Adults taking proton pump inhibitors such as Omeprazole on a chronic basis to block gastric acid secretion are more susceptible to gastrointestinal infections.

Repeated reflux of gastric juice can also cause reflux laryngitis - a voice disorder caused by inflammation of the larynx (voice box) by the acid. The patient will have hoarseness but may be unaware of the reflux (no burning sensation as with GERD or run of the mill heartburn).

Diarrheal fluids typically originate in the bowel (small or large intestine), not the stomach. In addition to the length of the small and large bowels, all of which are absorptive tissue, and the fact that gastric acid is neutralized in the duodenum, there are four sphincters between the stomach and the toilet bowl - the pyloric sphincter, the ileocecal sphincter and the internal and external anal sphincters.

Diarrheal fluids are typically alkaline, not acidic because of all the intestinal bicarbonate secretion.

It is essentially trial and error repeated hundreds of millions of times over hundreds of millions of years.