FIGURE 11-30 Transcellular transport of glucose from the intestinal lumen into the blood. The Na⁺/K⁺ ATPase in the basolateral surface membrane generates Na⁺ and K⁺ concentration gradients (step 1). The outward movement of K⁺ ions through nongated K⁺ channels generates an inside-negative membrane potential across the entire plasma membrane. Both the Na⁺ concentration gradient and the membrane potential are used to drive the uptake of glucose from the intestinal lumen by the two-Na⁺/one-glucose symporter located in the apical surface membrane (step 2). Glucose leaves the cell via facilitated transport catalyzed by GLUT2, a glucose uniporter located in the basolateral membrane (step 3).