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Gastrointestinal > Session 4 > Flashcards

Session 4 Flashcards

1
Q

What is the role of the stomach?

A

Stores food
Disinfects food
Breaks it down to Chyme

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2
Q

What are the 2 ways the stomach disrupts food?

A 
Chemical disruption (1st - Acid/Enzymes)
Physical disruption (2nd - Motility)
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3
Q

How does the stomach protect itself?

A

In the form of secretions - Mucus and alkali (HCO3-)

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4
Q

What stomach secretions would attack it if it wasn’t for the defense mechanisms?

A 
HCl (Luminal pH is below 2)
Proteolytic enzymes (Pepsin)
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5
Q

What cells secrete the enzymes into the stomach? (Such as Pepsin)

A

Chief cells

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6
Q

What cells secrete the acid into the stomach?

A

Parietal cells

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7
Q

What cells secrete the hormone Gastrin into the stomach?

A

G cells

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8
Q

What cells secrete mucus into the stomach?

A

Neck cells

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9
Q

Where is the stomach acid made?

A

In mitochondria

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10
Q

How is acid for the stomach made?

A

Cells split H2O into H+ and OH- (Which combines with CO2 to make HCO3-)
H+ goes to the stomach and HCO3- is released into the blood

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11
Q

Why do ‘Alkaline tides’ occur after someone has eaten?

A

Because the stomach makes a lot of stomach acid, therefore there is lots of HCO3- as a by product which goes into the blood = Alkaline tide

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12
Q

How is H+ prevented from building up in the cells?

A

The cells have canaliculi (Invaginations of the cell wall) that have proton pumps so H+ can be expelled against its concentration gradient (Uses a lot of energy)

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13
Q

What does Gastrin bind to?

A

Binds to surface receptors on parietal cells

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14
Q

What does binding of Gastrin cause?

A

Stimulates acid secretion
Stimulates intrinsic factor secretion via a secondary messenger pathway (Which aids B12 absorption to maintain normal red blood cells)

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15
Q

What cells release Histamine?

A

Mast cells

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16
Q

What type of substance is Histamine?

A

A Paracrine substance

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17
Q

What does Histamine bind to?

A

H2 surface receptors on Parietal cells

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18
Q

What does binding of Histamine cause?

A

Acid secretion via cyclic AMP

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19
Q

What released Ach?

A

Post ganglion Parasympathetic neurone

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20
Q

What does Ach act on?

A

M receptors on the Parietal cells

21
Q

What does binding of Ach cause?

A

Stimulates acid secretion by a secondary messenger pathway

22
Q

What stimulates Gastrin secretion?

A

Peptides
Ach
Distension

23
Q

What inhibits Gastrin secretion?

A

A low pH in the stomach (Feedback control)

24
Q

What is the role of HCl in the stomach?

A

Cleave Pepsinogen into Pepsin
Kills bacteria
Chemically disrupts food

25
Q

What stimulates Histamine release?

A

Gastrin
Ach
(Amplifier of of action)

26
Q

What is a clinical target for reducing acid secretion?

A

Antagonists of H2 receptors

27
Q

What are the phases of control?

A

Cephalic phase
Gastric phase
Intestinal phase

28
Q

\What is characteristic of a gastric ulcer?

A

Abdominal pain during the night (Due to the pH being low)

29
Q

Why does mucus protect the stomach?

A

It is sticky and basic
H+ ions get stuck in the unstirred mucus layer and HCO3- ions in the mucus join to it to make H2o (which enters the stomach) and CO2

30
Q

What do Prostaglandins do?

A

Make the stomach defend itself

Stimulates mucus and alkali secretion

31
Q

What promotes release of Prostaglandins?

A

Most factors that stimulate acid secretion

32
Q

What inhibits prostaglandins?

A

NSAIDS (Non steroidal anti inflammatory drugs)

Therefore reduce stomach defences

33
Q

How can stomach defences be damaged?

A

Alcohol can dissolve the mucus

Helicobacter pylori damages the defences is acid attacks the mucosa

34
Q

How can aspirin damage the stomach?

A

It is converted by to a non ionising form in the stomach acid then it passes into cells where it is re-ionised and lead to peptic ulcers

35
Q

How can you clinically reduce stomach acid?

A

Histamine receptor antagonists (Cimetidine)
Proton pump inhibitors (Omeprazole)
If ulcers due to Helicobacter pylori should treat with antibiotics

36
Q

How can you test easily for Helicobacter pylori?

A

Breath test for nitrogenous substances made by the bacteria in the stomach

37
Q

What is the shape of the stomach between meals?

A

The stomach is very contracted

The stomach is small

38
Q

What happens when you begin to eat?

A

Stomach relaxed to accommodate food
Contracts rhythmically to break down large particles
Delivers chyme slowly to the duodenum

39
Q

What is receptive relaxation?

A

A neural reflex that is triggered by swallowing via an efferent pathway using the vagus nerve.
Tension in the existing stomach is actively relaxed
Pressure in the stomach does not increase as it fills

40
Q

How often are the contractions in the stomach?

A

3 times a minute

41
Q

What drives the rhythmic contractions in the stomach?

A

By a pacemaker (small group of muscle cells able to make electrical impulses) in the cardiac regions of the stomach.

42
Q

What are the 2 muscle types in the stomach?

A

Longitudinal

Circular

43
Q

How does stomach contraction ensure that large lumps of food stay within the stomach?

A

Wave if peristalsis drives all of the stomach contents ahead of it, but it overtakes the larger lumps as it accelerates.
This means that only chyme reaches the pyloris and the lumps are pushed back to the fundus.
Small squirts can be ejected into the duodenum and the pylorus is closed by the peristalsis

44
Q

What controls gastric emptying into the duodenum?

A

Volume of each is affected by the rate of acceleration of the peristaltic wave
Affected by hormone from the intestine
can often go wrong

45
Q

What slows gastric emptying?

A

Fat
Low pH
Hypertonicity
in the duodenum

46
Q

What is the cephalic phase?

A

Detecting and ingesting food

Autonomic stimulation

47
Q

What is the gastric phase?

A

Food reaches the stomach
Buffers stomach acid
pH rises (disinhibits gastrin)
Stomach distends that stimulates intrinsic nerves that release Ach
Initial digestion releases peptides (detected by G cells) which stimulate gastrin release
Histamine release stimulated by gastrin and Ach

48
Q

What happens in the intestinal phase?

A

Stomach begins to empty
Chyme stimulates release of hormones from the intestines (antagonise gastrin)
Accumulation of acid in empty stomach inhibits gastrin secretion

Gastrointestinal (13 decks)

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