Digestion in the small intestine Flashcards
which symporter does oral rehydration therapy target?
Na and glucose
how does oral rehydration therapy work?
sodium and glucose taken into cell –> osmotic gradient –> water drawn in by osmosis
How does sodium enter enterocytes?
via several mechanisms
sodium and hydrogen antiport
sodium and glucose symporter (cotransport with glucose and AAs)
why does Chloride enter enterocytes and why is HCO3 secreted into the lumen?
Cl enters to balance the NA influx
antiport with HCO3
HCO3 maintains luminal microclimate
how does water diffuse from the lumen?
osmotic gradient from sodium
mostly transcellular
some via cell-cell junctions
where is water secreted into the intestinal lumen?
base of crypts = younger secreting cells
mature absorptive cells at apex
why is water secreted?
to disperse the chyme
maximise contact with the epithelium
efficient enzymatic digestion
what establishes the osmotic gradient?
influx and digestion of foodstuffs increase the luminal osmotic pressure
active secretion of Cl from crypt cells
what is the role of the Na/K pump in Cl secretion?
Na removed from cell establishes a concentration gradient for NA to enter via Na/Cl/K symporter (2 active transport)
how does high calcium levels increase Cl secretion?
increased cAMP which opens more CFTR channels so more Cl exits cell
How is sodium secreted?
accumulation of Cl in lumen –> electrical potential –> Na goes through gap junctions
how does water exit via osmosis?
NaCl accumulation in lumen –> transepithelial osmotic gradient –> water moves by osmosis –> fluid secretion
what is malabsorption?
difficulty in digestion and absorption
why might malabsorption occur?
impaired digestion or impaired absorption
why might impaired digestion occur?
pancreatic insufficiency
lack of bile
lack on enzymes
