The stomach is a part of the gastrointestinal tract used in the digestion of food. It is grossly shaped like a "J", and sometimes called "the big J", though its position varies when it is full or empty. The stomach consists of three sections:
The stomach is protected against the intense acidity by mucosa, which have pits and glands. The three different regions of the stomach can be histologically distinguished by the relative lengths of the pits and glands.
|Surface Mucosal cell||Produces mucin bicarbonate|
|Mucosal neck cell||Produces mucin|
|Parietal cell||Produces intrinsic factor HCl and pepsin|
|Enteroendocrine cell||Produces gastrin|
|Chief cell||produces pepsinogen lipase and pepsin|
During development, cells divide in the mucosal neck region, and then migrate bidirectionally and differentiate.
There are three main functions of the stomach that are directly related to motility. Gastric musculature tone must allow the stomach to accommodate the large volume of material ingested while eating. The stomach must contract to mix the ingested food with gastric juice. The motility pattern must be organized to propel partially digested gastric contents into the small bowel. At the same time, the rate of propulsion must be regulated so as not to exceed the absorptive capacity of the small intestine.
Receptive relaxation happens in the Orad stomach due to a nervous reflex having its afferent and efferent pathways in the vagus nerve. If the vagus is cut, receptive relaxation is impaired and the stomach becomes less distensible. The rate of gastric emptying is governed by the ability of the duodenum to deal with the material delivered to it. The most important qualities of the luminal material are its acidity, osmolarity, fat content and protein content. An increase in any of these components will delay the rate of emptying ("enterogastric reflex"). These factors influence the rate of gastric emptying by acting on "receptors" that lie in the duodenum.