Vomiting and Gut Motility Flashcards
Where is vomiting controlled in the brain
Medulla (medullary and pontile reticular formation)
What separate units control vomiting
- Vomiting centre
2. Chemoreceptor Trigger Zone
Which nerve fibres does the vomiting centre receive signals from
- Vagal afferent
- Sympathetic afferent
Where is the CTZ
Area postrema (floor of 4th ventricle)
Why is the CTZ sensitive to drugs
As the blood brain barrier is more permeable at the CTZ
Where is motion sickness mediated
CTZ
Where is the origin of the stimulus for motion sickness
Vestibular apparatus
What is the neural pathway for motion sickness
- Vestibular labyrinth
- Vestibular nuclei
- Cerebellum
- CTZ
- Vomiting centre
- Vomit
How can vomiting be triggered
- 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)
Where can inputs come from to the vomiting centre
- Higher cortical centre
- CTZ
- Vagal afferents
What do enterochromaffin cells sense
Toxic chemicals or toxins in gut
What are the stages of vomiting
- Nausea (associated with autonomic effects like salivation, pallor)
- Retching (strong involuntary effort to vomit which is unproductive)
- Vomiting (expulsion of gastric contents through mouth)
Give some examples of types of vomiting
- Projectile vomiting (suggestive of gastric outlet or upper GI obstruction)
- Haematemesis (vomiting fresh or altered blood in oesophageal varicose or bleeding gastric ulcers)
- Early-morning (e.g. in pregnancy, alcohol dependence)
What are some indications for anti-emetic drugs
- Hyperemesis gravidarum
- Postop nausea and vomiting
- Motion sickness
- Other vestibular disorders
- Palliative care
Give some examples of types of anti-emetics
- Antihistamines
- Antimuscarinics
- Dopamine antagonists
- 5HT3 antagonists
- Neurokinin 1 receptor antagonists
- Synthetic cannabinoids
- Steroids
Where do antihistamines act
H1 receptor (higher cortical centre)
Where does hyoscine act
Near vestibular nuclei
Which drugs act near CTZ
- Dopamine antagonists
- 5HT3 receptor antagonists
Which drugs act on enterocrhomaffin cells
- Cannabinoids
- Dopamine antagonists
- Neurokinin 1 receptor antagonists
Side effects of antihistamines
- Drowsiness
- Anti-muscarinic effects
Examples of antihistamines
- Cinnarizine (motion sickness, vestibular disorders)
- Cyclizine (motion sickness)
- Promethazine (severe morning sickness)
Give an example of an antimuscarinic
Hyoscine hydrobromide (motion sickness)
Which receptor do antimuscarinics act on
M1
Side effects of anti-muscarianics
- Constipation
- Transient bradycardia
- Dry mouth
What are dopamine receptor antagonists active against
CTZ -triggered vomiting
Give examples of D2 receptor antagonists
- Phenothiazines, chlorpromazine, prochlorperzine
- Domperidone
- Metoclopramide
Where do 5HT3 antagonists act
- GI tract
- CNS
When are 5HT3 receptor antagonists used
- Cytotoxics
- Postoperative
Give an example of a 5HT3 receptor antagonist
Ondansetron
When are neurokinin 1 receptor antagonists used
Adjunct to dexamethasone and 5HT3 receptor antagonist in preventing N/V associated with chemo
Give an example of a neurokinin 1 receptor antagonist
Aprepitant
Which receptors do cannabinoids act on
CB1
Give an example of a synthetic cannabinoid
Nabilone
When are synthetic cannabinoids used
Control N/V caused by chemo unresponsive to conventional anti-emetics
Side effects of cannabinoids
- Drowsiness
- Dizziness
Why are steroids prescribed
- Treat vomiting associated with cancer chemo
- In conjunction with other anti-emetics
- Appetite stimulating
What are the types of laxatives and examples
- Bulk-forming laxatives (ispaghula husk)
- Stimulant laxatives (Senna)
- Faecal softeners (Docusate)
- Osmotic laxatives (Lactulose)
- Peripheral opioid-receptor antagonists (Methylnaltrexone bromide)
What does diarrhoea involve
- Increase in GI tract motility
- Decrease in absorption of fluid, and hence a loss of electrolyte
How to treat acute diarrhoea
- Maintain hydration (e.g. oral rehydration preparation)
- Antimotility drugs
- Antispasmodics to reduce smooth muscle tone (e.g. hyoscine butyl bromide, mebeverine)
- Occasionally antibacterial agent is indicated (e.g. systemic bacterial infection, shigellosis)
How to treat chronic diarrhoea
- Antimotility agents (e.g. loperamide)
- Adsorbents (kaolin)
- Bulk forming drugs- useful in controlling diarrhoea associated with diverticular disease (e.g. ispaghula)
What does bile contain
- Bile salts
- Bilirubin
- Cholesterol
- Lecithin
- Plasma electrolytes
What can gallstones cause
- Biliary colic
- Infective cholycyctisis
- Jaundice
- Pancreatitis
How to treat gallstones
Ursodeoxycholic acid (dissolves gallstones)
How to treat biliary colic
- Opioid (e.g. morphine, pethidine)
- NSAID (diclofenac)
How are drugs for biliary colic given
Parenteral/rectal route as overcomes difficulty in absorption caused by vomiting
What is colestyramine
Anion-exchange resin
Why is colestyramine given
- Forms an insoluble complex with bile acids in intestine
- Relieves pruritus associated with partial biliary obstruction/primary biliary cirrhosis
When else can colestyramine be given
- Diarrhoea (Crohn’s disease related)
- Hypercholesterolaemia
