Gastrointestinal System — MCQs

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

SGLT1. ***SGLT1*** - SGLT1 (Sodium-Glucose Linked Transporter 1) is a symporter that transports **glucose and sodium** across the apical membrane of the enterocyte, which creates an **osmotic gradient** driving massive water absorption. - This mechanism remains intact even during secretory diarrheas, forming the physiological basis for **Oral Rehydration Therapy (ORT)** effectiveness. *CFTR* - The CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) is a chloride channel responsible for **secreting chloride** ions into the intestinal lumen, which drives fluid secretion. - Its activity is often pathologically upregulated in diarrheal diseases like **cholera**, contributing to the loss of fluids and electrolytes rather than absorption. *NHE* - The NHE (Sodium-Hydrogen Exchanger) is a sodium transporter involved in neutral sodium absorption primarily in the **jejunum and ileum**. - While it contributes to normal sodium uptake, it is not the target mechanism exploited by ORT solutions containing glucose to maximally stimulate fluid uptake. *Na+-K+ ATPase* - Located on the **basolateral membrane**, this pump maintains the electrochemical gradient by pumping sodium out of the cell and potassium into it. - While essential for secondary active transport, it provides the low intracellular sodium concentration necessary for transporters to function but is not the apical gateway utilized for **glucose-coupled uptake**.

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