A patient is prescribed Tolvaptan, a medication that acts as a competitive antagonist at the antidiuretic hormone (ADH) V2 V_2\,V2 receptors located on the cells lining the collecting duct. This drug promotes the excretion of a large volume of dilute urine to treat fluid retention.
Which of the following explains the cellular mechanism of this drug's action?
It prevents the intracellular signaling cascade that causes vesicles containing aquaporins to fuse with the cell surface membrane of the collecting duct.
It inhibits the active transport of sodium and chloride ions out of the ascending limb of the loop of Henle, lowering the concentration of solutes in the medulla.
It blocks the constitutively active aquaporin channels in the proximal convoluted tubule, preventing the majority of water reabsorption.
It decreases the hydrostatic pressure of blood within the glomerulus, thereby reducing the rate of ultrafiltration.
17 exam-style questions on OCR A A Level Biology Excretion as an example of homeostatic control. Each one has a worked solution and a mark scheme showing where the marks go.