Let us take a brief sight-seeing journey along its course. Food entering the mouth is chewed and moistened with saliva preparatory to swallowing. Before proceeding, let us not forget the nasal cavity. This is directly connected at the upper level of the oesophagus. One should realise that this may be a source of toxins being introduced into the intestinal environment.
Food entering and leaving the stomach is regulated by two sphincters.
A sphincter is a ring-like muscle which opens and closes a natural orifice. Imagine it as a drawstring on a cloth bag. Food entering the stomach is under the control of the cardiac sphincter. Food leaving the stomach is governed by the pyloric sphincter. These sphincters are controlled by the nervous system.