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Physiology 1 : GI > Pancreatic exocrine secretions and its control > Flashcards

Pancreatic exocrine secretions and its control Flashcards

1
Q

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

A

→The secretions from the pancreas join with the secretions from the gallbladder
→via the common bile duct

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2
Q

Where are the pancreatic secretions emptied?

A

→emptied into the duodenum via the Sphincter of Oddi

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3
Q

What are the functional units of the pancreas?

A

→ Acinar cells

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4
Q

What do acinar cells do?

A

→ Release enzymes

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5
Q

What are acinar cells connected to?

A

→Duct that secretes bicarbonate

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6
Q

What do the acini form?

A

→Acini form sacs that connect to the ductal tree and empty into the duodenum

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7
Q

What are intercalated ducts made from?

A

→ squamous epithelium

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8
Q

What are interlobular ducts made from?

A

→ cuboidal or low columnar epithelium

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9
Q

What are interlobular ducts made from?

A

→columnar epithelium/goblet cells

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10
Q

What do the ductal cells release?

A

→bicarbonate rich secretions that are identical to salivary secretions
→except that there is a lot more bicarbonate in it.
→This neutralizes acid.

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11
Q

Where do the bicarbonate secretions come from?

A

→ Ductal and acinar cells

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12
Q

What control are bicarbonate secretions under?

A

→ Secretin

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13
Q

What are the enzyme secretions of the acinar cells under?

A

→CCK

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14
Q

What is the pathway that enzymes take?

A

Acini → microvilli→ intercalated duct → intralobular duct → interlobular duct → pancreatic duct

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15
Q

How much fluid does the pancreas secrete per day?

A

→1.5L

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16
Q

What are the pancreatic secretions made from?

A

→Sodium and HCO3- rich juice, albumin, globulin and digestive enzymes

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17
Q

What do acinar cells secrete?

A

→digestive enzymes to break down carbohydrates, fats, proteins and nucleic acids

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18
Q

Why are enzymes secreted as zymogens?

A

→prevent autodigestion

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19
Q

Where does enzyme activation occur?

A

→in the duodenum

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20
Q

What are the anions that are secreted in pancreatic juice?

A

→HCO3-,
→Cl-
→SO42-
→HPO42-

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21
Q

What are the cations that are secreted in pancreatic juice?

A

→Na+
→K+,
→Ca2+
→Mg2+

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22
Q

What do the HCO3- secretions occur?

A

→ Secretions from the gallbladder help to neutralize gastric acid

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23
Q

How is the composition of the juice varied as it moves through the ducts?

A

→The composition of the juice is modified as it travels through the duct : epithelial cells actively exchange Cl-/HCO3-

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24
Q

How does H2CO3 form?

A

→H+ is actively eliminated by Na+/H+ exchanger
→H+ is exchanged for K+ driven by Na+/K+ ATPase
→H+ neutralizes HCO3- (H2CO3 is formed)
→More CO2 and HCO3- is produced in the blood
→CO2 diffuses in and forms H2CO3 with H2O

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25
Q

What is the rate of pancreatic juice production proportional to?

A

→ [HCO3-]pancreatic juice and its rate of production∝ [HCO3-]blood

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26
Q

What happens to Cl- and amylase after you infuse secretin?

A

→There is reciprocal change in the concentrations of Cl- and HCO3- after the infusion of secretin

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27
Q

Why does Cl- and amylase decrease after infusing secretin?

A

→The amount of chloride and amylase decreases

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

28
Q

What are the 3 major types of enzymes?

A

→Proteolytic enzymes (trypsin, chymotrypsin, carboxypeptidase)
→Amylase
→Lipase

29
Q

What is the activator and substrate of trypsin?

A

→A : Secreted as trypsinogen - activated by enterokinase/enteropeptidase and by trypsin

→S: Proteins and polypeptides

30
Q

What is the substrate of pancreatic lipase?

A

→triglycerides

31
Q

What is the activator and substrate of Pancreatic α amylase?

A

→ A: Cl-

→S: Starch

32
Q

What is the substrate of ribonuclease?

A

→ RNA

33
Q

What is the substrate of deoxyribonuclease?

A

→ DNA

34
Q

What is the activator and substrate of elastase?

A

→ A: Trypsin

→ S: Elastin

35
Q

What is the activator and substrate of Phospholipase A2?

A

→ A: Trypsin

→ S: Phospholipids (lecithin)

36
Q

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

A

→ A: Trypsin

→ S: Proteins and polypeptides

37
Q

What is the activator and substrate of colipase?

A

→ A: trypsin

→ B: fat droplets

38
Q

How are proteolytic enzymes secreted and why?

A

→Enzymes secreted as proenzymes

→ Prevent autodigestion

39
Q

Where is enterokinase and when is it secreted?

A

→ Brush border of duodenum

→ Secreted in response to CCK

40
Q

What does enterokinase do?

A

→ trypsinogen to trypsin

41
Q

What is meant by an autocatalytic reaction?

A

→ Once one trypsin is formed it can go on and convert more trypsinogens to trypsin

42
Q

What are inhibitors of autodigestion?

A

→Kazal inhibitor - enzyme Y (chymotrypsin C, caldecrin)

→Intracellular pH of zymogen granule = acidic (keeps zymogen inactive)

43
Q

What happens in acute pancreatitis?

A

→Trypsin activates phospholipase A2 in the pancreatic duct

→Increase in pancreatic alpha amylase - diagnostic test

44
Q

What does activation of PLA2 in the pancreatic duct do?

A

→converts Lecithin → Isolecithin (PLA2)

→Isolecithin → disruption of pancreatic tissue, membrane damage and necrosis

45
Q

What reaction does amylase catalyze?

A

→polysaccharides → disaccharides

46
Q

What reaction does lipase catalyze?

A

→triglycerides → fatty acids and glycerol

47
Q

What happens in pancreatic insufficiency?

A

→poor digestion of lipids and their malabsorption which causes steatorrhoea

48
Q

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

A

→Amylase - 75%
→Trypsin - 20%
→Lipase - 1%

49
Q

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

A

→Chymotrypsinogen and amylase cross the basolateral membrane of the pancreas
→Suggests bidirectional permeability of the basolateral membrane to digestive enzymes

50
Q

How are pancreatic secretions controlled?

A

→ Neuroendocrine secretions

51
Q

What happens to pancreatic secretions with parasympathetic stimulation?

A

→enhances the rate of secretion of enzymes and aqueous components of pancreatic juice

52
Q

What happens to pancreatic secretions with sympathetic stimulation?

A

→inhibits secretion

53
Q

What do secretin and CCK do?

A

→ stimulate secretion of pancreatic fluid ( enzyme and bicarbonate rich secretions)

54
Q

What happens during the cephalic phase?

A

→Vagal (ACh and VIP) stimulation of gastrin release from the antrum
→ some protein-rich pancreatic juice

55
Q

What happens during the gastric phase?

A

→Distension (vagal reflex on fundus or antrum) amino acid and peptide ( in antrum) stimulated gastrin secretion → release of enzyme rich pancreatic juice

56
Q

What happens as the result of a vagotomy?

A

Vagotomy → 50% decrease in response to acidic chyme

57
Q

What happens in the intestinal phase?

A

→Secretin and CCK
→Acidic chyme in the duodenum and jejunum induces secretion of pancreatic juice with bicarbonate in it to neutralize the acid.

58
Q

Where is secretin produced?

A

→from mucosa of duodenal and jejunum

59
Q

What does secretin induce?

A

→Induces pancreatic duct cells to secrete HCO3- rich pancreatic juice but decreased enzyme content

60
Q

What does secretin stimulate in the liver?

A

→ the production of bile by the liver

61
Q

Where is CCK secreted from and in response to what?

A

→ from duodenal and jejunum in response to fatty acids

62
Q

What does CCK stimulate?

A

→stimulates pancreatic acinar cells to synthesize and release enzyme rich pancreatic juice
→stimulates the secretion of concentrated bile from gallbladder for fat absorption

63
Q

What effect does CCK have on the gallbladder?

A

→Contracts the gallbladder and relaxes the sphincter of Oddi → release of bile into the duodenum

64
Q

What does CCK potentiate?

A

→Potentiates the effect of secretin which is a weak agonist of acinar cells

65
Q

What is a consequence of cystic fibrosis?

A

→The pancreatic ducts are blocked and the intestines cannot absorb nutrients fully
→Steatorrhea

Physiology 1 : GI (15 decks)

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