CSI 7 - Diarrhoea Flashcards
What is diarrhoea defined as?
The passage of:
- three or more loose or liquid stools per 24 hours and/or
- stools that are more frequent than what is normal for the individual lasting <14 days and/or
- stool weight greater than 200g/day
How would you classify diarrhoea based on duration? (3)
- acute (</=14 days)
- persistent (>14 days)
- chronic (>4 weeks)
Describe the normal basic pathophysiology of fluid digestion.
- normally approximately 10L of fluid consisting of ingested food and drink, in addition to secretions from the salivary glands, stomach, pancreas, bile ducts, and duodenum, enters the GI tract every day
- the small intestine is the major site for reabsorption
- overall about 99% of the fluid is reabsorbed, leaving 0.1L to be excreted in the faeces
What are the three main pathologies underlying diarrhoea in general?
- decreased absorption of fluid
- increased secretion of fluid and electrolytes
- increase in bowel motility
What is the pathophysiological classification of diarrhoea?
- inflammatory diarrhoea
- non-inflammatory diarrhoea:
- secretory diarrhoea
- osmotic diarrhoea –> maldigestion and malabsorption
What are the three types of infection that inflammatory diarrhoea can be due to?
- bacterial
- viral (children attending day care)
- parasitic (and protozoal - developing countries)
In what conditions can inflammatory diarrhoea present early in? (3)
- bowel ischaemia
- radiation injury
- inflammatory bowel disease
How would you describe the stool of inflammatory diarrhoea?
Mucoid and bloody stool
What are some symptoms of inflammatory diarrhoea? (3)
- tenesmus (urge to poop but cannot actually go)
- fever
- severe crampy abdominal pain
Describe the volume and frequency of bowel movements in inflammatory diarrhoea, and therefore does it result in volume depletion?
- small in volume
- frequent bowel movements
- therefore it does not usually result in volume depletion in adults, but may do so in children or older adults (dehydration)
What are the common causes of inflammatory diarrhoea (5)
Bacterial infection most common cause:
- Campylobacter (mainly)
- Salmonella
- Shigella
- Escherichia coli
- Clostridium difficile
What would you see on stool examination in inflammatory diarrhoea?
Leukocytes in the stool - test for faecal leukocytes is plagued by a high rate of false-negative results leading to low sensitivity, but a positive test is very informative
Would a faecal occult blood be positive in inflammatory diarrhoea?
Maybe - used to check stool samples for hidden (occult) blood which may indicate colon cancer or polyps (but not all bleed)
What is histology of the GI tract like in inflammatory diarrhoea?
Abnormal
Describe the volume and frequency of stool in non-inflammatory diarrhoea, and therefore is volume depletion possible?
- watery, large-volume, frequent stool (>10-20 per day)
- thus volume depletion is possible due to high volume and frequency of bowel movements
Is there tenesmus, blood in the stool, fever or faecal leukocytes in non-inflammatory diarrhoea?
No
Is the GI architecture preserved in non-inflammatory diarrhoea?
Yes
What is the pathophysiology of secretory diarrhoea?
Altered transport of ions across the mucosa, which results in increased secretion and decreased absorption of fluids and electrolytes from the GI tract, especially in the small intestine
Would secretory diarrhoea decrease by fasting?
No because there is decreased absorption of ions alongside continuous secretion of ions, so fasting would still mean secretion occurs
How do enterotoxins cause secretory diarrhoea?
Increased Cl- permeability leads to leakage into the lumen, followed by Na+ and H2O movenent
Give examples of enterotoxins that can cause secretory diarrhoea.
- from infection e.g. Vibrio cholera, S. aureus, enterotoxigenic E. coli
- possibly HIV and rotavirus
Give examples of hormonal agents that can cause secretory diarrhoea. (3)
- vaso-active intestinal peptide (prevents Na+, Cl-, H2O absorption)
- small-cell cancer of the lung
- neuroblastoma (secretes VIP)
What are some other causes of secretory diarrhoea? (4)
- laxative use (water drawn into gut)
- intestinal resection
- bile salts (more water and salt into large bowel from bloodstream)
- fatty acids
What other conditions is secretory diarrhoea seen in? (4)
- chronic diarrhoea with coeliac sprue
- collagenous colitis
- hyperthyroidism
- carcinoid tumours
How would you describe the stool volume in osmotic diarrhoea compared to that in secretory diarrhoea?
Stool volume is relatively small
Does osmotic diarrhoea improve with fasting?
Yes
What is the pathophysiology of osmotic diarrhoea?
Results form the presence of unabsorbed or poorly absorbed solute (Mg, sorbitol and mannitol) in the intestinal tract that causes an increased secretion of liquids into the gut lumen
What does measuring stool electrolytes in osmotic diarrhoea show?
- increased osmotic gap (>50) but the test has very limited practical value
- stool (normal or diarrhoea) is always isosmotic (260-290 mOsm/L) —> stool osmolarity = serum osmolarity
- to calculate: 290mOsm/kg - 2x[Na+K]
- secretory diarrhoea: <50mOsm/kg
- osmotic diarrhoea: >100mOsm/kg
What is maldigestion (osmotic diarrhoea)?
- refers to impaired digestion of nutrients within the intestinal lumen or at the brush border membrane of mucosal epithelial cells
- can be seen in pancreatic exocrine insufficiency and lactase deficiency
What is malabsorption (osmotic diarrhoea)?
- refers to impaired absorption of nutrients
- can be seen in small bowel bacterial overgrowth, mesenteric ischaemia, post bowel resection (short bowel syndrome) and mucosal disease (Coeliac disease)
What happens in inflammatory diarrhoea?
- inflammation affects enterocytes
- reduced paracellular pathways (reduced space) + reduced transport
- reduced water absorption
- {activation of WBCs —> secrete inflammatory mediators and cytokines —> stimulate secretion of fluids by gut into lumen (worsens inflammatory diarrhoea)}
- {ROS from leukocytes —> damage intestinal epithelial cells —> replaced with immature cells that typically are deficient in the brush border enzymes and transporters necessary for absorption of nutrients and water [hence, components of osmotic diarrhoea adds to the dilemma]}
What happens in secretory diarrhoea?
- caused by toxins e.g. cholera and some laxatives
- excessive activation of Cl- channels on lumen
- increased Cl- secretion, therefore increased Na+ secretion (paracellular transport) and H2O secretion (due to osmotic gradient)
- body cannot reabsorb this excess H2O
- (e.g. in cholera, toxin strongly activates adenylate cyclase —> prolonged increase of cyclic AMP within crypt enterocytes —> prolonged opening of CHLORIDE channels)
- (increased secretion of water from crypts)
- (cholera toxin affects theenteric nervous system, resulting in further independent stimulus of secretion)
