Pharmacology: Intestinal Motility Secretion, Nausea and Vomiting

Question 1

List some causes of nausea and vomiting.

Answer 1

• migraine
• anxiety
• motion sickness
• pregnancy
• side effects of medication

Question 2

In what part of the brain is the vomiting/emetic centre located?

Answer 2

Brain stem

Question 3

Where does the vomiting centre get signals from and what triggers these signals ?

Answer 3

• 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)

Question 4

What is the Chemoreceptor Trigger Zone, where is it, where does it receive signals from?

Answer 4

• 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

Question 5

What do enterochromaffin cells in the gut do?

Answer 5

Sense toxic chemicals or toxins

Question 6

What is the function of the vomiting centre?

Answer 6

To integrate all the signals and coordinates emesis

Question 7

What are the main neurotransmitters involved in nausea/vomiting?

Answer 7

• Acetylcholine
• Dopaine
• 5-HT

Question 8

What are the 5 main categories of anti-emetic drugs?

Answer 8

1. antihistamines (H1 receptor antagonists)
2. antimuscarinics (muscarinic acetylcholine receptor antagonists)
3. 5-HT3 receptor antagonists
4. Dopamine receptor antagonists
5. Neurokinin-1 receptor antagonists

Question 9

List 3 types of antihistamines used as anti-emetics

Answer 9

• cyclizine
• promethazine
• diphenydramine

Question 10

List a type of antimuscarinic used as an anti-emetics

Answer 10

-scopolamine (hyoscine)

Question 11

List 3 types of 5-HT3 receptor antagonists used as anti-emetics

Answer 11

• Ondansetron
• Granisetron
• Palonosetron

Question 12

List 6 types of dopamine receptor antagonists used as anti-emetics

Answer 12

• chlorpromazine
• droperidrol
• haloperidol
• prochlorperazine
• metoclopramide
• domperidone

Question 13

List 2 types of neurokinin-1 receptor antagonists used as anti-emetics

Answer 13

• fosaprepitant

- apreptant

Question 14

What receptor do antihistamines act on?

Answer 14

H1 receptors in the brain

Question 15

What are antihistamines indicated for?

Answer 15

Nausea and vomiting - specifically for motion sickness

Question 16

What is a side effect of antihistamines?

Answer 16

Sedation (because they act on H1 receptors in the brain)

Question 17

Where receptor do antimuscarinics act on?

Answer 17

muscarinic acetylcholine M1 receptors in the brain

Question 18

What are antimuscarinics indicated for?

Answer 18

motion sickness

Question 19

What are the side of effects of antimuscarinics?

Answer 19

antimuscarinic side effects e.g. dry mouth, tachycardia and constipation

Question 20

What receptors do 5-HT3 receptor antagonists act on?

Answer 20

• 5-HT3 receptors in the chemoreceptor trigger zone of the medulla in the hindbrain
• 5-HT3 receptors in the GI tract

Question 21

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

Answer 21

• constipation
• diarrhoea
• headaches

Question 22

What receptors do dopamine receptor antagonists act on (+ which exception)?

Answer 22

• D2 receptors in the chemoreceptor trigger zone in the medulla (exception - domperidone)
• D2 receptors in the GI tract

Question 23

What are the side effects of dopamine receptor antagonists?

Answer 23

• Diarrhoea

- extra pyramidal side effects (except domperidone) e.g. tremor, anxiety, slurred speech etc.

Question 24

What receptors do neurokinin-1 receptor antagonists act on?

Answer 24

• 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

Question 25

What are the side effects of neurokinin-1 receptor antagonists?

Answer 25

• constipation

- headache

Question 26

List 3 antidiarrhoeal drugs

Answer 26

• loperamide
• diphenoxylate
• electrolyte replacements

Question 27

List 3 laxatives

Answer 27

• ispaghula husk
• senna
• lactulose

Question 28

Outline how antidiarrhoeal drugs work.

Answer 28

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)

Question 29

What are side effects of antidiarrhoeal drugs

Answer 29

• constipation
• sedation
• respiratory depression (common for opiates)

Question 30

What type of laxative is ispaghula husk?

Answer 30

Bulk forming laxative - causes the stool to retain fluids

Question 31

What type of laxative is lactulose?

Answer 31

Osmotic laxative - pulls water out of the body and into the stools

Question 32

What is lactulose also used to treat aswell as diarrhoea?

Answer 32

Hepatic encephalopathy - increases ammonia excretion (removing toxin)

Question 33

What type of laxative is senna?

Answer 33

stimulant purgative - increases water and electrolyte secretion