lecture 28 - the gut 2: pancreatic secretion and bile

Question 1

what is the ampulla of Vater?

Answer 1

common entry of bile duct and pancreatic duct into the duodenum

Question 2

organisation of pancreas

Answer 2

acinar cells

pancreatic duct cell

intercalate duct

interlobular duct

main duct

Question 3

enzymes in pancreatic juice

Answer 3

digestion

pancreas key organ for digestion

acinar cells

Question 4

fluid and electrolyte (HCO3-) in pancreatic juice

Answer 4

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

Question 5

pancreatic enzymes

Answer 5

amylolytic - carbohydrate digestion
• amylase

proteolytic - protein digestion
• typist, chymotrypsin, elastase

lipolytic - fat digestion
• lipase, phospholipase

nucleolytic - nucleic acid digestion
• DNAase, RNAase

Question 6

what are inactive precursors?

Answer 6

zymogens

Question 7

pancreatic proteases

Answer 7

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

Question 8

difference between endo and exo peptidases

Answer 8

endo cut off somewhere in the middle

exo cut off at the ends

Question 9

pancreatic HCO3- secretion

Answer 9

acinar cell primary secretion
• isotonic NaCl secretion

duct HCO3- secretion
• isotonic via apical Cl-/HCO3- exchange and CFTR Cl- channels

Question 10

cystic fibrosis

Answer 10

• absence of CFTR channels
• lack of fluid secretion
• lack of washout of enzymes
• damage to pancreas
• poor nutrition

Question 11

control of pancreatic secretion

Answer 11

secretin

cholecystokinin-pancreozymin (CCK)

neural: vagus

Question 12

secretin in control of pancreatic secretion

Answer 12

duodenal S cells

release stimulated by acid and hyperosmolarity

increases HCO3- rich solution from duct cells in pancreas

decreases gastric acid secretion

Question 13

cholecystokinin-pancreozymin (CCK) in control of pancreatic secretion

Answer 13

duodenal I cells

release stimulated by fat and protein

stimulates gall bladder contraction

stimulates pancreatic enzyme secretion by stimulating ACh

Question 14

vagus in control of pancreatic secretion

Answer 14

stimulates both acinar and duct cells

Question 15

bile functions

Answer 15

elimination of waste products 
• cholesterol 
• bile pigmenets 
• minerals 
• lipophillic drugs 
• heavy metals 

promotion of lipid digestion and absorption

Question 16

bile

Answer 16

hepatocytes secrete bile into canaliculi

bile ducts secrete HCO3- rich fluid

bile enters duodenum by common bile duct

Question 17

what is bile made of?

Answer 17

biliary lipids
• bile acid
• phospholipids - lecithins
• cholesterol

bile pigmenets
• bilirubin

Question 18

what happens if cholesterol comes out of solution?

Answer 18

you get gall stones which block the exit of the gall bladder causing pain

bile acids keep cholesterol in solution

Question 19

bile acids (salts)

Answer 19

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

Question 20

enterohepatic circulation of bile acids

Answer 20

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

Question 21

how do bile salts act?

Answer 21

they coat lipids to make emulsions

emulsification of dietary lipids increases SA exposed to lipase and therefore promote digestion

Question 22

function of gall bladder

Answer 22

concentrates bile

absorbes electrolytes and water

isotonic

Na+ with bile salts

Question 23

control of biliary secretion

Answer 23

bile acid-dependent
• bile acid concentration in plasma

ductal
• secretin

gall bladder contraction
• CCK
• ACh
• pancreatic enzyme secretion