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MD3002 > Vomiting and Gut Motility > Flashcards

Vomiting and Gut Motility Flashcards

1
Q

Where is vomiting controlled in the brain

A

Medulla (medullary and pontile reticular formation)

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2
Q

What separate units control vomiting

A
  1. Vomiting centre

2. Chemoreceptor Trigger Zone

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3
Q

Which nerve fibres does the vomiting centre receive signals from

A
  • Vagal afferent

- Sympathetic afferent

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4
Q

Where is the CTZ

A

Area postrema (floor of 4th ventricle)

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5
Q

Why is the CTZ sensitive to drugs

A

As the blood brain barrier is more permeable at the CTZ

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6
Q

Where is motion sickness mediated

A

CTZ

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7
Q

Where is the origin of the stimulus for motion sickness

A

Vestibular apparatus

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8
Q

What is the neural pathway for motion sickness

A
  • Vestibular labyrinth
  • Vestibular nuclei
  • Cerebellum
  • CTZ
  • Vomiting centre
  • Vomit
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9
Q

How can vomiting be triggered

A
  • Stimulation of sensory nerve endings in stomach/duodenum
  • Drugs or endogenous emetic substances
  • Disturbances of vestibular apparatus
  • Rise in intracranial pressure
  • Nauseating smells, repulsive sights, emotional factors (from higher centre)
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10
Q

Where can inputs come from to the vomiting centre

A
  • Higher cortical centre
  • CTZ
  • Vagal afferents
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11
Q

What do enterochromaffin cells sense

A

Toxic chemicals or toxins in gut

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12
Q

What are the stages of vomiting

A
  1. Nausea (associated with autonomic effects like salivation, pallor)
  2. Retching (strong involuntary effort to vomit which is unproductive)
  3. Vomiting (expulsion of gastric contents through mouth)
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13
Q

Give some examples of types of vomiting

A
  1. Projectile vomiting (suggestive of gastric outlet or upper GI obstruction)
  2. Haematemesis (vomiting fresh or altered blood in oesophageal varicose or bleeding gastric ulcers)
  3. Early-morning (e.g. in pregnancy, alcohol dependence)
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14
Q

What are some indications for anti-emetic drugs

A
  1. Hyperemesis gravidarum
  2. Postop nausea and vomiting
  3. Motion sickness
  4. Other vestibular disorders
  5. Palliative care
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15
Q

Give some examples of types of anti-emetics

A
  1. Antihistamines
  2. Antimuscarinics
  3. Dopamine antagonists
  4. 5HT3 antagonists
  5. Neurokinin 1 receptor antagonists
  6. Synthetic cannabinoids
  7. Steroids
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16
Q

Where do antihistamines act

A

H1 receptor (higher cortical centre)

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17
Q

Where does hyoscine act

A

Near vestibular nuclei

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18
Q

Which drugs act near CTZ

A
  • Dopamine antagonists

- 5HT3 receptor antagonists

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19
Q

Which drugs act on enterocrhomaffin cells

A
  • Cannabinoids
  • Dopamine antagonists
  • Neurokinin 1 receptor antagonists
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20
Q

Side effects of antihistamines

A
  • Drowsiness

- Anti-muscarinic effects

21
Q

Examples of antihistamines

A
  1. Cinnarizine (motion sickness, vestibular disorders)
  2. Cyclizine (motion sickness)
  3. Promethazine (severe morning sickness)
22
Q

Give an example of an antimuscarinic

A

Hyoscine hydrobromide (motion sickness)

23
Q

Which receptor do antimuscarinics act on

A

M1

24
Q

Side effects of anti-muscarianics

A
  • Constipation
  • Transient bradycardia
  • Dry mouth
25
Q

What are dopamine receptor antagonists active against

A

CTZ -triggered vomiting

26
Q

Give examples of D2 receptor antagonists

A
  1. Phenothiazines, chlorpromazine, prochlorperzine
  2. Domperidone
  3. Metoclopramide
27
Q

Where do 5HT3 antagonists act

A
  • GI tract

- CNS

28
Q

When are 5HT3 receptor antagonists used

A
  • Cytotoxics

- Postoperative

29
Q

Give an example of a 5HT3 receptor antagonist

A

Ondansetron

30
Q

When are neurokinin 1 receptor antagonists used

A

Adjunct to dexamethasone and 5HT3 receptor antagonist in preventing N/V associated with chemo

31
Q

Give an example of a neurokinin 1 receptor antagonist

A

Aprepitant

32
Q

Which receptors do cannabinoids act on

A

CB1

33
Q

Give an example of a synthetic cannabinoid

A

Nabilone

34
Q

When are synthetic cannabinoids used

A

Control N/V caused by chemo unresponsive to conventional anti-emetics

35
Q

Side effects of cannabinoids

A
  • Drowsiness

- Dizziness

36
Q

Why are steroids prescribed

A
  • Treat vomiting associated with cancer chemo
  • In conjunction with other anti-emetics
  • Appetite stimulating
37
Q

What are the types of laxatives and examples

A
  1. Bulk-forming laxatives (ispaghula husk)
  2. Stimulant laxatives (Senna)
  3. Faecal softeners (Docusate)
  4. Osmotic laxatives (Lactulose)
  5. Peripheral opioid-receptor antagonists (Methylnaltrexone bromide)
38
Q

What does diarrhoea involve

A
  • Increase in GI tract motility

- Decrease in absorption of fluid, and hence a loss of electrolyte

39
Q

How to treat acute diarrhoea

A
  1. Maintain hydration (e.g. oral rehydration preparation)
  2. Antimotility drugs
  3. Antispasmodics to reduce smooth muscle tone (e.g. hyoscine butyl bromide, mebeverine)
  4. Occasionally antibacterial agent is indicated (e.g. systemic bacterial infection, shigellosis)
40
Q

How to treat chronic diarrhoea

A
  1. Antimotility agents (e.g. loperamide)
  2. Adsorbents (kaolin)
  3. Bulk forming drugs- useful in controlling diarrhoea associated with diverticular disease (e.g. ispaghula)
41
Q

What does bile contain

A
  • Bile salts
  • Bilirubin
  • Cholesterol
  • Lecithin
  • Plasma electrolytes
42
Q

What can gallstones cause

A
  • Biliary colic
  • Infective cholycyctisis
  • Jaundice
  • Pancreatitis
43
Q

How to treat gallstones

A

Ursodeoxycholic acid (dissolves gallstones)

44
Q

How to treat biliary colic

A
  • Opioid (e.g. morphine, pethidine)

- NSAID (diclofenac)

45
Q

How are drugs for biliary colic given

A

Parenteral/rectal route as overcomes difficulty in absorption caused by vomiting

46
Q

What is colestyramine

A

Anion-exchange resin

47
Q

Why is colestyramine given

A
  • Forms an insoluble complex with bile acids in intestine

- Relieves pruritus associated with partial biliary obstruction/primary biliary cirrhosis

48
Q

When else can colestyramine be given

A
  • Diarrhoea (Crohn’s disease related)

- Hypercholesterolaemia

MD3002 (14 decks)

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