lecture 28 - the gut 2: pancreatic secretion and bile Flashcards
what is the ampulla of Vater?
common entry of bile duct and pancreatic duct into the duodenum
organisation of pancreas
acinar cells
pancreatic duct cell
intercalate duct
interlobular duct
main duct
enzymes in pancreatic juice
digestion
pancreas key organ for digestion
acinar cells
fluid and electrolyte (HCO3-) in pancreatic juice
wash out enzymes - will digest pancreas otherwise
alkaline to neutralise gastric acid in duodenum
primary secretion from acinar cells
modified to HCO3- rich juice by duct cells
pancreatic enzymes
amylolytic - carbohydrate digestion
• amylase
proteolytic - protein digestion
• typist, chymotrypsin, elastase
lipolytic - fat digestion
• lipase, phospholipase
nucleolytic - nucleic acid digestion
• DNAase, RNAase
what are inactive precursors?
zymogens
pancreatic proteases
secreted as zymogens
• activation by enterokinase in the intestine
• trypsin can auto-activate
many different proteases
• endo and exo peptidases
• amino and specificity
• protein digestion completed by intestinal peptidases
difference between endo and exo peptidases
endo cut off somewhere in the middle
exo cut off at the ends
pancreatic HCO3- secretion
acinar cell primary secretion
• isotonic NaCl secretion
duct HCO3- secretion
• isotonic via apical Cl-/HCO3- exchange and CFTR Cl- channels
cystic fibrosis
- absence of CFTR channels
- lack of fluid secretion
- lack of washout of enzymes
- damage to pancreas
- poor nutrition
control of pancreatic secretion
secretin
cholecystokinin-pancreozymin (CCK)
neural: vagus
secretin in control of pancreatic secretion
duodenal S cells
release stimulated by acid and hyperosmolarity
increases HCO3- rich solution from duct cells in pancreas
decreases gastric acid secretion
cholecystokinin-pancreozymin (CCK) in control of pancreatic secretion
duodenal I cells
release stimulated by fat and protein
stimulates gall bladder contraction
stimulates pancreatic enzyme secretion by stimulating ACh
vagus in control of pancreatic secretion
stimulates both acinar and duct cells
bile functions
elimination of waste products • cholesterol • bile pigmenets • minerals • lipophillic drugs • heavy metals
promotion of lipid digestion and absorption
bile
hepatocytes secrete bile into canaliculi
bile ducts secrete HCO3- rich fluid
bile enters duodenum by common bile duct
what is bile made of?
biliary lipids
• bile acid
• phospholipids - lecithins
• cholesterol
bile pigmenets
• bilirubin
what happens if cholesterol comes out of solution?
you get gall stones which block the exit of the gall bladder causing pain
bile acids keep cholesterol in solution
bile acids (salts)
primary
• liver synthesis from cholesterol
• eg. cholic acid (cholate)
secondary
• modification by intestinal bacteria - dehydroxylation
• eg. deoxycholate
conjugation
• to amino acids - glycine/taurine
• increases solubility
enterohepatic circulation of bile acids
1) synthesis of primary bile acids in liver
2) secretion into duodenum in bile
3) involved in lipid digestion
4) reabsorption in terminal ileum
5) recirculation though hepatic portal vein to liver
6) taken up by liver and secreted into bile
how do bile salts act?
they coat lipids to make emulsions
emulsification of dietary lipids increases SA exposed to lipase and therefore promote digestion
function of gall bladder
concentrates bile
absorbes electrolytes and water
isotonic
Na+ with bile salts
control of biliary secretion
bile acid-dependent
• bile acid concentration in plasma
ductal
• secretin
gall bladder contraction
• CCK
• ACh
• pancreatic enzyme secretion
