出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2016/07/22 06:41:19」(JST)
Stomach | |
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The stomach is located centre left in the human body.
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1. Body of stomach 2. Fundus 3. Anterior wall 4. Greater curvature 5. Lesser curvature 6. Cardia 9. Pyloric sphincter 10. Pyloric antrum 11. Pyloric canal 12. Angular incisure 13. Gastric canal 14. Rugae[1]
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Details | |
Precursor | Foregut |
System | Digestive system |
Artery | Right gastric artery, left gastric artery, right gastro-omental artery, left gastro-omental artery, short gastric arteries |
Vein | Right gastric vein, left gastric vein, right gastroepiploic vein, left gastroepiploic vein, short gastric veins |
Nerve | Celiac ganglia, vagus nerve[2] |
Lymph | Celiac lymph nodes[3] |
Identifiers | |
Latin | Ventriculus |
Greek | Gaster |
MeSH | A03.556.875.875 |
Dorlands /Elsevier |
Stomach |
TA | A05.5.01.001 |
FMA | 7148 |
Anatomical terminology
[edit on Wikidata]
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The stomach is a muscular, hollow, dilated part of the gastrointestinal tract that functions as an important organ in the digestive system. The stomach is present in many animals including vertebrates, echinoderms, insects (mid-gut), and molluscs. In humans and many other vertebrates it is involved in the second phase of digestion, following mastication (chewing).
In most vertebrates, the stomach is located between the esophagus and the small intestine. It secretes digestive enzymes and gastric acid to aid in food digestion. The pyloric sphincter controls the passage of partially digested food (chyme) from the stomach into the duodenum where peristalsis takes over to move this through the rest of the intestines.
The stomach lies between the esophagus and the duodenum (the first part of the small intestine). It is in the left upper part of the abdominal cavity. The top of the stomach lies against the diaphragm. Lying behind the stomach is the pancreas. A large double fold of visceral peritoneum called the greater omentum hangs down from the greater curvature of the stomach.
Two sphincters keep the contents of the stomach contained; the lower esophageal sphincter (found in the cardiac region), at the junction of the oesophagus and stomach, and the pyloric sphincter at the junction of the stomach with the duodenum.
The stomach is surrounded by parasympathetic (stimulant) and sympathetic (inhibitor) plexuses (networks of blood vessels and nerves in the anterior gastric, posterior, superior and inferior, celiac and myenteric), which regulate both the secretions activity and the motor (motion) activity of its muscles.
In adult humans, the stomach has a relaxed, near empty volume of about 75 millilitres.[4] Because it is a distensible organ, it normally expands to hold about one litre of food.[5] The stomach of a newborn human baby will only be able to retain about 30 millilitres.
In classical anatomy, the stomach is divided into four sections, beginning at the Gastric cardia,[6] each of which has different cells and functions.
The lesser curvature of the stomach is supplied by the right gastric artery inferiorly, and the left gastric artery superiorly, which also supplies the cardiac region. The greater curvature is supplied by the right gastro-omental artery inferiorly and the left gastro-omental artery superiorly. The fundus of the stomach, and also the upper portion of the greater curvature, is supplied by the short gastric artery which arises from the splenic artery.
Like the other parts of the gastrointestinal tract, the stomach walls consist of an outer mucosa, and inner submucosa, muscularis externa, and serosa.
The gastric mucosa of the stomach consists of the epithelium and the lamina propria (composed of loose connective tissue), with a thin layer of smooth muscle called the muscularis mucosae separating it from the submucosa beneath. The submucosa lies under the mucosa and consists of fibrous connective tissue, separating the mucosa from the next layer. Meissner's plexus is in this layer. The muscularis externa lies beneath the submucosa, and is unique from other organs of the gastrointestinal tract, consisting of three layers:
The stomach also possesses a serosa, consisting of layers of connective tissue continuous with the peritoneum.
Different types of cells are found at the different layers of the gastric glands:
Layer of stomach | Name | Secretion | Region of stomach | Staining |
Isthmus of gland | Foveolar cells | Mucus gel layer | Fundic, cardiac, pyloric | Clear |
Body of gland | Parietal (oxyntic) cells | Gastric acid and intrinsic factor | Fundic only | Acidophilic |
Base of gland | Chief (zymogenic) cells | Pepsinogen and gastric lipase | Fundic only | Basophilic |
Base of gland | Enteroendocrine (APUD) cells | Hormones gastrin, histamine, endorphins, serotonin, cholecystokinin and somatostatin | Fundic, cardiac, pyloric | – |
Cardiac glands (at cardia)
Pyloric glands (at pylorus)
Fundic glands (at fundus)
A bolus (a small rounded mass of chewed up food) enters the stomach through the esophagus via the lower esophageal sphincter. The stomach releases proteases (protein-digesting enzymes such as pepsin) and hydrochloric acid, which kills or inhibits bacteria and provides the acidic pH of two for the proteases to work. Food is churned by the stomach through muscular contractions of the wall called peristalsis – reducing the volume of the fundus, before looping around the fundus[9] and the body of stomach as the boluses are converted into chyme (partially digested food). Chyme slowly passes through the pyloric sphincter and into the duodenum of the small intestine, where the extraction of nutrients begins. Depending on the quantity and contents of the meal, the stomach will digest the food into chyme anywhere between forty minutes and a few hours. The average human stomach can comfortably hold about a litre of food.
Gastric juice in the stomach also contains pepsinogen. Hydrochloric acid activates this inactive form of enzyme into the active form, pepsin. Pepsin breaks down proteins into polypeptides.
Although the absorption is mainly a function of the small intestine, some absorption of certain small molecules nevertheless does occur in the stomach through its lining. This includes:
The parietal cells of the stomach are responsible for producing intrinsic factor, which is necessary for the absorption of vitamin B12. B12 is used in cellular metabolism and is necessary for the production of red blood cells, and the functioning of the nervous system.
The movement and the flow of chemicals into the stomach are controlled by both the autonomic nervous system and by the various digestive system hormones:
Gastrin | The hormone gastrin causes an increase in the secretion of HCl from the parietal cells, and pepsinogen from chief cells in the stomach. It also causes increased motility in the stomach. Gastrin is released by G cells in the stomach in response to distension of the antrum, and digestive products (especially large quantities of incompletely digested proteins). It is inhibited by a pH normally less than 4 (high acid), as well as the hormone somatostatin. |
Cholecystokinin | Cholecystokinin (CCK) has most effect on the gall bladder, causing gall bladder contractions, but it also decreases gastric emptying and increases release of pancreatic juice which is alkaline and neutralizes the chyme. CCK is synthesized by I-cells in the mucosal epithelium of the small intestine. |
Secretin | In a different and rare manner, secretin, produced in the small intestine, has most effects on the pancreas, but will also diminish acid secretion in the stomach. |
Gastric inhibitory peptide | Gastric inhibitory peptide (GIP) decreases both gastric acid release and motility. |
Enteroglucagon | Enteroglucagon decreases both gastric acid and motility. |
Other than gastrin, these hormones all act to turn off the stomach action. This is in response to food products in the liver and gall bladder, which have not yet been absorbed. The stomach needs to push food into the small intestine only when the intestine is not busy. While the intestine is full and still digesting food, the stomach acts as storage for food.
Epidermal growth factor (EGF) results in cellular proliferation, differentiation, and survival.[14] EGF is a low-molecular-weight polypeptide first purified from the mouse submandibular gland, but since then found in many human tissues including submandibular gland, parotid gland. Salivary EGF, which seems also regulated by dietary inorganic iodine, plays also an important physiological role in the maintenance of oro-oesophageal and gastric tissue integrity. The biological effects of salivary EGF include healing of oral and gastroesophageal ulcers, inhibition of gastric acid secretion, stimulation of DNA synthesis as well as mucosal protection from intraluminal injurious factors such as gastric acid, bile acids, pepsin, and trypsin and to physical, chemical and bacterial agents.[15]
The stomach can "taste" sodium glutamate using glutamate receptors[16] and this information is passed to the lateral hypothalamus and limbic system in the brain as a palatability signal through the vagus nerve.[17] The stomach can also sense, independently to tongue and oral taste receptors, glucose,[18] carbohydrates,[19] proteins,[19] and fats.[20] This allows the brain to link nutritional value of foods to their tastes.[18]
A large number of studies have indicated that most cases of peptic ulcers, gastritis, and stomach cancer are caused by Helicobacter pylori infection. The stomach has to regenerate a new layer of mucus every two weeks, or else damage to the epithelium may result.
Many bariatric surgery procedures involve the stomach, in order to lose weight. A gastric band may be placed around the cardia area, which can adjust to limit intake. The anatomy of the stomach may be modified, or the stomach may be bypassed entirely.
Surgical removal of the stomach is called a Gastrectomy, and removal of the cardia area is a called a "cardiactomy". "Cardiectomy" is a term that is also used to describe removal of the heart.[21][22][23] The former procedure may be carried out because of gastric cancer or severe perforation of the stomach wall.
There were previously conflicting statements in the academic anatomy community[24][25][26] over whether the cardia is part of the stomach, part of the esophagus or a distinct entity. Modern surgical and medical textbooks have agreed that "The gastric cardia is now clearly considered to be part of the stomach."[27][28]
The word stomach is derived from the Latin stomachus which is derived from the Greek word stomachos (στόμαχος), ultimately from stoma (στόμα), "mouth".[29] The words gastro- and gastric (meaning related to the stomach) are both derived from the Greek word gaster (γαστήρ, meaning "belly"[30][31]).[32]
Comparison of stomach glandular regions from several mammalian species. Frequency of glands may vary more smoothly between regions than is diagrammed here. Asterisk (ruminant) represents the omasum, which is absent in Tylopoda (Tylopoda also has some cardiac glands opening onto ventral reticulum and rumen[33]) Many other variations exist among the mammals.[34][35]
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Although the precise shape and size of the stomach varies widely among different vertebrates, the relative positions of the esophageal and duodenal openings remain relatively constant. As a result, the organ always curves somewhat to the left before curving back to meet the pyloric sphincter. However, lampreys, hagfishes, chimaeras, lungfishes, and some teleost fish have no stomach at all, with the esophagus opening directly into the anus. These animals all consume diets that either require little storage of food, or no pre-digestion with gastric juices, or both.[36]
The gastric lining is usually divided into two regions, an anterior portion lined by fundic glands, and a posterior with pyloric glands. Cardiac glands are unique to mammals, and even then are absent in a number of species. The distributions of these glands vary between species, and do not always correspond with the same regions as in man. Furthermore, in many non-human mammals, a portion of the stomach anterior to the cardiac glands is lined with epithelium essentially identical to that of the esophagus. Ruminants, in particular, have a complex stomach, the first three chambers of which are all lined with esophageal mucosa.[36]
In birds and crocodilians, the stomach is divided into two regions. Anteriorly is a narrow tubular region, the proventriculus, lined by fundic glands, and connecting the true stomach to the crop. Beyond lies the powerful muscular gizzard, lined by pyloric glands, and, in some species, containing stones that the animal swallows to help grind up food.[36]
Greater omentum and stomach
Stomach
A more realistic image, showing the celiac artery and its branches; the liver has been raised, and the lesser omentum and anterior layer of the greater omentum removed.
An autopsy of a stomach. 2012 Instituto Nacional de Cardiología
Stomach
The gastrointestinal wall of the stomach.
Wikimedia Commons has media related to Stomach. |
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value (help) (PDF (eBook)). Montrouge: John Libbey Eurotext. p. 129. ISBN 9782742000371. Retrieved 2015-04-26. Look up stomach in Wiktionary, the free dictionary. |
Anatomy of the gastrointestinal tract, excluding the mouth
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リンク元 | 「食道」「食道胃接合部」「食道胃移行部」「EGJ」 |
関連記事 | 「junction」 |
O:食道入口部 esophageal orifice | |||
Ce: 頚部食道 cervical esophagus | |||
S: 胸骨上縁 margin of the sternum | |||
Te: 胸部食道 thoracic esophagus | Ut: 胸部上部食道 upper thoracic esophagus | ||
Mt: 胸部中部食道 middle thoracic esophagus | ↑ | B: 気管分岐部下縁 tracheal bifurcation | |
↓ | |||
Lt: 胸部下部食道 lower thoracic esophagus | ↑ | ||
D: 横隔膜 diaphragm | |||
H: 食道裂孔 esophageal hiatus | |||
Ae: 腹部食道 abdominal esophagus | ↓ | ||
EGJ: 食道胃接合部 esophagogastric junction |
部位 | 名称 | 筋肉 | 神経 | 運動性 | シナプスする構造 | 最終的な伝達物質 | 運動 | |
上部1/3 | 上食道括約部 | UES | 横紋筋 | 舌咽神経、迷走神経(疑核) | 随意性 | 運動終板のアセチルコリン受容体 | アセチルコリン | 弛緩 |
平滑筋 | 迷走神経 | 不随意性 | 壁内コリン作動性運動神経 | |||||
下端部 | 下食道括約部 | LES | 平滑筋 | 迷走神経 | 不随意性 | 壁内非アドレナリン作動性抑制運動神経 | NO, VIP | 弛緩 |
交感神経 | 平滑筋α受容体 | アドレナリン | 収縮 |
層構造 | 1 | 2 | 3 | 4 | 5 | 6 | |||||||||
器官 | 単層扁平上皮 | 単層立方上皮 | 単層円柱上皮 | 角化重層扁平上皮 | 非角化重層扁平上皮 | 上皮表層の構成細胞 | 粘膜固有層 | 腺の構成細胞 | 粘膜筋板 | 粘膜下組織 (大抵、粗結合組織) |
筋層 | 漿膜(結合組織+単層扁平上皮) 外膜(結合組織のみ) | |||
食道 | ○ | 食道噴門腺 (咽頭付近と胃付近に局在)、粘液腺 |
粘液細胞 (スムーズに食べ物を流す) |
縱層 (縦走筋のみ) |
固有食道腺(粘液腺、管状胞状、ペプシノーゲン、リゾチーム) | 内輪筋層 外縱筋層 (食道上1/3:骨格筋、食道中1/3:骨格筋、平滑筋、食道下1/3:平滑筋) |
外膜(横隔膜まで) 漿膜 |
[★] 食道胃接合部 esophagogastric junction
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