Human Stomach
Where the stomach is located in the human body.
Diagram from cancer.gov: * 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 notch * 13. Gastric canal * 14. Rugal folds Work of the United States Government
Latin	Ventricular
Gray's	subject #247 1161
Nerve	celiac ganglia, vagus[1]
Lymph	celiac preaortic lymph nodes[2]
MeSH	Stomach
Dorlands/Elsevier	Stomach

The stomach is a muscular, hollow, dilated part of the digestion system which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects (mid-gut), and molluscs. It is involved in the second phase of digestion, following mastication (chewing).

The stomach is located between the esophagus and the small intestine. It secretes protein-digesting enzymes and strong acids to aid in food digestion, (sent to it via oesophageal peristalsis) through smooth muscular contortions (called segmentation) before sending partially digested food (chyme) to the small intestines.

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

Role in digestion[link]

Bolus (masticated food) enters the stomach through the oesophagus via the 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^[3] 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, 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.

Anatomy of the stomach[link]

The stomach lies between the esophagus and the duodenum (the first part of the small intestine). It is on the left upper part of the abdominal cavity. The top of the stomach lies against the diaphragm. Lying behind the stomach is the pancreas. The greater omentum hangs down from the greater curvature.

Greater omentum and stomach

Two sphincters keep the contents of the stomach contained. They are the esophageal sphincter (found in the cardiac region, not an anatomical sphincter) dividing the tract above, and the Pyloric sphincter dividing the stomach from the small intestine.

Stomach

The stomach is surrounded by parasympathetic (stimulant) and orthosympathetic (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 45 ml. Because it is a distensible organ, it normally expands to hold about one litre of food,^[4] but can hold as much as two to three litres. The stomach of a newborn human baby will only be able to retain about 30 ml.

Sections[link]

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

Sections of the stomach

Blood supply[link]

Schematic image of the blood supply to the stomach: left and right gastric artery, left and right gastro-omental artery and short gastric artery.^[5]

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.

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, is supplied by the short gastric artery which arises from splenic artery.

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

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

Glands[link]

Cardiac glands (at cardia)	Pyloric glands (at pylorus)	Fundic glands (at fundus)

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

Control of secretion and motility[link]

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:

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.

EGF in gastric defense[link]

Epidermal growth factor or EGF results in cellular proliferation, differentiation, and survival.^[6] 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.^[7]

Stomach as nutrition sensor[link]

The stomach can "taste" sodium glutamate using glutamate receptors^[8] and this information is passed to the lateral hypothalamus and limbic system in the brain as a palatability signal through the vagus nerve.^[9] The stomach can also sense independently to tongue and oral taste receptors glucose,^[10] carbohydrates^[11] proteins,^[11] and fats.^[12] This allows the brain to link nutritional value of foods to their tastes.^[10]

Absorption[link]

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:

• Water, if the body is too dehydrated
• Medication, like aspirin
• Amino acids (e.g. whey protein shake)
• Vitamin B12

Diseases of the stomach[link]

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.

In other animals[link]

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

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 intestine. These animals all consume diets that either require little storage of food, or no pre-digestion with gastric juices, or both.^[13]

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 oesophagus. Ruminants, in particular, have a complex stomach, the first three chambers of which are all lined with oesophageal mucosa.^[13]

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.^[13]

Comparison of stomach glandular regions from several mammalian species. Yellow: oesophagus; green: glandular epithelium; purple: cardiac glands; red: gastric glands; blue: pyloric glands; dark blue: duodenum. 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 nrumen^[14]) Many other variations exist among the mammals.^[15][16]

See also[link]

• Bariatric surgery, weight loss surgery
• Foveolar cells, mucous producing cells of the stomach
• Peristalsis, muscular movement that occurs in the stomach
• Borborygmus, growling of stomach
• Digestion
• Gastroesophageal reflux disease
• Discovery and development of proton pump inhibitors

References[link]

External links[link]

Look up stomach in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Stomach

• "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