Gut Motility

Question 1

What cells act as pacemakers for myogenic control or gut motility?

Answer 1

Interstitial cells of Cajal - current spreads

Question 2

What is the main plexus in the enteric nervous system for the gut and where is it located?

Answer 2

Myenteric plexus

Between the circular and longitudinal muscle layers

Question 3

Name 3 extrinsic nerve reflexes affecting motility

Answer 3

Intestino intestinal reflex - distension of one segment causes inhibition

Anointestinal inhibitory reflex - distension of the anus causes intestinal inhibition

Gastrocolic, duodenocolic - stimulates motility after food has entered stomach

Question 4

What are the main neurotransmitters used in hormonal control?

Answer 4

Gastrin, CCK, secretin

Question 5

Where is the vomiting centre found and what can trigger it?

Answer 5

Floor of the 4th ventricle

Smell, pain, pregnancy, rotational movements, medications,

Question 6

What neurotransmitters are involved in emesis thus can be targeted?

Answer 6

Vomiting centre - dopamine

Medullary centre - ACh, H1, 5HT

Vestibular apparatus - ACh, H1

Question 7

Name a dopamine antagonist used to treat emesis, how it works, when it is indicated, its route and ADRs

Answer 7

Domperidone

Acts on the poster a on the floor of the 4th ventricle and also increases gastric emptying so there is less to vomit

Indicated in acute nausea

Oral/PR

Stimulates prolactin release

Question 8

Name a 5HT3 receptor antagonist, where it acts, where it is indicated, route and ADRs

Answer 8

Ondasteron

5HT released into the gut causes a gal stimulation thus this is reduced

Indicated in radiation/chemotherapy sickness

Route depends

Headaches, constipation, flushing

Question 9

What is metoclopramide? How does it work? What are the indications? What are the ADRs?

Answer 9

Dopamine antagonist, GI anticholinergic effects, blocks vagaries afferent using 5HT

GI cause of nausea and vomiting, migraine, post op

Extrapyramidal symptoms

Question 10

Name an ACH antagonist used to treat emesis, when it is used and the ADRs

Answer 10

Hyoscine

Used to treat motion sickness

Systemic anticholinergic effects

Question 11

Name a H1 antagonist, when it is used and the ADRs

Answer 11

Cyclizine

Acute nausea or vomiting

Prolongs QT interval and crosses blood brain barrier so can be sedative

Question 12

What are the 4 types of laxatives? Give an example for each

Answer 12

Bulk laxatives e.g. Fybogel

Faecal softners e.g. Glycerol

Osmotic e.g. Lactulose, macrogols, phosphate enema

Irritant and stimulants e.g. Caster oil, senna, sodium picosulphate

Question 13

How do bulk laxatives work?

Answer 13

Act as a non degradable fibre to distend the gut and aid in peristaltic contractions. They take a few days to work and can reestablish normal bowel habits in simple constipation e.g. IBS

Question 14

What is the main ADR of bulk laxatives?

Answer 14

Flactulance

Question 15

When should bulk laxatives not be used?

Answer 15

Adhesions and ulcerations

Question 16

How do stool softners work? When are they indicated?

Answer 16

Lubricate and soften stool. Simple constipation as with bulk laxatives but can be used in adhesions, for anal fissures and haemorrhoids

Question 17

How do osmotically active laxatives work, when are they indicated, route? E.g. Magnesium (lactulose works by fermentation to acid causing oedema via tablet but takes 48 hours)

Answer 17

Cause water retention in the bowels to increase peristalsis

They act quickly and are used for resistant constipation or if urgent relief is required

PR

Question 18

What caution is there with osmotic laxatives?

Answer 18

Prevent obstruction

Question 19

How do stimulant laxatives work? When are they used?

Answer 19

They excite nerve endings leading to water and electrolyte retention thus increased peristaltic movement. Used for rapid treatment e.g. Faecal impaction or pre surgery.

Question 20

What 3 types of drugs can be used to treat diarrhoea?

Answer 20

Anti motility

Bulk forming

Fluid absorbents

Question 21

What type of laxative would you use for soft faeces?

Answer 21

Stimulant

Question 22

What laxative would you use for hard faeces?

Answer 22

Osmotic, bulk forming

Question 23

How do anti motility drugs work, when are they used and where should they be avoided?

Answer 23

Opioid analogue that acts on receptors in the bowel to reduce bowel motility and increase anal tone

Chronic diarrhoea

IBD as risks toxic megacolon

Question 24

How do bulk forming agents work for diarrhoea, when are they used?

Answer 24

Increase water absorption, useful for patients with IBS and ileostomy

Question 25

Name a fluid absorbent

Answer 25

Kaolin