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The Correct Answer is {"dropdown-group-1":"A"}
A. Apical: The apical membrane, or mucosal surface, contains the microvilli (brush border) that extend into the lumen. This surface is specialized for the initial transport of solutes from the filtrate into the epithelial cell. It is the primary site for nutrient and ion recovery.
B. Lateral: These surfaces are located between adjacent epithelial cells and contain junctional complexes like tight junctions. They regulate the paracellular movement of water and ions but do not directly face the lumen. They maintain the structural integrity and polarity of the tubule.
C. Interstitial: This refers to the space surrounding the exterior of the tubule, which contains the peritubular fluid and capillaries. It is the destination for reabsorbed substances but does not contact the primary filtrate. It is separated from the lumen by the epithelial barrier.
D. Basal: The basal membrane sits on the basement membrane and faces the interstitial space and blood vessels. It contains transporters like the Na+/K+ ATPase pump that move solutes out of the cell toward the blood. It is the opposite side of the apical surface.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
B. False: The Na+/K+ ATPase pump is localized exclusively to the basolateral membrane of renal tubular epithelial cells. It maintains a low intracellular sodium concentration, which drives secondary active transport of glucose via SGLT proteins on the apical side. It does not transport glucose.
Correct Answer is D
Explanation
A. Carrier proteins can only function on the basal surface of the cell: In polarized renal epithelial cells, carrier proteins are strategically located on both the apical and basolateral membranes. For example, SGLT transporters are on the apical side, while GLUT transporters are on the basal side. Both are essential for reabsorption.
B. Increasing concentration always increases reabsorption rate: This is true only until the carrier proteins become fully saturated. Once all available binding sites are occupied, the rate of transport reaches a plateau. Further increases in solute concentration will not result in additional reabsorption, leading to excretion.
C. Specific substrates bind to any available carrier protein to cross the membrane: Carrier proteins exhibit high specificity for their substrates based on molecular shape and charge. A glucose transporter will not move amino acids or ions. This selectivity is a defining characteristic of carrier-mediated transport versus simple diffusion.
D. Transport maximum (Tm) determines the renal threshold of a substance: The Tm is the maximum rate at which a substance can be reabsorbed by the renal tubules. When the filtered load exceeds this capacity, the substance begins to appear in the urine. This point of spillover is known as the renal threshold.
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