The Stomach

Question 1

Mucus neck cells secrete

Answer 1

bicarbonate and mucus

Question 2

Parietal cells secrete

Answer 2

HCl

Intrinsic factor

Question 3

ECL cells secrete

Answer 3

histamine

Question 4

Chief cells secrete

Answer 4

pepsinogen

lipase

Question 5

G cells secrete

Answer 5

gastrin

Question 6

D cells secrete

Answer 6

somatostatin

Question 7

Body of the stomach contains which cells

Answer 7

Parietal cells and chief cells mainly

Question 8

Antrum and pylorus of the stomach contains

Answer 8

G & D cells

no parietal cells

Question 9

What is pump via which parietal cells secrete HCl

Answer 9

H+/K+ pump

H+ out into stomach lumen, K+ into parietal cell (then gets recycled back out)

Question 10

Describe the alkaline tide (where the H and Cl comes from in parietal cells)

Answer 10

The H+ used in HCl secretion comes from water.
Resulting OH reacts with CO2 to from HCO3 via carbonic andhydrase.
Bicarbonate/chloride exchanger - bicarbonate is moved into the interstitial space and then into the blood - the is the alkaline tide. Cl moves into parietal cell

Question 11

What are the direct and indirect methods of stimulation of acid secretion in the stomach

Answer 11

Direct (to parietal cells)
Vagal nerve - Ach/M3 receptors
Histamine
Gastrin

Indirect:
Ach and gastrin mediated histamine release by ECL cells

Question 12

The biggest signal to acid secretion is

Answer 12

histamine from ECL cells

Question 13

How are G cells stimulated

Answer 13

• by the vagus which acts through gastrin receptor protein (GRP)-mediated gastrin release
• or by small peptides in the stomach (+ve feedback!)

gastrin stimulates parietal cells directly or indirectly via ECL cells

Question 14

What triggers Ach release by the vagus

Answer 14

distension of the stomach

Question 15

how can gastrin and somatostatin secreted by G and D cells in the antrum of the stomach act on parietal cells in the body of the stomach?

Answer 15

endocrine mechanism - they are hormones they go via the blood

Question 16

D cells secrete somatostatin. What does somatostatin do?

Answer 16

Antagonises histamine-mediated acid secretion
- stops ECL cells making histamine and inhibits parietal cells from responding to it

Inhibits gastrin release from G cells

Question 17

Where in the stomach is somatostatin produced and how does it act on parital cells in the body of the stomach from these locations?

Answer 17

• by D cells in the body of the stomach - paracrine action

- by D cells in the antrum of the stomach - endocrine action

Question 18

Effect of vagal stimulation on D cells

Answer 18

Inhibits somatostatin secretion

No vagal stimulation - somatostatin is secreted inhibit acid secretion as no food in stomach

Question 19

What is the negative feedback in the stomach which prevents pH getting too low?

Answer 19

When pH gets very low (below 2) it stimulates D cells to release somatostatin

Question 20

How are prostagladins important in maintaining the mucosal barrier in the stomach?

Answer 20

inhibit acid secretion, stimulate bicarbonate and mucus secretion from mucus neck cells

Question 21

What does intrinsic factor do?

Answer 21

Needed for vitamin B12 absorption - binds B12 in stomach and facilitates absorption in the ileum

Question 22

The basal phase of acid secretion

Answer 22

stomach acid secretion follows circadian rhythm - low in morning, high in evening

Question 23

The cephalic phase of acid secretion

Answer 23

smell, sight, thought, swallowing of food triggers secretion via the vagus
30% of total acid secretion

Question 24

The gastric phase of acid secretion

Answer 24

Food present in the stomach causes secretion

50-60% of total secretion

Question 25

The intestinal phase of acid secretion

Answer 25

Partially digested peptides/amino acids in the proximal portion of the small intestine stimulates duodenal G cells to secrete gastrin

(whether it is stimulatory or not is questionable)
Accounts for 5-10% of acid secretion

Question 26

What does pepsinogen secreted by chief cells do?

Answer 26

converted to pepsin below pH 5
pepsin degrades proteins to peptides, but only has a small role in digestion
Inactivated in intestine above pH 7.2