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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