Distal GI tract pathology Flashcards
Define diarrhoea
- Loose or watery stools
- More than 3x per day
- Acute diarrhoea (less than 2 weeks)
What is the pathophysiology of diarrhoea?
- Unwanted substance in gut stimulates secretion and motility to get rid of it
- Epithelial cells secrete into gut
- Gut motility increases
- Colon is overwhelmed and cannot absorb the quantity of water it receives from ileum
How does increased gut motility lead to diarrhoea?
- Decreases contact time molecules in gut have with epithelial surface and decrease absorption
What are the 2 categories of diarrhoea?
- Osmotic
- Secretory
How does water get drawn into the gut?
- Follows osmotic forces generated by the movement of electrolytes/nutrients
- Paracellular/transcellular
Describe osmotic diarrhoea
- Moderately increased stool volume
- Diarrhoea stops on fasting
- Normal to increased stool osmolality
Describe secretory diarrhoea
- Very large stool volume
- Diarrhoea continues on fasting
- Normal stool osmolality
Outline the broad causes of secretory diarrhoea
- Too much secretion of ions (net secretion of Cl- or HCO3-)
- Cause of diarrhoea will affect the messenger systems that control ion transport
- E.g. infectious toxins
Outline the molecular mechanism behind secretory diarrhoea
- Toxins increase cyclic AMP
- CFTR channel affected
- More Cl- pumped out
- Na+ follows Cl-
- Water follows Na+ into gut lumen
Outline the broad causes of osmotic diarrhoea
- Gut lumen contains too much osmotic material (malabsorption)
- Will settle if you stop consuming offending substance
What kind of osmotic material could cause diarrhoea?
- Ingesting material that is poorly absorbed (antacids e.g. magnesium sulphate)
- Inability to absorb nutrients (e.g. lactose in lactase deficiency)
What are other causes of diarrhoea?
Too little absorption of sodium so not enough water is reabsorbed. Caused by:
- Reduced surface area for absorption
- Mucosal disease/bowel resection (e.g. in coeliac or IBD)
- Reduced contact time (intestinal rush)
Define constipation
- Suggestive if hard stools, difficulty passing stools or inability to pass stools
What is classed as constipation?
- Straining during >25% of defecations
- Lumpy or hard stools in >25% of defecations
- Feeling of incomplete evacuation in >25% of stools
-Feeling of obstruction or blockage to defecation in >25% of defecations - Having fewer than 3 unassisted bowel movements a week
What are the risk factors for constipation?
- Female vs male (3:1)
- Certain medications (opioids, anti-diarrhoeal)
- Low level of physical activity
- Increasing age
- Also common in children under 4 years of age
What is the pathophysiology of constipation?
- Normal transit constipation due to other psychological stressors
- Slow colonic transport - more contact time, so more water is reabsorbed
- Defaecation problems - cannot coordinate muscles of defaecation /disorders of pelvic floor or anorectum
What are some causes of slow colonic transport?
- Large colon/megacolon (lower pressure in colon so harder to move stool)
- Fewer peristaltic movements/shorter peristaltic movements
- Fewer intestinal pacemaker cells present
- Systemic disorders (diabetes, hypothyroidism)
- Nervous system disease (Parkinson’s, MS)
What are the treatments for constipation?
- Psychological support
- Increased fluid intake
- Increased activity
- Increased dietary fibre
- Fibre medication
- Laxatives
What are the different types of laxatives?
- Osmotic (magnesium sulphate, disaccharides) - draw water into gut
- Stimulatory (chloride channel activators)
- Stool softeners
