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SGUL - Physiology 1 > Pancreatic Exocrine Secretions and Control *** > Flashcards

Pancreatic Exocrine Secretions and Control *** Flashcards

1
Q

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

A

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

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2
Q

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

A
  • stimulated by CCK
  • secretes digestive enzymes into the pancreatic ducts
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3
Q

What do the Islets of Langerhan secrete?

A

Hormones into bloodstream

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4
Q

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

A
  • Secrete NaHCO3
  • Stimulated by secretin
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5
Q

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

A
  • acini (a cluster of acinar cells)
  • intercalated ducts
  • intralobular ducts
  • extralobular ducts
  • interlobular ducts
  • pancreatic duct
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6
Q

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

A
  • Sodium and HCO3-
  • Albumin, globulin and digestive enzymes.
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7
Q

Name some anions that are secreted in the pancreatic juice.

A
  • HCO3-
  • Cl-
  • SO4 2-
  • HPO4 2-
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8
Q

Name some cations that are secreted in the pancreatic juice.

A
  • Na+
  • K+
  • Ca2+
  • Mg2+
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9
Q

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

A
  • 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)
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10
Q

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

A
  • CO2 and HCO3- are produced in the blood
  • CO2 diffuses in and forms H2CO3 with H2O
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11
Q

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

A

Concentration of HCO3- in the blood

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12
Q

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

A

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

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13
Q

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

A
  • Na+ levels don’t change much, but the Cl- goes down while the HCO3- goes up
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14
Q

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

A
  • Less time for HCO3- and Cl- exchange
  • Flow rate is greater following stimulation
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15
Q

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

A
  • proteolytic enzymes
  • amylase
  • lipase
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16
Q

Give examples of proteolytic enzymes secreted by the pancreas.

A
  • Trypsin
  • Carboxypeptidase
  • Chymotrypsin
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17
Q

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

A

(Deoxy)ribonucleases

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18
Q

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

A
  • Phospholipase A2
  • Chymotrypsins
  • Carboxypeptidase
  • Colipase
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19
Q

What does phospholipase A2 do?

A
  • Breakdown of membrane phospholipids.
  • Converts lecithin to isolecithin.
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20
Q

What does colipase do?

A

Enhance pancreatic lipase activity

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21
Q

How does colipase enhance pancreatic lipase activity? PART 1

A
  • Acts on some of the fat droplets
  • Enhances binding capacity of lipase
  • Allows lipase to access the lipid core.
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22
Q

How does colipase enhance pancreatic lipase activity? PART 2

A
  • 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.
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23
Q

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

A

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

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24
Q

How is pancreatic secretion controlled?

A

Neuroendocrine signalling

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25
Q

What is the effect of parasympathetic stimulation of the pancreas?

A
  • Enhances rate of secretion of enzymes and aqueous components of pancreatic juice
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26
Q

What is the effect of sympathetic stimulation of the pancreas?

A
  • Inhibits secretion
  • (Possibly) decreases blood flow - (diverting blood flow from GI tract)
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27
Q

Which two chemicals help stimulate secretion of pancreatic fluid?

A
  • Secretin
  • CCK
28
Q

What are the 3 stages of digestion?

A

CEPHALIC PHASE
GASTRIC PHASE
INTESTINAL PHASE

29
Q

Describe the control of pancreatic secretion in the cephalic phase.

A

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

30
Q

Describe the control of pancreatic secretion in the gastric phase.

A
  • 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
31
Q

Describe the control of pancreatic secretion in the intestinal phase.

A
  • Secretin and CCK
  • Chyme in the duodenum and jejunum
  • Both induce secretion of pancreatic juice
32
Q

How does secretin work?

A
  • Induces pancreatic duct cells to secrete HCO3- rich pancreatic juice, with a lowered enzyme content.
  • Stimulates bile production
33
Q

Where is CCK released from?

A

Duodenum and jejunum

34
Q

What is CCK released in response to?

A
  • Fatty acids
  • Amino acids and peptides
35
Q

What is the effect of CCK stimulation of acinar cells?

A

Synthesis and release of enzyme-rich pancreatic juice

36
Q

What is the effect of CCK stimulation of bile release?

A

Stimulates the secretion of concentrated bile for fat absorption

37
Q

How does CCK cause bile release into the duodenum?

A
  • Contracts the gallbladder
  • Relaxes the Sphincter of Oddi
38
Q

How does CCK enhance acinar cell activity?

A
  • Potentiates the effects of secretin - weak agonist for acinar cells.
39
Q

How would cystic fibrosis affect the pancreas?

A
  • 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
40
Q

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

A

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

41
Q

Where are the pancreatic secretions emptied?

A

→emptied into the duodenum via the Sphincter of Oddi

42
Q

Where is secretin produced?

A

→from mucosa of duodenal and jejunum

43
Q

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

A

50% decrease in response to acidic chyme

44
Q

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

A

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

45
Q

What are inhibitors of autodigestion?

A

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

46
Q

Give an example of an autocatalytic reaction.

A

→ 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

47
Q

Where is enterokinase and when is it secreted?

A

→ Brush border of duodenum
→ Secreted in response to CCK

48
Q

What does enterokinase do?

A

→ trypsinogen to trypsin

49
Q

How are proteolytic enzymes secreted and why?

A

→Enzymes secreted as proenzymes
→ Prevent autodigestion

50
Q

What is the activator and substrate of colipase?

A

→ A: trypsin
→ B: fat droplets

51
Q

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

A

→ A: Trypsin
→ S: Proteins and polypeptides

52
Q

What is the activator and substrate of Phospholipase A2?

A

→ A: Trypsin
→ S: Phospholipids (lecithin)

53
Q

What is the activator and substrate of elastase?

A

→ A: Trypsin
→ S: Elastin

54
Q

What is the activator and substrate of Pancreatic α amylase?

A

→ A: Cl-
→S: Starch

55
Q

In general, what are the substrates for most lipases?

A

Triglycerides

56
Q

What is the activator and substrate of trypsin?

A

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

57
Q

Why do Cl- and amylase decrease after infusing secretin?

A

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

58
Q

What do secretions from the gall bladder help to do?

A

Help neutralise gastric acid

59
Q

Where does enzyme activation occur?

A

Duodenum

60
Q

Why are enzymes secreted as zymogens?

A

→prevent autodigestion

61
Q

What are acinar cells connected to?

A

→Duct that secretes bicarbonate

62
Q

What do the acini form?

A

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

63
Q

What are intercalated ducts made from?

A

→ squamous epithelium

64
Q

What are intralobular ducts made from?

A

→ cuboidal or low columnar epithelium

65
Q

What are interlobular ducts made from?

A

→columnar epithelium

SGUL - Physiology 1 (68 decks)

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