After the food has been swallowed, it passes through the oesophagus to the stomach to undergo further mechanical disintegration and chemical changes, primarily in the protein constituents.
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The fundus is the large main part of the stomach and is attached to the oesophagus. The part of the stomach attached to the duodenum is called the pyloric portion and is a narrow constricted region.
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The muscular walls of the stomach can expand when the stomach has received the food and contract in the emptying process of passing the partially digested food to the duodenum.
Digestion in the stomach is accomplished by gastric juice. Spallanzani (1783) was the first who pointed out about the gastric- digestion.
According to him the food is digested in the stomach with the help of liquid, now called gastric juice secreted by the cells or glands of stomach wall. He also noted that the juice was acidic but its acidic nature and active agents were not demonstrated until later.
A great advance in our knowledge of gastric digestion, particularly in man, was made through the observations of Beaumont on his patient, Alexis st Martin who in 1822, following a gunshot wound, was left with an opening from the stomach through the abdominal wall to the exterior.
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Through this fistula Beaumont found it possible to follow the course of gastric digestion of different food under varying conditions of health and obtained pure gastric juice for digestion experiments outside the body.
Pavlov also extended our knowledge of gastric digestion after creating, in dogs, a small stomach pouch separate from the main stomach. He studied the secretion of small pouch without interfering the proper stomach.