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.
Anatomy of the Stomach, Gallbladder, and Pancreas Stomach. A hollow muscular organ about the size of 2 closed fists, the stomach is located inferior to the diaphragm and lateral to the liver on the left side of the abdominal cavity. The stomach forms part of the gastrointestinal tract between the esophagus and the duodenum (the first section of the small intestine).