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Phases of gastric secretion
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The stomach does not make its juice all at once when food arrives. It does it in three stages, and each one has its own name: cephalic, gastric and intestinal.
The cephalic phase happens before a single bite goes in, and it is short. It is set off by the smell of food, its taste, the sight of it, or even just thinking about it. It is the brain telling the stomach to get ready.
The gastric phase starts once the food is already inside and lasts three to four hours. That arrival makes certain nerves .. the parasympathetics .. release acetylcholine, a chemical signal that triggers secretion. At the same time, partly digested proteins make cells called G cells release gastrin, a hormone that goes on to push the parietal cells to make more hydrochloric acid.
The intestinal phase is the odd one out of the three, because it does both things: it speeds secretion up and it slows it down. When the intestine fills and stretches with chyme .. the mush that leaves the stomach .., the enterogastric reflex kicks in and slows secretion down.
In brief
Gastric juice is secreted in three phases: cephalic, gastric and intestinal.
The cephalic phase is brief and happens before food arrives: the smell, taste or sight of food, or thinking about it, sets it off.
The stomach gets ready with the food still on the plate.
The gastric phase lasts three to four hours: as food enters, parasympathetic nerves release acetylcholine and partly digested proteins release gastrin, which drives the parietal cells.
The intestinal phase both stimulates and inhibits: once chyme distends the intestine, the enterogastric reflex slows secretion.
Sources (1)
- OpenStax, Rice UniversityAnatomy and Physiology 2e, 23.4 The Stomach
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