Sphincter Contraction—one way flow : explain
Well that brings us to the end of the GI tract.
As a reminder, there are a series of sphincters
(modifications of the circular layer of the muscularis externa)
that insure one way flow of food, chyme and feces.
Be sure you know where the valves are located and their role.
Vomiting or emesis is an exception to the one-way flow rule,
however, this only happens under physiologically atypical conditions—
you really overate, you drank too much alcohol, you have bacterial toxins from "food poisoning", took certain drugs, etc.
The emetic (vomiting) center is located in the medulla oblongata of the brainstem.