Stomach

This article is about the internal organ. For the middle part of the body, see Abdomen. For other uses, see Stomach (disambiguation).

"Cardia" redirects here. For the ancient Greek colony, see Cardia (Thrace).

"Gastric" redirects here. For the sauce flavoring, see Gastrique.

Stomach
The stomach is located centre left in the human body.
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
Details
Latin	Ventriculus
Greek	Gaster
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
Lymph	Celiac lymph nodes
Identifiers
MeSH	A03.556.875.875
Dorlands /Elsevier	Stomach
TA
TH	{{#property:P1694}}
TE	{{#property:P1693}}
FMA	{{#property:P1402}}
Anatomical terminology [[[d:|edit on Wikidata]]]

The stomach is a muscular, hollow, dilated part of the gastrointestinal tract that functions as a vital digestive organ. The stomach is present in humans and many other animals, including several invertebrates. In the digestive system the stomach is involved in the second phase of digestion, following mastication (chewing).

In humans and many other animals, the stomach is located between the oesophagus 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.

Structure

Sections of the human stomach

In humans the stomach lies between the oesophagus 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 oesophageal 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. Because it is a distensible organ, it normally expands to hold about one litre of food. The stomach of a newborn human baby will only be able to retain about 30 millilitres.

Sections

In classical anatomy, the human stomach is divided into four sections, beginning at the Gastric cardia, each of which has different cells and functions.

• The cardia is where the contents of the oesophagus empty into the stomach. The cardia is defined as the region following the "z-line" of the gastroesophageal junction, the point at which the epithelium changes from stratified squamous to columnar. Near the cardia is the lower oesophageal sphincter.
• The fundus (from Latin, "bottom") is formed by the upper curvature of the organ.
• The body is the main, central region.
• The pylorus (from Greek, "gatekeeper") is the lower section of the organ that facilitates emptying the contents into the small intestine.

Blood supply

Schematic image of the blood supply to the human stomach: left and right gastric artery, left and right gastro-omental artery and short gastric artery.

The lesser curvature of the human 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.

Histology

Micrograph showing a cross section of the human stomach wall, in the body portion of the stomach. H&E stain.

Main article: Gastrointestinal wall

Like the other parts of the gastrointestinal tract, the human 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 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.
• The middle circular layer: At this layer, the 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.
• Auerbach's plexus (AKA myenteric plexus) is found between the outer longitundinal and the middle circular layer and is responsible for the innervation of both (causing peristalsis and mixing)
• The outer longitudinal layer is responsible for moving the bolus towards the pylorus of the stomach through muscular shortening.

The stomach also possesses a serosa, consisting of layers of connective tissue continuous with the peritoneum.

Gastric glands

Main article: Gastric glands

In humans, 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	–

• 

  Human cardiac glands (at cardia)

• 

  Human pyloric glands (at pylorus)

• 

  Human fundic glands (at fundus)

Function

Digestion

Main article: Digestion

In the human digestive system, a bolus (a small rounded mass of chewed up food) enters the stomach through the oesophagus via the lower oesophageal 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 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.

Absorption

Although the absorption in the human stomach 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:

• Water, if the body is dehydrated
• Medication, like aspirin
• Amino acids
• 10–20% of ingested ethanol (e.g. from alcoholic beverages)
• Caffeine
• To a small extent water-soluble vitamins (most are absorbed in the small intestine)

The parietal cells of the human 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.

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 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.

Stomach acid

Main article: Gastric acid

Epidermal growth factor (EGF) results in cellular proliferation, differentiation, and survival. 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.

Sequence of total-body scintigraphies of a woman after intravenous injection of iodine-123 demonstrating iodine uptake by the gastric mucosa

Stomach as nutrition sensor

The human stomach can "taste" sodium glutamate using glutamate receptors and this information is passed to the lateral hypothalamus and limbic system in the brain as a palatability signal through the vagus nerve. The stomach can also sense, independently to tongue and oral taste receptors, glucose, carbohydrates, proteins, and fats. This allows the brain to link nutritional value of foods to their tastes.

Clinical significance

An endoscopy of a normal stomach of a healthy 65-year-old woman.

Diseases

Main article: Stomach disease

A large number of studies have indicated that most cases of peptic ulcers, gastritis, and stomach cancer in humans 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.

Surgery

In humans, 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. The former procedure may be carried out because of gastric cancer or severe perforation of the stomach wall.

History

There were previously conflicting statements in the academic anatomy community over whether the cardia is part of the stomach, part of the oesophagus 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."

Etymology

The word stomach is derived from the Latin stomachus which is derived from the Greek word stomachos (στόμαχος), ultimately from stoma (στόμα), "mouth". The words gastro- and gastric (meaning related to the stomach) are both derived from the Greek word gaster (γαστήρ, meaning "belly").

Other animals

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) Many other variations exist among the mammals.

Yellow Oesophagus Green Glandular epithelium Purple Cardiac glands Red Gastric glands Blue Pyloric glands Dark blue Duodenum

Although the precise shape and size of the stomach varies widely among different vertebrates, the relative positions of the oesophageal 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 oesophagus 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.

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 humans. 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 oesophagus. Ruminants, in particular, have a complex stomach, the first three chambers of which are all lined with oesophageal mucosa.

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.

In insects there is also a crop. The stomach is called the midgut.

Additional images

• 

  Greater omentum and stomach of humans

• 

  Human stomach

• 

  A more realistic image, showing the celiac artery and its branches in humans; the liver has been raised, and the lesser omentum and anterior layer of the greater omentum removed.

• 

  An autopsy of a human stomach. 2012 Instituto Nacional de Cardiología

• 

  Human stomach

• 

  The gastrointestinal wall of the human stomach.

• 

  Endoscopic image of human fundic gland polyposis.

See also

• Borborygmus, growling of stomach
• Gut flora
• Gastroesophageal reflux disease
• Proton pump inhibitors

External links

• "Stomach" article from the Encyclopedia of Nursing & Allied Health, from enotes.com
• Digestion of proteins in the stomach or tiyan
• Site with details of how ruminants process food
• Medical diagram of gastric blood supply