You may also have diarrhea or a fever. It is sometimes called stomach flu, but it is not the flu. Germs like viruses and bacteria can cause it. You can catch it from someone else who has it, or you can get it from food poisoning. Food poisoning can happen if you eat foods that contain harmful germs.
The circular muscle located at the entrance and exit to the stomach is called the sphincter. So for this question, you are talking about two distinct sphincters. This anatomical structure is able to open, and contract or close as needed.
What is the stomach muscle that controls the passage of food into the small intestine? At the bottom of the esophagus, just before the opening to the stomach is a ring-shaped muscle known as the lower esophageal sphincter (LES).