Small intestine 99610 222886716 2008-07-01T16:24:03Z KhanBot 6891585 robot Modifying: [[da:Tyndtarmen]] {{Infobox Anatomy | Name = Small intestine | Latin = intestinum tenue | GraySubject = 248 | GrayPage = 1168 | Image = Stomach_colon_rectum_diagram.svg | Caption = Diagram showing the small intestine | Image2 = | Caption2 = | Precursor = | System = | Artery = | Vein = | Nerve = [[celiac ganglia]], [[vagus]] <ref>{{GeorgiaPhysiology|6/6ch2/s6ch2_30}}</ref> | Lymph = | MeshName = Small+intestine | MeshNumber = A03.556.124.684 | DorlandsPre = i_11 | DorlandsSuf = 12456563 | }} In [[biology]] the '''small [[intestine]]''' is the part of the [[gastrointestinal tract]] (gut) between the [[stomach]] and the [[large intestine]], and comprises the [[duodenum]], [[jejunum]], and [[ileum]]. It is where the vast majority of digestion takes place. Nutrients diffuse through the villi, projections sticking out of the walls of the small intestine, into the blood.<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> In [[human]]s over 5 years old it is approximately 7 m (22.97 ft) long and can vary from 4-7 m (13.12-22.97 ft). [[Image:Illu small intestine.jpg|thumb|left|250px|Small intestine.]]It is divided into three structural parts: * '''[[Duodenum]]''' 26 cm (9.84 in) in length * '''[[Jejunum]]''' 2.5 m (8.2 ft) * '''[[Ileum]]''' 3.5 m (11.5 ft) Although the small intestine is much longer than the [[large intestine]] (typically 4-5 times longer), it is referred to as such due to its comparatively smaller diameter. On average, the diameter of the small intestine of an adult human measures approximately 2.5-3 cm, and the large intestine measures about 7.6 cm in diameter. ==Peristalsis== Food from the stomach is allowed into the duodenum by a muscle called the pylorus, or [[pyloric sphincter]], and is then pushed through the small intestine by a process of muscular-wavelike contractions called [[peristalsis]]. ==Extensions into lumen== The small intestine is the site where most of the nutrients from ingested food are absorbed and is covered in wrinkles or folds called [[plicae circulares]]. These are considered permanent features in the wall of the organ. They are distinct from [[rugae]] which are considered non-permanent or temporary allowing for distention and contraction. From the plicae circulares project microscopic finger-like pieces of tissue called [[villi]] (Latin for "shaggy hair"). The small intestine is lined with simple columnar [[intestinal epithelium|epithelial]] tissue. The epithelial cells also have finger-like projections known as microvilli. The function of the plicae circulares, the villi and the microvilli is to increase the amount of surface area available for secretion of enzymes and absorption of nutrients. ==Absorption== The purpose of these [[wrinkles]] and projections is to increase surface area for absorption of nutrients. Each villus is covered in [[microvilli]], which increase the surface area manyfold. Each villus contains a [[lacteal]] and capillaries. The lacteal absorbs the digested [[fat]] into the [[lymphatic system]] which will eventually drain into the [[circulatory system]]. The capillaries absorb all other digested [[nutrient]]s. The surface of the cells on the microvilli are covered with a water layer, which has a number of functions in absorption of nutrients. Absorption of the majority of nutrients takes place in the [[jejunum]], with the following notable exceptions: * [[Iron]] is absorbed in the duodenum * [[Vitamin B12]] and [[bile salts]] are absorbed in the terminal ileum. * Water and [[lipids]] are absorbed by passive diffusion throughout * [[Sodium]] is absorbed by active transport and [[glucose]] and [[amino acid]] co-transport. * [[Fructose]] is absorbed by [[facilitated diffusion]]. == Digestion == The digested food can now pass into the blood vessels in the wall of the intestine. This process is called absorption. The inner walls of the small intestine have thousands of finger like outgrowths called villi (singular villus). The villi increases the surface area for absorption of the digested food. Each villus has a network of thin and small blood vessels close to its surface. The suface of the villi absorbs the digested food materials. The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by our body. This is called assimilation. The food that remains undigested and unabsorbed passes into the large intestine. The digestion of proteins into peptides and amino acids principally occurs in the stomach but some also occurs in the small intestine. The small intestine is where the most chemical digestion takes place: * peptides are degraded into [[amino acid]]s. Chemical breakdown begins in the stomach and is further broken down in the small intestine. Proteolytic enzymes, [[ trypsin]] and [[chymotrypsin]], which are secreted by the [[pancreas]] cleave proteins into smaller peptides. Carboxypeptidase, which is a pancreatic brush border enzyme, splits one amino acid at a time. Aminopeptidase and dipeptidase free the end amino acid products. * [[lipid]]s (fats) are degraded into [[fatty acid]]s and [[glycerol]]. Pancreatic lipase is secreted here. Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides. Pancreatic lipase performs its job with the help of the salts from the [[bile]] secreted by the [[liver]] and the [[gall bladder]]. Bile salts attach to triglycerides which aids in making them easier for pancreatic lipase to access. This occurs because the lipase is water-soluble but the fatty triglycerides are hydrophobic and tend to orient towards each other and away from the watery intestinal surroundings. The bile salts are the "middle man" that holds the triglycerides in the watery surroundings until the lipase can break them into the smaller components that are able to enter the villi for absorption. * [[carbohydrate]]s are degraded into simple sugars (e.g., [[glucose]]). In the small intestine pancreatic amylase breaks down carbohydrates into oligosaccharides. Brush border enzymes take over from there. The most important brush border enzymes are dextrinase and glucoamylase which further break down oligosaccharides. Other brush border enzymes are maltase, sucrase and lactase. ==Histology== The three sections of the small intestine look similar to each other at a microscopic level, but there are some important differences. The parts of the intestine are as follows: {| class="wikitable" | '''Layer''' || '''Duodenum''' || '''Jejunum''' || '''Ileum''' |- | [[serosa]] || normal || normal || normal |- | [[muscularis externa]] || longitudinal and circular layers, with [[Auerbach's plexus|Auerbach's (myenteric) plexus]] in between || same as duodenum || same as duodenum |- | [[submucosa]] || [[Brunner's glands]] and [[Meissner's plexus|Meissner's (submucosal) plexus]] || no BG || no BG |- | [[mucosa]]: [[muscularis mucosae]] || normal || normal || normal |- | mucosa: [[lamina propria]] || no PP || no PP || [[Peyer's patches]] |- | mucosa: [[intestinal epithelium]] || [[Simple columnar epithelium|simple columnar]]. Contains [[goblet cells]], [[Paneth cell]]s || Similar to duodenum. Villi very long. || Similar to duodenum. Villi very short. |} ==Small intestine disorders== <div style="-moz-column-count:2; column-count:2;"> * [[Small intestine cancer]] * Small intestine obstruction ("high" mechanic ileus) ** Obstruction from external pressure ** Obstruction by masses in the lumen ([[foreign body|foreign bodies]], [[bezoar]], [[gallstone]]s) * Paralytic [[ileus]] * [[Maropthisis]] * [[Crohn's disease]] * [[Celiac disease]] * [[Carcinoid]] * [[Meckel's Diverticulum]] * [[Gastric dumping syndrome]] * [[Infectious diseases]] ** [[Giardiasis]] ** [[Scariasis]] ** [[Tropical sprue]] ** [[Tapeworm infection]] * [[Mesenteric ischemia]] * [[Short bowel syndrome]] * [[Inguinal hernia]] </div> ==References== * Solomon et al (2002) Biology Sixth Edition, Brooks-Cole/Thomson Learning ISBN 0-03-033503-5 * Townsend et al (2004) Sabiston Textbook of Surgery, Elsevier ISBN 0-7216-0409-9 * {{cite journal | author = Thomson A, Drozdowski L, Iordache C, Thomson B, Vermeire S, Clandinin M, Wild G | title = Small bowel review: Normal physiology, part 1. | journal = Dig Dis Sci | volume = 48 | issue = 8 | pages = 1546–64 | year = 2003 | pmid = 12924651 | doi = 10.1023/A:1024719925058}} * {{cite journal | author = Thomson A, Drozdowski L, Iordache C, Thomson B, Vermeire S, Clandinin M, Wild G | title = Small bowel review: Normal physiology, part 2. | journal = Dig Dis Sci | volume = 48 | issue = 8 | pages = 1565–81 | year = 2003 | pmid = 12924652 | doi = 10.1023/A:1024724109128}} ==Notes== <references/> ==Additional images== <gallery> Image:Gray849.png|Lower half of right sympathetic cord. Image:Gray1224.png|Topography of thoracic and abdominal viscera. </gallery> {{digestive_system}} [[Category:Abdomen]] [[Category:Digestive system]] [[ar:أمعاء دقيقة]] [[bn:ক্ষুদ্রান্ত্র]] [[zh-min-nan:Sió-tn̂g]] [[bs:Tanko crijevo]] [[ca:Intestí prim]] [[cs:Tenké střevo člověka]] [[da:Tyndtarmen]] [[de:Dünndarm]] [[dv:ކުޑަ ގޮހޮރު]] [[et:Peensool]] [[es:Intestino delgado]] [[eo:Maldika intesto]] [[eu:Heste mehar]] [[fr:Intestin grêle]] [[gl:Intestino delgado]] [[ko:소장 (장기)]] [[hr:Tanko crijevo]] [[id:Usus halus]] [[is:Mjógirni]] [[it:Intestino tenue]] [[he:המעי הדק]] [[jv:Usus alus]] [[pam:Malating bituka]] [[la:Intestinum tenue]] [[lt:Plonoji žarna]] [[hu:Vékonybél]] [[mk:Тенко црево]] [[mr:लहान आतडे]] [[ms:Usus kecil]] [[nl:Dunne darm]] [[ja:小腸]] [[no:Tynntarmen]] [[pl:Jelito cienkie]] [[pt:Intestino delgado]] [[qu:Ñañu ch'unchul]] [[ru:Тонкая кишка]] [[simple:Small intestine]] [[sk:Tenké črevo]] [[sl:Tanko črevo]] [[sr:Танко црево]] [[fi:Ohutsuoli]] [[sv:Tunntarm]] [[te:చిన్న ప్రేగు]] [[th:ลำไส้เล็ก]] [[tr:İnce bağırsak]] [[uk:Тонкий кишечник]] [[zh:小肠]]