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DIG > Secretions of the Stomach > Flashcards

Secretions of the Stomach Flashcards

1
Q

Functions of the stomach

A
  • Store food
  • Mix food with secretions
  • Regulate release of food into duodenum
  • Secrete gastric juices
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2
Q

Which structure is responsible for acid secretion in the stomach?

A

H-K pump

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3
Q

In which part of which cells is the H-K pump found?

A
  • Apical membrane
  • Parietal cells
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4
Q

2 subunits of the H-K pump (and what they are for)

A
  • Alpha subunit (catalytic function)
  • Beta subunit (apical membrane targetting)
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5
Q

How does the H-K pump work?

A

Extrudes H+ into lumen of gastric gland in exchange for K+

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6
Q

What happens to the K+ brought in by the H-K pump?

A

Recycled via K+ channels

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7
Q

What is the function of the enzyme carbonic anhydrase?

A

Converts H2O + CO2 –> H2CO3 (eventually forms H+ + HCO3-)

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8
Q

What is alkaline tide?

A

HCO3- exiting parietal cells across the basolateral membrane

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9
Q

Which structure transports HCO3-

A

Cl-HCO3 exchanger

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10
Q

Direct regulators of acid secretion

A
  • Acetylcholine (vagus nerve)
  • Histamine
  • Gastrin
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11
Q

Indirect regulators of acid secretion

A

Acetylcholine/gastrin-mediated histamine release from ECL cells

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12
Q

How does acetylcholine directly regulate acid secretion?

A
  • ACh binds M3 (ACh receptor) on parietal cell
  • Increased secretion
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13
Q

How does histamine directly regulate acid secretion?

A
  • Histamine binds to H2 (histamine receptor) on parietal cells
  • Increased secretion
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14
Q

How does gastrin directly regulate acid secretion?

A
  • Gastrin binds CCKB (gastrin receptor) on parietal cells
  • Increased secretion
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15
Q

How does ACh indirectly regulate acid secretion?

A
  • ACh binds M3 (ACh receptor) on ECL cell
  • Increased histamine release
  • Histamine binds H2 receptor on parietal cell
  • Increased secretion
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16
Q

How does gastrin indirectly regulate acid secretion?

A
  • Gastrin binds CCKB (gastrin receptor) on ECL cell
  • Increased histamine release
  • Histamine binds H2 receptor on parietal cell
  • Increased secretion
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17
Q

What happens in the corpus of the stomach to cause ACh release from the vagus nerve?

A

Distension

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18
Q

What 3 things does ACh cause regarding acid secretion?

A
  • Stimulation of parietal cells to release acid
  • Stimulation of ECL cells to release histamine
  • Stimulation of D cells to inhibit somatostatin release
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19
Q

Which cells involved in regulating acid secretion are found in the antrum of the stomach

A
  • G cells
  • D cells
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20
Q

Which 2 things can stimulate G cells in the antrum, and what does this cause?

A
  • Vagal release of GRP which binds receptors
  • Products of protein digestion
  • Both cause cell to release gastrin
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21
Q

Which 2 things can stimulate D cells in the antrum, and what does this cause?

A
  • Vagal release of ACh which binds receptors
    > Inhibits somatostatin release
  • High luminal H+
    > Stimulates somatostatin release
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22
Q

Endogenous inhibitors of acid secretion

A
  • Somatostatin
  • CCK
  • VIP
  • GIP
  • Neurotensin
  • Peptide YY
  • Prostaglandins
  • Secretin
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23
Q

Which cells release secretin and what stimulates this?

A
  • Duodenal S-cells
  • Stimulated by fat and acid in duodenum
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24
Q

How does secretin inhibit acid secretion?

A
  • Inhibits antral gastrin release
  • Somatostatin release
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25
Q

Which cells release CCK and what stimulates this?

A
  • I-cells in duodenum and jejunum
  • Fats
26
Q

How does CCK inhibit acid secretion?

A

Directly reduces parietal cell acid secretion

27
Q

Pharmacological inhibitors of acid secretion

A
  • Proton pump inhibitors
  • H2 receptor antagonists
28
Q

Common example of a proton pump inhibitor

A

Omeprazole

29
Q

Common examples of H2 receptor antagonists

A
  • Cimetidine
  • Ranitidine
30
Q

What are proton pump inhibitors and H2 receptor antagonists used in the treatment of?

A
  • Peptic ulcer disease
  • GORD
  • Barrett’s
  • Dyspepsia
  • Zollinger Ellison syndrome
31
Q

4 phases of gastric acid secretion

A
  • Basal
  • Cephalic
  • Gastric
  • Intestinal
32
Q

Which stimuli initiate the cephalic phase of acid secretion?

A
  • Smell…
  • Sight…
  • Taste…
  • Thought…
  • Swallowing…
  • …of food
33
Q

What mediates the cephalic phase of acid secretion?

A

Vagus nerve

34
Q

What percentage of total acid secretion is the cephalic phase?

A

30%

35
Q

What percentage of total acid secretion is the gastric phase?

A

50-60%

36
Q

What mediates the gastric phase of acid secretion?

A
  • Stretch of stomach
  • Amino acids + peptides
37
Q

What mediates the intestinal phase of acid secretion?

A

Partially digested peptides/amino acids in proximal portion of SI

38
Q

Which cells are stimulated in the intestinal phase of acid secretion?

A

Duodenal G cells

39
Q

What percentage of total acid secretion is the intestinal phase?

A

5-10%

40
Q

What are pepsinogens?

A

Proteolytic proenzymes

41
Q

What cells are pepsinogens secreted by?

A

Chief cells

42
Q

What triggers pepsinogen secretion?

A

Acetylcholine

43
Q

At what pH is pepsinogen converted to pepsin a) spontaneously b) most actively

A

a) pH <5
b) pH <3

44
Q

At what pH is pepsinogen irreversibly inactivated?

A

pH7.2

45
Q

How is the stomach protected from the low pH?

A

There is a mucous layer which traps HCO3- secretions

46
Q

How do prostaglandins maintain the mucosal diffusion barrier?

A
  • Inhibit acid secretion
  • Stimulate HCO3- secretion
  • Stimulate mucous secretion
47
Q

Why do non-selective NSAIDs cause GI side effects such as gastric ulceration?

A
  • COX-2 inhibited to prevent inflammation
  • COX-1 also inhibited, which is usually responsible for gastric mucosa secretion, which protects against stomach acid
48
Q

What can helicobacter pylori cause?

A
  • Gastritis
  • Gastric + duodenal ulcers
  • Gastric cancer class 1 carcinogen
49
Q

Which enzyme is produced by helicobacter pylori?

A

Urease

50
Q

Conversions of urease produced by helicobacter pylori

A

Urea –> NH3 + CO2 + H2O –> NH4+ + HCO3-

51
Q

What does a helicobacter pylori infection of the antrum directly cause?

A
  • G-cells to hypersecrete gastrin
  • Decreased antral D-cell somatostatin release
52
Q

What does a helicobacter pylori infection of the antrum lead to?

A
  • Hypergastrinaemia
  • Duodenal ulcers
53
Q

What does a helicobacter pylori infection of the corpus directly cause?

A
  • Reduced acid secretion
  • Hypochlorhydria
54
Q

What does a helicobacter pylori infection of the corpus lead to?

A

Gastric ulcers

55
Q

Treatment of helicobacter pylori infection

A

Triple therapy (antibiotics amoxicillin + clarithromycin, proton pump inhibitor)

56
Q

What is intrinsic factor produced by?

A

Parietal cells

57
Q

What is intrinsic factor necessary for?

A

Absorption of vitamin B12 in terminal ileum

58
Q

What is caused by a loss of intrinsic factor production?

A

Pernicious (Addison’s) anaemia

59
Q

What is pernicious anaemia?

A
  • Autoimmune atrophic gastritis
    > Auto-antibodies are directed against parietal cells
60
Q

What occurs as a result of pernicious anaemia?

A

Megaloblastic anaemia

DIG (19 decks)

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