Function of the stomach

The stomach serves as a reservoir for the food taken in. It can store food for hours and thus ensures that we can cover our daily food requirements with a few large meals. Through peristalsis, the chyme is mixed with the gastric juice, the food is chemically crushed, partially digested and then transferred in portions to the duodenum.

Gastric acid

The gastric juice/stomach acid contains acid (HCL), mucus, electrolytes, intinsic factor and some enzymes, mainly pepsin. Hydrochloric acid is used to kill the bacteria ingested with food and thus protects against infections. Pepsin is an enzyme that breaks down proteins.

Interestingly, both the hydrochloric acid and the pepsin are of minor importance for digestion, which is also shown by the fact that after surgical removal of the stomach, the digestive function is still largely maintained. The intrinsic factor, however, proves to be very important, as the absence of this substance can lead to severe anaemia. Since the enzymes for fat digestion (lipases) and carbohydrate digestion (amylases) are only produced in very small quantities in the stomach, these food components are hardly digested at all in the stomach, but only in the intestine.

The gastric mucosa produces 2-3 liters of gastric juice daily. Compared to fasting, the gastric juice secretion can increase by a factor of 100 when food is consumed. There are different phases of digestion in which nerve signals and various hormones and mediators play a role: Head phaseCephalic (vagal) phase:Some food signals (smell, taste, appearance) cause a gastrin secretion from the G-cells via the parasympathetic vagus nerve (nervus vagus) and thus an increase in gastric juice production even before eating.

Gastric phaseGastric phase: Here the stretching stimulus caused by food intake is the one that increases gastric juice production via the vagus nerve.Some chemical stimuli such as protein breakdown products, alcohol and coffee cause an increased release of gastrin and histamine, which in turn increases gastric juice production. Intestinal phaseIntestinal phase: Here the most important function is the inhibition of gastric juice production. When strong acid chyme passes into the duodenum, there is a risk of damage to the intestinal mucosa. This stimulus causes a release of the hormone secretin, which inhibits gastrin production. A reduction in gastrin in turn reduces the production of gastric acid.