Explain the reabsorption of glucose and Na+ from the lumen of the nephron tubule into the blood, using both the Na+/K+ ATPase and Na+/glucose transporter in your answer. Use a diagram if necessary

Question

What will be an ideal response?

Answer 1

Answer: The concentrations of Na+ and glucose in the primary urine are not different from that of the blood, so without a concentration gradient, these compounds will not move across membranes. To overcome this problem, the Na+/K+ ATPase in the basolateral membrane of the nephron pumps sodium from the cell into the peritubular space, and this creates a favorable inward Na+ electrochemical gradient on the apical side that can be used to pull Na+ into the tubule epithelial cell from the tubule lumen. This sodium movement happens through sodium channels, Na+/H+ exchangers, or other carriers. Additionally, Na+-coupled glucose uptake will also pull glucose into the epithelial cell through the action of a Na+-glucose cotransporter. Concentrating glucose within the cell causes a favorable outward chemical gradient that moves glucose out of the cell into the peritubular space (via glucose permease: facilitated diffusion). Once in the peritubular space, capillaries can recover these compounds.