Pharmacology: Intestinal Motility Secretion, Nausea and Vomiting Flashcards
List some causes of nausea and vomiting.
- migraine
- anxiety
- motion sickness
- pregnancy
- side effects of medication
In what part of the brain is the vomiting/emetic centre located?
Brain stem
Where does the vomiting centre get signals from and what triggers these signals ?
- From the CTZ - Chemoreceptor Trigger Zone (receives signals from vagal afferents and vestibular nuclei)
- From vagal afferents (signals from gut)
- From higher cortical centres (pain, repulsive sights and smells, emotional factors)
What is the Chemoreceptor Trigger Zone, where is it, where does it receive signals from?
- The main site for sensing emetic stimuli
- Below vomiting centre
- Receives signals from the vagal afferents from gut and from the vestibular nuclei (input from the labyrinth - fluid filled part of ear that regulates balance)
- enterochromaffin cells in the gut sense toxic chemicals or toxins in the gut
What do enterochromaffin cells in the gut do?
Sense toxic chemicals or toxins
What is the function of the vomiting centre?
To integrate all the signals and coordinates emesis
What are the main neurotransmitters involved in nausea/vomiting?
- Acetylcholine
- Dopaine
- 5-HT
What are the 5 main categories of anti-emetic drugs?
- antihistamines (H1 receptor antagonists)
- antimuscarinics (muscarinic acetylcholine receptor antagonists)
- 5-HT3 receptor antagonists
- Dopamine receptor antagonists
- Neurokinin-1 receptor antagonists
List 3 types of antihistamines used as anti-emetics
- cyclizine
- promethazine
- diphenydramine
List a type of antimuscarinic used as an anti-emetics
-scopolamine (hyoscine)
List 3 types of 5-HT3 receptor antagonists used as anti-emetics
- Ondansetron
- Granisetron
- Palonosetron
List 6 types of dopamine receptor antagonists used as anti-emetics
- chlorpromazine
- droperidrol
- haloperidol
- prochlorperazine
- metoclopramide
- domperidone
List 2 types of neurokinin-1 receptor antagonists used as anti-emetics
- fosaprepitant
- apreptant
What receptor do antihistamines act on?
H1 receptors in the brain
What are antihistamines indicated for?
Nausea and vomiting - specifically for motion sickness
What is a side effect of antihistamines?
Sedation (because they act on H1 receptors in the brain)
Where receptor do antimuscarinics act on?
muscarinic acetylcholine M1 receptors in the brain
What are antimuscarinics indicated for?
motion sickness
What are the side of effects of antimuscarinics?
antimuscarinic side effects e.g. dry mouth, tachycardia and constipation
What receptors do 5-HT3 receptor antagonists act on?
- 5-HT3 receptors in the chemoreceptor trigger zone of the medulla in the hindbrain
- 5-HT3 receptors in the GI tract
What are the side effects of 5-HT3 receptor antagonists?
- constipation
- diarrhoea
- headaches
What receptors do dopamine receptor antagonists act on (+ which exception)?
- D2 receptors in the chemoreceptor trigger zone in the medulla (exception - domperidone)
- D2 receptors in the GI tract
What are the side effects of dopamine receptor antagonists?
- Diarrhoea
- extra pyramidal side effects (except domperidone) e.g. tremor, anxiety, slurred speech etc.
What receptors do neurokinin-1 receptor antagonists act on?
- NK1 receptors in the GI tract
- NK1 receptors in the chemoreceptor zone in the medulla
- they block the effects of substance P which evokes vomiting
What are the side effects of neurokinin-1 receptor antagonists?
- constipation
- headache
List 3 antidiarrhoeal drugs
- loperamide
- diphenoxylate
- electrolyte replacements
List 3 laxatives
- ispaghula husk
- senna
- lactulose
Outline how antidiarrhoeal drugs work.
Loperamide and diphenoxylate are opiates that bind to μ-opioid receptors.
-opiate agonists that reduced muscle tone of muscles of the intestinal wall (slows movement)
(they have reduced effect on brain compared to some other opiates)
What are side effects of antidiarrhoeal drugs
- constipation
- sedation
- respiratory depression (common for opiates)
What type of laxative is ispaghula husk?
Bulk forming laxative - causes the stool to retain fluids
What type of laxative is lactulose?
Osmotic laxative - pulls water out of the body and into the stools
What is lactulose also used to treat aswell as diarrhoea?
Hepatic encephalopathy - increases ammonia excretion (removing toxin)
What type of laxative is senna?
stimulant purgative - increases water and electrolyte secretion
