13.2 - Drugs affecting Gut motility

Question 1

What 3 ways is gastric motility controlled by?

Answer 1

myogenic - rhythmic contraction of smooth muscle cells by pacemaker cells
neural - enteric plexus
hormonal - cck, gastrin, secretin

Question 2

Explain how emesis occurs

Answer 2

Closing of pyloric sphincter –> relaxing of cardia and esophagus –> Contraction of abdominal muscles and diaphragm

Question 3

Where is the vomiting centre found?

Answer 3

Part of ependymal cells on the floor of the 4th ventricle

Question 4

What neurotransmitters are involved in emesis control?

Answer 4

At Vestibular apparatus - ACh and H1
Medullar centre - ACh, H3, serotonin
Vomiting centre - Dopamine

Question 5

What are the types of anti-emetic drugs? Give example types

Answer 5

D2 receptor antagonists - domperidone, metoclopramide
5-HT3-receptor antagonist - ondansetron
Anti-muscarinincs
H1-receptor antagonists- cyclizine

Question 6

How does domperidone work? ADRs?

Answer 6

Increases gastric emptying. D2 receptor antagonist

ADR - galactorrhoea, hyperprolactinemia

Question 7

How dos ondensteron work? ADRs?

Answer 7

Reduces vagal afferent neves. 5-HT3 receptor antagonist

ADR - headaches, constipation, flushing

Question 8

How does metoclopramide work? ADRs?

Answer 8

Blocks vagal afferents. D2 receptor antagonist

ADR - extra-pyramidal

Question 9

How does cyclizine work? ADRs?

Answer 9

H1 receptor antagonist

ADR - prolongs QT interval

Question 10

What type of laxatives are used for constipation with soft and hard faeces?

Answer 10

soft - use stimulant laxative

Hard - Use osmotic or bulk laxative

Question 11

what are exampes of bulk laxatives? How do they work? ADR?

Answer 11

e.g. ispaghula. Non degradable fibre gives bulk to aid in peristalsis. Takes few days to work.
ADR - flatus,

Question 12

What are examples of osmotically active laxatives? How do they work?

Answer 12

e.g. movicol.

Works by causing water retention in small and large bowel to increase peristalsis. Acts quickly and severely.

Question 13

What are examples of stimulant laxatives? How do they work?

Answer 13

e.g. senna, bisacodyl

Excites sensory nerve ending, leading to water and electrolyte retention –> peristalsis. Work in 6-8 hrs.

Question 14

Name an example anti-motility drug and how it works. When should it be avoided and why?

Answer 14

Loperamide - opiate reduce GI motility. Good for chronic diarrhoea. Avoid in IBD due to toxic megacolon

Question 15

Name a bulk forming agent and how it works in diarrhoea

Answer 15

ispaghula. Increases water absorption by gut.