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Physiology II > L28: Gastric, Pancreatic, and Intestinal Secretions > Flashcards

L28: Gastric, Pancreatic, and Intestinal Secretions Flashcards

1
Q

What is the stimulus for conversion of pepsinogen to pepsin?

A

H+

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2
Q

____ is an inactive proenzyme secreted from chief cells of gastric mucosa

A

Pepsinogen

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3
Q

At which pH is pepsin most active in?
A. Acidic
B. Basic
C. Neutral

A

A. Acidic

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4
Q

True or False: Pepsin is active at pH of 7

A

False

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5
Q

Pepsin digests 10-20% of the total ___ in a meal
A. Protein
B. Fiber
C. Carbohydrates

A

A. Protein

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6
Q

True or False: Most protein enters the duodenum intact

A

True

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7
Q

True or False: Gastric lipase is an enzyme secreted from chief cells of gastric mucosa in its inactive form

A

False - while gastric lipase is secreted from chief cells of gastric mucosa, it is secreted in its ACTIVE form

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8
Q

What is the function of Gastric Lipase?
A. Digest dietary carbohydrates
B. Digest dietary protein
C. Digest dietary triglycerides

A

C. Digest dietary triglycerides
(into FFA)

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9
Q

What pH ranges is Gastric Lipase active at?

A

pH of 4-5; pH of 2

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10
Q

Gastric lipase secretion is stimulated by _____

A

Ach

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11
Q

____, secreted by Parietal Cels, binds Vit B12 in the duodenal lumen, protecting it from enzymatic degradation and transporting it to the ileum where it is absorbed

A

Intrinsic Factor

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12
Q

Where it Vit B 12 absorbed?

A

Ileum

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13
Q

True or False: The same substances that stimulate HCl secretion from parietal cells also stimulate IF secretion

A

True

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14
Q

The gastric mucosal barrieris made of both ___ and ____

A

mucins; bicarbonate

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15
Q

Three functions of the gastric mucosal barrier?

A

1) Prevent mixing of gastric luminal contents with enterocytes
2) Protect underlying mucosa from digestion by pepsin and damage by H+
3) Buffer any luminal H+ that enters barrier with secreted HCO3

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16
Q

What are the two mechanisms by which enterocytes secrete mucins?

A

1) Exocytosis - continuos secretion of mucin
2) Cell exfoliation

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17
Q

Which three molecules increase the production of mucin and secretion?

A

Ach, gastrin, and prostaglandins

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18
Q

What is the pH of the gastric lumen? pH of the enterocyte surface?

A

gastric lumen = less than 3.0
enterocyte surface = 7.0

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19
Q

All gastric enterocytes secrete ___ and ___ to form gastric mucosal barrier

A

mucins; HCO3

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20
Q

How do enterocytes secrete HCO3?

A

HCO3-Cl antiporter in apical membrane

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21
Q

Which two molecules stimulate HCO3 secretion in the enterocyte?

A

Prostaglandins and Ach

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22
Q

___ are important in maintaining health and integrity of the gastric mucosal barrier. It is said to have “cytoprotection.”

A

Prostaglandins

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23
Q

What are the four benefits of prostaglandins?

A

1) Decrease HCl secretion
2) Increased mucin secretion
3) Increase HCO3 secretion
4) Increase mucosal blood flow

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24
Q

How can NSAID use affect the gastric mucosal barrier?

A

NSAID’s decrease PG synthesis, thereby decreasing the thickness and integrity of the GMB

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25
Q

Why is pepsin not active in the gastric mucosal barrier?

A

Only active in acidic conditions (e.g gastric lumen) ; the gastric mucosal barrier is pH = 4-7

  • Prevents digestion of gastrin protein by pepsin
26
Q

True or False: Pancreatic juice is required for normal digestion of carbohydrates, protein, and fat. Its absence produces severe maldigestion and diarrhea

A

True

27
Q

What are the 4 main functions of pancreatic exocrine secretions?

A

1) Secrete enzymes and proteins needed for digestion of dietary carbs, protein, and fat

2) Neutralize H+ delivery to duodenum from stomach

3) Maintain pH in duodenal lumen at level compatible w pancreatic enzyme activity (pH = 7)

4) Maintain neutral pH in duodenal lumen to protect mucosa (there is NO mucosal barrier in the pancreas to limit enterocyte contact, as is the case in the stomach)

28
Q

The exocrine pancreas is composed of two groups of cells with special functions: ____ and ____

A

1) Acinar cells
2) Ductal cells

29
Q

True or False: Acinar cells have tight junctions that are impermeable to water while Ductal cells have tight junctions that are permeable to water

A

False - acinar cells have tight junctions that ARE PERMEABLE to water while ductal cells have tight junctions that are NOT PERMEABLE to water

30
Q

Two functions of acinar cells of the pancreas?

A

1) Secretes enzymes, zymogens, and proteins for digestion of carbs, protein, and fat
2) Primary secretion - isotonic to plasma

31
Q

Two functions of ductal cells of pancreas?

A

1) Modifies primary secretion
2) Actively secretes HCO3 into duct

32
Q

True or False: The ductal cells reabsorb Na and secrete K

A

False - ductal cells do NOT reabsorb Na or secrete K

33
Q

What is the primary acinar cell secretion made of?

A

1) Enzymes
2) Zymogens
3) Proteins that are needed for normal digestion of fats, proteins, and carbohydrates

34
Q

Which two enzymes are found in pancreatic juice and secreted in their active form?

A

1) alpha amylase - breaks down carbs
2) lipase - breaks down fat

35
Q

Which endopeptidase is found in pancreatic juice and is secreted in its inactive form
A. Lipase
B. Alpha amylase
C. Trypsinogen
D. Procarboxypeptidase A

A

C. Trypsinogen

36
Q

Pro-carboxypeptidase A and B are examples of ____

A

exopeptidases

37
Q

True or False: All proteolytic enzymes are secreted in their INACTIVE (ZYMOGEN) form while lipolytic and amylotic enzymes are secreted in their ACTIVE form

A

True

38
Q

All proteolytic pro(enzymes) and (pro)colipase, except for trypsinogen, are always initially activated by ____

A

trypsin

39
Q

Trypsinogen is initially activated in the ____ by which enzymes?

A

Intestinal lumen; enterokinase

40
Q

After its initial activation of enterokinase, ____ can auto-catalytically activate trypsinogen

A

trypsin

41
Q
A
42
Q

Which two small proteins do pancreatic acinar cells secrete that are NOT enzymes?

A

1) Trypsin Inhibitor
2) (Pro)colipase

43
Q

The presence of what molecule protects the pancreas and ducts from auto-digestion by trypsin?

A

Trypsin Inhibitor

44
Q

___ is a cofactor that enhances enzymatic activity of pancreatic lipase

A

Colipase

45
Q

(Pro)colipase is converted to colipase via ____

A

trypsin

46
Q

Activation of which nerve will slightly increase pancreatic exocrine secretions?
A. Sympathetic nerves
B. Renal n.
C. Parasympathetic Vagus n.

A

C. Parasympathetic Vagus n.

47
Q

Activation of ____ nerves will reduce pancreatic exocrine secretions secondary to reduction in ___ to the pancreas

A

sympathetic; blood flow

48
Q

Which two hormones GREATLY increase pancreatic exocrine secretions?

A

1) CCK
2) Secretin

49
Q

CCK is secreted from ___ cells of the ___ mucosa in response to what?

A
  • Endocrine I cells (small intestinal mucosa)
  • In response to luminal long-chain FFA
50
Q

Which cell type is secretin secreted from? Secreted in response to what?

A

Endocrine S cells (small intestinal mucosa)

  • In response to: acidic chyme
51
Q

The combined actions of which two hormones are synergistic?

A

CCK and Secretin

52
Q

When both CCK and secretin are elevated in the plasma, they activate their receptors on ___ cells to increase what two molecules in the cytosol, which will ultimately promote secretion of pancreatic juice?

A

Acinar Cells
1) Ca+
2) cAMP

53
Q

Under what conditions is pancreatic exocrine secretion synergistically increased?

A

When both CCK and Secretion are simultaneously elevated

54
Q

The greatest volume of GI secretions is production by which cell type in the small intestinal mucosa?

A

Enterocytes

55
Q

All small intestinal enterocytes secrete ___ ions into the lumen

A

chloride

56
Q

Chloride secretion is electrogenic. What does this mean?

A

Not accompanied by another ion

57
Q

Under which conditions does chloride secretion increase?

A

1) Intracellular cAMP is elevated (e.g when basolateral receptors for VIP are activated)

58
Q

As small intestinal enterocytes secrete Cl ions into the lumen, what happens to the charge of the lumen?

A

With increased chloride secretion, lumen becomes more negatively charge and Na is retained in lumen

  • Accumulation of Na promotes passive flux of water into lumen
59
Q

What is the primary anion that promotes flux of sodium and water into the lumen?

A

Cl

60
Q

True or False: Electrogenic Cl secretion is essential for maintaining fluidity of contents in small intestine lumen, as it promotes digestion, absorption, and normal gut transit

A

True

61
Q

What is the effect of abnormally high/sustained rates of chloride secretion?

A

Diarrhea

62
Q

Which toxin can cause diarrhea by increasing intracellular cAMP?

A

Cholera Toxin

Physiology II (23 decks)

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