Question 6

Describe pancreatic secretions and their regulation.

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College Answer

It was vital to recognise and describe both the exocrine and endocrine secretions of the pancreas and their regulation. Insulin, glucagon, and somatostatin are all secreted from the pancreas and their omission was the most common reason for not passing this question. Many candidates unfortunately wrote solely on exocrine secretions. Satisfactory answers provided a moderate amount of detail on both the endocrine (insulin, glucagon and somatostatin) and exocrine (bicarbonate and digestive enzymes; trypsin/chymotrypsin, pancreatic amylase and lipase) secretions of the pancreas including what determines their secretion.


Exocrine function: 80-90% of the total pancreatic mass

  • 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)
    • digest fats, proteins and lipids, alkalinise and buffer the acidic gastric contents
  • 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

Endocrine function: 1-2% of the total pancreatic mass

  • Pancreatic endocrine hormones are large (14-50 amino acid) polypeptides
    • Glucagon, which increases glucose release from the liver
      • Stimulated by hypoglycaemia, protein meals,. fasting, exercise, autonomic (sympathetic or parasympathetic) stimulation, and catecholamines
      • Inhibited by somatostatin, insulin, zinc (which is released along with insulin), and obviously hyperglycaemia
    • Insulin, which increases the uptake of glucose by (most) cells
      • Stimulated by vagal tone, growth hormone, prolactin, gonadotropins
      • Inhibited by sympathetic tone, catecholamines, cortisol, somatostatin, glucagon
    • Pancreatic polypeptide, which inhibits gastrointestinal secretions
    • Somatostatin, which inhibits endocrine and exocrine secretion everywhere
      • Stimulus for the release of somatostatin
        • Acidic duodenal pH (most potent stimulus)
        • Raised levels of insulin, glucagon, gastrin, cholecystokinin, GIP, VIP
        • Sympathetic stimulation and β-agonists
        • Duodenal lumen contents (carbohydrate, fat and protein)
      • Inhibition of the release of somatostatin
        • α-agonists
        • Muscarinic agonists, and vagal tone
        • Fasting
    • Ghrelin, which regulates appetite and growth hormone secretion


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

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

Susan, Bonner-Weir. "Endocrine pancreas." (2004): 675-680.

Henderson, J. R. "Why are the islets of Langerhans?." The Lancet 294.7618 (1969): 469-470.