system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the scientific explanation as to why you can “feel your chest and stomach tighten” when your feelings are hurt?
gpt
You know when you fill your car tires with air and they get harder? Or when a balloon gets old it's a lot easier to poke your finger into it.

When you have a stress response, your body releases chemicals into your bloodstream. These increase your blood pressure which makes your blood vessels just a bit "stiffer" like a filled balloons/tires and you can feel that. You can also probably feel yourself getting warmer for similar reasons. Your stomach and nearby organs are part of a nerve system responsible for digesting the food you eat, and these power down and divert blood flow to other places when this happens - so you feel it most in those places. 

The purpose is from olden times when the stress would come from a lion roaring at you, and you needed the extra energy/pressure to be able to respond quickly and run faster (or fight better if you couldn't run). Now when it happens because someone was calling you names, it is just a feeling.

If it happens too often or for too long, it can be damaging. (Imagine poking a balloon until it gets a tear.) If you're going through a rough emotional time, it can be very helpful for your body if you take some time a few times a week to go for walks, runs, or pick up a sport or something to clear out this extra energy.