Diarrhoea Flashcards
The surface of the small intestine is increased by what?
- increased by presence of villi
Where are villi longest and where are they shortest?
- longer in the jejunum
- shorter but more numerous in the ileum
Villus tips die and shed where and after how many days?
- villus tips die and shed into lumen
- after 3-5 days
What are crypts?
- cells formed by miotic division
What develops the brush border enzymes and carrier proteins?
- cells that migrate from the crypts to villus tips develop these absorptive and surface digestive capacities
By how much do villi increase surface area for absorption?
- 10 fold
By how much do microvilli increase surface area for absorption?
- 20 fold
What is the total fold increase in surface area for absorption?
- 200 fold
What are the brush border enzymes?
- carbohydrates and proteins
Where are brush border enzymes found and what process are they involved in?
- brush border enzymes are found on mature enterocytes
- are involved in final digestion to monosaccharides, amino acids and peptides
The final absorption end products of brush border digestion are dependant on what?
- absorption of end products is ATP dependant
What happens is mature enterocytes are destroyed?
- the final digestion process is hampered
How are monoglycerides and free fatty acids up taken?
and
How is this process hampered?
- by diffusion across villi into the lymph lacteals
- processes that increase the width of the villi hamper this process
What is the total secretion (to lumen) in ml?
- 2700 ml
What is the total absorption (to the blood) in ml?
- 2665 ml
- 98%
How much secretion is lost in faecal water?
- 35 ml
What equation can be used to work out normal fluid intake for a dog?
- 50ml/kg/24hrs
Villous tips contain mature enterocytes - what are these?
- absorptive cells with tight intracellular junctions
Within villous tip ….
What do enterocytes do?
What happens to the sodium?
What does this process result in?
- absorb sodium, glucose and amino acids across the brush border on the apical surface
- sodium is pumped out of the cell on the basolateral aspect
- results in net absorption of fluid (water follows sodium)
The crypt base contains what cell?
- stem cells
What are the stem cells in the crypt base?
Within the crypt base what do the stem cells do?
What does this process result in?
- stem cells = secreting cells with leaky intercellular junctions
- allow sodium to leak back into the intestinal lumen
- this results in net secretion of fluid
In a normal animal what happens to the net absorption in the SI?
- The net absorption at the villus tips is larger to net secretions in crypts
What happens to fluid dynamics in the SI if there is diarrhoea?
- either decreased absorption and or increased secretion
What does diarrhoea do to volume and fluid content of faeces?
- increases both
What is diarrhoea is common clinical sign of?
- disease affecting the intestinal tract
Pathogenesis of diarrhoea - what are the 4 basic mechanisms?
- altered epithelial cell transport = secretory diarrhoea
- altered structure or permeability of mucosa
- osmotic effects
- altered motility
What is altered epithelial cell transport?
- secretory diarrhoea
Secretory diarrhoea:
What are involved in intestinal fluid absorption and secretion by enterocytes?
- luminal and basolateral membrane transporters
- intracellular signally mechanisms
Secretory Diarrhoea:
What are the electrochemical driving force for this process?
- the basolateral Na+/K+-ATPase
Secretory Diarrhoea:
The movement of fluid between the intestinal lumen and blood is driven by what?
- the active transport of ions, mainly Na+, Cl -, HCO3-, and K+, and solutes, mainly glucose
Secretory Diarrhoea:
Fluid absorption or secretion involves the coordinated activity of what?
and where are they located?
- coordinated activity of membrane transported
- located on the apical (lumen facing) and basolateral (circulation-facing) epithelial membranes
Secretory Diarrhoea:
Some bacteria secrete enterotoxins that increase what?
What does this result in?
- increase intracellular cyclic nucleotides
- resulting in Cl - secretion and inhibition of NHE3 and Na+ absorption
Secretory Diarrhoea:
Some bacteria such as E.coli attach to villous enterocytes and produce enterotoxins - what does this cause?
- cause a block of the activity of the sodium pump
Secretory Diarrhoea:
What does a block of the sodium pump result in?
- results in net loss of sodium into the intestinal lumen
Secretory Diarrhoea: - blocked sodium pump
water follows sodium - of there is a blocked pump what does this result in?
- results in massive fluid loss into the lumen of the intestine
What does secretory diarrhoea produce?
- produces a profuse, watery Diarrhoea
What type of condition is secretory diarrhoea and why?
- the condition is self-limiting as the mature villous epithelial cells are shed at the normal turnover rate after 3-5 days
Enterocytes play a key role in the absorption and terminal digestion of nutrients and this function is reliant on what?
- reliant in healthy enterocytes
What accounts for the majority of cases of diarrhoea?
- damage to enterocytes/mucosa
How do bacterial infections cause diarrhoea?
- some bacteria produce toxins (cytotoxins) that damage and kill cells
- death to enterocytes allows blood, fluid, protein and other contents of the villus core to leak into the intestinal lumen
- the villus will no longer be absorptive as mature enterocytes have been lost
- there is clearly altered structure and altered permeability with loss of normal function
- the appearance of blood and shreds if the intestinal tissue in the diarrhoea
What is dysentery?
- the appearance of blood and shreds of intestinal tissue in the diarrhoea
What happens during haemorrhagic enteritis?
- lost of enterocytes at the apex
- large number of bacterial colonies on luminal surface and within the lumen
- haemorrhage into the lumen is associated with the loss of epithelial cells
- much more severe diarrhoea
Other pathologies can cause loss of normal structure - e.g., a massive increase in cellularity of the villus core will cause what?
- cause the width of the villus to increase and the height of the villus to decrease
= there aren’t enough epithelial cells to cover a tall fat villus
What does increased cellularity lead to within the intestines?
- this results in a decreased SA for absorption of nutrients leading to malabsorption
What happens if there is persistent unabsorbed nutrients within the lumen of the intestine?
- leads to an altered osmotic gradient and the overgrowth of bacteria
What happens of epithelial cells have to stretch to cover the altered villus?
- they flatten and lose their brush border
- loss of SA and enzymes of final stages of digestion
= lack of nutrients absorption
= diarrhoea
Causes of cellular infiltration can be varied what can they include?
- neoplasia
- chronic inflammation
- infection
intestinal lymphoma can lead to a cobblestone gut - what is this?
- intestine had been infiltrated by neoplastic lymphoid cells and associated with marked and corrugations
What happens as a result of intestinal lymphoma?
- distortion of villi due to infiltration by neoplastic lymphocytes
- loss of structure leading to loss of function
How does intestinal lymphoma occur?
- massive number of neoplastic lymphoid cells infiltrating the mucosa and submucosa increased widening and shortening of the villus leads to a decreased SA for absorption
What can intestinal lymphoma cause?
= malabsorption
= severe diarrhoea
What is lymphocytic enteropathy?
- chronic inflammation as a cause of cellular infiltration into villi
What is IBD syndrome?
- very commonly recognised in dogs and cats
- inappropriate inflammatory reaction to commensal bacteria or dietary antigens
What does infiltration of macrophages within the villus lead to?
- shortening and widening of the villi reducing the ability for absorption due to decrease in SA
Different virusues can do what to the villi in different species?
- attack villi in different regions
- Where does TGE attack the villi?
- where does parvovirus attack the villi
- the tips
- the crypts
TGE in piglets is a corona virus what does it do?
- villi = shorter as enterocytes have been destroyed by virus
What can be used to indicate the location of the infection of TGE in piglets?
- immunostaining with antibiosis specific for the virus
What is feline infectious enteritis cause by?
- parvovirus
What does feline infectious enteritis cause?
- reddish brown discolouration of the mucosa
- increased fluid content and much more serve diarrhoea
If the crypts are destroyed what happens?
- villi are unable to regenerate due to cells in the crypts being destroyed
What leads to secondary bacterial infections in the intestines?
- bacterial overgrowth sitting in the lumen
What does osmotic diarrhoea result from?
- from the presence of osmotically active, poorly absorbed solutes in the bowel lumen that inhibit normal water and electrolyte absorption
Osmotic Diarrhoea:
What does a lack of specific brush border enzymes result in?
- the accumulation of small osmotic solutes in the intestinal lumen, drawing water from the bloodstream into the intestine
What are most laxatives designed to induce?
- induce mild osmotic diarrhoea
Osmotic diarrhoea:
An increased osmotic load can b measure in what?
- stool
How can osmotic diarrhoea be ceased?
- with fasting
What di mammals normally lose the ability to digest?
- lose the ability to digest lactose after weaning and there has been a recent evolution of lactase persistence in humans
Diarrhoea of altered motility:
There may not be alterations to the intestinal structure but there can be alterations to function what are these?
- disruption/disorganisation/reduced co-ordination of segmental movements of intestine
Diarrhoea of altered motility:
What is hypermotility?
- this increases the transit time which therefore reduced the time for digestion and absorption.
Diarrhoea of altered motility:
What does hypermotility cause and result in?
- causes include infection and parasitic disease
- results in the overgrowth of bacteria and therefore osmotic draw of fluid into the lumen
Diarrhoea of altered motility:
What is hypomotility?
- decrease intestinal transit time enables the overgrowth of bacteria in the intestinal lumen due to stasis of the intestinal contents
Diarrhoea of altered motility:
What can cause hypomotility?
- recent abdominal surgery
- post op ileus or stasis
Diarrhoea of altered motility:
What is a risk related to hypomotility?
What does this increase?
- risk of increased microbial load due to the increased nutrient source for them in the more static intestine and bacterial load not kept at lower levels by their expulsion in faeces
- this increased bacterial load can lead to secondary causes if diarrhoea
What does SI diarrhoea lead to?
- enteritis due to problems in the duodenum, jejunum or ileum
- may also be related to the pancreas
What does LI diarrhoea cause?
- colitis = due to problems in the colon
What does mixed intestine diarrhoea involve?
- both SI and LI
What does SI diarrhoea look like?
- watery
- large volume
- not usually urgent
- light coloured
- soupy or greasy
- not bloody
What does LI diarrhoea look like?
- mucoid
- small volume but frequent
- often urgent
- darker colour
- jellylike
- often blood
