Question 5

Describe the hormonal response to a meal.

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College Answer

For a good answer candidates were expected to have an integrated knowledge of 
gastrointestinal physiology. Gut function is regulated by the enteric nervous system and by paracrine and endocrine hormones released by hormone secreting cells in the mucosa of the gut (enteroendocrine cells). These cells secrete hormones in response to neural innervation or in response to triggers associated with ingested food. Gut functions influenced include secretion, digestion, absorption and motility. The endocrine system also has an important role in the handling of nutrients following absorption and some mention of insulin was required.

Discussion

Stimuli Neurohormonal  response
Cephalic phase: anticipatory neuroendocrine responses
Anticipation of food;
thoughts about food;
sensory characteristics of food (taste, smell, mouthfeel, mastication, appearance of food)
  • Mainly vagal responses:
    • Accommodative relaxation of proximal gastric smooth muscle
    • Stimulation of gastrin and histamine release
    • Cholinergic stimulus for the release of pancreatic secretions and insulin
    • Increased small intestine motility)
  • Saliva is also secreted (parasympathetic effect)
  • Specific hormones involved in this phase:
    • Histamine (stimulates gastric acid secretion)
    • Gastrin (stimulates gastric acid and pepsin secretion)
Gastric phase: reactive gastric hormonal and local reflex responses

Pharyngeal sensation of swallowing;
gastric mechanoreceptor stretch;
the increase in gastric pH results in the release of hormones that stimulate gastric acid secretion (gastrin, ghrelin and histamine)

  • Mechanical stretch stimulates antral pump activity
  • Specific hormones acting in this phase:
    • Histamine, increases gastric acid secretion
    • Gastrinslight increase to the overall gastric motility, major stimulus for gastric acid and pepsin secretion
    • Ghrelin, secreted by the ghrelin cells of the oxyntic glands, which increases gastric motility substantially, and which slightly increases acid secretion
Intestinal phase: endocrine modulation of gastric and biliary activity by  the duodenum 
Stimulated by the volume, osmolality and chemical composition of the chyme entering the duodenum
  • Cholecystokinin, which causes gall bladder contraction and increased pancreatic secretions
  • Secretin, which increases the 
  • Motilin, which stimulates small bowel peristalsis
  • Leptingastric inhibitory polypeptide, glucagon and glucagon-like peptides 1 and 2, all of which mainly act to decrease the gastric emptying rate
Absorptive phase: endocrine response to absorbed nutrients
Stimulated by increased blood glucose
  • Insulin secreted in response to increased blood glucose

References

Pandol, Stephen J. "Integrated response to a meal." Journal of Parenteral and Enteral Nutrition 32.5 (2008): 564-566.

Camilleri, Michael. "Integrated upper gastrointestinal response to food intake." Gastroenterology 131.2 (2006): 640-658.

Livovsky, Dan M., Teorora Pribic, and Fernando Azpiroz. "Food, eating, and the gastrointestinal tract." Nutrients 12.4 (2020): 986.

Raybould, H. E., S. J. Pandol, and H. Yee. "The integrated responses of the gastrointestinal tract and liver to a meal." Textbook of Gastroenterology, (2003): 2-12.

Lim, Robert KS, A. C. Ivy, and J. E. McCarthy. "Contributions to the physiology of gastric secretion. I: gastric secretion by local (mechanical and chemical) stimulation." Quarterly Journal of Experimental Physiology: Translation and Integration 15.1 (1925): 13-53.

Power, Michael L., and Jay Schulkin. "Anticipatory physiological regulation in feeding biology: cephalic phase responses." Appetite 50.2-3 (2008): 194-206.