Digestive enzymes

The role of enzymes is to stimulate chemical reactions in the food; to achieve this they require a specific temperature and pH.


Rennin is required in infants. Its function is to curdle the milk ingested by the young child, which prevents milk from leaving the stomach too quickly, allowing time for the absorption process.


Pepsinogen is secreted into the gastric juice from both mucus cells and chief cells. When it is secreted, stomach acid instigates the conversion into pepsin, which breaks down protein into its simplest form of peptones. Pepsin requires a pH of 2 to work.

Hydrochloric acid

Hydrochloric acid is secreted into the lumen, which turns the stomach into an acid environment. The hydrochloric acid is required to activate the pepsin, so it too is required to digest protein. A hormone called gastrin is important in the control of acid secretion. Hydrochloric acid has quite a few functions:

• It provides an acid reaction needed by the gastric enzymes

• It is a solution for killing some bacteria

• It controls the pylorus

• It inhibits the action of amylase/ptyalin

• It changes pepsinogen into pepsin.

The production is controlled by the vagus nerve and the hormone gastrin. Gastrin is a peptide that contains 17 amino acids. The total amount of gastric juice produced is approximately 3 litres in 24 hours. Mucus covers the entire surface of the stomach to coat and lubricate the stomach wall, so preventing digestion of the stomach itself.

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