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