GI Secretions

Question 1

Which cells secrete gastric acid in the body

Answer 1

Parietal cells of the stomach

Question 2

What glands are the parietal cells found

Answer 2

Gastric glands

Question 3

What are some stimuli for acid secretion from the parietal cells

Answer 3

Gastrin
Vagus nerve

Question 4

What cells produce gastrin

Answer 4

G cells

Question 5

What receptor does gastrin bind to on parietal cells to cause acid secretion

Answer 5

CCKb receptor

Question 6

What is the indirect method gastrin uses to secrete acid

Answer 6

Gastrin binds to (enterochromaffin-like cells) ECL cells which releases histamine which then stimulates the parietal cells to secrete HCl

Question 7

How does the vagal nerve cause acid secretion

Answer 7

The vagus nerve can release ACh which can bind to the M3 receptors on parietal cells and stimulate them to secrete acid
Can activate G cells to secrete gastrin using gastrin releasing peptide this time not ACh

Blocking ACh does not block vagal nerve function because GRP will continue to function and stimulate acid secretion

Question 8

Vagotomy could lead to a decreased acid production
True or false

Answer 8

True

Question 9

Atropine is a muscarinic blocker and could block acid secretion but it’s not as potent. Why

Answer 9

It can block acid secretion by blunting parietal stimulation by ACh but does not block stimulation by the vagus -> gastrin -> HCl

Question 10

Intrinsic factor is produced by ……. along with H+

Answer 10

Parietal cells

Question 11

How does vomiting cause a metabolic alkalosis

Answer 11

Vomiting leads to a decrease in HCl which causes the parietal cells to secrete more HCl causing an increase in bicarbonate production thus causing a metabolic alkalosis. Patients also lose chloride in the HCl thus urinary chloride will be relatively low

Question 12

When a patient has a metabolic alkalosis of an unknown cause what electrolyte could be a useful measurement

Answer 12

Urinary chloride

Question 13

What could cause a high urinary chloride >20

Answer 13

When patient is taking a diuretic (diuretics block NaCl resorption)

Question 14

What could cause a low urinary chloride <10-20

Answer 14

Vomiting

Question 15

Mention two naturally occurring substances that could inhibit secretion of HCl by parietal cells

Answer 15

Somatostatin and prostaglandins

Question 16

Which acid secretion stimulating hormones work by Gq proteins with IP3/Ca

Answer 16

ACh and gastrin

Gq proteins activate PLC which converts PIP2 to IP3. IP3 will then stimulate calcium release and the calcium will activate proton pumping

Question 17

Which acid secretion stimulating or inhibitory hormones work by Gs/i and CAMP

Answer 17

Histamine (increases cAMP), somatostatin and PGs (inhibit cAMP)

Question 18

What PGE1 analog blunts acid secretion

Answer 18

Misoprostol

Question 19

Which layer in the stomach are chief cells found

Answer 19

Mostly in deeper layers
Dark colored (basophilic)

Question 20

Which cells secrete pepsin

Answer 20

Chief cells

Question 21

Which pH works best for pepsin

Answer 21

pH 1 to 3

Question 22

What is the stimulus for the release of pepsin

Answer 22

Vagus nerve

Question 23

Which layer of the stomach are parietal cells found

Answer 23

More in the upper layers
Mucosal layer
Pink colored (eosinophilic)

Question 24

How do parietal cells secrete HCl

Answer 24

There are separate pumps in the membranes of the parietal cells that secrete H+ and Cl- for HCl. There is an ATPase pump which pumps out hydrogen ions in exchange for potassium and there is a separate channel by which chloride is secreted into the lumen of the stomach. The H+ ions that are pumped out into the lumen of the stomach are formed by carbonic anhydrase (takes molecules of water and CO2 and converts them into molecules of bicarbonate and H+). The H+ gets pumped out of the lumen of the stomach via the hydrogen potassium ATPase pump. The bicarbonate then goes out into the serum via a bicarbonate-Cl antiporter (alkaline tide)