Describe the process by which gut epithelial cells use transporters to take up ingested glucose (against the concentration gradient) and to distribute glucose to other tissues by moving it back out of the cell (down the concentration gradient)
What will be an ideal response?
Gut epithelial cells use two different transporters to take glucose up from the gut and distribute it into the bloodstream and to other tissues. These transporters are located at opposite sides of the cell: the apical side of the cell (which faces the gut) contains a Na+-glucose symporter. This symporter couples the entry of Na+down its electrochemical gradient to the active import of glucose against its concentration gradient. The Na+-glucose symporter is restricted to the apical side of the cell by tight-junction complexes in the plasma membrane, which link neighboring epithelial cells together. On the basolateral side of the cell, there is another transporter that facilitates movement of glucose down its concentration gradient, out of the cell. This transporter is a uniporter that only transports glucose in one direction: from the cytosol to the extracellular matrix. The location of this uniporter is also restricted by the presence of the tight junctions, so that the epithelial cell will not transport glucose back into the lumen of the gut.
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