Distal GI tract pathology

Question 1

Define diarrhoea

Answer 1

• Loose or watery stools
• More than 3x per day
• Acute diarrhoea (less than 2 weeks)

Question 2

What is the pathophysiology of diarrhoea?

Answer 2

• 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

Question 3

How does increased gut motility lead to diarrhoea?

Answer 3

• Decreases contact time molecules in gut have with epithelial surface and decrease absorption

Question 4

What are the 2 categories of diarrhoea?

Answer 4

• Osmotic
• Secretory

Question 5

How does water get drawn into the gut?

Answer 5

• Follows osmotic forces generated by the movement of electrolytes/nutrients
• Paracellular/transcellular

Question 6

Describe osmotic diarrhoea

Answer 6

• Moderately increased stool volume
• Diarrhoea stops on fasting
• Normal to increased stool osmolality

Question 7

Describe secretory diarrhoea

Answer 7

• Very large stool volume
• Diarrhoea continues on fasting
• Normal stool osmolality

Question 8

Outline the broad causes of secretory diarrhoea

Answer 8

• 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

Question 9

Outline the molecular mechanism behind secretory diarrhoea

Answer 9

• Toxins increase cyclic AMP
• CFTR channel affected
• More Cl- pumped out
• Na+ follows Cl-
• Water follows Na+ into gut lumen

Question 10

Outline the broad causes of osmotic diarrhoea

Answer 10

• Gut lumen contains too much osmotic material (malabsorption)
• Will settle if you stop consuming offending substance

Question 11

What kind of osmotic material could cause diarrhoea?

Answer 11

• Ingesting material that is poorly absorbed (antacids e.g. magnesium sulphate)
• Inability to absorb nutrients (e.g. lactose in lactase deficiency)

Question 12

What are other causes of diarrhoea?

Answer 12

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)

Question 13

Define constipation

Answer 13

• Suggestive if hard stools, difficulty passing stools or inability to pass stools

Question 14

What is classed as constipation?

Answer 14

• 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

Question 15

What are the risk factors for constipation?

Answer 15

• 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

Question 16

What is the pathophysiology of constipation?

Answer 16

• 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

Question 17

What are some causes of slow colonic transport?

Answer 17

• 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)

Question 18

What are the treatments for constipation?

Answer 18

• Psychological support
• Increased fluid intake
• Increased activity
• Increased dietary fibre
• Fibre medication
• Laxatives

Question 19

What are the different types of laxatives?

Answer 19

• Osmotic (magnesium sulphate, disaccharides) - draw water into gut
• Stimulatory (chloride channel activators)
• Stool softeners