Lecture 31 - Pancreatic and Biliary Secretion

Question 1

Where is CCK released from?

Answer 1

I-cells in the duodenum due to fat and protein digestive products

Question 2

What does CCK do?

Answer 2

Inhibits gastrin secretion in the antrum (via D-cell)
Increases protein secretion in the pancreatic acini

Question 3

Where is secretin released from?

Answer 3

S-cells in the small intestine due to acidification of the duodenum

Question 4

What does secretin do?

Answer 4

Inhibits gastrin secretion in the antrum (via D-cell)
Increases fluid secretion in the pancreatic duct

Question 5

What is the structure of the exocrine pancreas?

Answer 5

Lobules
- acini
Ducts
- intercalated
- common bile
Secretory units
- acini
- intercalated ducts

Question 6

What are the secretory cells of the pancreas?

Answer 6

Acinus
Intercalated ducts

Question 7

What is the site of majority of fluid secretion in the pancreas?

Answer 7

Duct cells

Question 8

What do the acinar cells in pancreas secrete?

Answer 8

Isotonic NaCl solution - 25% of secretion

Question 9

What do the duct cells in pancreas secrete?

Answer 9

HCO3- rich fluid - 75% of secretion

Question 10

What is the difference in osmolarity between the saliva and pancreas?

Answer 10

Saliva: 100 mOsm
Pancreas: 300 mOsm

Question 11

What is the volume and composition of secretions from pancreas?

Answer 11

1-1.5 L of alkaline fluid and 5 -15 g protein secreted per day

Question 12

Where are the proteins in pancreatic secretions made?

Answer 12

Acinar cells

Question 13

What proteins do the pancreatic acinar cells secrete?

Answer 13

20 different proteins secreted - mainly digestive enzymes
- zymogens - inactive precursors of digestive enzymes
- (trypsinogen, procarboxypeptidase)
- amylase, lipase
Enzymes for all major nutrient groups

Question 14

What cell produces the alkaline fluid in pancreatic secretion?

Answer 14

Intercalated duct cells

Question 15

What does the alkaline fluid in pancreatic secretion do?

Answer 15

Neutralises acidic chyme from the stomach

Question 16

What is the alkaline fluid in pancreatic secretion?

Answer 16

Isosmotic NaHCO3 solution

Question 17

When do we have the largest volume of pancreatic secretion?

Answer 17

Intestinal phase due to CCK and secretin

Question 18

What stimulates pancreatic secretion?

Answer 18

CCK
Secretin
- minor regulation via vagus (ACh)

Question 19

What stimulates pancreatic acinar cells?

Answer 19

CCK and vagus (ACh)

Question 20

What stimulates pancreatic duct cells?

Answer 20

Secretin

Question 21

Pancreatic secretion
A. is hypotonic due to high Na+ re-absorption in pancreatic ducts.
B. is stimulated by somatostatin.
C. contains trypsinogen released from zymogen granules.
D. is elevated during the gastric phase.

Answer 21

C. contains trypsinogen released from zymogen granules.

A - Salivary gland not pancreatic
B - Somatostatin always switch off - not involved with pancreatic secretion
D - Elevated in intestinal phase

Question 22

What are pancreatic acinar cells specialised for?

Answer 22

Protein secretion
- zymogen granules

Question 23

How does CCK and ACh stimulate secretion of pancreatic acinar cells?

Answer 23

Increase in intracellular Ca2+

Question 24

How do acinar cells secrete isotonic NaCl solution/What is fluid secretion in pancreatic acinar cells driven by?

Answer 24

By electrogenic Cl- secretion

Question 25

Why does increase in Ca+ in pancreatic acinar cells increase secretion?

Answer 25

By activating a Ca2+ dependent apical Cl- channel (CFTR) - also stimulates secretion of enzymes

Question 26

What is secretion by pancreatic duct cell dependent on?

Answer 26

Dependent on apical Cl-/HCO3- exchanger

Question 27

Why is Cl-/HCO3- exchanger inactive at rest?

Answer 27

Due to little Cl- in duct lumen

Question 28

What is Cl- in pancreatic duct lumen controlled by?

Answer 28

Controlled indirectly via a cAMP-dependent Cl- channel (CFTR) activated by secretin

Question 29

How does secretin increase pancreatic duct cell secretion?

Answer 29

Increasing cAMP Activation of apical Cl- channel (cAMP-activated) Increased Cl- in duct lumen luminal Cl- exchanged for HCO3- Result: HCO3- secretion

Question 30

Why does Na+ diffuse paracellular in pancreatic duct cells?

Answer 30

Due to electric gradient set up by Cl- and HCO3- movement

Question 31

Why do we also have the secretion of NaHCO3 in pancreatic duct cells?

Answer 31

Na+ diffuses across the paracellular pathway due to potential set up by Cl- and HCO3- movement Water follows because of the osmotic gradient

Question 32

The secretion of a bicarbonate-rich solution by pancreatic duct cells is driven by CCK, BECAUSE bicarbonate secretion in stimulated pancreatic duct cells is facilitated by CFTR.

Answer 32

D - First false, second true Driven by secretin not CCK, CCK for acinar cells

Question 33

What epithelia are the pancreatic duct cells?

Answer 33

Leaky

Question 34

What are the differences in salivary and pancreatic duct secretion?

Answer 34

Tight vs leaky epithelium Chloride secreted to drive bicarbonate secretion (boosted by secretin in pancreas) NO change in sodium content (pancreas) Major site of fluid secretion in pancreas

Question 35

How does the liver process absorbed nutrients and control metabolism?

Answer 35

Gluconeogenesis, glucose buffering, fatty acid oxidation, synthesis of plasma proteins (e.g., albumin)

Question 36

What is the exocrine function of the liver?

Answer 36

Secretion and excretion

Question 37

What is secretion and excretion of liver?

Answer 37

Provision of bile acids and alkaline fluid to: - aid digestion and absorption of fats - neutralise gastric acid Degradation and conjugation of waste products of metabolism Detoxification of poisonous substances Excretion of waste metabolites and detoxified substance in bile

Question 38

What is function of liver assisted by?

Answer 38

Blood supply

Question 39

Where is bile secreted in liver?

Answer 39

Bile secreted by hepatocytes lining canaliculi

Question 40

What do ducts in liver secrete?

Answer 40

HCO3- rich fluid

Question 41

Where is liver secretion stored and concentrated?

Answer 41

Gall bladder between meals

Question 42

What is the volume and composition of liver secretion?

Answer 42

0.5 L day-1 - secreted continuously Excretory products - bile pigments - waste products - cholesterol - excreted by liver - steroids, heavy metal, drugs Products associated with digestion - HCO3- rich fluid - secreted by duct cells - bile salts

Question 43

What makes up bile salts?

Answer 43

Amphipathic compounds - hydrophillic and hydrophobic surface Primary bile acid - Cholic acid

Question 44

What are the two sources of bile salts in liver secretion?

Answer 44

Newly synthesised Enterohepatic circulation

Question 45

What percentage of bile salts are absorbed in the enterohepatic circulation?

Answer 45

95%

Question 46

What is the mechanism of bile salt absorption in the enterohepatic circulation?

Answer 46

Small intestine - limited passive absorption - active absorption in ileum Colon - limited role

Question 47

What are the three mechanisms of biliary secretion?

Answer 47

Nervous Hormonal Bile salts

Question 48

What is the control of biliary secretion in the cephalic and gastric phases?

Answer 48

Minor, PNS

Question 49

What is the control of biliary secretion in the intestinal phase?

Answer 49

Hormonal - secretin stimulates production of HCO3- rich solution by ducts - CCK stimulates contraction of gallbladder Bile salts - arrival of bile salts in portal venous blood stimulates absorption by liver and subsequent secretion

Question 50

The liver produces a bicarbonate-rich bile, BECAUSE bile acids are required to reabsorb protein in the intestine.

Answer 50

C - First true, second false Bile acids to reabsorb fat

Question 51

What stimulates biliary secretion?

Answer 51

CCK and secretin

Question 52

What is the purpose of bile acids in biliary secretion?

Answer 52

To reabsorb fat