Pancreas

Question 1

Lobular structure

Answer 1

Main pancreatic duct - interlobular ducts - intralobular ducts - intercalated ducts - acinus
Secretory unit = intercalated ducts + acinus
Acinus: thick proteinaceous substance with zymogens, digestive proteins + isotonic plasma
Duct epithelial cells: rich HCO3 watery solution to bathe the proteinaceous solution so it doesn’t block the ducts

Question 2

Activation of acinar cells

Answer 2

Ach + CCK, VIP + secretin

CCK triggered by acid in lumen of S.I - I cells release CCK - triggers pancreas to make zymogens
CCK + Ach also trigger acinar cell to release Na-Cl rich isotonic fluid - they trigger Cl to be excreted

Question 3

Activation of pancreatic duct cell

Answer 3

HCO3 rich fluid. Ach + secretin trigger this as the presence of acid in the lumen of SI stimulates them - HCO3 comes out in exchange for Cl so Cl must go out via CFTR channel that’s why in CF - the duct cells get blocked because can’t secrete the watery hco3 fluid

Question 4

Inhibition

Answer 4

Somatostatin (from D cells in islets of langerhans) inhibits the release of CCK + secretin

Question 5

Phases of pancreatic secretion

Answer 5

1. Cephalic - 25%, smell sight taste of food - Ach mediated
2. Gastric - 10-20%
3. Intestinal - 50-80% - chyme entering SI stimulates: acid - S cells to release secretin which tells ducts cells to release HCO3
   lipids - stimulate I cells to release CCK which tells acinar cells to release digestive enzymes

Question 6

How does the pancreas prevent auto-digestion?

Answer 6

1. Digestive proteins stored in secretory granules as inactive precursors - zymogens become activated only after contact with SI brush border enzyme enterokinase. trypsinogen - trypsin - initiates conversion of all other zymogens
2. Secretory granule membrane (stored in granules)
3. Enzyme inhibitors - co-packaged in vesicle e.g. SPINK1
4. Low pH in granules so enzyme can’t work