system
Given the following post, respond as if you're commenting on Reddit:
human
Why is it that whenever we are anxious or nervous, we feel it so strongly in our stomachs? What is the link between the two?
gpt
Being in a situation that provokes anxiety or nervousness can activate the body's sympathetic nervous system (fight-or-flight response).  This causes a release of epinephrine (adrenaline) which inhibits motility in the small and large intestine (your body does not need to waste energy digesting food while you are running away from a bear).  You also have changes in blood pressure and blood flow to the gut.  The sensation you feel in your stomach is likely a result of these physiological changes.

The enteric nervous system of the gastrointestinal system also probably plays a role.