system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does our anus have receptors for spicy stuff?
gpt
The TRPV1 is the receptor that capsaicin (spicy) binds to. It exists all over your digestive tract and nervous system. Your rectum and anus are included in this. These receptors are designed to detect “heat” to keep you safe. But they can get confused with foods that taste “hot.” They cause a reaction to cool you down, and you have a response that says, “No, this is dangerous.” 

So you sweat, and blood flow increases, causing redness. These receptors exist in all of your digestive tract, which is why you may experience stomach pains or some cramps after eating this. Not all of it digested and so the response is activated again at the anus.