D2  Digestion

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Essential Idea:

Digestion is controlled by  

nervous and hormonal mechanisms


  • Nervous and hormonal mechanisms control the secretion of digestive juices
  • Exocrine glands secrete to the surface of the body or the lumen of the gut
  • The volume and content of gastric secretions are controlled by nervous and hormonal mechanisms
  • Acid conditions in the stomach favour some hydrolysis reactions and help to control pathogens in ingested food
  • The structure of cells of the epithelium of the villi is adapted to the absorption of food
  • The rate of transit of materials through the large intestine is positively correlated with their fibre content
  • Materials not absorbed are egested


  • The reduction of stomach acid secretion by proton pump inhibitor drugs
  • Dehydration due to cholera toxin
  • Helicobacter pylori infection as a cause of stomach ulcers


  • Identification of exocrine gland cells that secrete digestive juices and villus epithelium cells that absorb digested foods from electron micrographs