Pancreatic & biliary secretions

Question 1

What is secreted by pancreatic ductal (a.k.a centroacinar) cells? What is its function?

Answer 1

Sodium bicarbonate - NaHCO3

Neutralises acidic chyme and brings intestinal pH to optimal range for pancreatic enzyme function (6.5 - 7)

Question 2

Which two pancreatic enzymes are secreted in their active form?

Answer 2

Lipase

Amylase

Question 3

List the components of pancreatic juice

Answer 3

Trypsinogen
Chymotrypsinogen
Procarboxypeptidase
NaHCO3 (LOTS in horse to maintain appropriate pH in colon)
Water
Pancreatic amylase
Pancreatic lipase

Question 4

List the components of bile

Answer 4

Bile salts
Cholesterol
Lecithin
Bilirubin
HCO3- (added by ductal cells)

Question 5

Describe the cephalic phase of pancreatic secretion

Answer 5

Presence of food in the oral cavity causes vagal efferent activation - stimulates pancreas to increase volume and enzyme content of secretions
Can be blocked with atropine - entirely cholinergic-mediated

Question 6

Describe the gastric phase of pancreatic secretion

Answer 6

Distension of the stomach with ingesta leads to vagally-mediated increase in pancreatic secretions
- sectioning vagus nerve will inhibit
Also get presence of food in the pyloric antrum leading to gastrin release which stimulates pancreas to secrete enzymes - local enterogastric reflex independent of vagus

Question 7

Describe the intestinal phase of pancreatic secretion

Answer 7

Secretin release stimulated by low pH in the intestine > HCO3 production by pancreas
CCK release stimulated( by protein and fat in the intestine > zymogen granule fusion and enzyme release from pancreas (little effect to overall volume of secretions)

The nature of the pancreatic secretion is responsive to the composition of the chyme i.e the more acidic, the more HCO3- is released

Question 8

Describe the three main functions of secretin

Answer 8

1. Inhibit gastrin release
2. Stimulate NaHCO3 production and release by pancreatic ductal cells
3. Stimulate HCO3- production and release by bile duct cells

Question 9

Describe the three main functions of CCK

Answer 9

1. Inhibit gastrin release
2. Stimulate zymogen granule fusion and pancreatic enzyme release from the pancreatic acinar cells
3. Stimulate GB contraction and thence bile flow

Question 10

What amino acids might be conjugated to cholesterol to form bile salts by hepatocytes?

Answer 10

Taurine or glycine

Question 11

What factor sets off pancreatitis?

Answer 11

Overstimulation of pancreas + consumption of all anti-trypsin inhibitor - activation of trypsin - activation of other enzymes - autodigestion of pancreas

Question 12

Three animals that don’t have a gall bladder.

Answer 12

Horse
Rat
Elephant

Question 13

How does the gall bladder concentrate bile?

Answer 13

Active resorption of Na+ whilst in the GB, and water along with it