View source for Stomach

__NOTOC__
{{CMG}}



==Overview==
{{Infobox Anatomy
|Name         = Stomach
|Latin        = Ventriculus
|Greek        = Gaster
|GraySubject  = 247
|GrayPage     = 1161
|Image        = Stomach_diagram.svg
|Caption      = The location of the stomach in the body.
|Image2       = Illu stomach.jpg
|Caption2='''Diagram from [http://training.seer.cancer.gov/ss_module07_ugi/unit02_sec02_anatomy.html cancer.gov]:<BR>'''* 1. [[Body of stomach]]<BR>* 2. [[Fundus (stomach)|Fundus]]<BR>* 3. Anterior wall<BR>* 4. [[Greater curvature]]<BR>* 5. [[Lesser curvature]]<BR>* 6. [[Cardia]]<BR>* 9. [[Pyloric sphincter]]<BR>* 10. [[Pyloric antrum]]<BR>* 11. [[Pyloric canal]]<BR>* 12. [[Angular notch]]<BR>* 13. [[Gastric canal]]<BR>* 14. [[Rugal folds]]<BR><BR>Work of the United States Government
|Precursor    =
|System       = |pqp35ykyj 4oh
|Artery       =
|Vein         =
|Nerve        = [[celiac ganglia]], [[vagus]]<ref>{{GeorgiaPhysiology|6/6ch2/s6ch2_30}}</ref>
|Lymph        = celiac [[preaortic lymph node]]s<ref>{{NormanAnatomy|stomach}}</ref>
|MeshName     = Stomach
|MeshNumber   = A03.556.875.875
|DorlandsPre  = g_03
|DorlandsSuf  = 12386049  |
}}
{{SI}}
In [[anatomy]], the '''stomach''' is a bean-shaped hollow muscular [[organ (anatomy)|organ]] of the [[gastrointestinal tract]] involved in the second phase of [[digestion]], following [[mastication]].  The word ''stomach'' is derived from the [[Latin|Latin]] ''stomachus'', which derives from the [[Greek language|Greek]] word ''stomachos'' ({{polytonic|στόμαχος}}). The words ''gastro-'' and ''gastric'' (meaning related to the stomach) are both derived from the Greek word ''gaster'' ({{polytonic|γαστήρ}}).  

==Functions==

The stomach is a highly acidic environment due to [[gastric acid]] production and secretion which produces a [[lumen (anatomy)|luminal]] pH range usually between 1 and 4 depending on the species, food intake, time of the day, drug use, and other factors. Such an environment is able to break down large molecules (such as from food) to smaller ones so that they can eventually be absorbed from the [[small intestine]].  The human stomach can produce and secrete about 2 to 3 liters of gastric acid per day with basal secretion levels being typically highest in the evening.The body produce enzymes to break down different foods.

[[Pepsinogen]] is secreted by [[chief cells]] and turns into [[pepsin]] under low pH conditions and is a necessity in [[protein]] digestion.    

Absorption of [[vitamin B12]] from the [[small intestine]] is dependent on conjugation to a [[glycoprotein]] called [[intrinsic factor]] which is produced by [[parietal cells]] of the stomach.

Other functions include absorbing some [[ions]], [[water]], and some [[lipid]] [[soluble]] [[compounds]] such as [[alcohol]], [[aspirin]], and caffeine.

Another function of the stomach is simply a food storage cavity.

==Anatomy of the human stomach==

The stomach lies between the [[esophagus]] and the [[duodenum]] (the first part of the [[small intestine]]). It is on the left side of the [[abdominal cavity]]. The top of the stomach lies against the [[diaphragm (anatomy)|diaphragm]]. Lying beneath the stomach is the [[pancreas]], and the [[greater omentum]] which hangs from the ''greater curvature''.

Two [[smooth muscle]] valves, or sphincters, keep the contents of the stomach contained. They are the [[esophageal sphincter]] (found in the cardiac region) dividing the tract above, and the [[Pyloric sphincter]]  dividing the stomach from the small intestine.

The stomach is surrounded by parasympathetic (stimulant) and orthosympathetic (inhibitor) plexuses (anterior gastric, posterior, superior and inferior, celiac and myenteric), which regulate both the secretory activity and the motor activity of the muscles.

In humans, the stomach has a volume of about 50 mL when empty. After a meal, it generally expands to hold about 1 litre of food, <ref>Sherwood, Lauralee (2004) ''Human Physiology - From Cells to Systems'' (International Student Edition, 5th ed) p604 Books/Cole - Thomson Learning ISBN 0-534-39536-8</ref> but it can actually expand to hold as much as 4 litres. When drinking milk it can expand to just under 6 pints, or 3.4 litres. <ref>Saladin, Kenneth S. (2004) "Anatomy & Physiology - The Unity of Form and Function" (International Edition, 3rd ed) p950 - The McGraw Hill Companies ISBN 0-07-242903-8</ref>

===Sections===
The stomach is divided into four sections, each of which has different cells and functions. The sections are: 

{| class="wikitable"
| Cardia || Where the contents of the oesophagus empty into the stomach. 
 |- 
 | Fundus || Formed by the upper curvature of the organ. 
 |- 
 | Body or corpus || The main, central region.
 |- 
 | [[Pylorus]] or [[antrum]] || The lower section of the organ that facilitates emptying the contents into the small intestine. 
|}

===Blood supply===
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 gastroepiploic artery]] inferiorly and the  [[left gastroepiploic artery]] superiorly. The fundus of the stomach, and also the upper portion of the greater curvature, are supplied by the [[short gastric artery]]

==Histology of the human stomach==
===Layers===
Like the other parts of the gastrointestinal tract, the stomach walls are made of the following layers, from inside to outside:

{| class="wikitable"
| [[mucosa]] || The first main layer. This consists of an [[epithelium]], the [[lamina propria]] underneath, and a thin layer of [[smooth muscle]] called the [[muscularis mucosae]].
 |- 
 | [[submucosa]] || This layer lies under the mucosa and consists of [[fibrous connective tissue]], separating the mucosa from the next layer. The [[Meissner's plexus]] is in this layer.
 |- 
 | [[muscularis externa]] || 
Under the submucosa, the muscularis externa in the stomach differs from that of<!--parallelism, PLEASE--> other GI organs in that it has three layers of [[smooth muscle]] instead of two. 

* ''inner oblique layer:'' This layer is responsible for creating the motion that churns and physically breaks down the food. It is the only layer of the three which is not seen in other parts of the [[digestive system]]. The antrum has thicker skin cells in its walls and performs more forceful contractions than the fundus. 
* ''middle circular layer:'' At this layer, the [[pyloric valve|pylorus]] is surrounded by a thick circular muscular wall which is normally tonically constricted forming a functional (if not anatomically discrete) pyloric [[sphincter]], which controls the movement of [[chyme]] into the [[duodenum]]. This layer is concentric to the longitudinal axis of the stomach.
* ''outer longituditinal layer:'' [[Auerbach's plexus]] is found between this layer and the middle circular layer.
 |- 
 | [[serosa]] || This layer is under the muscularis externa, consisting of layers of connective tissue continuous with the [[peritoneum]].
|}
[[Image:Stomach.jpg|thumb|left|200px|Cross section of stomach wall.]]
[[Image:Pyloric stomach LPO.jpg|thumb|left|200px|Microscopic cross section of the pyloric part of the stomach wall.]]

===Glands===

The [[epithelium]] of the stomach forms deep pits. The glands at these locations are named for the corresponding part of the stomach:

{| class="wikitable"
| '''[[Cardiac glands]]'''<BR>(at [[cardia]]) || ''' [[Pyloric glands]]'''<BR>(at [[Fundus (stomach)|pylorus]])  || '''[[Fundic glands]]'''<BR>(at [[fundus]])
 |- 
 | [[Image:Gray1053.png|100px]] || [[Image:Gray1054.png|100px]] || [[Image:Gray1055.png|100px]] 
|}

Different types of cells are found at the different layers of these glands:

{| class="wikitable"
| '''Layer of stomach''' || '''Name''' || '''Secretion''' || '''Region of stomach''' || '''Staining'''
 |- 
 | Isthmus of gland ||  [[goblet cells]] || [[mucus]] gel layer || Fundic, cardiac, pyloric || Clear
 |- 
 | Neck of gland || [[parietal cell|parietal (oxyntic) cell]]s  || [[gastric acid]] and [[intrinsic factor]] || Fundic, cardiac, pyloric || [[Acidophilic]]
 |- 
 | Base of gland || [[Gastric chief cell|chief (zymogenic) cell]]s || [[pepsinogen]], [[rennin]] || Fundic only || [[Basophilic]]
 |- 
 | Base of gland || [[enteroendocrine cells|enteroendocrine (APUD) cells]] || [[hormones]] || Fundic, cardiac, pyloric || -
|}

==Control of secretion and motility==
The movement and the flow of chemicals into the stomach are controlled by both the [[autonomic nervous system]] and by the various digestive system [[hormone]]s:

{| class="wikitable"
| [[Gastrin]] || The hormone ''gastrin'' causes an increase in the secretion of HCl, pepsinogen and [[intrinsic factor]] from [[parietal cell]]s in the stomach. It also causes increased motility in the stomach. Gastrin is released by [[G-cells]] in the stomach to distenstion of the antrum, and digestive products. 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]], but it also decreases gastric emptying. 
 |- 
 | [[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 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 only to push food into the small intestine when the intestine is not busy. While the intestine is full and still digesting food, the stomach acts as storage for food.

==Diseases of the stomach==
* [[Dyspepsia]]
* [[Stomach ache]]
* [[Peptic ulcer]]
* [[Achlorhydria]]
* [[Hypochlorhydria]]
* [[Linitis plastica]]
* [[Zollinger-Ellison syndrome]]
* [[Gastroparesis]]
* [[Gastroesophageal reflux disease|GERD]]
* [[Borborygmus]]

Historically, it was widely believed that the highly acidic environment of the stomach would keep the stomach immune from [[infection]].  However, a large number of studies have indicated that most cases of stomach ulcers, [[gastritis]], and stomach [[cancer]] are caused by ''[[Helicobacter pylori]]'' infection.  One of the ways it is able to survive in the stomach involves its [[urease]] enzymes which metabolize [[urea]] (which is normally secreted into the stomach) to [[ammonia]] and [[carbon dioxide]] which neutralizes gastric acid and thus prevents its digestion.  In recent years, it has been discovered that other ''[[Helicobacter]]'' bacteria are also capable of colonizing the stomach and have been associated with gastritis.  

Having too little or no gastric acid is known as [[hypochlorhydria]] or [[achlorhydria]] respectively and are conditions which can have negative health impacts.  Having high levels of gastric acid is called [[hyperchlorhydria]].  Many people believe that hyperchlorhydria can cause [[stomach ulcers]].  However, recent research indicates that the gastric mucosa which secretes gastric acid is acid-resistant.

==Differences among animals==
In ruminants, such as bovines, the stomach is a large multichamber organ which hosts symbiotic [[bacterium|bacteria]] that produce [[enzyme]]s required for the digestion of [[cellulose]] from plant matter, primarily [[cellulase]]. The partially digested plant matter passes through each of the intestine chambers in sequence, being regurgitated and rechewed at least once in the process.

In some animals (such as cats and dogs), the pH of the lumen is lower, usually between 1 and 2.  In contrast, the human stomach pH is usually between 1 and 3.

==References==

{{reflist|2}}

==External links==
{{wiktionary}}
* [http://www.med.uiuc.edu/m1/biochemistry/TA%20reviews/sam/AminoAcids.htm Digestion of proteins in the stomach]
* {{McGrawHillAnimation|physiology|Gastric%20Secretion}}
* [http://uk.geocities.com/bacterial_ed/bacteria_and_food.htm Site with details of how ruminants process food]
*[http://www.comedycentral.com/motherload/index.jhtml?ml_video=83957 Interview with Dr. Jerome Groopman, Highlight at 2:30]


{{Digestive tract}}

[[Category:Abdomen]]
[[Category:Digestive system]]
[[Category:Endocrinology]]

[[ar:معدة]]
[[bs:Želudac]]
[[ca:Estómac]]
[[cs:Žaludek]]
[[da:Mave]]
[[de:Magen]]
[[el:Στομάχι]]
[[es:Estómago]]
[[eo:Stomako]]
[[eu:Urdail]]
[[fr:Estomac]]
[[ko:위 (기관)]]
[[hr:Želudac]]
[[io:Stomako]]
[[id:Lambung]]
[[it:Stomaco]]
[[he:קיבה]]
[[ku:Mîde]]
[[la:Stomachus]]
[[ln:Líkundú]]
[[lt:Skrandis]]
[[hu:Gyomor]]
[[mk:Желудник]]
[[ms:Perut]]
[[nl:Maag]]
[[ja:胃]]
[[ug:ئاشقازان]]
[[pl:Żołądek]]
[[pt:Estômago]]
[[ru:Желудок человека]]
[[scn:Stòmmacu]]
[[simple:Stomach]]
[[sk:Žalúdok]]
[[sl:Želodec]]
[[su:Burih]]
[[fi:Mahalaukku]]
[[sv:Magsäck]]
[[th:กระเพาะอาหาร]]
[[vi:Dạ dày]]
[[tr:Mide]]
[[uk:Шлунок]]
[[yi:מאגען]]
[[zh:胃]]

{{WikiDoc Help Menu}}
{{WikiDoc Sources}}