Enterocytes!!!

[peacefulheart]

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In EK book, it says"In all cells except enterocytes and the cells of the renal tubule, glucose is transported from high concentration to low concentration via facilitated diffusion."

Does this mean the apical side ( lumen side )of enterocytes has higher concentration than inside of enterocytes( cells of brush border cells in small intestine)?

thanks a lot?

 

[contraband]

The concentration of glucose inside the cell is higher than the concentration in the lumen of the gut. This means that it's impossible for glucose to be transported inside the cell by facilitated diffusion, since any type of diffusion just uses the existing gradient. In order to get the glucose to move against its gradient, it's necessary to use active transport (in this case, sodium-glucose co-transporter; sodium moves down its gradient into the cell, which has a negative deltaG, which makes up for the smaller positive deltaG of moving the glucose against its gradient).

Does that answer your question?

 

[peacefulheart]

Thanks a lot for the good explanation. What about protein? Does protein has lower concentration in the lumen of intestine than enterocytes ?


thanks a lot

 

[contraband]

Remember that digestive enzymes in the gut (such as trypsin, pepsin, chymotrypsin, etc) digest proteins into amino acids and very small peptides. Amino acids have a similar mechanism of uptake to glucose (sodium cotransporter) and very small (less than 4 AA) peptides use an H+ cotransporter. This makes sense, since like glucose, we want to uptake as much of the AA in our gut as possible, even if the concentration inside the cell is higher than in the gut lumen.

 

[peacefulheart]

thanks a lot for the explanation.