Describe the mechanism of sodium-coupled glucose absorption across the intestinal epithelium, and explain how phlorizin and ouabain inhibit this process.

Question

Accepted Answer

Glucose is transported into intestinal epithelial cells across the apical membrane via a sodium-glucose cotransporter (secondary active transport), coupling the movement of glucose against its concentration gradient to the movement of sodium down its electrochemical gradient. The intracellular-to-extracellular sodium gradient is maintained by the basolateral Na+/K+-ATPase pump using energy derived from ATP hydrolysis.

Inhibition occurs through two distinct targets:
1. Phlorizin directly blocks the apical sodium-glucose cotransporter (SGLT) by competitively binding to the transporter's glucose-binding site.
2. Ouabain inhibits the basolateral Na+/K+-ATPase pump, which abolishes the sodium gradient required to drive secondary active transport of glucose.. ### What a good answer covers
- A carrier binds sodium and glucose at distinct sites.
- Sodium-linked transport moves glucose into the cell.
- The sodium gradient is maintained by the sodium-potassium pump using energy from adenosine triphosphate hydrolysis.
- Ouabain and phlorhizin inhibit the described active transport process.

### Terms
- **Carrier**: A membrane protein that binds and transports specific substances.
- **Sodium-potassium pump**: A membrane transporter that uses energy to maintain ion gradients.
- **Ouabain**: A plant-derived inhibitor identified in the material.
- **Phlorhizin**: A plant glycoside identified as an inhibitor of glucose transport.

### Remember
Glucose uptake depends on the sodium gradient, which depends on pump activity.

Describe the mechanism of sodium-coupled glucose absorption across the intestinal epithelium, and explain how phlorizin and ouabain inhibit this process.

Explanation

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