Metabolism

Master answer

GIT

• Complex interplay between neuronal (ANS and ENS) and hormonal functions

Cephalic phase

• Initiation of GI secretions in preparation of a meal
• Vagal stimulation via acetylcholine
  • Enterochromaffin cells cause release of histamine
    • Acts on histamine receptors on gastric parietal cells
    • Increase gastric HCl secretion
  • G-cells → secreation of Gastrin

Gastric phase

• Gastric wall stretch and peptide content in gastric lumen → stimulates G-cells in antrum → increases secretion of gastrin
  • Peptide hormone
  • Acts on CCK B receptors on enterochromaffin cells
    • Increased histamine release → HCl secretion
  • Stimulates secretion of pepsinogen by chief cells
  • Increases antral pump function

Intestinal phase

• As gastric contents emptied into duodenum, low pH stimulates secretion of secretin by duodenal S cells
  • Peptide hormone
  • Inhibits gastric emptying
  • Increases pancreatic secretion of a bicarbonate rich fluid
• Protein and FFA content in the duodenum stimulates secretion of cholecystokinin by enteroendocrine cells of the duodenum
  • Peptide hormone
  • Inhibits gastric emptying
  • Increases pancreatic secretion of enzymes for digestion of fats and proteins
  • Causes gall bladder contraction and release of bile for absorption of fats

As nutrients is absorbed from intestine

• Blood [glucose] increases → insulin secretion by pancreatic β cells
  • Increases hepatic glucose uptake and glycogenesis, protein and lipid synthesis
  • Increases skeletal muscle glucose uptake and glycogenesis, protein synthesis
  • Increases adipocyte lipid storage
    • Adipocytes secrete leptin in response to increased fat stores → suppress appetite

Long after meal

• Stomach Ghrelin cells secrete ghrelin in response to decreased gastric stretch
  • Increased sensation of hunger

Sakurai 2016

Answer by Sakurai