Question 13

College Answer

Most candidates were able to mention some pancreatic enzymes, though often in insufficient detail to attract full marks. The amount, type, pH, etc. of pancreatic  secretions was often not included. Many candidates did not describe the stimuli for pancreatic secretion. Better answers described the cephalic, gastric and intestinal phases of pancreatic secretion.

Discussion

• The exocrine pancreas is 80-90% of the total pancreatic mass
• It is an arrangement of secretory acini and intercalated ducts
  • Acini secrete an enzyme-rich fluid which resembles plasma
  • Ducts alkalinise this fluid
  • Ducts join into the main pancreatic duct in a herringbone pattern
  • The main pancreatic duct (3mm) joins the bile duct and empties into the duodenum
• Contents and properties of pancreatic exocrine secretions:
  • 2500ml/day in total volume
  • High alkaline (pH 8.0) 
    • alkalinised by exchanging chloride for bicarbonate
    • the chloride is recycled via the CFTR chloride channel
  • Rich in enzymes (amylase, lipase, trypsin, elastase, nucleases) and proenzymes
  • Alkalinity and enzyme content increases in proportion to the rate of flow (higher flow produces more enzyme and bicarbonate secretion)
• Role of pancreatic exocrine secretions:
  • digest fats, proteins lipids
  • alkalinise and buffer the acidic gastric contents to moderate their corrosive effects on the duodenal mucosa
  • increase the pH of the duodenal lumen to the point where the pancreatic enzymes are activated
• Regulation of pancreatic exocrine secretion:
  • ​​​​​​Pancreatic secretion is increased by:
    • Cholecystokinin (mainly increases enzyme secretion and rate of pancreatic secretory flow)
    • Vagovagal enteropancreatic reflex
    • Secretin (mainly increases the bicarbonate secretion)
  • Pancreatic secretion is decreased by
    • Sympathetic stimulus, eg. shock, surgery
    • Somatostatin, octreotide
  • During a meal:
    • 20-25% is released during the cephalic phase
    • 10% is released during the gastric phase
    • 60-80% is released during the intestinal phase

Owyang, Chung, and John A. Williams. "Pancreatic secretion." Yamada's Textbook of Gastroenterology (2015): 450-473.

Mahadevan, Vishy. "Anatomy of the pancreas and spleen." Surgery (Oxford) 37.6 (2019): 297-301.

Cade, Jennifer E., and James Hanison. "The pancreas." Anaesthesia & Intensive Care Medicine 18.10 (2017): 527-531.

Lee, Min Goo, et al. "Molecular mechanism of pancreatic and salivary gland fluid and HCO3− secretion." Physiological reviews 92.1 (2012): 39-74.