Tasks of the stomach
The stomach (ventricle, gaster) is a tubular, muscular hollow organ that is used to store, chop up and homogenize the ingested food.
The capacity for adults is usually between 1200 and 1600 ml, although the external shape of the stomach can be very variable.
About the esophagus gets mixed with saliva, Food from the oral cavity to the stomachwhere by adding Stomach acid the Chyme arises.
By peristalsis (a wave-like movement pattern of the muscles) becomes the Food mixed with gastric juice and further crushed.
After a Dwell time of 1-6 hours becomes the chyme that has already been thrown on in portions in the following Duodenum (Duodenum) emptied.
Functions of the stomach in digestion
The stomach is functionally divided into different sections: the esophagus opens into the upper part, the Cardia, followed by Fundus and the Corpuswhich forms the main part of the stomach. Located further down are Antrum and Pylorus, the lower stomach opening.
The Stomach wall consists of the structure typical of the organs of the gastrointestinal tract smooth muscles and adjacent mucous membrane, with the tunica muscularis however additionally a third layer for the longitudinal and transverse muscles oblique muscle fibers (Fibrae obliquae). These Muscle layer enables strong peristalsis, the the Mixing and Crushing of Stomach contents serve.
In addition to homogenizing the chyme, peristaltic waves also serve to homogenize it Onward transport in the direction of the pylorus, where it is emptied in portions into the Duodenum comes.
The stomach also serves as a reservoir, in which food can be stored so that the body's need for nutrients can be met with a few meals throughout the day.
The regular, portion-wise emptying of the stomach into the Small intestine ensures that the chyme is passed on evenly and smoothly to the subsequent sections of the digestive tract.
The Length of stay of the chyme is in the stomach depending on the food consumed: Easily digestible foods, such as fruit and carbohydrates, stay in the stomach for only 1-2 hours, while foods rich in fat and protein are difficult to digest and only reach the small intestine after 6 - 8 hours. Ingested fluid flows on the inner wall of the lesser curvature, the so-called gastric street, directly into the distal area of the stomach.
The Gastric mucosa produced continuously Gastric juicewho made Hydrochloric acid, mucins, bicarbonate, digestive enzymes and intrinsic factor consists.
The hydrochloric acid takes care of her low pH for a strongly acidic environment in the stomach, which on the one hand is the Killing of microorganisms serves and on the other hand in the Digestion of proteins helps.
Surface cells secrete the gastric mucosa Bicarbonate and slime, whereby the Gastric mucosa self Protected from the aggressive stomach acid becomes.
Read more about the topic here: Gastric mucosa
After the food reaches the stomach, it comes through Increase in volume to stretch the stomach and to increased secretion of Stomach acid. In addition to the mechanical crushing of the food by the peristaltic waves, start with the Mixing the chyme with stomach acid the first steps of digestion.
You can find more information on the topic here: Stomach acid
Abandonment of stomach acid
in the Fundus and corpus area of the stomach secrete the parietal cells the lining of the stomach hydrochloric acid (HCl)that the Main component of gastric juice forms.
The hydrochloric acid reaches a concentration of up to 150 mM, which means that the pH value can locally drop to values below 1.0. This low pH makes it Growth of bacteria and other pathogens prevented.
also denature (= the structure is destroyed) contained in the food pulp Proteins in an acidic environment and can thus be more easily cleaved by peptidases.
Another important function of stomach acid is that Activation of the inactive pepsinogen, which is produced by the main cells of the stomach lining, into pepsin, a peptidase that breaks down proteins ingested with food.
Parietal cells ("Parietal cells") in the mucosa form HCl, by hydrogen protons via H + K + -ATPases ("Proton pumps“) Are secreted into the gastric lumen in the apical (above) membrane of the activated parietal cells.
The proton concentration in gastric juice can be up to 150 mmol / l and is therefore 106 times higher than in blood. Chloride ions follow the protons through apical chloride channels into the stomach lumen and HCl is formed.
The rate-determining step of hydrochloric acid secretion is the installation of the proton pumps in the apical membrane of the parietal cells: in the resting state, the H + K + -ATPases are stored in tubulovesicles, after activation they fuse with the cell membrane.
Read more about the topic here: Stomach acid
Abandonment of gastric juice
In the Glands of the stomach lining are located different cell types, the adjoining cells, parietal or parietal cells, main cells and endocrine cells.
They produce together 2-3 liters of gastric juice daily, an isotonic liquid whose Main ingredients hydrochloric acid, pepsinogens, mucus, bicarbonate and intrinsic factor are.
The pH value of the gastric juice is largely determined by the gastric acid and fluctuates between 1 and 7 depending on the acid production.
The Secretion is adjusted as needed and so in the interdigestive phases (phases between meals) a small amount of gastric juice is continuously secreted while it is after ingestion of maximum secretion comes.
The production of gastric juice is subject to a complex endocrine regulation that is controlled by a large number of gastrointestinal hormones and neurotransmitters: gastrin, histamine and acetylcholine promote the secretion of gastric juice, whereas somatostatin, GIP (gastric inhibitory protein), secretin, CCK (cholecystokinin) and Prostaglandin E2 have an inhibitory effect.
Task of the gatekeeper
The Gastric gatekeeper (pylorus) consists from smooth muscles arranged in a ring, the one strong sphincter muscle (M. sphinkter pylori) forms at the exit of the stomach and thus separates the stomach from the duodenum.
The job of the pylorus is to provide that in the stomach homogenized chyme in portions through rhythmic contractions to be transported to the duodenum. In addition, a Backflow of Prevents intestinal contents in the stomach.
The Opening of the gastric porter is through the Vagus nerve controlled by a reflex (pyloric reflex) triggering peristaltic waves of contraction and so small portions (bolus) of the stomach contents (chyme) get into the duodenum.
In addition, the Area of the pyloric glands, which give off an alkaline secretion that the Neutralization of the sour food pulp serves.
Functions of the gastric mucosa
The Surface of the gastric mucosa is through numerous Crypts (stomach glands) greatly enlarged. Inside these glands are located different cell typeswho together the Produce gastric juice.
At the Glandular base are the so-called Main cells localized. These are basophilic cells with apical seceret granules, which Pepsinogen contain a protease for Protein digestion.
In addition to pepsinogen, major cells also secrete Gastric lipase for splitting fats.
Parietal cells (Parietal cells) are located in the Glandular center and are the only cells that Produce hydrochloric acid can.
In addition, parietal cells produce the Intrinsic factor, a transport protein that is responsible for the absorption of Vitamin B12 is needed in the terminal ileum.
Adjoining cells sit in the area of the Glandular neck and secrete Bicarbonate and phlegm (mucins).
Neuroendocrine cells (H, D and G cells) are found in the entire gastric mucosa distributed and produce Neurotransmitters and gastrointestinal hormones to control digestion.
In addition to the gastric glands, the mucous membrane consists of the actual ones Surface epithelial cells, the dem Protection of the mucosa Serve against aggressive stomach acid by releasing mucus and bicarbonate to neutralize it.
You can find out more about the topic here: Gastric mucosa