Gut Motility Flashcards
What cells act as pacemakers for myogenic control or gut motility?
Interstitial cells of Cajal - current spreads
What is the main plexus in the enteric nervous system for the gut and where is it located?
Myenteric plexus
Between the circular and longitudinal muscle layers
Name 3 extrinsic nerve reflexes affecting motility
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
What are the main neurotransmitters used in hormonal control?
Gastrin, CCK, secretin
Where is the vomiting centre found and what can trigger it?
Floor of the 4th ventricle
Smell, pain, pregnancy, rotational movements, medications,
What neurotransmitters are involved in emesis thus can be targeted?
Vomiting centre - dopamine
Medullary centre - ACh, H1, 5HT
Vestibular apparatus - ACh, H1
Name a dopamine antagonist used to treat emesis, how it works, when it is indicated, its route and ADRs
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
Name a 5HT3 receptor antagonist, where it acts, where it is indicated, route and ADRs
Ondasteron
5HT released into the gut causes a gal stimulation thus this is reduced
Indicated in radiation/chemotherapy sickness
Route depends
Headaches, constipation, flushing
What is metoclopramide? How does it work? What are the indications? What are the ADRs?
Dopamine antagonist, GI anticholinergic effects, blocks vagaries afferent using 5HT
GI cause of nausea and vomiting, migraine, post op
Extrapyramidal symptoms
Name an ACH antagonist used to treat emesis, when it is used and the ADRs
Hyoscine
Used to treat motion sickness
Systemic anticholinergic effects
Name a H1 antagonist, when it is used and the ADRs
Cyclizine
Acute nausea or vomiting
Prolongs QT interval and crosses blood brain barrier so can be sedative
What are the 4 types of laxatives? Give an example for each
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
How do bulk laxatives work?
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
What is the main ADR of bulk laxatives?
Flactulance
When should bulk laxatives not be used?
Adhesions and ulcerations
How do stool softners work? When are they indicated?
Lubricate and soften stool. Simple constipation as with bulk laxatives but can be used in adhesions, for anal fissures and haemorrhoids
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)
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
What caution is there with osmotic laxatives?
Prevent obstruction
How do stimulant laxatives work? When are they used?
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.
What 3 types of drugs can be used to treat diarrhoea?
Anti motility
Bulk forming
Fluid absorbents
What type of laxative would you use for soft faeces?
Stimulant
What laxative would you use for hard faeces?
Osmotic, bulk forming
How do anti motility drugs work, when are they used and where should they be avoided?
Opioid analogue that acts on receptors in the bowel to reduce bowel motility and increase anal tone
Chronic diarrhoea
IBD as risks toxic megacolon
How do bulk forming agents work for diarrhoea, when are they used?
Increase water absorption, useful for patients with IBS and ileostomy
Name a fluid absorbent
Kaolin
