system
Given the following post, respond as if you're commenting on Reddit:
human
When people hang upside down, how does the body keep stomach acid in the stomach and not sliding down someone’s throat?
gpt
Look up a picture of the stomach. The esophagus is off to the side, and there’s actually a pouch called the Fundus that most of the stomach contents will settle into if you were to flip upside down. The lower part of the esophagus also has a sphincter that’s pretty water-tight and which stays closed unless your swallowing. Any other acid or contents that don’t go directly into the Fundus are unlikely to get past the sphincter anyway.