[Campbell Biology P.1043] Which of the following sequences correctly describes the mechanism ... | Practice Question

Which of the following sequences correctly describes the mechanism by which ADH increases water reabsorption in the collecting duct cells, as depicted in Figure 44.18?

  • A: ADH binds to receptor → cAMP activated → Aquaporin channels directly open.
  • B: ADH binds to membrane receptor → Receptor triggers signal transduction (e.g., cAMP, Protein kinase A) → Vesicles with aquaporin water channels are inserted into the membrane lining the lumen → Aquaporin channels enhance reabsorption of water.
  • C: ADH binds to receptor → Aquaporin channels are synthesized de novo → Water reabsorption increases.
  • D: ADH binds to receptor → Collecting duct cells shrink → Water moves out of the cells.

Explanation

Figure 44.18 clearly illustrates the sequence: ADH binds to its membrane receptor, initiating a signal transduction cascade involving cAMP and Protein kinase A . This cascade directs storage vesicles containing aquaporin water channels to fuse with the membrane lining the lumen of the collecting duct, thereby inserting the channels. The presence of more aquaporin channels then enhances the reabsorption of water from the collecting duct into the interstitial fluid.