This was classically defined in Palov's dog experiment. Since it is mediated by the CNS the major stimulus will be parasympathetic and sympathetic input to the enteric nervous system. All secretions are initiated and hormones are stimulated. Salivary secretion and HCl secretion begins and motility increases. Gastric and Intestinal phases are regulated by the presence and composition of food in the gut.
Digestion begins in the mouth with the action of salivary amylase.
Salivary secretion is initiated during the cephalic phase, but mechano and chemoreceptors increase the secretory rate. ACH is a major stimulus for salivary secretion. Other important constituents of salvia are H2O and mucus that lubricates. This initiates carbohydrate digestion, however, most of digestion occurs in the small intestine. The arrival of food in the stomach initiates the gastric phase of digestion.