system
Given the following post, respond as if you're commenting on Reddit:
human
How does the stomach disallow acids into the intestines and bowels?

I was talking with a friend about a lecture from biochemistry back in school regarding digestion. It occurred to me that I wasn't clear on how stomach acids and digestive enzymes are relegated to the stomach and/or prevented from damaging the pipes downstream.
gpt
The stomach itself doesn't disallow the acid into the rest of the plumbing; when the pyloric sphincter opens, chyme (the mix of food, ingested fluids, and stomach acid) flows into the duodenum of the small intestine. Here, the acid would present a hazard to the intestinal epithelium, so it is neutralized by added secretions, in part composed of bicarbonate (which is basic) from the pancreatic duct.