13.2 - Drugs affecting Gut motility Flashcards

1
Q

What 3 ways is gastric motility controlled by?

A

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

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2
Q

Explain how emesis occurs

A

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

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3
Q

Where is the vomiting centre found?

A

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

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4
Q

What neurotransmitters are involved in emesis control?

A

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

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5
Q

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

A

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

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6
Q

How does domperidone work? ADRs?

A

Increases gastric emptying. D2 receptor antagonist

ADR - galactorrhoea, hyperprolactinemia

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7
Q

How dos ondensteron work? ADRs?

A

Reduces vagal afferent neves. 5-HT3 receptor antagonist

ADR - headaches, constipation, flushing

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8
Q

How does metoclopramide work? ADRs?

A

Blocks vagal afferents. D2 receptor antagonist

ADR - extra-pyramidal

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9
Q

How does cyclizine work? ADRs?

A

H1 receptor antagonist

ADR - prolongs QT interval

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10
Q

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

A

soft - use stimulant laxative

Hard - Use osmotic or bulk laxative

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11
Q

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

A

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

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12
Q

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

A

e.g. movicol.

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

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13
Q

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

A

e.g. senna, bisacodyl

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

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14
Q

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

A

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

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15
Q

Name a bulk forming agent and how it works in diarrhoea

A

ispaghula. Increases water absorption by gut.

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