salivary glands are activated; the stomach secretes gastric acid, gastrin, lipase,
leptin, and ghrelin; the intestines secrete bicarbonate and CCK; the gallbladder:
bile; the pancreas: insulin, pancreatic polypeptide (PP), and digestive enzymes; and
the adipose tissue secretes leptin. Both the vagus nerve and cerebral cortex are
involved in the response. Severing the vagus nerve abolishes the cephalic-phase
response (Power and Schulkin 2009 ).
Ultimately, appetite and the desire to eat are determined by the integration of all
signals in the CNS: the subcortical homeostatic and reward systems and the cerebral
cortex. Activities of the orexigenic (associated with increased feeding) and
anorexigenic (associated with decreased feeding) neurons in the hypothalamus
control the homeostatic system monitoring the body’s energy balance. Food choice
in the cephalic phase of digestion is based on immediate sensory perceptions of
appearance, smell and taste of foods, and memories of food-related experiences
(e.g., pleasurable/not pleasurable). The reward system controls not only food choice
Table 10.2 Cephalic-phase responses to food stimuli
Organ Response Functions
Mouth Saliva production
and secretion
Lubricates foods, starts starch digestion, dissolves food
particles
Stomach Gastrin secretion Stimulates gastric acid secretion
Stomach Gastric acid
secretion
Hydrolyzes food
Stomach,
Pancreas
Lipase secretion Fat digestion
Stomach Ghrelin secretion Stimulates appetite, growth hormone secretion, fat
absorption
Stomach Gastric emptying Regulates food passage
Intestine Intestinal motility Regulates food passage
Intestine Bicarbonate
secretion
Neutralizes stomach acid
Small
intestine
Cholecystokinin
secretion
Terminates feeding
Pancreas Insulin secretion Regulates blood glucose
Pancreas Pancreatic
polypeptide
secretion
Regulates other pancreatic and gastrointestinal
secretions
Pancreas Digestive
enzymes secretion
Aids digestion of proteins, fats, and carbohydrates
Gallbladder Bile secretion Emulsifies fat
Adipose
tissue,
stomach
Leptin secretion Reduces appetite
Multiple
organs
Diet-induced
thermogenesis
Increase in energy metabolism due to digestive and
physiological responses to food ingestion
Power and Schulkin ( 2009 ), after Table 9.1 Some known cephalic-phase responses, p. 210
212 L.S. Lieberman