small intestine

小腸

WordNet

1. slight or limited; especially in degree or intensity or scope; "a series of death struggles with small time in between"
2. a garment size for a small person
3. the slender part of the back
4. limited or below average in number or quantity or magnitude or extent; "a little dining room"; "a little house"; "a small car"; "a little (or small) group" (同)little
5. have fine or very small constituent particles; "a small misty rain"
6. on a small scale; "think small"
7. the part of the alimentary canal between the stomach and the anus (同)bowel, gut

PrepTutorEJDIC

1. (大きさが)『小さい』,小形の;(量が)『少ない』,わずかな / 『取るに足りない』,ささいな(trivial) / 《名詞の前にのみ用いて》(仕事・活動などが)『小規模の』,ささやかな / 心が狭い,利己的な / (音・声が)弱い,小さい / (文字が)小型の,小文字の / 《the~》小さいもの;(…の)細い部分《+『of』+『名』》 / 《複数形で》《英》(衣類・ハンカチなどの)小物,小間物 / 小さく,細かく / (声などが)低く,弱く / 小規模に,こぢんまりと
2. 腸

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/03/09 22:03:41」(JST)

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Small intestine
Diagram showing the small intestine
Latin	Intestinum tenue
Gray's	subject #248 1168
Artery	Superior mesenteric artery
Vein	Hepatic portal vein
Nerve	Celiac ganglia, vagus
Lymph	Intestinal lymph trunk
MeSH	Small+intestine
Code	TA A05.6.01.001
Dorlands/Elsevier	Small intestine

The small intestine (or small bowel) is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. The small intestine is composed of a duodenum, jejunum, and ileum. It receives bile juice and pancreatic juice through the hepatopancreatic duct, controlled by Sphincter of oddi. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to describe the entire intestine. This article is primarily about the human gut, though the information about its processes is directly applicable to most placental mammals. The primary function of the small intestine is the absorption of nutrients and minerals found in food. (A major exception to this is cows; for information about digestion in cows and other similar mammals, see ruminants and platypus.)

Structure

The average length of the small intestine in an adult human male is 6.9 m (22 ft 8 in), and in an adult female 7.1 m (23 ft 4 in). It can vary greatly, from as short as 4.6 m (15 ft) to as long as 9.8 m (32 ft). It is approximately 2.5–3 cm in diameter.

The small intestine is divided into three structural parts:

• Duodenum
• Jejunum
• Ileum

Histology

Main article: Gastrointestinal wall

Micrograph of the small intestine mucosa showing the intestinal villi and crypts of Lieberkühn.

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:

Layer	Duodenum	Jejunum	Ileum
serosa	1st part serosa, 2nd - 4th adventitia	normal	normal
muscularis externa	longitudinal and circular layers, with Auerbach's (myenteric) plexus in between	same as duodenum	same as duodenum
submucosa	Brunner's glands and 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. Contains goblet cells, Paneth cells	Similar to duodenum	?

Function

Food from the stomach is allowed into the duodenum through the pylorus by a muscle called the pyloric sphincter.

Digestion

The small intestine is where most chemical digestion takes place. Most of the digestive enzymes that act in the small intestine are secreted by the pancreas and enter the small intestine via the pancreatic duct. Enzymes enter the small intestine in response to the hormone cholecystokinin, which is produced in the small intestine in response to the presence of nutrients. The hormone secretin also causes bicarbonate to be released into the small intestine from the pancreas in order to neutralize the potentially harmful acid coming from the stomach.

The three major classes of nutrients that undergo digestion are proteins, lipids (fats) and carbohydrates:

• Proteins are degraded into small peptides and amino acids before absorption. Chemical breakdown begins in the stomach and continues in the small intestine. Proteolytic enzymes, including trypsin and chymotrypsin, are secreted by the pancreas and 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.
• Lipids (fats) are degraded into fatty acids and glycerol. Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides. Pancreatic lipase works with the help of the salts from the bile secreted by the liver and the gall bladder. Bile salts attach to triglycerides to help emulsify them, which aids access by pancreatic lipase. 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 emulsify 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.
• Some carbohydrates are degraded into simple sugars, or monosaccharides (e.g., glucose). Pancreatic amylase breaks down some carbohydrates (notably starch) into oligosaccharides. Other carbohydrates pass undigested into the large intestine and further handling by intestinal bacteria. 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. Lactase is absent in most adult humans and for them lactose, like most poly-saccharides, are not digested in the small intestine. Some carbohydrates, such as cellulose, are not digested at all, despite being made of multiple glucose units. This is because the cellulose is made out of beta-glucose, making the inter-monosaccharidal bindings different from the ones present in starch, which consists of alpha-glucose. Humans lack the enzyme for splitting the beta-glucose-bonds, something reserved for herbivores and bacteria from the large intestine.

Absorption

Digested food is now able to pass into the blood vessels in the wall of the intestine through the process of diffusion. The small intestine is the site where most of the nutrients from ingested food are absorbed. The inner wall, or mucosa, of the small intestine is lined with simple columnar epithelial tissue. Structurally, the mucosa is covered in wrinkles or folds called plicae circulares, which 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 individual 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 the absorption of nutrients.

Each villus has a network of capillaries and fine lymphatic vessels called lacteals close to its surface. The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries (amino acids and carbohydrates) and lacteals (lipids). 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. The food that remains undigested and unabsorbed passes into the large intestine.

Absorption of the majority of nutrients takes place in the jejunum, with the following notable exceptions:

• Iron is absorbed in the duodenum.
• Vitamin B12 (Extrinsic factor) and bile salts are absorbed in the terminal ileum.
• Water and lipids are absorbed by passive diffusion throughout the small intestine.
• Sodium bicarbonate is absorbed by active transport and glucose and amino acid co-transport.
• Fructose is absorbed by facilitated diffusion.

Immunological

The small intestine supports the body's immune system. The presence of probiotic flora appear to contribute positively to the host's immune system.

Clinical relevance

See also: Gastrointestinal disease

The small intestine is a complex organ, and as such, there are a very large number of possible conditions that may affect the function of the small bowel. A few of them are listed below, some of which are common, with up to 10% of people being affected at some time in their lives, while others are vanishingly rare.

• Small intestine obstruction or obstructive disorders
  • Paralytic ileus
  • Volvulus
  • Hernia
  • Adhesions
  • Obstruction from external pressure
  • Obstruction by masses in the lumen (foreign bodies, bezoar, gallstones)

• Infectious diseases
  • Giardiasis
  • Ascariasis
  • Tropical sprue
  • Tape worm (Diphyllobothrium latum, Taenia Solium, Taenia solium, Hymenolepsis nana)
  • Hookworm (e.g. Necator americanus, Ancylostoma duodenale)
  • Nematodes (e.g. Ascaris lumbricoides)
  • Other Protozoa (e.g. Cryptosporidium parvum, Isopora belli, Cyclospora, Microsporidia, Entamoeba histolytica)
  • Bacterial Infections
    • Enterotoxigenic E. coli
    • Salmonella enterica
    • Campylobacter
    • Shigella
    • Yersinia
    • Clostridium difficile (antibiotic-associated colitis, Pseudomembranous Colitis
    • Mycobacterium (disseminated Mycobacterium tuberculosis)
    • Whipple's Disease
    • Vibrio (Cholera)
    • Enteric (Typhoid) Fever (Salmonella enterica var. typhii) and Paratyphoid fever
    • Bacillus cereus
    • Clostridium perfringens (Gas Gangrene)
  • Viral Infections
    • Rotavirus
    • Norovirus
    • Astrovirus
    • Adenovirus
    • Calicivirus
  • Small bowel bacterial overgrowth syndrome

• Neoplasms (Cancers)
  • Adenocarcinoma
  • Carcinoid
  • Gastrointestinal Stromal Tumor (GIST)
  • Lymphoma
  • Sarcoma
  • Leiomyoma
  • metastatic tumors, especially SCLC or Melanoma

• Developmental, Congenital or Genetic Conditions
  • Duodenal (Intestinal) Atresia
  • Hirschsprung's Disease
  • Meckel's Diverticulum
  • Pyloric Stenosis
  • Pancreas Divisum
  • Ectopic Pancreas
  • Enteric duplication cyst
  • Situs Inversus
  • Cystic Fibrosis
  • Malrotation
  • Persistent Urachus
  • Omphalocele
  • Gastroschisis
  • Disachharidase (lactase) deficiencies
  • Primary Bile Acid Malsorption
  • Gardner Syndrome
  • Familial Adenomatous Polyposis Syndrome (FAP)

• Other Conditions
  • Crohn's disease, and the more general Inflammatory Bowel Disease
  • Typhlitis (neutropenic colitis in the immunosuppressed
  • Coeliac disease (Sprue or Non-Tropical Sprue)
  • Mesenteric ischemia
  • Embolus or Thrombus of the Superior Mesenteric Artery or the Superior Mesenteric Vein
  • Arteriovenous malformation
  • Gastric dumping syndrome
  • Irritable Bowel Syndrome
  • Duodenal (Peptic) Ulcers
  • Gastrointestinal perforation
  • Lymphatic Obstruction due to various causes
  • Hyperthyroidism
  • Diabetic Neuropathy
  • Diverticula
  • Radiation Enterocolitis
  • Drug Induced Injury
  • Diversion Colitis
  • Mesenteric cysts
  • Peritoneal Infection
  • Sclerosing Retroperitonitis

In other animals

The small intestine is found in all tetrapods and also in teleosts, although its form and length vary enormously between species. In teleosts, it is relatively short, typically around one and a half times the length of the fish's body. It commonly has a number of pyloric caeca, small pouch-like structures along its length that help to increase the overall surface area of the organ for digesting food. There is no ileocaecal valve in teleosts, with the boundary between the small intestine and the rectum being marked only by the end of the digestive epithelium.

In tetrapods, the ileocaecal valve is always present, opening into the colon. The length of the small intestine is typically longer in tetrapods than in teleosts, but is especially so in herbivores, as well as in mammals and birds, which have a higher metabolic rate than amphibians or reptiles. The lining of the small intestine includes microscopic folds to increase its surface area in all vertebrates, but only in mammals do these develop into true villi.

The boundaries between the duodenum, jejunum, and ileum are somewhat vague even in humans, and such distinctions are either ignored when discussing the anatomy of other animals, or are essentially arbitrary.

There is no small intestine as such in non-teleost fish, such as sharks, sturgeons, and lungfish. Instead, the digestive part of the gut forms a spiral intestine, connecting the stomach to the rectum. In this type of gut, the intestine itself is relatively straight, but has a long fold running along the inner surface in a spiral fashion, sometimes for dozens of turns. This valve greatly increases both the surface area and the effective length of the intestine. The lining of the spiral intestine is similar to that of the small intestine in teleosts and non-mammalian tetrapods.

In lampreys, the spiral valve is extremely small, possibly because their diet requires little digestion. Hagfish have no spiral valve at all, with digestion occurring for almost the entire length of the intestine, which is not subdivided into different regions.

Additional images

• The small intestine lies behind the greater omentum.

• Small intestine in situ, gerter omentum folded upwards.

• Small intestine pulled out to the left, showing the underlying peritoneum, and the mesentierial connection.

• Small intestine removed, showing underlying structures, and mesentery.

• Cross section showing the small intestine as it passes back and forth in the peritoneal cavity.

• Third state of the development of the intestinal canal and peritoneum, seen from in front (diagrammatic). The mode of preparation is the same as in Fig 400

• Second stage of development of the intestinal canal and peritoneum, seen from in front (diagrammatic). The liver has been removed and the two layers of the ventral mesogastrium (lesser omentum) have been cut. The vessels are represented in black and the peritoneum in the reddish tint.

• First stage of the development of the intestinal canal and the peritoneum, seen from the side (diagrammatic). From colon 1 the ascending and transverse colon will be formed and from colon 2 the descending and sigmoid colons and the rectum.

• Lower half of right sympathetic cord

• Topography of thoracic and abdominal viscera

See also

• Large intestine
• Stomach

Notes and references

Bibliography

• Sherwood, Lauralee (2006). Fundamentals of physiology: a human perspective (Third ed.). Florence, KY: Cengage Learning. p. 768. ISBN 0-534-46697-4. 
• 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
• Thomson A, Drozdowski L, Iordache C, Thomson B, Vermeire S, Clandinin M, Wild G (2003). "Small bowel review: Normal physiology, part 1.". Dig Dis Sci 48 (8): 1546–64. doi:10.1023/A:1024719925058. PMID 12924651. 
• Thomson A, Drozdowski L, Iordache C, Thomson B, Vermeire S, Clandinin M, Wild G (2003). "Small bowel review: Normal physiology, part 2.". Dig Dis Sci 48 (8): 1565–81. doi:10.1023/A:1024724109128. PMID 12924652. 

UpToDate Contents

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• Lovy J1, Friend SE1.
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• European journal of pharmacology.Eur J Pharmacol.2015 Jul 5;758:72-81. doi: 10.1016/j.ejphar.2015.03.072. Epub 2015 Apr 6.
• Monoacylglycerol acyltransferase 2 (MGAT2) plays an important role in intestinal fat absorption. We discovered the novel MGAT2 inhibitor, JTP-103237, and evaluated its pharmacological profile. JTP-103237 selectively inhibited MGAT2 without remarkable species differences and reduced absorbed lipids i
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Japanese Journal

• 症例 腹腔鏡補助下に切除した上腸間膜動脈血栓塞栓症による狭窄型虚血性小腸炎の2例

• 松本 奏吉,前山 良,真鍋 達也 [他]
• 外科 = Surgey : 臨床雑誌 77(9), 1063-1067, 2015-09
• NAID 40020567571

• 第444回東京医科大学臨床懇話会 大量消化管出血にて緊急手術を要した小腸GIST症例

• 島崎 二郎,田渕 崇伸,村上 昌 [他]
• 東京医科大学雑誌 73(3), 298-307, 2015-07
• NAID 40020566042

• 放射線誘導性小腸上皮傷害におけるTLR3の役割

• 武村 直紀,植松 智
• 臨床免疫・アレルギー科 = Clinical immunology & allergology 64(1), 70-77, 2015-07
• NAID 40020540511

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Related Pictures

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★リンクテーブル★

リンク元	「小腸」「small intestinal」
拡張検索	「small intestine carcinoma」「nonspecific multiple ulcer of small intestine」
関連記事	「small」「intestine」

「小腸」

　　[★]

英

small intestine (Z)

ラ

intestinum tenue

関

管腔内消化

• 小腸は3大栄養素の消化、吸収を行う重要な部位である
• 腸液を分泌する

解剖学

定義

• 胃の幽門より盲腸に至るまで。
• 十二指腸＋腸間膜小腸

組織学

→腸腺

生理学

運動の型

• 1. 食後期

• a．分節運動 segmentation
• b．蠕動運動 peristalsis

蠕動ラッシュperistalic rush：急速移動。感染性下痢など腸粘膜の異常刺激による。

• c. 振子運動

• 2. 空腹期

消化間欠期伝播性収縮

運動の発生機構

• 1. 筋原性

腸平滑筋固有リズムによる。ペースメーカーとなる細胞により発生する。

徐波 slow wave、基本的電気リズム basic electric thythm (BER)

• 2. 神経性

外来神経系

副交感性：促進

交感性　：抑制

内在神経系

胃小腸反射により食後期運動誘発

なお、IMCの調節には外来、内在神経系のいずれも関係する

• 3. 液性

ガストリン、コレシストキニン、インスリン

食後期運動増大

ガストリン

IMC抑制

モチリン

IMC誘発

セクレチン、グルカゴン

運動抑制

炭水化物の吸収

• 食物中の3大炭水化物.
• 1. 二糖類disaccharides

スクロース(グルコース+フルクトース)

マルトース(グルコース+グルコース)

ラクトース(グルコース+ガラクトース)

• 2.ポリサッカライド

植物性でん粉

アミロース　　：グルコースが直鎖状に重合

アミロペクチン：グルコースが樹枝状に重合

直鎖部はα1,4結合

分枝部はα1,6結合

動物性でん粉

グリコーーゲン

• 3.セルロース

グルコースのβ1,4結合(消化不可)

炭水化物の消化

• 1. 管内消化

管内消化は、主に口腔、十二指腸で起こる

唾液αアミラーゼと膵αアミラーゼにより、直鎖状に2～9分子重合したグルコースまで分解される

αアミラーゼは直鎖部分(α1,4結合)を加水分解する

唾液αアミラーゼは作用が弱く、また胃で失活する

マルトース(グルコース2分子)

マルトリオース(グルコース3分子)

α1,4結合マルトオリゴ糖(グルコース4-9分子)

α限界デキストリン(グルコース5-9分子、分岐したオリゴ糖)

• 2. 膜消化 membrane digestion (終末消化terminal digestion)

膜消化は小腸の刷子縁で起こる。

刷子縁にはオリゴ糖消化酵素が存在する。

ラクターゼ：ラクトース→グルコース+ガラクトース

スクラーゼ：スクロース→グルコース+フルクトース

マルターゼ：マルトース→グルコース+グルコース

トレハラーゼ：トレハロース→グルコース+グルコース

αデキストリナーゼ：α1,4結合,α1,6結合の分解(=isomaltase)

グルコアミラーゼ：マルトオリゴ糖(α1,4結合)→グルコース

• 3. 吸収(炭水化物の90-95%が小腸で吸収される。)

• グルコース、ガラクトース～一能動輸送

刷子縁膜

Na依存性能動輸送を介して細胞内に取り込まれる。Na+とグルコース(ガラクトース)の共輸送体であるSGLT1が、Na+の濃度勾配を利用して細胞内に取り込む(2次的能動輸送)

外側基底膜

GLUT2による促進拡散により細胞外に拡散する

• フルクトース

刷子縁膜

GLUT5によるNa非依存的促進拡散により細胞内に取り込まれる。

細胞内

フルクトース+Pi→グルコース+乳酸

外側基底膜

GLUT2による促進拡散により細胞外に拡散する

炭水化物の吸収傷害

腸内炭水化物濃度↑→腸内浸透圧↑　　　　　→下痢

　　　　　　　　　→腸内フローラ(細菌叢)　→腸内ガス発生

乳糖不耐症

小腸上皮細胞刷子縁におけるラクターゼ産生不能

タンパク質の吸収

• 1. 管内消化

胃や膵臓でタンパク質を分解してオリゴペプチド(アミノ酸4個以上)を生成

1-1. 消化酵素の活性化

ペプシン

胃液ペプシノーゲン　→　(H+が触媒:::)　→　ペプシン

胃液ペプシノーゲン　→　(ペプシンが触媒)　→　ペプシン

トリプシン

膵液トリプシノーゲン　→　(エンテロペプチダーゼ)　→　トリプシン

膵液トリプシノーゲン　→　(トリプシンが触媒::)　→　トリプシン

その他のタンパク質分解酵素(カルボキシペプチダーゼA,B)

トリプシンが活性化

• 2. 終末消化 (膜消化＋細胞内消化)

刷子縁でオリゴペプチドの分解がおき、そのための酵素ペプチド分解酵素が存在する。

アミノペプチダーゼ

N末から加水分解してアミノ酸を遊離

ジペプチダーゼ

ジペプチドを2個のアミノ酸に分解

ジペプチジルアミノペプチダーゼ

N末よりジペプチドを遊離する

• 3. 吸収

• アミノ酸輸送

刷子縁膜

Na+依存性能動的輸送

中性アミノ酸、イミノ酸(プロリン、水酸化プロリン)、酸性アミノ酸:::::::::::Na＋非依存性促進拡散

塩基性アミノ酸、中性アミノ酸(疎水基を有するもの)

外側基底膜

Na＋依存性能動的輸送、Na＋非依存性促進拡散、単純拡散(外側基底膜はアミノ酸透過性高い)

• ペプチド輸送

刷子縁膜

Na+/H+ antiporter

2H+/ペプチド synporter

細胞内

プロリダーゼ、ジペプチダーゼ、トリペプチダーゼによる分解

外側基底膜

Na+-K+-ATPase

脂質の吸収

• 1. 食物中の脂質

トリグリセリド(中性脂肪)：C14～C18

コレステロール

コレステロールエステル

リン脂質::::::::：主にレシチン

• 2. 消化

• 2-1. 乳化

乳化は脂肪水解を速める

胆汁酸、レシチンなどにより1μm以下の脂肪滴形成

• 2-2. 脂肪水解

膵リパーゼ

トリグリセリド　→　２分子の遊離脂肪酸(FFA)　+　2-モノグリセリド

コレステロールエステラーゼ

コレステロールエステル　→　FFA　+　コレステロール

ホスホリパーゼA2

レシチン　→　FFA　+　リゾレシチン

• 2-3. ミセル形成

脂肪分解産物(モノグリセリド，リゾレシチン，FFA，コレステロール，脂溶性ビタミン)

胆汁酸、レシチンとミセル形成

• 3. 吸収

ミセルが微絨毛周囲の非撹拝層に侵入→単純拡散により吸収(脂肪の消化・吸収過程の律速過程)

• 4. カイロミクロン形成

ミセルにより細胞内に脂肪分解産物が運ばれ、滑面小胞体内で脂肪分解産物から脂質が再合成される。その後、リポ蛋白にと結合してカイロミクロンとなり、ゴルジ装置に入りエキソサイトーシスにより絨毛リンパ管に入る。

栄養の吸収部位

• 鉄：十二指腸
• カルシウム：十二指腸　←　Billroth II法により骨萎縮
• 葉酸：十二指腸、空腸
• ビタミンD：十二指腸、空腸　←　Billroth II法により骨萎縮
• ビタミンB12：回腸
• 胆汁：回腸

「small intestinal」

　　[★]

• 小腸の、小腸性の

関

small intestine

「small intestine carcinoma」

　　[★]

小腸癌、小腸がん

関

cancer of the intestine

「nonspecific multiple ulcer of small intestine」

　　[★] 非特異性多発性小腸潰瘍症

「small」

　　[★]

• adj.

• 小さい

関

little、petit、tiny

　 　 　 　 　 　 　

「intestine」

　　[★]

• n.

• 腸

関

bowel、entero、gut、intestinal