The general scheme of digestion
To maintain normal metabolism, the human body requires a constant renewal of the expended resources in the form of organic compounds, vitamins, macro- and microelements.
The respiratory system delivers only molecules contained in the air, while the rest of the substrates a person receives through the digestive system. However, if the absorption processes occur in the intestine and partly in the oral cavity, then the stomach carries out the mechanical and chemical processing of the food received. The structure of its walls ensures the splitting of macromolecules into smaller parts for better digestion in the intestine and promotes the chyme to the lower sections of the gastrointestinal tract. However, in the acidic environment of this organ, enzymes responsible for the breakdown of carbohydrates are inactivated, therefore, after the evacuation of the food lump, further chemical processes occur in the duodenum. This ensures that chyme is not regurgitated back into the stomach: the structure of its second sphincter allows it to contract immediately after the end of the evacuation. And by the time the nutrients reach the small intestine, almost all of them will be in the form of dimers, monomers and ions that can pass through the
intestinal villi and be absorbed into the blood.
How is it arranged?
The structure of the human stomach can be represented in the form of a hollow muscle sac with two main sections: cardiac (including the vestibule, bottom and body) and pyloric (consisting of successively located pyloric caves and canals). Further, the latter communicates with the lumen of the duodenum. And to ensure proper movement of food along the tract, the stomach has two sphincters: gastroesophageal, which prevents return to the esophagus, and m. sphincter pylori, which protects duodenum from the acidic environment that the stomach has. The structure of its wall includes parietal cells. They actively produce hydrochloric acid for protein swelling, enzyme activation, death of infections in the food lump and the start of its evacuation. These cells also synthesize the so-called Castle's intrinsic factor, which has antianemic activity.
A bit about others
Parietal cells of the stomach produce pepsinogen, and mucocytes produce mucus, which creates a natural barrier against the action of HCl on the stomach. The structure of the muscle wall is three-layered: myocytes have a longitudinal, transverse and oblique direction. They are most active when a person is standing and almost zero when lying down. Also, peristalsis is stimulated by the tension of the abdominal muscles. Thus, the structure and functions of the stomach are extremely important in the digestion process. Therefore, with a partial resection of this organ or hyper- / hypo- / asecretion of hydrochloric acid and gastric juice, all further stages are blocked - and gastric dyspepsia syndrome occurs. And with insufficiency of barrier mechanisms, gastritis develops, and subsequently a stomach ulcer.