Question

Why would continuously open enterocyte CFTR channels cause secretory diarrhea and dehydration in humans?

Which type of IV solution would you select for Anish, and why? Your choices are normal (isotonic) saline, half-normal saline, and 5% dextrose in water (D-5-W).

Answer 1

CFTR

*Cystic fibrosis transmembrane conductance regulator .
*Mutation in this channel is responsible for Cystic fibrosis .
*The apical or luminal membrane of crypt epithelial cells of small intestine contain a ion channel - a cyclic AMP dependent chloride channel known as CFTR .This CFTR is responsible for secretion of water into intestinal lumen

*First step is Chloride ions enter the crypt epithelial cell by cotransport with sodium and potassium also sodium is pumped back out via sodium pumps, and potassium is pushed inside cells via a number of channels.

*Activation of adenylyl cyclase by a number of secretagogues increasing secretion leads to generation of cyclic AMP.

*Elevated intracellular concentrations of cAMP in crypt cells activate the CFTR, resulting in secretion of chloride ions into the lumen.

*Accumulation of negatively-charged Cl- chloride anions in the crypt attracts sodium as electric potential is created and pulling it into the lumen, the net result is secretion of NaCl.

*Secretion of NaCl into the crypt creates an osmotic gradient across the tight junction and water is drawn into the lumen.

*.Excess water is withdrawn into lumen os because of osmotic gradient that is created by Cl- Na + transport into lumen and dragging water along with leads to secretory diarrhea. If episodes are diarrhea are more it may result in severe dehydration.

****Normal saline is used
Intravenous fluids used to treat dehydration. Normal saline contains sodium and chloride, both 154 meq / Litre so it replaces lost fluid and prevents and   corrects electrolyte imbalances along with correction of dehydration ..