GIT – Secretions

Master answer

Exocrine pancreas

• produces 1.5L/day pancreatic juice
• Pancreatic juice – digestive enzymes and bicarbonate
• Enzymes: synthesized and secreted from the exocrine acinar cells
• Bicarbonate: secreted from epithelial cells lining small pancreatic ducts

Contents

• Digestive Enzymes:
  • Proteases: trypsin and chymotrypsin: proteolysis
  • Pancreatic Lipase: Hydrolysis of triglycerides
  • Amylase: Hydrolysis of carbohydrates
  • Other Pancreatic Enzymes: Ribonuclease, deoxyribonuclease, gelatinase and elastase
• Bicarbonate and water:
  • Bicarbonate neutralizes acid coming into small intestine from stomach
  • Produced by carbonic anhydrase → secreted into the lumen of the duct → pancreatic juice

Control of pancreatic exocrine secretions

• Vagus nerve:
  • Low level stimulus via Ach in response to anticipation of meal
• Enteric endocrine system:
  • Cholecystokinin:
    • secreted in duodenum
      • Stimulated by partially digested proteins and fats
    • CCK released into blood → binds to pancr acinar cells
  • Secretin:
    • Secreted in proximal small intestine
      • In response to acid in duodenum
    • Stimulates duct cells to secrete water and bicarb
  • Gastrin:
    • Secreted by stomach
      • in response to gastric distension and irritation
    • Stimulates acinar cells to secrete digestive enzymes

Occurs in three phases: cephalic → Gastric → Intestinal

JC 2019

Answer by JC