Acid Secretion Bythe Stomach

Gastric acid is secreted by the parietal cells in gastric mucosa. The basolateral membranes of these cells contain receptors for the three main stimulants of acid secretion, namely gastrin (from antral G cells), histamine (from enterochromaffin-like cells) and acetylcholine (from vagal efferents). The action

Aggressive

Acid

Pepsin

NSAIDs

Helicobacter pylori

Fig. 31.1 Factors involved in maintaining acid balance

Protective

Prostaglandins Mucus Bicarbonate Mucosal blood flow of all these is to stimulate the gastric acid (proton) pump, which is the final common pathway for acid secretion. The pump is an H+/K+ ATPase, and when stimulated it translocates from cytoplasmic vesicles to the secretory canaliculus of the parietal cell and uses energy, derived from hydrolysis of ATP, to transport H+ out of parietal cells in exchange for K+. Hydrogen ions combine with chloride ions to form HC1, which is secreted into the gastric lumen.

On average, patients with duodenal ulcer produce about twice as much HC1 as normal subjects, but there is much overlap, and about half the patients with duodenal ulcer have acid outputs in the normal range. Patients with gastric ulcer produce normal or reduced amounts of acid.

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