Stomach Acid

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•  Acid conditions in the stomach favor some hydrolysis reactions and help to control pathogens in ingested food

The gastric glands that line the stomach wall secrete an acidic solution that creates a low pH environment within the stomach

  • The normal pH of the stomach is roughly 1.5 – 2.0, which is the optimum pH for hydrolysis reactions by stomach enzymes

The acid conditions in the stomach serve a number of functions:

  • Assists in the digestion of food (by dissolving chemical bonds within food molecules)
  • Activates stomach proteases (e.g. pepsin is activated when pepsinogen is proteolytically cleaved in acid conditions)
  • Prevents pathogenic infection (stomach acids destroy microorganisms in ingested food)

The stomach wall is lined by a layer of mucus, which protects the stomach lining from being damaged by the acid conditions

  • The pancreas releases bicarbonate ions into the duodenum which neutralises the stomach pH (intestinal pH ~7.0 – 8.0)
  • Certain foods (e.g. antacids) may also neutralise stomach acids, impairing digestion and increasing chances of infection

Acid Conditions in the Stomach

                         Conditions:             pH                     Optimal Enzyme Activity                  Zymogen Function

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•  The reduction of stomach acid secretion by proton pump inhibitor drugs

The low pH environment of the stomach is maintained by proton pumps in the parietal cells of the gastric pits

  • These proton pumps secrete H+ ions (via active transport), which combine with Cl ions to form hydrochloric acid
  • Certain medications and disease conditions can increase the secretion of H+ ions, lowering the pH in the stomach

Proton pump inhibitors (PPIs) are drugs which irreversibly bind to the proton pumps and prevent H+ ion secretion

  • This effectively raises the pH in the stomach to prevent gastric discomfort caused by high acidity (e.g. acid reflux)
  • Individuals taking PPIs may have increased susceptibility to gastric infections due to the reduction of acid secretion

Proton Pump Inhibitors (PPIs)