbladder]] as a reservoir. Apart from storing and concentrating bile, the gallbladder has no other specific function. The [[pancreas]] secretes an isosmotic fluid containing [[bicarbonate]] and several enzymes, including [[trypsin]], [[chymotrypsin]], [[lipase]], and pancreatic [[amylase]], as well as nucleolytic enzymes ([[deoxyribonuclease]] and [[ribonuclease]]), into the small intestine. Both of these [[secretion|secretory]] organs aid in [[digestion]]. ==Embryology== The gut is an [[endoderm]]-derived structure. At approximately the 16th day of human development, the embryo begins to fold ventrally (with the embryo's ventral surface becoming concave) in two directions: the sides of the embryo fold in on each other and the head and tail fold towards one another. The result is that a piece of the [[yolk sac]], an [[endoderm]]-lined structure in contact with the ventral aspect of the embryo, begins to be pinched off to become the primitive gut. The yolk sac remains connected to the gut tube via the [[vitelline duct]]. Usually this structure regresses during development; in cases where it does not, it is known as [[Meckel's diverticulum]]. During fetal life, the primitive gut can be divided into three segments: [[foregut]], [[midgut]], and [[hindgut]]. Although these terms are often used in reference to segments of the primitive gut, they are nevertheless used regularly to describe components of the definitive gut as well. Each segment of the primitive gut gives rise to specific gut and gut-related structures in the adult. Components derived from the gut proper, including the [[stomach]] and [[Colon (anatomy)|colon]], develop as swellings or dilatations of the primitive gut. In contrast, gut-related derivatives—that is, those structures that derive from the primitive gut but are not part of the gut proper—in general develop as outpouchings of the primitive gut. The blood vessels supplying these structures remain constant throughout development.<ref>{{cite book | author = Bruce M. Carlson | title = Human Embryology and Developmental Biology | publisher = Mosby | location = Saint Louis | edition = 3rd edition | year = 2004 | id = ISBN 0-323-03649-X}}</ref> {| class="wikitable" | '''part''' || '''age in adult''' || '''Gives rise to''' || '''Arterial supply''' |- | [[foregut]] || the [[pharynx]], to the upper [[duodenum]] || [[pharynx]], [[esophagus]], [[stomach]], upper [[duodenum]], [[respiratory tract]] (including the [[lung]]s), [[liver]], [[gallbladder]], and [[pancreas]] || branches of the [[celiac artery]] |- | [[midgut]] || lower duodenum, to the first two-thirds of the transverse colon || lower duodenum, [[jejunum]], [[ileum]], [[cecum]], [[appendix]], [[ascending colon]], and first two-thirds of the [[transverse colon]] || branches of the [[superior mesenteric artery]] |- | [[hindgut]] || last third of the transverse colon, to the upper part of the anal canal || last third of the transverse colon, [[descending colon]], [[rectum]], and upper part of the [[anal canal]] || branches of the [[inferior mesenteric artery]] |} ==Physiology== ===Specialization of organs=== Four organs are subject to specialization in the [[kingdom Animalia]]. *The first organ is the ''[[tongue]]'' which is only present in the phylum [[Chordata]]. *The second organ is the ''[[esophagus]]''. The ''[[crop (anatomy)|crop]]'' is an enlargement of the [[esophagus]] in birds, insects and other invertebrates that is used to store food temporarily. *The third organ is the ''[[stomach]]''. In addition to a glandular stomach (proventriculus), birds have a muscular "stomach" called the ventriculus or "gizzard." The gizzard is used to mechanically grind up food. *The fourth organ is the ''[[large intestine]]''. An outpouching of the large intestine called the ''[[cecum]]'' is present in non-ruminant herbivores such as rabbits. It aids in digestion of plant material such as ''[[cellulose]]'' ==Pathology== There are a number of diseases and conditions affecting the gastrointestinal system, including: *[[Colorectal cancer]] *[[Diverticulitis]] *[[Gastroenteritis]], also known as "stomach flu";an inflammation of the stomach and intestines *[[Giardiasis]] *[[Inflammatory bowel disease]] ([[Crohn's disease]] and [[ulcerative colitis]]) *[[Irritable bowel syndrome]] *[[Pancreatitis]] ==Immune function== The gastrointestinal tract is also a prominent part of the [[immune system]].<ref>{{cite book | author = Richard Coico, Geoffrey Sunshine, Eli Benjamini | title = Immunology: a short course | publisher = Wiley-Liss | location = New York | year = 2003 | id = ISBN 0-471-22689-0}}</ref> The low [[pH]] (ranging from 1 to 4) of the stomach is fatal for many [[microorganism]]s that enter it. Similarly, [[mucus]] (containing [[IgA]] [[antibodies]]) neutralizes many of these microorganisms. Other factors in the GI tract help with immune function as well, including [[enzyme]]s in the [[saliva]] and [[bile]]. [[Enzyme]]s such as Cyp3A4, along with the antiporter activities, are also instrumental in the intestine's role of detoxification of [[antigen]]s and [[xenobiotics]], such as drugs, involved in [[first pass metabolism]]. Health-enhancing [[intestinal bacteria]] serve to prevent the overgrowth of potentially harmful [[bacteria]] in the gut. Microorganisms are also kept at bay by an extensive immune system comprising the [[gut-associated lymphoid tissue]] (GALT). ==Histology== [[Image:Gut wall.svg|thumb|right|250px|General structure of the gut wall. ]] The gastrointestinal tract has a uniform general histology with some differences which reflect the specialization in functional anatomy.<ref>{{cite book | author = Abraham L. Kierszenbaum | title = Histology and cell biology: an introduction to pathology | publisher = Mosby | location = St. Louis | year = 2002 | id = ISBN 0-323-01639-1}}</ref> The GI tract can be divided into 4 concentric layers: * [[Mucosa]] * [[Submucosa]] * ''[[Muscularis externa]]'' (the external muscle layer) * [[Adventitia]] or [[serosa]] ===Mucosa=== The mucosa is the innermost layer of the gastrointestinal tract that is surrounding the [[lumen]], or space within the tube. This layer comes in direct contact with the food (or bolus), and is responsible for [[absorption (digestive)|absorption]] and [[secretion]], important processes in digestion. The mucosa can be divided into: * [[Epithelium]] * ''[[Lamina propria]]'' * ''[[Muscularis mucosae]]'' The mucosae are highly specialized in each organ of the gastrointestinal tract, facing a low pH in the stomach, absorbing a multitude of different substances in the small intestine, and also absorbing specific quantities of water in the large intestine. Reflecting the varying needs of these organs, the structure of the mucosa can consist of invaginations of secretory glands (e.g., [[gastric pit]]s), or it can be folded in order to increase surface area (examples include [[intestinal villus|villi]] and ''[[plicae circulares]]''). ===Submucosa===<!-- This section is linked from [[Intestine]] --> The submucosa consists of a dense irregular layer of connective tissue with large blood vessels, lymphatics and nerves branching into the mucosa and muscularis. It contains [[Meissner's plexus]], an [[enteric nervous system|enteric nervous plexus]], situated on the inner surface of the ''muscularis externa''. ===Muscularis externa===<!-- This section is linked from [[Intestine]] --> The ''muscularis externa'' consists of an inner circular layer and a [[longitudinal]] outer muscular layer. The circular muscle layer prevents the food from going backwards and the longitudinal layer shortens the tract. The coordinated contractions of these layers is called [[peristalsis]] and propels the bolus, or balled-up food, through the GI tract. Between the two muscle layers are the myenteric or [[Auerbach's plexus]]. ===Adventitia=== The [[adventitia]] consists of several layers of [[epithelia]]. When the adventitia is facing the [[mesentery]] or peritoneal fold, the adventitia is covered by a mesothelium supported by a thin [[connective tissue]] layer, together forming a [[serosa]], or serous membrane. ==Uses of animal gut by humans== * The stomachs of calves have commonly been used as a source of [[rennet]] for making [[cheese]]. * The use of animal gut [[Strings (music)|strings]] by musicians can be traced back to the [[third dynasty of Egypt]]. In the recent past, strings were made out of [[domestic sheep|lamb]] gut. With the advent of the modern era, musicians have tended to use strings made of [[silk]], or synthetic materials such as [[nylon]] or [[steel]]. Some instrumentalists, however, still use gut strings in order to evoke the older tone quality. Although such strings were commonly referred to as "[[catgut]]" strings, [[cat]]s were never used as a source for gut strings. * Sheep gut was the original source for natural gut string used in [[racquet]]s, such as for [[tennis]]. Today, synthetic strings are much more common, but the best strings are now made out of [[cow]] gut. * Gut cord has also been used to produce strings for the snares which provide the [[snare drum]]'s characteristic buzzing timbre. While the snare drum currently almost always uses metal wire rather than gut cord, the [[North Africa]]n [[bendir]] frame drum still uses gut for this purpose. * "Natural" sausage hulls (or [[Casing (sausage)|casings]]) are made of animal gut, especially hog, beef, and lamb. * Animal gut was used to make the cord lines in [[longcase clock]]s and for [[fusee (horology)|fusee]] movements in [[bracket clock]]s, but may be replaced by metal wire. * The oldest known [[condom]]s, from 1640 CE, were made from animal intestine.<ref>{{cite web | url = http://www.ananova.com/news/story/sm_1870958.html?menu=news.quirkies.sexlife | title = World's oldest condom | accessdate = 2008-04-11 | date = 2008| publisher = [[Ananova]] }}</ref> ==See also== {{commonscat|Digestive system}} *[[Dysbiosis]] *[[Gastrointestinal hormone]] *[[Dorland's Illustrated Medical Dictionary]] *[[Major systems of the human body]] ==Notes== {{reflist}} ==References== * National Institute of Diabetes and Digestive and Kidney Diseases, [[National Institutes of Health]]. ==External links== * [http://www.innerbody.com/image/digeov.html Anatomy atlas of the Digestive System] * [http://www.vivo.colostate.edu/hbooks/pathphys/digestion/ Overview] at [[Colorado State University]] {{Digestive tract}} {{Digestive glands}} {{Development of digestive system}} {{Gastroenterology}} {{Gastrointestinal physiology}} {{Digestive system surgical procedures}} {{organ systems}} [[Category:Digestive system]] [[Category:Gastroenterology]] [[Category:Abdomen]] [[af:Spysverteringstelsel]] [[ar:جهاز هضمي]] [[ast:Aparatu dixestivu]] [[ay:Manq'a kamana]] [[bn:পাচনতন্ত্র]] [[zh-min-nan:Siau-hoà hē-thóng]] [[bs:Probavni sistem]] [[bg:Храносмилателна система]] [[ca:Aparell digestiu]] [[cs:Trávicí soustava]] [[cy:System dreulio]] [[de:Verdauungstrakt]] [[dv:ހަޖަމުކުރާ ނިޒާމް]] [[el:Γαστρεντερικό σύστημα]] [[es:Aparato digestivo]] [[eo:Digesta sistemo]] [[fa:دستگاه گوارش]] [[fr:Système digestif humain]] [[ko:소화 기관]] [[hr:Ljudska probava]] [[id:Saluran pencernaan]] [[io:Digestiva sistemo]] [[is:Meltingarkerfið]] [[it:Apparato gastrointestinale]] [[he:מערכת העיכול]] [[la:Apparatus digestorius]] [[ln:Nzelá elekaka bilía na líkundú]] [[lv:Gremošanas orgānu sistēma]] [[jbo:canti]] [[mk:Систем за варење]] [[mt:Sistema diġestiva]] [[nl:Maag-darmstelsel]] [[ja:消化器]] [[no:Fordøyelsessystemet]] [[pl:Układ pokarmowy człowieka]] [[pt:Aparelho digestivo]] [[qu:Mikhuna yawri]] [[ru:Желудочно-кишечный тракт]] [[sq:Sistemi i tretjes]] [[simple:Gastrointestinal system]] [[sk:Tráviaca sústava]] [[sl:Prebavni trakt]] [[sr:Систем органа за варење]] [[su:Saluran cerna]] [[fi:Ruoansulatuskanava]] [[sv:Mag-tarmkanalen]] [[tl:Sistemang panunaw]] [[ta:செரித்தல்]] [[th:ระบบย่อยอาหาร]] [[vi:Hệ tiêu hóa]] [[tr:Sindirim sistemi]] [[uk:Травна система]] [[yi:פארדייאונג סיסטעם]] [[zh:消化系统]]