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Digestion and Renal Sciences > Secretion of the stomach and its control > Flashcards

Secretion of the stomach and its control Flashcards

1
Q

What are the four functions of the stomach?

A

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

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2
Q

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

A 
Cardia
Fundus
Corpus
Antrum
Pylorus
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3
Q

Name the 7 layers of the stomach

A 
Mucosa
Muscularis mucosa
Submucosa
Oblique muscle
Circular muscle
Longitudinal muscle
Peritoneum
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4
Q

What cells make up gastric glands?

A 
Mucous neck cell
Parietal cell
EC like cell
Chief cell
D cell
G cell
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5
Q

Where is the majority of acid produced in the stomach?

A

In the fundus and corpus

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6
Q

Where are there no parietal cells?

A

In the pylorus and antrum

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7
Q

What cells predominate the fundus and corpus?

A

Parietal and chief cells

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8
Q

What is the biological mechanism of acid secretion?

A

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

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9
Q

What role does carbonic anhydrase play in acid secretion?

A

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

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10
Q

What is the alkaline tide?

A

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

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11
Q

Name the direct regulators of acid secretion

A

Acetylcholine
Histamine
Gastrin

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12
Q

Name the indirect regulators of acid secretion

A

Acetylcholine

Gastrin-mediated histamine

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13
Q

What is somatostatin?

A

A peptide hormone made by D-cells

A direct and indirect inhibitor of acid secretion

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14
Q

Where is somatostatin produced?

A

D cells in the corpus of the stomach

D cells in the antrum of the stomach

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15
Q

Describe paracrine production of somatostatin

A

Triggered by neural and hormonal mechanisms

Corpus of the stomach

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16
Q

Describe endocrine production of somatostatin

A

Triggered by low intra-luminal pH

Antrum of the stomach

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17
Q

How does somatostatin inhibit acid secretion?

A

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

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18
Q

What intracellular signal-transduction pathway does acetylcholine use?

A

Binds to M3 muscarinic receptor

Activates PKC

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19
Q

What intracellular signal-transduction pathway does gastrin use?

A

Binds to cholecystokinin B receptor

Activates PKC

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20
Q

What intracellular signal-transduction pathway does histamine use?

A

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

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21
Q

What are the two ways somatostatin indirectly inhibits acid secretion?

A

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

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22
Q

Which cells are subject to vagal stimulation?

A

G cells

D cells

23
Q

What does vagal stimulation of G cells result in?

A

Promotes gastrin release

Subsequently triggers parietal cell acid release

24
Q

What does vagal stimulation of D cells result in?

A

Inhibition of the release of somatostatin

25
Q

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

A

Somatostatin is released by the D cells

This is a -ve feedback loop

26
Q

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

A

Gastrin is released by the G cells

This stimulates acid secretion in a +ve feedback loop

27
Q

What does distension of the corpus result in?

A

Release of acetylcholine by the vagus nerve

28
Q

Name the effects of acetylcholine on the cells of the stomach

A

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

29
Q

What is secretin?

A

An inhibitor of acid secretion

30
Q

What is CCK?

A

An inhibitor of acid secretion

31
Q

What stimulates the release of secretin?

A

Fat and acid in the duodenum

32
Q

What stimulates the release of CCK?

A

Fat in the duodenum

33
Q

What does secretin inhibit?

A

Antral gastrin release

34
Q

What does secretin trigger?

A

Somatostatin release

35
Q

What does CCK inhibit?

A

Parietal cell acid secretion

36
Q

Give two examples of H2 receptor antagonists

A

Cimetidine

Ranitidine

37
Q

How do H2 receptor antagonists work?

A

Competitive antagonists of histamine at parietal cell H2 receptor

38
Q

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

A

Proton pump inhibitor

39
Q

What is the mechanism of a proton pump inhibitor?

A

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

40
Q

How can acid secretion be reduced surgically?

A

Ablating nerves

Prevents acetylcholine release to reduce acid production

41
Q

What are the 4 phases of gastric acid secretion?

A

Basal
Cephalic
Gastric
Intestinal

42
Q

Describe the basal phase of gastric acid secretion

A

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

43
Q

Describe the cephalic phase of gastric acid secretion

A

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

44
Q

Describe the gastric phase of gastric acid secretion

A

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

45
Q

Describe the intestinal phase of gastric acid secretion

A

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

46
Q

What are pepsinogens?

A

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

47
Q

How is the stomach protected from the acid it produces?

A

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

48
Q

What is helicobacter pylori?

A

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

49
Q

What can helicobacter pylori cause?

A

Gastritis
Duodenal ulcers
Gastric cancer

50
Q

What does a HP infection of the antrum cause?

A

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

51
Q

What does a HP infection of the corpus cause?

A

Reduced acid secretion
Hypochlorhydria
Gastric ulcers

52
Q

What is intrinsic factor?

A

Produced by parietal cells

Necessary for the absorption of vitamin b12 in the terminal ileum

53
Q

What is pernicious anaemia?

A

Autoimmune atrophic gastritis
Directed against parietal cells
Results in megaloblastic anaemia

Digestion and Renal Sciences (27 decks)

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