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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
Which cells release CCK and what stimulates this?
- I-cells in duodenum and jejunum - Fats
26
How does CCK inhibit acid secretion?
Directly reduces parietal cell acid secretion
27
Pharmacological inhibitors of acid secretion
- Proton pump inhibitors - H2 receptor antagonists
28
Common example of a proton pump inhibitor
Omeprazole
29
Common examples of H2 receptor antagonists
- Cimetidine - Ranitidine
30
What are proton pump inhibitors and H2 receptor antagonists used in the treatment of?
- Peptic ulcer disease - GORD - Barrett's - Dyspepsia - Zollinger Ellison syndrome
31
4 phases of gastric acid secretion
- Basal - Cephalic - Gastric - Intestinal
32
Which stimuli initiate the cephalic phase of acid secretion?
- Smell... - Sight... - Taste... - Thought... - Swallowing... - …of food
33
What mediates the cephalic phase of acid secretion?
Vagus nerve
34
What percentage of total acid secretion is the cephalic phase?
30%
35
What percentage of total acid secretion is the gastric phase?
50-60%
36
What mediates the gastric phase of acid secretion?
- Stretch of stomach - Amino acids + peptides
37
What mediates the intestinal phase of acid secretion?
Partially digested peptides/amino acids in proximal portion of SI
38
Which cells are stimulated in the intestinal phase of acid secretion?
Duodenal G cells
39
What percentage of total acid secretion is the intestinal phase?
5-10%
40
What are pepsinogens?
Proteolytic proenzymes
41
What cells are pepsinogens secreted by?
Chief cells
42
What triggers pepsinogen secretion?
Acetylcholine
43
At what pH is pepsinogen converted to pepsin a) spontaneously b) most actively
a) pH <5 b) pH <3
44
At what pH is pepsinogen irreversibly inactivated?
pH7.2
45
How is the stomach protected from the low pH?
There is a mucous layer which traps HCO3- secretions
46
How do prostaglandins maintain the mucosal diffusion barrier?
- Inhibit acid secretion - Stimulate HCO3- secretion - Stimulate mucous secretion
47
Why do non-selective NSAIDs cause GI side effects such as gastric ulceration?
- COX-2 inhibited to prevent inflammation - COX-1 also inhibited, which is usually responsible for gastric mucosa secretion, which protects against stomach acid
48
What can helicobacter pylori cause?
- Gastritis - Gastric + duodenal ulcers - Gastric cancer class 1 carcinogen
49
Which enzyme is produced by helicobacter pylori?
Urease
50
Conversions of urease produced by helicobacter pylori
Urea --> NH3 + CO2 + H2O --> NH4+ + HCO3-
51
What does a helicobacter pylori infection of the antrum directly cause?
- G-cells to hypersecrete gastrin - Decreased antral D-cell somatostatin release
52
What does a helicobacter pylori infection of the antrum lead to?
- Hypergastrinaemia - Duodenal ulcers
53
What does a helicobacter pylori infection of the corpus directly cause?
- Reduced acid secretion - Hypochlorhydria
54
What does a helicobacter pylori infection of the corpus lead to?
Gastric ulcers
55
Treatment of helicobacter pylori infection
Triple therapy (antibiotics amoxicillin + clarithromycin, proton pump inhibitor)
56
What is intrinsic factor produced by?
Parietal cells
57
What is intrinsic factor necessary for?
Absorption of vitamin B12 in terminal ileum
58
What is caused by a loss of intrinsic factor production?
Pernicious (Addison's) anaemia
59
What is pernicious anaemia?
- Autoimmune atrophic gastritis > Auto-antibodies are directed against parietal cells
60
What occurs as a result of pernicious anaemia?
Megaloblastic anaemia

DIG (19 decks)

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