Key Concepts of Section 11.6

• The apical and basolateral plasma-membrane regions of epithelial cells contain different transport proteins and carry out quite different transport processes.

• In intestinal epithelial cells, the coordinated operation of Na⁺-linked symporters in the apical membrane and Na⁺/K⁺ ATPases and uniporters in the basolateral membrane mediates transcellular transport of amino acids and glucose from the intestinal lumen to the blood (see Figure 11-30).

• The increased osmotic pressure created by transcellular transport of salt, glucose, and amino acids across the intestinal epithelium draws water from the intestinal lumen into the body, a phenomenon that serves as the basis for rehydration therapy using sugar-salt solutions.

• The combined action of carbonic anhydrase and four different transport proteins permits parietal cells in the stomach lining to secrete HCl into the lumen while maintaining their cytosolic pH near neutrality (see Figure 11-31).

• Bone resorption requires coordinated function in osteoclasts of a V-class proton pump and the ClC-7 chloride channel (see Figure 11-32).