5. Pancreas and pancreatitis Flashcards
What are the 5 anatomical parts of the pancreas from inferior/right to left?
- Uncinated process
- Head (fits into the C-shaped duodenum)
- Neck
- Body
- Tail (sits in the hilium of the spleen)
Describe the anatomy of the liver/gall bladder ducts joining with the pancreatic ducts
- Gall bladder secretes into the cystic ducts
- Liver drains into the right + left hepatic ducts => common hepatic duct
- Cystic duct + common hepatic duct => common bile duct
- Common bile duct joins the pancreatic duct at the Ampulla of Vater
- Pancreatic ducts run along the pancreas, converging into one
- They drain into the duodenum at the Sphincter of Oddi
Where is the pancreas located?
Behind the stomach, between the duodenum and spleen
Describe the vascular anatomy of the pancreas
- Superior mesenteric artery => inferior pancreatic-duodenal artery
- Coeliac trunk => splenic artery
- Head of pancreas drains into hepatic portal vein
- Rest of pancreas drains into splenic vein
Describe the microanatomy of the pancreas (cells/tissue)
• 98% are exocrine acini cells and duct cells
• Acini cells
• Duct cells
• Islets of Langerhans (endocrine tissue)
- beta cells (insulin) - most common
- alpha cells (glucagon) - 1/5 of endocrine tissue
- delta cells (somatostatin) - fewest in number
• Connective tissue
Describe the acinar cells
• Secretory machinery for enzymes:
- RER
- Ribosomes
- Zymogen granules with pro-enzymes, enzyme inhibitors and active enzymes (lipases and amylase)
• Terminal end of the duct (as they secrete enzyme-rich viscous fluid)
• Duct cells modify it as it moves along
Describe the centroacinar cells
- Separate the acinar cells from the duct cells
* Act like duct cells
Describe the duct cells
• Secrete a watery, dilute bicarbonate fluid
- dilutes and mobilises viscous enzymes
- helps carry them into pancreatic duct/duodenum
- neutralises stomach acid in the duodenum (enters via pyloric sphincter)
How is bicarbonate produced in the duct cells?
• CO2 diffuses into cell
• CO2 + H2O => H+ + HCO3- [carbonic anhydrase]
• Na+ moves through tight junction from interstitium to duct lumen
- H2O follows
- duct lumen becomes watery
• Chloride is pumped from duct cell to lumen (CFTR - a chloride ion channel)
• Comes back in, exchanging with bicarbonate (Cl/HCO3 exchange pump)
• Bicarbonate can leave the cell into the lumen
Why does duct cell bicarbonate secretion make the pancreatic venous blood acidic?
• H+ is also made when HCO3- is made
• Moves out of the cell (basolateral) to prevent build up
- K+ moves out through potassium channels
- K+ swaps back in with Na+ going out (ATPase)
- Na+ swaps back in with H+ going out
What enzymes are found in the zymogen vesicles of acinar cells?
• Protease zymogens - Trypsinogens • Procolipase - coenzyme for lipid digestion • Active enzymes - pancreatic amylase - lipase • Trypsin inhibitor
How is trypsinogen activated and what does it do?
• Converted into trypsin by enterokinase - in the duodenum brush border
• Trypsin catalyses:
- protease zymogens => proteases
- procolipase => colipase
- trypsinogen => trypsin (autocatalysis)
• Converts long peptides into shorter peptides
Describe the secretion problems with bile?
- Liver secretes bile
- Collects in gall bladder which contracts to release
- Common bile duct => Ampulla of Vater => duodenum
- Gallstone or blockage can cause enzyme accumulation
- Trypsin inhibitor can’t work efficiently
- Trypsinogen converts automatically to trypsin [trypsin] without the enterokinase from brush borders
- Auto-digestion => acute pancreatitis
What are 3 of the protease zymogens?
- Trypsinogen
- Chymotrypsin
- Procarboxypeptidase
Summarise the hormonal control of bicarbonate secretion
- Acid chyme in proximal duodenum (from broken down bolus)
- Low pH stimulates S-cells to release secretin into the blood
- Secretin travels to the pancreas (via liver and heart)
- Binds to receptors on the basolateral surface of duct cells
- Increased cAMP
- Activation of chloride channels in apical membrane
- Efflux of chloride
- More HCO3- leaves the cells
- forms carbonic acid => water + CO2
- More alkaline - optimal pH for enzymes
