Q- A 58-year-old woman is brought to the emergency room complaining of lightheadedness for 4 hours. She has diarrhea with loose stool for 2 days. She explains her symptoms as the flu, and she drinks lots of water as her neighbor advised her to avoid dehydration. Her physician told her that she should take a combined solution of sodium chloride (NaCl) and glucose to prevent dehydration.
What is the mechanism of action of this mixture to improve dehydration?
A- It reduces bowel contractions and consequently improves diarrhea
B- Glucose provides energy for NaCl to increase gastric emptiness
C- The mixture helps to increase the secretion of water and Na through the large intestine
D- Cotransport of glucose and NaCl across the intestinal membrane facilitates the absorption of water and Na.
Answer and Explanation
The combined glucose–NaCl solution works through the sodium–glucose cotransporter (SGLT-1) in the small intestine.
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Glucose and sodium are absorbed together across the intestinal epithelium.
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This cotransport creates an osmotic gradient that pulls water along with sodium into the bloodstream.
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Importantly, this mechanism remains functional even during diarrhea, which is why oral rehydration therapy is effective.
Why the other options are incorrect:
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A: It does not reduce bowel contractions.
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B: Glucose does not provide energy to increase gastric emptying.
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C: The goal is absorption, not secretion, of water and sodium.
The correct answer is D
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