Functional and infective pathology of the lower GI tract: diarrhoea and constipation Flashcards
According to the NICE guidelines, what is the definition of diarrhoea?
- abnormal passage of loose or liquid stools
According to the NICE guidelines, what is the definition of acute diarrhoea?
- >3 times/day daily and/or a volume of stool greater than 200g/day
- <14 days in duration
According to the NICE guidelines, what is the definition of chronic diarrhoea?
- >3 times/day daily and/or a volume of stool greater than 200g/day
- >4 weeks in duration
How common is chronic diarrhoea in the UK, and is it more common on young or elderly?
- 7% prevalence in UK
- 14% prevelence in elderly
If a patient has chronic diarrhoea (>4 weeks) what does this generally suggest?
- pathology is present
- investigations my be required
What is the most common cause of acute diarrhoea?
- viral infections
- norovirus, rotavirus
Following viral infections as the most common cause of diarrhoea, what is the second most common cause of diarrhoea?
- bacterial infections
- Salmonella, Campylobacter, Clostridium difficile, cholera
In addition to viral and bacterial infections, what else that is nasty can cause acute diarrhoea?
- parasites
In addition to viral, bacterial and parasitic infections, what is the next major cuase of acute diarrhoea?
- medications
- antibiotics, metformin and meprazole are common
What must all chronic pathology causing diarrhoea start out as?
- acute pathology
At a very basic level what causes infections and medications to cause diarrhoea?
- increased secretion or decreased absorption of fluids and electrolytes
The cystic fibrosis transmembrane conductance regulator (CFTR) can be affected in infections such as cholera. How does cholera/Salmonella cause diarrhoea?
- increase cAMP and protein kinase A
- efflux of ATP mediated Cl- into lumen
- Na+ moves down electro charged gradient paracellularly
- K+ and H2O will follow

The sodium–glucose cotransporters (SGLTs) in the GIT are responsible for glucose absorption. If pathology is present what can this cause to SGLTs?
- SGLTs do not function causing Na+ and glucose not to be absorbed and remain in the lumen
- H2O moves into the lumen due to osmosis
Diarrhoea can have a direct effect on the bowel. What does a direct effect relate to?
- cell death leading to loss of absorptive area
- inflammation causing fluid to be extruded into the bowel
Diarrhoea can have an indirect effect on the bowel. An indirect effect relates to the toxins that are secreted by pathogens. What are they able to mimic and what can this cause?
- endogenous cell signalling
- able to act on ion channels
Diarrhoea can have an indirect effect on the bowel. An indirect effect relates to the toxins that are secreted by pathogens. What can these toxins do the epithelial cells of the GIT that can cause leakage into the GIT?
- form pores in the cell membrane
- increase the permeability of tight junctions
Diarrhoea can have an indirect effect on the bowel. An indirect effect relates to the toxins that are secreted by pathogens. What can some toxins become that can trigger diarrhoea?
- can be cytotoxic or pro-inflammatory
- both can cause fluid increase into GIT
In addition to pathogens causing diarrhoea, medications are able to induce diarrhoea. What % of adverse effects of drugs are diarrhoeal and roughly how many different drugs can cause diarrhoea?
- 7%
- >700 drugs
In addition to pathogens causing diarrhoea, medications are able to induce diarrhoea. What % of drugs are antimicrobials (kills bacteria?
- 25%
There are a number of mechanisms in which drugs are able to cause diarrhoea. What are osmotically active drugs?
- drug is poorley digested and absorbed
- H2O is pumped into lumen to reduce drug concentration through osmosis
There are a number of mechanisms in which drugs are able to cause diarrhoea. How can drugs cause secretory changes which affect on ion absorption and cause diarrhoea?
- alter ion secretion
- ions are pumped into GIT like Cl- and Na+
- H2O follows due to osmosis
There are a number of mechanisms in which drugs are able to cause diarrhoea. How can drugs cause changes in bowel times?
- laxatives speed up bowel movements
- H2O and electrolytes cannot therefore be absorbed
There are a number of mechanisms in which drugs are able to cause diarrhoea. How can drugs cause malabsorption of macronutrients such as carbohydrates and fat, that ultimately lead to diarrhoea?
- fat and carbohydrates are not digested
- H2O is pumped into lumen due to osmosis
In a patient who presents with acute diarrhoea (>3 loose bowel movements/day for <14 days), do you generally need to doing any investigations?
- no






