The stomach of an adult is about the size of a fist. This organ has the ability to expand as much as 40 times its original size in order to hold a big meal or large fluid intake.
The stomach produces the hormone ghrelin, which helps produce hunger pangs. A different hormone, PYY, is responsible for making a person feel full. However, PYY is not excreted by the stomach. Instead, it is released by a section of the small intestine called the ileum. The hormone is not released until food reaches the ileum, which typically takes about 20 minutes after a person starts eating. Eating slowly gives food a chance to reach the small intestines and trigger PYY, helping to prevent overeating.