Cephalic phase of digestion

The process of chewing also activates signaling messages to the rest of the gastrointestinal system that triggers it to begin the entire digestive process. This is because when chewing is a well-paced, thorough process, it can actually be said to belong to the "cephalic stage of digestion", the phase in which you first see, smell and taste your food. The length of time spent chewing the food is related to the length of the cephalic stage of digestion since with more extensive chewing the longer the food gets to be seen, tasted and smelled.

Cephalic phase responses have been extensively analyzed in the research literature. The release of small messaging molecules that is critical for digestion, such as cholecystokinin, somatostatin and neurotensin, have been found to increase by over 50% just by the mere sight and smell of food. Additionally, research has shown how chewing, as well as the activation of taste receptors in the mouth, can prompt the nervous system to relay information to the gastrointestinal system to expedite the process of digestion. For example, stimulation of the taste receptors can signal the stomach lining to produce hydrochloric acid that helps in the breakdown of protein. Additionally, chewing signals the pancreas to prepare to secrete enzymes and bicarbonate into the lumen of the small intestines.
From WHFoods