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GI Liver > Gastric physiology > Flashcards

Gastric physiology Flashcards

1
Q

What are the 4 cell types in the stomach?

A

Mucous cells, parietal cells, chief cells and enteroendocrine cells.

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2
Q

List as many functions of the stomach you know.

A 
Store and mix food. 
Dissolve and continue digestion. 
Regulate the emptying of the stomach into the duodenum. 
Kill microbes. 
Secrete proteases. 
Secrete intrinsic factor for the absorption of vitamin B12. 
Activate proteases. 
Lubrication, mechanical movement. 
Mucosal protection.
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3
Q

What do parietal cells secrete?

A

HCl and intrinsic factor.

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4
Q

What is the role of chief cells?

A

Create pepsinogen and gastric lipase.

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5
Q

What do enteroendocrine cells secrete?

A

Secrete gastrin, histamine, endorphins, serotonin and somatostatin

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6
Q

What do D cells secrete?

A

Somatostatin.

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7
Q

What do G cells secrete?

A

Gastrin.

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8
Q

What stimulates parietal cells to secrete their product?

A

ACh, histamine and gastrin.

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9
Q

What stimulates G cells to secrete their product?

A

ACh, proteins and peptidases.

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10
Q

what is the role of somatostatin?

A

to inhibit the parietal cells from releasing HCl to reduce pH in the stomach.

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11
Q

How does chloride move into the stomach lumen from the parietal cell?

A

through the use of a H+ and K+ pump allowing Cl to move passively into the lumen.

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12
Q

what regulates the secretion from the parietal cells?

A

neurohumoral regulation.

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13
Q

What is the cephalic phase?

A

The ‘turning on’ of gastric acid secretion.

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14
Q

What initiates the cephalic phase?

A

Sight, smell, taste and chewing all initiate.

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15
Q

Which system is involved in the cephalic phase?

A

the parasympathetic nervous system.

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16
Q

Which molecule directly acts on the parietal cells first during stimulation?

A

ACh.

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17
Q

What does the release of ACh trigger to be released?

A

Gastrin, Histamine.

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18
Q

Why does the gastric wall stretch during the cephalic phase?

A

It stretches due to the presence of peptides and amino acids.

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19
Q

What is the role of proteins in the lumen for pH?

A

They act as a buffer and mop up H+ molecules. this causes a reduce of somatostatin to be released which means more parietal cell activity.

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20
Q

What is the intestinal phase ?

A

The ‘turning off’ of the action of parietal cells.

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21
Q

What stimulates somatostatin release from D cells?

A

low luminal pH.

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22
Q

What conditions in the duodenum are linked with the intestinal phase?

A

Duodenal distension.
Low luminal pH
Hypertonic luminal contents.
Presence of amino and fatty acids.

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23
Q

How does low luminal pH effect gastrin and histamine?

A

it decreases the release of gastrin and this in turn will reduce the release of histamine.

24
Q

How does ACh release decrease during the intestinal phase?

A

There are short and long neural pathways which reduce the amount of ACh released.

25
Q

What is the role of CCK [cholecystokinin]?

A

to inhibit gastrin release.

26
Q

What cells release Histamine?

A

Enterochromaffin like cells.

27
Q

What is the definition of an ulcer?

A

An ulcer is a breach of the mucosal surface?

28
Q

What are the two main ways that ulcers are formed?

A
  1. increased mucosal attack

2. Reduced mucosal defence.

29
Q

What are the 3 main causes of gastric ulcers?

A
  1. helicobacter pylori infection.
  2. NSAIDs
  3. chemical irritants.
30
Q

what are the 4 main defences in the gastric mucosa?

A
  1. Alkaline mucus.
  2. Tight junctions between epithelia.
  3. Replacement of damaged cells due to stem cells.
  4. Short feedback loops.
31
Q

What does the helicobacter pylori secrete?

A

It secretes urease an enzyme.

32
Q

How does urease create a gastric ulcer?

A

It breaks down urea into CO2 and ammonia. The ammonia combines with the free H+ to create ammonium. Ammonium damages the gastric epithelium and causes an inflammatory response.

33
Q

How do NSAIDs reduce mucosal defence?

A

They inhibit cyclo-oxygenase 1 which is needed for prostaglandin synthesis. Prostaglandins stimulate mucus secretion.

34
Q

How does duodeno-gastric reflux cause gastric ulcers?

A

because it releases regurgitated bile which strips away mucus layer.

35
Q

Which cell secretes pepsin?

A

NO CELL. Chief cells secrete pepsinogen but it is then activated in the lumen to pepsin.

36
Q

What pH is optimum for the conversion of pepsinogen to pepsin?

A

A pH less than 2.

37
Q

What is the catalyst for the conversion of pepsinogen to pepsin?

A

Pepsin. It is a positive feedback loop.

38
Q

What inactivates pepsin and where?

A

Irreversible reaction takes place in the small intestine by carbonate ions.

39
Q

How much of total protein digestion does pepsin account for?

A

About 20% so protein digestion can occur without it.

40
Q

How does pepsin act specifically on meat?

A

It breaks down the collagen in meat which shreds the meat into smaller pieces with greater surface area.

41
Q

What is the empty volume of the stomach?

A

about 50ml.

42
Q

What is the volume we can have in the stomach without much change in luminal pressure?

A

1.5l. Changes for each person but in general.

43
Q

How many layers of smooth muscle are there in the stomach and give their names.

A
  2. oblique layer.
  3. circular layer.
  4. longitudinal layer.
44
Q

What 2 molecules mediate receptive relaxation?

A

Serotonin and Nitric oxide.

Part of the parasympathetic system that acts on the enteric nerve plexuses.

45
Q

where do peristaltic waves in the stomach begin?

A

In the body of the stomach.

46
Q

where is the most powerful contraction during gastric peristalsis?

A

The antrum of the stomach.

47
Q

How are the contents of the stomach mixed during peristalsis?

A

The pyloric sphincter closes as the peristaltic wave reaches it causing a contents to be forced backwards creating a churning motion.

48
Q

What are the contents of the stomach called?

A

Chyme.

49
Q

what controls the frequency of peristaltic waves?

A

Pacemaker cells in the muscularis propria.

50
Q

How often are depolarisation waves created by the pacemaker cells?

A

The depolarisation is slow and happens about 3 times per minute.

51
Q

What causes an increase in the strength of the peristaltic waves?

A

Gastrin and gastrin distension.

52
Q

What causes an decrease in the strength of the peristaltic waves?

A
  1. Duodenal distension
  2. Increase of duodenal luminal fat.
  3. Decrease of duodenal lumen pH.
  4. Increase in sympathetic NS action.
53
Q

Why does gastric emptying not occur?

A

The capacity of the stomach is much larger than that of the duodenum and would cause several problems.

54
Q

What is meant by gastroparesis?

A

Delayed gastric emptying where chyme will remain in the stomach for a long time.

55
Q

What is meant by zymogen?

A

an inactive form of a molecule.

GI Liver (1 decks)

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