GI Secretion

Question 1

Type of fluid from Parotid Gland

Answer 1

Serous Fluid

Question 2

Type of fluid from Submandibular Gland

Answer 2

Mixed (mostly serous)

Question 3

Type of fluid from Sublingual Gland

Answer 3

Mixed (mostly mucous)

Question 4

Properties of Saliva

Answer 4

Saliva is always hypotonic

Basal secretion is more hypotonic and acidic than final secretion due to neutralization by HCO3-

Question 5

Stimulation of saliva production

Answer 5

Mostly parasympathetic (submandibular = sympathetic)
ACh acting of M3 receptor activates Gq
CN VII and IX stim fluid and enzyme secretion

Question 6

Properties of Parietal cells

Answer 6

Main function is HCl secretion
Apical K/H ATPase
Apical K+ and Cl - Channel
Basal Na/K ATPase
Internal CA with basal HCO3-/Cl- antiporter
Also make intrinsic factor (IF) for B12 absorption

Question 7

Which cell is most effected by a proton pump inhibitor?

Answer 7

Parietal cells (K/H ATPase)

Question 8

Major Regulator of HCl secretion

Answer 8

Histamine
acts via H2 receptor
Activates cAMP –> PKA
Increases number of proton pumps in membrane

Question 9

Minor Regulators of HCl secretion

Answer 9

Gastrin via CCK_B
ACh via M3
Somatostatin: Gi inhibits cAMP

Question 10

What cells and when does Gastrin get released?

Answer 10

Gastrin is released by G-cells in the antrum of the stomach

Gastrin is released when the pH increases due to rise in food content

Question 11

Which cells does Gastrin effecct?

Answer 11

Gastrin stimulates ECL cells to produce Histamine and Parietal cells to produce HCl

Question 12

Three Phases of HCl secretion?

Answer 12

1. Cephalic
2. Gasric
3. Intestinal

Question 13

Characteristics of Cephalic phase

Answer 13

HCl secretion stimulated by vagus

Question 14

Characteristics of Gastric phase

Answer 14

HCl secretion stimulated by vago-vagal reflex
Gastrin +Histamine increase HCl secretion
Bulk of HCl secretion occurs during gastric pase

Question 15

Characteristics of Intestinal phase

Answer 15

mediated by enterogastrones (GLP-1 and CCK)
inhibit HCl secretion
CCK binds to CCK_B and inhibits the effects of gastrin

Question 16

Which cells secrete pepsinogen

Answer 16

Chief Cells

Question 17

Factors that promote mucous formation by epithelial cells

Answer 17

1. Vagal stimulation
2. Presence of food in stomach
3. Prostaglandins (E2)
4. Gastrin

Question 18

Mechanisms so pancreatic enzymes do not get activated early

Answer 18

1. Lipase: not a pro-enzyme, but is safe at low concentrations
2. SPINK-1 deactivates trypsin if it gets activated too early
3. Enzymes are stored with protease inhibitors
4. secretory granules have higher pH
5. Only intestinal epithelial cells express enterokinase to activate trypsinogen to trypsin

Question 19

CCK is stimulated by which gastric contents

Answer 19

Fatty Acids and Amino Acids

nb: sugars do not activate release of CCK

Question 20

Mechanism of Ductus Secretion

Answer 20

Secretion from duct is stimulated by secretein (S Cells) and VIP
both increase cAMP –>PKA

Question 21

Role of Secretin and S Cells

Answer 21

Ensures that H+ = HCO3-

S cells sense pH in the lumen