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Gastrointestinal > Pharmacology > Flashcards

Pharmacology Flashcards

1
Q

Describe the pathway of H+ and Cl- leaving parietal cells

A
  • Cl- enters parietal cell from blood via chloride-bicarbonate exchanger
  • Cl- leaves parietal cell to gastric lumen via chloride-potassium symporter
  • H+ leaves parietal cell via H+/K+ ATPase into gastric lumen
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2
Q

What is the role of carbonic anhydrase in parietal cells?

A

Converts CO2 and H2O into H2CO3 (carbonic acid)

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3
Q

What is the role of carbonic acid in parietal cells?

A

Dissociates into HCO3- ions for the chloride-bicarbonate exchanger and H+ ions for HCl

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4
Q

Which cells in the gastric pit form histamine?

A

Enterochromaffin-like cells

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5
Q

Describe the mode of action of histamine on gastric acid secretion

A
  • Histamine acts on H2R receptors
  • Causes an increase in adenylyl cyclase
  • Leads to increased cAMP production
  • increases the number of proton pumps
  • increases gastric acid secretion from parietal cells
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6
Q

What stimulates histamine release?

A

Acetylcholine via parasympathetic innervation

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7
Q

Describe the mode of action of acetylcholine on gastric acid secretion

A
  • ACh activates muscarinic M3 receptors on parietal cells
  • Activates phospholipase C causing increased Ca2+
  • This causes increase in number or proton pumps
  • Causes increased gastric acid secretion
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8
Q

Describe the mode of action of gastrin on gastric acid secretion

A
  • Gastrin from G cells activates CCK2 receptors
  • Causes an increase in Ca2+ via PLC
  • Causes an increase in proton pump numbers
  • Causes increased gastric secretion
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9
Q

Describe the mode of action of somatostatin on gastric acid secretion IN PARIETAL CELLS

A
  • Somatostatin from D cells activates SST2 receptors on parietal cells
  • Inhibits AC, decreases cAMP, decreases number of proton pumps
  • Causes decrease in gastric acid secretion
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10
Q

Describe the mode of action of somatostatin on gastric acid secretion IN ENTEROCHROMAFFIN-LIKE CELLS

A
  • Activates SST2 receptors
  • Opposes ACh stimulation: inhibits histamine
  • decreased histamine decreases gastric secretion
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11
Q

What are the active components in antacids?

A

Sodium bicarbonate, NaHCO3
Calcium carbonate, CaCO3
Sodium alginate

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12
Q

How do antacids work?

A

Their active components are bases which dissociate and react with H+ to buffer excess acid

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13
Q

What are NSAIDs?

A

Non steroidal anti-inflammatory drugs, can cause NSAID-induced gastric ulceration

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14
Q

Describe the mechanism of action of NSAIDs on gastric acid secretion

A
  • NSAIDs inhibit cyclooxygenase 1, inhibiting prostaglandins production
  • Decreased prostaglandins causes increased histamine release
  • causes increased HCl secretion
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15
Q

What is the role of prostaglandins in gastric acid secretion?

A

Inhibits histamine, causing decreased HCl secretion

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16
Q

What is the drug indicated for prophylaxis of NSAID-induced peptic ulcers?

A

Misoprostol, an analogue of prostaglandin E1

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17
Q

What are the side effects of misoprostol?

A

Abdominal pain, diarrhoea, can induce labour

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18
Q

Name 3 proton pump inhibitors

A

Lansoprazole
Omeprazole
Pantoprazole

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19
Q

How do proton pump inhibitors work?

A

They bind irreversibly to H+/K+ ATPase, directly decreasing HCl secretion

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20
Q

What conditions indicate PPIs?

A

Benign gastric acid ulceration
NSAID-induced gastric ulceration
gastro-oesophageal reflux disease
Zollinger-Ellison syndrome

21
Q

What is a side effect of PPIs?

A

Increased stomach pH making patients more susceptible to infections in the GI tract

22
Q

Name 3 histamine H2 receptor antagonists

A

Ranitidine
Cimetidine
Famotidine

23
Q

How do H2 receptor antagonists work?

A

Block H2R on parietal cells, causing decreased HCl secretion

24
Q

Which conditions indicate H2 receptor antagonists?

A

Benign gastric acid ulceration

NSAID-induced gastric ulceration

25
Q

How does H. pylori cause peptic ulcers?

A

HP migrates into mucus layer
Damages mucus cells
Depletion of mucus layer
Exposure of mucosa to low pH causes ulcers

26
Q

How are HP peptic ulcers treated?

A

PPIs

Antibiotics: clarithromycin and amoxicillin or metronidazole

27
Q

What types of anti-emetics are there?

A 
Histamine H1 receptor antagonists
Antimuscarinics
5-HT3 receptor antagonists
Dopamine receptor antagonists
Neurokinin-1 receptor antagonists
28
Q

Name 3 H1 receptor antagonists

A

Cyclizine
Promethazine
Diphenhydramine

29
Q

Name an antimuscarinic

A

Scopolamine (hyoscine)

30
Q

Name 3 5-HT3 receptro antagonists

A

Ondansetron
Granisetron
Palonosetron

31
Q

Name 4 dopamine receptor antagonists

A

Chlorpromazine
Haloperidol
Prochlorperazine
Metoclopramide (also a 5-HT3 RAnt at high conc)

32
Q

Name 2 neurokinin-1 receptor antagonists

A

Fosaprepitant

Apreptant

33
Q

What areas of the brain and body are involved in vomiting signalling?

A
  • Chemoreceptor trigger zone (CTZ) in brain
  • Vomiting centre, dorsal to CTZ
  • Cortical areas (anxiety)
  • Vestibular nuclei (motion sickness)
  • Plexuses in the gut
34
Q

Where is information about vomiting coordinated in the brain?

A

Psychological, vascular, and gastric information is coordinated at the chemoreceptor trigger zone and vomiting centre

35
Q

What drugs are indicated for motion sickness?

A

Histamine H1 receptor antagonists and antimuscarinics

36
Q

What are the side effects of H1 receptor antagonists?

A

Sedation

37
Q

What receptor do antimuscarinics work on?

A

Muscarinic cholinergic M1 receptors in the brain

38
Q

What are the side effects of antimuscarinics?

A

Dry mouth
Tachycardia
Constipation

39
Q

Where do 5-HT3 receptor antagonists affect?

A

The CTZ in the medulla

The enteric plexuses

40
Q

What are the side effects of 5-HT3 receptor antagonists?

A

Constipation
Diarrhoea
Headache

41
Q

Where do dopamine receptor antagonists act?

A

At D2 receptors in CTZ and D2 receptors in GI tract

42
Q

What are the side effects of dopamine receptor antagonists?

A

Diarrhoea

Extrapyrimidal side effects

43
Q

Where do NK-1 receptor antagonists act and what are their side effects?

A

Neurokinin-1 receptors in the CTZ and GI tract
Side effects:
Constipation
Headache

44
Q

What is the first line of treatment for diarrhoea?

A

Electrolyte replacements

45
Q

Name 2 antidiarrhoeal drugs

A

Loperamide
Diphenoxylate
(opiates)

46
Q

Give the side effects for antidiarrhoeal drugs

A

Constipation
Sedation
Respiratory depression

Can be addictive at higher doses

47
Q

How do antidiarrhoeal drugs work?

A

Inhibit gut motility - agonists of opiate receptors

48
Q

Name 3 laxatives

A

Lspaghula husk
Lactulose
Senna

49
Q

How do laxatives work?

A

By stimulating peristalsis, and/or increasing water/electrolyte secretion

Gastrointestinal (5 decks)

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