The upper gastrointestinal is made up of three main parts: esophagus, stomach and small intestines. When we take a bite of food, it is
chewed and processed in the mouth, where saliva begins the chemical and mechanical digestion. When we mix up food with saliva,
the resulting mushy wad is called a bolus. The bolus gets swallowed, and begins its journey through the upper gastrointestinal tract.
How does the bolus travel into the stomach?
The force of gravity moves the bolus from the mouth to the stomach.
by
Digestive enzymes change the bolus to chyme, which slides easily down
the walls of the esophagus.
Waves of muscle movement in the muscular wall of the esophagus move
the bolus down to the stomach.
Digestive enzymes in the mouth and esophagus change the solid to a
liquid and it runs down the smooth walls of the esophagus.