Secretion of the stomach and its control

Question 1

What are the four functions of the stomach?

Answer 1

Stores food
Mixes food with secretions
Regulates release of food into the duodenum
Secretes gastric juices

Question 2

Name the five parts of the stomach (in order top to bottom)

Answer 2

Cardia
Fundus
Corpus
Antrum
Pylorus

Question 3

Name the 7 layers of the stomach

Answer 3

Mucosa
Muscularis mucosa
Submucosa
Oblique muscle
Circular muscle
Longitudinal muscle
Peritoneum

Question 4

What cells make up gastric glands?

Answer 4

Mucous neck cell
Parietal cell
EC like cell
Chief cell
D cell
G cell

Question 5

Where is the majority of acid produced in the stomach?

Answer 5

In the fundus and corpus

Question 6

Where are there no parietal cells?

Answer 6

In the pylorus and antrum

Question 7

What cells predominate the fundus and corpus?

Answer 7

Parietal and chief cells

Question 8

What is the biological mechanism of acid secretion?

Answer 8

A parietal H-K pump embedded in the apical membrane
The pump exudes H+ into the lumen in exchange for K+
K+ is recycled by K+ channels

Question 9

What role does carbonic anhydrase play in acid secretion?

Answer 9

Water is broken down into H+ and OH-
H+ excreted into the lumen
OH- combines with bicarbonate ion

Question 10

What is the alkaline tide?

Answer 10

The release of HCO3 across the basolateral membrane into the blood stream

Question 11

Name the direct regulators of acid secretion

Answer 11

Acetylcholine
Histamine
Gastrin

Question 12

Name the indirect regulators of acid secretion

Answer 12

Acetylcholine

Gastrin-mediated histamine

Question 13

What is somatostatin?

Answer 13

A peptide hormone made by D-cells

A direct and indirect inhibitor of acid secretion

Question 14

Where is somatostatin produced?

Answer 14

D cells in the corpus of the stomach

D cells in the antrum of the stomach

Question 15

Describe paracrine production of somatostatin

Answer 15

Triggered by neural and hormonal mechanisms

Corpus of the stomach

Question 16

Describe endocrine production of somatostatin

Answer 16

Triggered by low intra-luminal pH

Antrum of the stomach

Question 17

How does somatostatin inhibit acid secretion?

Answer 17

Binds to SST receptor on parietal cell
Inhibits adenylyl cyclase
Inhibits parietal cell

Question 18

What intracellular signal-transduction pathway does acetylcholine use?

Answer 18

Binds to M3 muscarinic receptor

Activates PKC

Question 19

What intracellular signal-transduction pathway does gastrin use?

Answer 19

Binds to cholecystokinin B receptor

Activates PKC

Question 20

What intracellular signal-transduction pathway does histamine use?

Answer 20

Binds to the H2 receptor
Stimulates the enzyme adenylyl cyclase
Production of cAMP
Activates PKA

Question 21

What are the two ways somatostatin indirectly inhibits acid secretion?

Answer 21

Somatostatin released by D-cells of the corpus inhibits the release of histamine from ECL cells in the corpus
Somatostatin released by D-cells of the antrum can inhibit the release of gastrin from G cells in the antrum

Question 22

Which cells are subject to vagal stimulation?

Answer 22

G cells

D cells

Question 23

What does vagal stimulation of G cells result in?

Answer 23

Promotes gastrin release

Subsequently triggers parietal cell acid release

Question 24

What does vagal stimulation of D cells result in?

Answer 24

Inhibition of the release of somatostatin

Question 25

What is the consequence of high luminal H+ in the antrum?

Answer 25

Somatostatin is released by the D cells | This is a -ve feedback loop

Question 26

What do the products of protein digestion in the antrum stimulate?

Answer 26

Gastrin is released by the G cells | This stimulates acid secretion in a +ve feedback loop

Question 27

What does distension of the corpus result in?

Answer 27

Release of acetylcholine by the vagus nerve

Question 28

Name the effects of acetylcholine on the cells of the stomach

Answer 28

Direct stimulation of the parietal cell to induce acid release Direct stimulation of the ECL cells enhancing histamine release Stimulation of D cells in corpus inhibits somatostatin release

Question 29

What is secretin?

Answer 29

An inhibitor of acid secretion

Question 30

What is CCK?

Answer 30

An inhibitor of acid secretion

Question 31

What stimulates the release of secretin?

Answer 31

Fat and acid in the duodenum

Question 32

What stimulates the release of CCK?

Answer 32

Fat in the duodenum

Question 33

What does secretin inhibit?

Answer 33

Antral gastrin release

Question 34

What does secretin trigger?

Answer 34

Somatostatin release

Question 35

What does CCK inhibit?

Answer 35

Parietal cell acid secretion

Question 36

Give two examples of H2 receptor antagonists

Answer 36

Cimetidine | Ranitidine

Question 37

How do H2 receptor antagonists work?

Answer 37

Competitive antagonists of histamine at parietal cell H2 receptor

Question 38

What is more effective, a H2 RA or proton pump inhibitor?

Answer 38

Proton pump inhibitor

Question 39

What is the mechanism of a proton pump inhibitor?

Answer 39

Blocks the proton pump Directly stops all 3 acid triggers More effective than targeting them individually

Question 40

How can acid secretion be reduced surgically?

Answer 40

Ablating nerves | Prevents acetylcholine release to reduce acid production

Question 41

What are the 4 phases of gastric acid secretion?

Answer 41

Basal Cephalic Gastric Intestinal

Question 42

Describe the basal phase of gastric acid secretion

Answer 42

Follows a circadian rhythm Acid secretion is low in the a.m and high in the p.m Acid secretion directly related to number of parietal cells

Question 43

Describe the cephalic phase of gastric acid secretion

Answer 43

Senses (smell, sight, taste) initiate the cephalic phase Mediated by the vagus nerve Accounts for 30% of total acid secretion

Question 44

Describe the gastric phase of gastric acid secretion

Answer 44

Distension of the stomach and the products of digestion trigger acid release Accounts for 50-60% of total acid secretion

Question 45

Describe the intestinal phase of gastric acid secretion

Answer 45

Partially digested peptides in the proximal portion of the small intestine stimulates acid secretion G cells of the duodenum release gastrin Accounts for 5-10% of gastric acid secretion

Question 46

What are pepsinogens?

Answer 46

Proteolytic proenzymes secreted by chief cells Mainly triggered by acetylcholine Spontaneously converts to pepsin at pHs lower than 5 Resulting peptides trigger astral G cell gastrin secretion

Question 47

How is the stomach protected from the acid it produces?

Answer 47

Mucous layer which traps local HCO3- Prostaglandins maintain mucosal diffusion barrier Prostaglandins inhibit acid secretion, stimulate HCO3- and mucous secretion

Question 48

What is helicobacter pylori?

Answer 48

Gram-negative, microaerophilic bacterium Colonises stomach of 40% of humans Leading cause of peptic ulcers Carcinogen

Question 49

What can helicobacter pylori cause?

Answer 49

Gastritis Duodenal ulcers Gastric cancer

Question 50

What does a HP infection of the antrum cause?

Answer 50

G cells hypersecrete gastrin Decrease of antral D-cell somatostatin release Leads to hypergastrinaemia Duodenal ulcers

Question 51

What does a HP infection of the corpus cause?

Answer 51

Reduced acid secretion Hypochlorhydria Gastric ulcers

Question 52

What is intrinsic factor?

Answer 52

Produced by parietal cells | Necessary for the absorption of vitamin b12 in the terminal ileum

Question 53

What is pernicious anaemia?

Answer 53

Autoimmune atrophic gastritis Directed against parietal cells Results in megaloblastic anaemia