Question

Oral rehydration solutions given to dehydrating patients, contains both glucose and sodium. The uptake of sodium is dependent on which one of the following cell transport mechanisms?

• A. Uniporter
• B. Antiporter
• C. Symporter
• D. Vesicular transporter

Hint:

Membrane Transporter Types:
Symporter = Transports 2 solutes in the SAME direction (e.g., SGLT-1 $\text{Na}^+$/glucose).
Antiporter = Opposite directions ($\text{Na}^+/\text{H}^+$ exchanger).
Uniporter = Single solute (GLUT).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Secondary active transport in the intestinal brush border couples the downhill electrochemical gradient of sodium to the uphill transport of glucose.
Key Formula or Approach:
\[ 2\text{Na}^+_{\text{extracellular}} + \text{Glucose}_{\text{luminal}} \xrightarrow{\text{SGLT-1 (Symporter)}} 2\text{Na}^+_{\text{cytosolic}} + \text{Glucose}_{\text{cytosolic}} \]

Step 2: Detailed Explanation:
In intestinal enterocytes:
- Oral Rehydration Therapy (ORT) works via the Sodium-Glucose Cotransporter 1 (SGLT-1), which is a Symporter (cotransporter) located on the apical brush border membrane.
- SGLT-1 transports $2\text{ Na}^+$ ions down their steep concentration gradient simultaneously with $1\text{ glucose}$ molecule in the same direction into the enterocyte. Water follows osmotically, rapidly reversing severe dehydration.

Step 3: Final Answer:
Thus, the uptake of sodium and glucose is mediated by a Symporter, corresponding to option (C).