L28: Gastric, Pancreatic, and Intestinal Secretions

Question 1

What is the stimulus for conversion of pepsinogen to pepsin?

Answer 1

H+

Question 2

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

Answer 2

Pepsinogen

Question 3

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

Answer 3

A. Acidic

Question 4

True or False: Pepsin is active at pH of 7

Answer 4

False

Question 5

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

Answer 5

A. Protein

Question 6

True or False: Most protein enters the duodenum intact

Answer 6

True

Question 7

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

Answer 7

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

Question 8

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

Answer 8

C. Digest dietary triglycerides
(into FFA)

Question 9

What pH ranges is Gastric Lipase active at?

Answer 9

pH of 4-5; pH of 2

Question 10

Gastric lipase secretion is stimulated by _____

Answer 10

Ach

Question 11

____, 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

Answer 11

Intrinsic Factor

Question 12

Where it Vit B 12 absorbed?

Answer 12

Ileum

Question 13

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

Answer 13

True

Question 14

The gastric mucosal barrieris made of both ___ and ____

Answer 14

mucins; bicarbonate

Question 15

Three functions of the gastric mucosal barrier?

Answer 15

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

Question 16

What are the two mechanisms by which enterocytes secrete mucins?

Answer 16

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

Question 17

Which three molecules increase the production of mucin and secretion?

Answer 17

Ach, gastrin, and prostaglandins

Question 18

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

Answer 18

gastric lumen = less than 3.0
enterocyte surface = 7.0

Question 19

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

Answer 19

mucins; HCO3

Question 20

How do enterocytes secrete HCO3?

Answer 20

HCO3-Cl antiporter in apical membrane

Question 21

Which two molecules stimulate HCO3 secretion in the enterocyte?

Answer 21

Prostaglandins and Ach

Question 22

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

Answer 22

Prostaglandins

Question 23

What are the four benefits of prostaglandins?

Answer 23

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

Question 24

How can NSAID use affect the gastric mucosal barrier?

Answer 24

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

Question 25

Why is pepsin not active in the gastric mucosal barrier?

Answer 25

Only active in acidic conditions (e.g gastric lumen) ; the gastric mucosal barrier is pH = 4-7 - Prevents digestion of gastrin protein by pepsin

Question 26

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

Answer 26

True

Question 27

What are the 4 main functions of pancreatic exocrine secretions?

Answer 27

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)

Question 28

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

Answer 28

1) Acinar cells 2) Ductal cells

Question 29

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

Answer 29

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

Question 30

Two functions of acinar cells of the pancreas?

Answer 30

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

Question 31

Two functions of ductal cells of pancreas?

Answer 31

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

Question 32

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

Answer 32

False - ductal cells do NOT reabsorb Na or secrete K

Question 33

What is the primary acinar cell secretion made of?

Answer 33

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

Question 34

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

Answer 34

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

Question 35

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

Answer 35

C. Trypsinogen

Question 36

Pro-carboxypeptidase A and B are examples of ____

Answer 36

exopeptidases

Question 37

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

Answer 37

True

Question 38

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

Answer 38

trypsin

Question 39

Trypsinogen is initially activated in the ____ by which enzymes?

Answer 39

Intestinal lumen; enterokinase

Question 40

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

Answer 40

trypsin

Question 41

Answer 41

Question 42

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

Answer 42

1) Trypsin Inhibitor 2) (Pro)colipase

Question 43

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

Answer 43

Trypsin Inhibitor

Question 44

___ is a cofactor that enhances enzymatic activity of pancreatic lipase

Answer 44

Colipase

Question 45

(Pro)colipase is converted to colipase via ____

Answer 45

trypsin

Question 46

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

Answer 46

C. Parasympathetic Vagus n.

Question 47

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

Answer 47

sympathetic; blood flow

Question 48

Which two hormones GREATLY increase pancreatic exocrine secretions?

Answer 48

1) CCK 2) Secretin

Question 49

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

Answer 49

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

Question 50

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

Answer 50

Endocrine S cells (small intestinal mucosa) - In response to: acidic chyme

Question 51

The combined actions of which two hormones are synergistic?

Answer 51

CCK and Secretin

Question 52

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?

Answer 52

Acinar Cells 1) Ca+ 2) cAMP

Question 53

Under what conditions is pancreatic exocrine secretion synergistically increased?

Answer 53

When both CCK and Secretion are simultaneously elevated

Question 54

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

Answer 54

Enterocytes

Question 55

All small intestinal enterocytes secrete ___ ions into the lumen

Answer 55

chloride

Question 56

Chloride secretion is electrogenic. What does this mean?

Answer 56

Not accompanied by another ion

Question 57

Under which conditions does chloride secretion increase?

Answer 57

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

Question 58

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

Answer 58

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

Question 59

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

Answer 59

Cl

Question 60

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

Answer 60

True

Question 61

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

Answer 61

Diarrhea

Question 62

Which toxin can cause diarrhea by increasing intracellular cAMP?

Answer 62

Cholera Toxin