During oral rehydration therapy in diarrhoea, which transporter is most active in promoting fluid absorption?

INI-CET EXAM -2026

Applied Physiology

Medium

Appeared in: INI-CET EXAM -2026

Explanation

The fundamental principle of Oral Rehydration Therapy (ORT) is the coupled transport of sodium and glucose.
The Sodium-Glucose Linked Transporter 1 (SGLT1) is located on the apical surface of intestinal enterocytes.
SGLT1 simultaneously binds and transports sodium ions and glucose from the intestinal lumen into the cell.
This influx of solutes creates a powerful osmotic gradient, which drives the passive absorption of water from the gut into the body, thereby combating dehydration.
This transport mechanism remains intact even during severe secretory diarrheas like cholera, making it the target for ORT.

Option A: The CFTR (Cystic Fibrosis Transmembrane conductance Regulator) is a chloride channel. In many forms of secretory diarrhea (e.g., cholera), this channel is over-activated, leading to the secretion of chloride and water into the gut, which causes or worsens dehydration. It promotes fluid loss, not absorption.
Option B: The NHE (Sodium-Hydrogen Exchanger) does absorb sodium from the intestinal lumen. However, its capacity is limited, and it is not the primary mechanism leveraged by ORS. The glucose-coupled transport via SGLT1 is significantly more efficient for rapid fluid uptake during rehydration therapy.
Option D: The Na+-K+ ATPase pump is located on the basolateral (blood-facing) membrane of the intestinal cell, not the apical (lumen-facing) membrane. It does not directly absorb substances from the gut lumen. Its crucial role is to actively pump sodium out of the cell into the bloodstream, which maintains the low intracellular sodium concentration necessary for SGLT1 to function effectively.

Clinical Relevance

Nursing practice connection: Knowing Mechanism of Oral Rehydration Therapy and Intestinal Fluid Absorption helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding the SGLT1 mechanism is fundamental for nurses to appreciate why Oral Rehydration Solution (ORS) is not just salt water, but a precisely formulated life-saving intervention for managing diarrheal diseases, which are a major cause of mortality in children worldwide.
Nurses play a key role in educating caregivers on the correct preparation and administration of ORS to ensure its effectiveness.
What if the patient has a rare genetic defect causing glucose-galactose malabsorption (a mutation in the SGLT1 gene)? In this case, standard glucose-based ORS would be ineffective and could worsen the diarrhea due to the unabsorbed glucose. The patient would require intravenous rehydration or a special fructose-based ORS.

How to Approach the Question

First, identify the keywords in the question: 'oral rehydration therapy (ORT)', 'diarrhoea', and 'fluid absorption'. This points to the physiological basis of ORS.
Recall the composition of ORS, which critically includes both sodium and glucose.
Consider the function of a transporter that would utilize both sodium and glucose to move substances into a cell. This immediately suggests a co-transporter.
Evaluate the options provided. SGLT1 stands for Sodium-Glucose Linked Transporter 1, which perfectly matches the required mechanism.
Rule out the other options by recalling their primary functions: CFTR causes secretion, NHE is a different type of sodium absorber, and Na+-K+ ATPase is on the wrong side of the cell and serves to maintain a gradient, not for initial absorption from the lumen.

Concept Tested & Keywords

Concept Tested: Mechanism of Oral Rehydration Therapy and Intestinal Fluid Absorption
Stem keywords: oral rehydration therapy, diarrhoea, fluid absorption, transporter
Lead-in keywords: most active

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E6 Physiology Ganong 27e Vol 2 Part 1 pp. 18-20, 39-41, 21-23