7. Diarrhoea and constipation Flashcards
What is the pathophysiology of diarrhoea?
Unwanted substance in gut stimulates secretion and motility to get rid of it
Primarily down to epithelial function rather than increase gut motility
Colon is overwhelmed and cannot absorb the quantity of water it received from the ileum
What is osmotic diarrhoea?
Water is drawn into the gut by molecules in lumen of high osmotic pressure
Could be from malabsorption
Diarrhoea stops when fasting
Moderately increased volume
What is secretory diarrhoea?
When water is actively secreted into lumen of gut
Large volume of stool
Diarrhoea continues after fasting
How does secretory diarrhoea happen?
Too much secretion of ions (net secretion of chloride or bicarbonate) - through cystic fibrosis transmembrane conductance regulator (CFTR)
Cause of diarrhoea will affect the messenger systems that control ion transport e.g. infectious toxins
Give an example of osmotic diarrhoea and how it works
Lactose
Lactase expressed as brush border enzyme - not enough lactase, locator remains in gut
Lactose draws water into lumen
Lactose then ferments in large intestine, produces gases and bloating
How does too little absorption of sodium cause osmotic diarrhoea?
Sodium stays in gut lumen
Wherever sodium goes water follows, causes more water in gut therefore diarrhoea
Why can too little sodium be reabsorbed?
Reduced surface area for absorption
Mucosal disease/bowel resection - coeliac or IBD
Reduced contact time (intestinal rush) - diabetics
What are the risk factors for constipation?
Female vs male (3:1)
Certain medications
Low level of physical activity
Increasing age
What is the pathophysiology of constipation?
Normal transit constipation, often related to other psychological stressors
Slow colonic transport
Demarcation problems
What can cause slow colonic transport?
Large colon
Fewer peristaltic movements and shorter ones
Fewer intestinal pacemaker cells present
Systemic disorders (hypothyroidism, diabetes)
Nervous system disease (Parkinson’s, MS)
What can cause defaecation problems?
Cannot coordinate the muscles of defaecation/disorders of the pelvic floor or anorectum
What are the treatments for constipation?
Psychological support Increased fluid intake Increased activity Increased dietary fibre Fibre mediation Laxatives
What are the types of laxatives?
Osmotic (magnesium sulphate)
Stimulatory (chloride channel activators)
Stool softeners
