Gut Motility Flashcards
What is the myogenic control of gut motility?
- Rhythmic contraction – slow waves of depolarisation in smooth muscle
- Current spreads passively – gap junctions
- Interstitial cells of Cajal act as pacemaker cells
How is gut motility controlled by the nervous system?
- Parasympathetic input via post ganglionic enteric nerves increases force of contraction
- Noradrenergic from the sympathetic nervous system inhibits contraction
- There is a complex neuronal network
What are GI hormones? and functions?
Gastrin - promotes acid secretion by parietal cells
Secretin (duodenum) - inhibits gastric acid production
Cholecyteokinin (duodenum) - stimulates pancreatic secretion
Motilin (duodenum and jejunum) - affects GI motility and increases gastric emptying
Paracrine (histamine, somatostatin, prostaglandin)
Describe gut motility in the fed and fasted states.
Fed: a few hours of irregular contractions to mix and propel food
Fasted: every ninety minutes high intensity “housekeeping” contractions – clear residual food and secretions
What drugs cause constipation?
• Opioids • Verapamil • Iron supplements • Indapamide (thiazide) • Calcium • Antipsychotics - clozapine, quetiapine • Antidepressants - TCAs, SSRIs • Aluminium antacids Anticholinergics
What are the different types of laxatives?
Bulk - fybogel
Faecal softeners - glycerol suppository
Osmotic - Lactulose, macrogols, phosphate enemas
Irritant/stimulatns - castor oil, senna, sodium picosulfate
Describe Indication, MOA, ADR CI of bulk laxatives
o Insoluble, inabsorbable – osmotic draw distends gut and stimulates contraction
o Take a few days to work, use to re-establish normal bowel habit, need to maintain fluid intake
o ADR: flatulence, contraindicated in adhesions and ulceration as may cause obstruction
CI: bowel obstruction
Use in IBS and pregnancy
Describe Indication, MOA, ADR CI of faecal softeners?
o Glycerol
o Lubricate and soften stool – safe but not always effective
o Can give in adhesions as they don’t risk obstruction, can give with anal fissures and haemorrhoids
Describe Indication, MOA, ADR CI of faecal softeners?
o Glycerol
o Lubricate and soften stool – safe but not always effective
o Can give in adhesions as they don’t risk obstruction, can give with anal fissures and haemorrhoids
Use in IBS, pregnancy, bowel obstruction, haemorrhoids
Describe Indication, MOA, ADR CI of lactulose?
- Cannot be hydrolysed by digestive enzymes so instead is fermented by colonic bacteria to acetic and lactic acid, have an osmotic effect
- Take orally
- Takes 48 hours to work
- Use in liver failure to reduce bacterial production of ammonia
Describe Indication, MOA, ADR CI of macrogols?
- Movicol (polyethylene glycol)
- Given as a powder – prevents dehydration, acts within hours but takes days to get full effect
- Need to take care with intestinal obstruction
Describe Indication, MOA, ADR CI of phosphate enemas (magnesium and sodium salts)?
- Water retention in small + large bowel, increase peristalsis
- Act quickly and are severe
- Give PR
- Use in resistant constipation or if urgent relief needed.
Describe Indication, MOA, ADR CI of irritants/stimulants?
Excite sensory nerve endings, leads to water and electrolyte retention and so causes peristalsis.
Used for rapid treatment (impaction or surgical prep) takes 6-8 hours so give at bedtime.
ADR
Repeated use can cause colonic atony (constipation) and hypokalaemia
What should you use for soft faces? Hard faeces?
If faeces are soft give stimulant laxatives – Senna, glycerol (softener), if hard faeces give osmotic laxatives (movicol) or bulk forming (ispaghula – fybogel)
What should you be aware of in constipation?
Potassium levels - hypokalaemia
You lose potassium enterally, and this causes hypokalaemia, which again causes constipation through bowel inertia, and so you give laxatives, so you lose more potassium.
Dehydration due to laxatives means you also lose potassium renally due to aldosterone secretion.
