Stomach

Stomach
The location of the stomach in the 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
Details
Nerve	celiac ganglia, vagus
Lymph	celiac preaortic lymph nodes
Identifiers
Latin	Ventriculus
Greek	Gaster
MeSH	D013270
TA98	A05.5.01.001
TA2	2901
FMA	7148
Anatomical terminology

In most mammals, the stomach is a hollow, muscular organ of the gastrointestinal tract (digestive system), between the throat and the small intestine. It is involved in the second phase of digestion, following mastication (chewing). The word stomach is derived from the Latin stomachus, which derives from the Greek word stomachos (στόμαχος). The words gastro- and gastric (meaning related to the stomach) are both derived from the Greek word gaster (γαστήρ).

This article is primarily about the human stomach, though the information about its processes are directly applicable to most mammals. A major exception to this is cows. For information about the stomach of cows, buffalo and similar mammals, see ruminants.

Functions

The three main functions of the stomach are: 1. to kill parasites and bad bacteria ingested (a few types of bacteria are helpful, such as acidophilus and bifidus), 2. break down the food into smaller particles (mainly by acid, enzymes, and its "churning" motions), so the food is easier to digest, and 3. temporarily hold food and release it at a steady, constant rate, down to lower parts of the digestive system.

The stomach is a highly acidic environment due to the hydrochloric acid it produces and secretes into its hollow interior. An acidic environment (as opposed to alkaline) is necessary to break down and digest many food nutrients, especially proteins which are the basic building blocks for most of the body. Sufficient acid in the stomach also kills many harmful bacteria and parasites.

The stomach's hydrochloric acid usually produces a pH of 1 or 2 (measure of acidity vs alkaline), depending on the mammal species, food intake, time of day, any drugs and other factors. For example, sugar is alkaine, thus, when ingested with proteins, sugar neutralizes the acid to some degree, making it less acidic, so that proteins are less broken down and digested, and fewer bacteria and parasites are killed.

When combined with digestive enzymes in the stomach, a sufficiently acidic (low pH) environment is able to break down large molecules of food into smaller ones, so that they can eventually be absorbed into the blood system, and thus carried to all cells of the body.

An enzyme precursor called pepsinogen is secreted into the stomach by chief cells, and under low pH conditions it turns into pepsin which is necessary for protein digestion.

The human stomach can produce and secrete about 2.2 to 3 liters of gastric acid (stomach acid) per day, with basic secretion levels being typically highest in the evening. The stomach can expand to hold between 1-1.5 liters of food at any one time. It is a temporary food storage area.

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

Oils and fatty acids are broken down mainly by bile that is secreted into the duodenum, the first part of the small intestine, immediately below the stomach. The pancreas secretes additional digestive enzymes (e.g. trypsin, lipase and amylase) into the duodenum as needed.

Absorption of vitamin B12 in the small intestine is dependent on its conjugation with a glycoprotein, called an intrinsic factor which is produced by parietal cells of the stomach.

Abraham liconlon ate a stomach for 5 bucks and i jollyrancher

The stomach lies between the oesophagus (food and liquid throat tube) 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. 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 (network 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 humans, the stomach has a relaxed, empty volume of about 45 ml. It generally expands to hold about 1 litre of food, but can hold as much as 1.5 liters.

Sections

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

Cardia	Where the contents of the esophagus 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

Blood supply to the stomach: left and right gastric artery, left and right gastro-omental artery and short gastric artery.

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..

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

mucosa	The first main layer. This consists of an epithelium, the lamina propria composed of loose connective tissue and which has gastric glands in it 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 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 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 longitudinal 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.

Cross section of stomach wall.

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:

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:

Layer of stomach	Name	Secretion	Region of stomach	Staining
Isthmus of gland	mucous cells	mucus gel layer	Fundic, cardiac, pyloric	Clear
Body of gland	parietal (oxyntic) cells	gastric acid and intrinsic factor	Fundic, cardiac, pyloric	Acidophilic
Base of gland	chief (zymogenic) cells	pepsinogen, rennin	Fundic only	Basophilic
Base of gland	enteroendocrine (APUD) cells	hormones gastrin, histamine, endorphins, serotonin, cholecystokinin and somatostatin	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 hormones:

Gastrin	The hormone gastrin causes an increase in the secretion of HCl, pepsinogen and intrinsic factor from parietal cells 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 and increases release of pancreatic juice which is alkaline and neutralizes the chyme.
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.
Glycogen	Glycogen, produced in the brain and stomach, affects the liver and level of glucose in the stomach.

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

Main article: Stomach disease

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.

See also

• Borborygmus, growling of stomach

External links

• Digestion of proteins in the stomach or tiyan
• Interview with Dr. Jerome Groopman, Highlight at 2:30
• Site with details of how ruminants process food