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Gastro-intestinal System > Functions Of The Stomach > Flashcards

Functions Of The Stomach Flashcards

1
Q

What are the basic functions of the stomach?

A

Short term storage of food
Mechanical and chemical disruption of food
Continue digestion (proteins mainly)
Disinfect

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2
Q

What epithelium lines the stomach?

A

Simple columnar

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3
Q

What are rugae?

A

Fold in the mucosa and submucosa

Allow distension of the stomach

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4
Q

How many layers of smooth muscle are there in the stomach?

A

3

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5
Q

Why do we want to grind our food?

A

Increase the surface area for enzymes to work on

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6
Q

Describe receptive relaxation of the stomach

A

Vagus nerve mediated
Allows food to enter the stomach without raising the intragastric pressure too much
Prevents reflux
Distension of rugae

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7
Q

Why do we have acidic conditions in the stomach?

A

Help to unravel protein
Activates proteases
Disinfects stomach contents

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8
Q

What do the parietal cells secrete?

A

HCl and intrinsic factor

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9
Q

What do the G cells secrete?

A

Gastrin

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10
Q

What do the enterochromaffin like cells (ECL) secrete?

A

Histamine

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11
Q

What do the chief cells of the stomach secrete?

A

Pepsinogen

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12
Q

What do the D cells secrete?

A

Somatostatin

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13
Q

What do the mucous cells in the stomach secrete?

A

Mucus

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14
Q

What is the predominant secretion in the cardia of the stomach?

A

Mucus

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15
Q

What is secreted in the body and fundus of the stomach?

A

Mucus, HCl, pepsinogen

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16
Q

What is secreted at the pylorus of the stomach?

A

Gastrin, somatostatin

17
Q

The parietal cells are stimulated to release HCl via …

A

Gastrin
Histamine
ACh

18
Q

How are parietal cells adapted for acid release?

A

Have many invaginations of the cell membrane to increase the surface area for acid release

19
Q

What receptors are present on the parietal cells and what binds to them?

A

CCK receptor - gastrin binds
H2 receptor - histamine
Muscarinic receptor - ACh

20
Q

What stimulates gastrin secretion?

A

Peptides/amino acids in the stomach lumen

Vagal stimulation

21
Q

Where are the G cells located?

A

Antrum

22
Q

What factors inhibit HCl production?

A

Inhibition of G cells - less gastrin
Food leaving the stomach, decrease in pH, activates D cells - somatostatin which inhibits G cells
Stomach distension reduces - reduced vagal stimulation
Somatostatin also prevents the production of histamine

23
Q

Describe HCl production

A

Water split inside the parietal cells (OH- and H+)
H+ moved into stomach lumen
Cl- moved into stomach lumen (the 2 combine)
CO2 combines with the OH- forming bicarbonate which is moved into the blood stream creating the alkaline tide during acid production

24
Q

Describe the antiporter present on the basolateral surface of parietal cells

A

HCO3- moves into blood (out of cell)

Cl- moves into cell (out of blood)

25
Q

How do we scientifically write the proton pump?

A

H+/K+/ATPase

26
Q

How does the proton pump work?

A

Uses ATP to pump H+ into stomach lumen against huge conc gradient
In exchange for a K+ ion

27
Q

What are the 3 phases of digestion?

A

Cephalic
Gastric
Intestinal

28
Q

Describe the cephalic phase of digestion

A 
Before things arrive in the stomach 
30% total HCl secreted 
PNS stimuli - direct stimulation of parietal and G cells via vagus nerve
Anticipating food 
Also increases gastric motility slightly
29
Q

Describe the gastric phase of digestion

A

Food actually in the stomach
60% of total HCl secreted in this stage
Distension stimulates vagus -> parietal and G cells
Presence of amino acids -> G cells
Food acts as a buffer
Enteric NS and gastrin cause strong muscular contractions - acceleration of food towards pyloric sphincter

30
Q

Describe the intestinal phase of digestion

A

10% of HCl production done in this phase
Chyme initially stimulates HCl secretion
Soon overtaken by inhibiton of G cells
Presence of lipids activates enterogastric reflex - reduced vagal stimulation - reduced secretions
Chyme stimulates CCK and secretin which help suppress secretions

31
Q

Name some factors that protect the stomach

A

Mucus
Bicarbonate
Rapid turnover of epithelial cells

32
Q

Why do we need the thick alkaline layer at the epithelium in the stomach?

A

Higher pH so that proteases are not activated near the stomach surface

33
Q

Why are NSAIDs bad for the stomach?

A

Reduce synthesis of prostaglandins
Decrease the mucosal blood flow
Decreased nutrients to epithelium
Breaching stomach defences

34
Q

How does alcohol breach the stomach defences?

A

Dissolves the mucus layer

35
Q

What is the most effective way to stop acid production?

A

PPIs

Eg. Omeprazole, lansoprazole

36
Q

Give examples of H2 antagonists

A

Cimetidine

Ranitidine

Gastro-intestinal System (10 decks)

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