Gastric acid
The main constituent of gastric acid is hydrochloric acid which is produced by parietal cells (also called oxyntic cells) in the gastric glands in the stomach. Its secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the hydrochloric acid is secreted into the lumen of the stomach. The pH of gastric acid is 1.5 to 3.5 in the human stomach lumen, the acidity being maintained by the proton pump H/K ATPase. The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as an alkaline tide.
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Normally, saliva is slightly acidic and has a pH less than 7, but it can vary between 6 and 8. The pH inside the mouth depends on the salival flow rate because the higher the flow rate of saliva the more salival bicarbonates are present. Bicarbonates in the saliva raise the pH inside the mouth. When there is no or low saliva flow, also known as xerostomia, the pH inside the mouth is around 6. When salival flow rate is high the pH is about 8. During a concert, if a musician is suffering from xerostomia, also known as dry mouth, the saliva pH is expected to be acidic.