2.Water and electrolyte absorption and secretion in the gastrointestinal tract Flashcards
Surface of small intestine is amplified (folded) at 3 levels
- Folds of Kerchring
- Microvilli and crypts of Lieberkuhn
- Submicroscopic microvilli
Surface of Large intestine is amplified (folded) at 3 levels
- Semiluminar folds
- Crypts, but no villi
- Microvilli
Absorption of the _______nutrients occurs mainly in small intestine, whereas both the small and large intestine absorb _____ and ______
non-electrolyte
water and electrolytes (Na+, Cl-etc)
he small intestine absorbs net amounts of water, Na+, Cl-and K+and secretes ___
whereas the large intestine absorbs net amounts of water, Na+, Cl-and secretes both _________
HCO3-,
K+and HCO3-
Absorption of water entirely by osmosis, Coupled tosolute movement.
Occurs via _________ or _______ routes. ________ route is dominant
transcellular or paracellular routes
Paracellular
Absorption of water primarily in the?
jejunum
______ responsible for considerable Na+ and urea absorption in jejunum
‘Solvent drag’
Na+absorption occurs in
villus epithelial cells of the small intestine and surface epithelial cells of the large intestine
Na+absorption Maintains a low _______ Na concentration
intracellular
Na+absorption Provides force for Na movement from diffusion from _____ across_______
lumen across apical membrane•
______transport mediated by Na+ coupled transporters (e.g. Na/glucose transporters) or Na+ channels
Apical
Cl-absorption Closely linked to ?
Na+absorption
Cl-absorption Active generally involves ?
Cl-HCO3 transporter.
In voltage-dependent Cl-absorption, Cl-may passively diffuse from lumen to blood across the _____junctions, driven by the lumen-negative transepithelial voltage (paracellular route). Alternatively, Cl-may diffuse through?
tight
apical and basolateral Cl-channels.
, In the absence of a parallel Na-H exchanger, electroneutral Cl-HCO3 exchange at the apical membrane results in?
Cl-absorption and secretion.
In the absence of a parallel Na-H exchanger, electroneutral Cl-HCO3 exchange at the apical membrane results in?
Cl-absorption and secretion.
The small intestine is a net absorber of??
water
Na+
l-
K+
The small intestine is a net secreter of?
Bicarbonates.
The human colon carries out net absorption of water, Na, Cl but it carries out net secretion of??
K+ and Bicarbonates
Fluid movement is always coupled to
active solute movement
solute movement may be coupled to Fluid movement by?
Solvent drag
A phenomenon in which the dissolved solute is swept along by bulk movement of solvent (water)
diarrhoea
Dysfunction of fluid absorption in the gi
definition: >200g/day faeces
•Osmotic diarrhoea:
results from disturbances of absorption
•Secretory diarrhoea:
results from disturbances in secretion
diarrhoea Small intestinal origin results in
voluminous diarrhoea
diarrhoea large intestinal origin results in
small volume diarrhoea
Osmotic diarrhoea Generally caused by
macronutrients malabsorption retaining osmotic pressure in the lumen and therefore water is retained
Examples of Osmotic diarrhoea
pancreatic disease (proteases, lipase and amylase), large intakes of sugar alcohols such as sorbitol , fructose intolerance, lactose intolerance, coeliac disease
Lactose intolerance
- Lack of the enzyme lactase in adulthood
- 75% world population show some intolerance with 5% incidencerate in northern Europe to > 90% in part of Africa and Asia
Coeliac disease
- Also called non tropical spruce, or gluten enteropathy
- Autoimmune reaction to gluten
- Results in destruction of the epithelial cells and if sever blunting of the villi
- Nutrient malabsorption
Secretory diarrhoea.most common cause of this type of diarrhoea is
a exposure to the E. Coli or cholera toxin.
Enterotoxins produced by the bacterial microorganisms raise intracellular [cAMP], [cGMP] or [Ca+2]
Secretory diarrhoea. leads to stimulation of
Also congenital absence of?
anion secretion, especially Cl-. To maintain a charge balance in the lumen Na+ is carried with it, along with water
of Cl-HCO3exchanger
Secretory diarrhoea does not have an impact on __________________,
nutrient coupled Na absorption
ORS containing _________________is an effective treatment for secretory diarrhoea
glucose and Na+
