Pancreatic Exocrine Secretions and Control ***

Question 1

What are the three types of cells found in the pancreas?

Answer 1

ACINAR CELLS (exocrine)
ISLETS OF LANGERHAAN (endocrine)
DUCT CELLS

Question 2

What are acinar cells stimulated by, and what do they secrete?

Answer 2

• stimulated by CCK
• secretes digestive enzymes into the pancreatic ducts

Question 3

What do the Islets of Langerhan secrete?

Answer 3

Hormones into bloodstream

Question 4

What do duct cells secrete and what are they stimulated by?

Answer 4

• Secrete NaHCO3
• Stimulated by secretin

Question 5

List the structures a substance has to go through to get from acinar cells to the pancreatic duct.

Answer 5

• acini (a cluster of acinar cells)
• intercalated ducts
• intralobular ducts
• extralobular ducts
• interlobular ducts
• pancreatic duct

Question 6

The pancreas secretes around 1.5 litres of fluid every day.
What are some components of this fluid?

Answer 6

• Sodium and HCO3-
• Albumin, globulin and digestive enzymes.

Question 7

Name some anions that are secreted in the pancreatic juice.

Answer 7

• HCO3-
• Cl-
• SO4 2-
• HPO4 2-

Question 8

Name some cations that are secreted in the pancreatic juice.

Answer 8

• Na+
• K+
• Ca2+
• Mg2+

Question 9

The composition of the juice is modified as it travels through the duct.
Describe how this happens. PART 1

Answer 9

• Cl- is actively exchanged for HCO3- by the epithelial cells
• H+ is actively eliminated and exchanged for K+ and Na+
• H+ neutralises the HCO3- (and H2CO3 is formed)

Question 10

The composition of the juice is modified as it travels through the duct.
Describe how this happens. PART 2

Answer 10

• CO2 and HCO3- are produced in the blood
• CO2 diffuses in and forms H2CO3 with H2O

Question 11

What is HCO3- concentration in juice, and rate of production proportional to?

Answer 11

Concentration of HCO3- in the blood

Question 12

Describe the effect of stimulating the pancreas (via secretin) on the components of pancreatic juice. PART 1

Answer 12

Change in the concentration of Cl- and HCO3- after secretin infusion.
- [HCO3-]-rich secretions

Question 13

Describe the effect of stimulating the pancreas (via secretin) on the components of pancreatic juice. PART 1

Answer 13

• Na+ levels don’t change much, but the Cl- goes down while the HCO3- goes up

Question 14

Normally it would be expected that [HCO3-] secretions are high following secretin-induced stimulation but this is not the case. Suggest a reason why.

Answer 14

• Less time for HCO3- and Cl- exchange
• Flow rate is greater following stimulation

Question 15

What are the three major types of enzymes secreted by the pancreas?

Answer 15

• proteolytic enzymes
• amylase
• lipase

Question 16

Give examples of proteolytic enzymes secreted by the pancreas.

Answer 16

• Trypsin
• Carboxypeptidase
• Chymotrypsin

Question 17

What is the fourth additional enzyme type sometimes secreted by the pancreas?

Answer 17

(Deoxy)ribonucleases

Question 18

Trypsin activates many other enzymes.
List some enzymes that it activates.

Answer 18

• Phospholipase A2
• Chymotrypsins
• Carboxypeptidase
• Colipase

Question 19

What does phospholipase A2 do?

Answer 19

• Breakdown of membrane phospholipids.
• Converts lecithin to isolecithin.

Question 20

What does colipase do?

Answer 20

Enhance pancreatic lipase activity

Question 21

How does colipase enhance pancreatic lipase activity? PART 1

Answer 21

• Acts on some of the fat droplets
• Enhances binding capacity of lipase
• Allows lipase to access the lipid core.

Question 22

How does colipase enhance pancreatic lipase activity? PART 2

Answer 22

• Allows lipase to break down the fat droplet further to make micelles
• Small enough to travel to the surface of the epithelial cells to get absorbed.

Question 23

What is the percentage of secreted enzymes that reach the small intestine?

Answer 23

amylase: 75%
trypsin: 20%
lipase: 1%

Question 24

How is pancreatic secretion controlled?

Answer 24

Neuroendocrine signalling

Question 25

What is the effect of parasympathetic stimulation of the pancreas?

Answer 25

- Enhances rate of secretion of enzymes and aqueous components of pancreatic juice

Question 26

What is the effect of sympathetic stimulation of the pancreas?

Answer 26

- Inhibits secretion - (Possibly) decreases blood flow - (diverting blood flow from GI tract)

Question 27

Which two chemicals help stimulate secretion of pancreatic fluid?

Answer 27

- Secretin - CCK

Question 28

What are the 3 stages of digestion?

Answer 28

CEPHALIC PHASE GASTRIC PHASE INTESTINAL PHASE

Question 29

Describe the control of pancreatic secretion in the cephalic phase.

Answer 29

Vagal (ACh and VIP) stimulation of gastrin release from the antrum leads to some pancreatic secretion

Question 30

Describe the control of pancreatic secretion in the gastric phase.

Answer 30

- Distention (vagal reflex on the fundus or antrum) - Amino acid and peptide stimulated gastrin secretion - Both lead to the release of enzyme-rich pancreatic juice

Question 31

Describe the control of pancreatic secretion in the intestinal phase.

Answer 31

- Secretin and CCK - Chyme in the duodenum and jejunum - Both induce secretion of pancreatic juice

Question 32

How does secretin work?

Answer 32

- Induces pancreatic duct cells to secrete HCO3- rich pancreatic juice, with a lowered enzyme content. - Stimulates bile production

Question 33

Where is CCK released from?

Answer 33

Duodenum and jejunum

Question 34

What is CCK released in response to?

Answer 34

- Fatty acids - Amino acids and peptides

Question 35

What is the effect of CCK stimulation of acinar cells?

Answer 35

Synthesis and release of enzyme-rich pancreatic juice

Question 36

What is the effect of CCK stimulation of bile release?

Answer 36

Stimulates the secretion of concentrated bile for fat absorption

Question 37

How does CCK cause bile release into the duodenum?

Answer 37

- Contracts the gallbladder - Relaxes the Sphincter of Oddi

Question 38

How does CCK enhance acinar cell activity?

Answer 38

- Potentiates the effects of secretin - weak agonist for acinar cells.

Question 39

How would cystic fibrosis affect the pancreas?

Answer 39

- Blocked pancreatic duct - Secretion will cease to end up in the duodenum - Nutritional deficiencies, due to improper digestion of food - Causes pancreatic insufficiency leading to steatorrhea

Question 40

What do the secretions of the pancreas join with and where?

Answer 40

Join with the secretions from the gallbladder via the common bile duct

Question 41

Where are the pancreatic secretions emptied?

Answer 41

→emptied into the duodenum via the Sphincter of Oddi

Question 42

Where is secretin produced?

Answer 42

→from mucosa of duodenal and jejunum

Question 43

What happens as a result of a vagotomy during the intestinal phase?

Answer 43

50% decrease in response to acidic chyme

Question 44

What membranes do chymotrypsinogen and amylase cross in the pancreas and what does this suggest?

Answer 44

→Cross the basolateral membrane of the pancreas →Suggests bidirectional permeability of membrane to digestive enzymes

Question 45

What are inhibitors of autodigestion?

Answer 45

→Kazal inhibitor - inhibits chymotrypsin C, caldecrin etc. →Intracellular pH of zymogen granule = naturally acidic (keeps zymogen inactive)

Question 46

Give an example of an autocatalytic reaction.

Answer 46

→ Once one trypsin is formed it can go on and convert more trypsinogens to trypsin - Trypsin is a reaction product and is able to catalyse its own formation

Question 47

Where is enterokinase and when is it secreted?

Answer 47

→ Brush border of duodenum → Secreted in response to CCK

Question 48

What does enterokinase do?

Answer 48

→ trypsinogen to trypsin

Question 49

How are proteolytic enzymes secreted and why?

Answer 49

→Enzymes secreted as proenzymes → Prevent autodigestion

Question 50

What is the activator and substrate of colipase?

Answer 50

→ A: trypsin → B: fat droplets

Question 51

What is the activator and substrate of carboxypeptidase A+B?

Answer 51

→ A: Trypsin → S: Proteins and polypeptides

Question 52

What is the activator and substrate of Phospholipase A2?

Answer 52

→ A: Trypsin → S: Phospholipids (lecithin)

Question 53

What is the activator and substrate of elastase?

Answer 53

→ A: Trypsin → S: Elastin

Question 54

What is the activator and substrate of Pancreatic α amylase?

Answer 54

→ A: Cl- →S: Starch

Question 55

In general, what are the substrates for most lipases?

Answer 55

Triglycerides

Question 56

What is the activator and substrate of trypsin?

Answer 56

→A : Secreted as trypsinogen - activated by enterokinase/enteropeptidase autocatalytically →S: Proteins and polypeptides

Question 57

Why do Cl- and amylase decrease after infusing secretin?

Answer 57

→ there are more increased watery secretions so the other components decrease.

Question 58

What do secretions from the gall bladder help to do?

Answer 58

Help neutralise gastric acid

Question 59

Where does enzyme activation occur?

Answer 59

Duodenum

Question 60

Why are enzymes secreted as zymogens?

Answer 60

→prevent autodigestion

Question 61

What are acinar cells connected to?

Answer 61

→Duct that secretes bicarbonate

Question 62

What do the acini form?

Answer 62

Sacs that connect to the ductal tree and empty into the duodenum

Question 63

What are intercalated ducts made from?

Answer 63

→ squamous epithelium

Question 64

What are intralobular ducts made from?

Answer 64

→ cuboidal or low columnar epithelium

Question 65

What are interlobular ducts made from?

Answer 65

→columnar epithelium