system
Given the following post, respond as if you're commenting on Reddit:
human
How does my body keep stomach acid in my stomach, but let food and water through?
gpt
The answer is essentially that it doesn't. The gastric acid moves through the pyloric sphincter into the duodenum with the foodstuffs (now broken down into chyme). In the duodenum, bicarbonate is released which neutralizes the acid so that the low pH doesn't go through and destroy the rest of your GI tract. The stomach in response makes more acid.