How does aldosterone affect renal sodium handling?

• A. It decreases sodium reabsorption
• B. It increases sodium reabsorption and potassium secretion in the distal tubule and collecting duct
• C. It has no effect on sodium handling
• D. It reduces potassium excretion

Answer: (B)

Aldosterone acts on the distal parts of the nephron (the distal tubule and collecting duct) to increase sodium reabsorption and potassium secretion. It binds to intracellular mineralocorticoid receptors in principal cells, which ramps up the transcription of key proteins like ENaC channels on the apical membrane and Na+/K+ ATPase on the basolateral membrane. With more ENaC channels, sodium reabsorption from the filtrate into the blood rises; water follows this reabsorption, helping to expand blood volume. At the same time, the increased Na+/K+ ATPase activity and the electrochemical gradient drive more potassium into the tubular lumen to be excreted, lowering plasma potassium.

So the main effect is to boost sodium reabsorption in the distal nephron while promoting potassium secretion, which matches the described option. The other statements don’t fit because aldosterone does not decrease sodium reabsorption, it does have a clear effect on sodium handling, and it actually increases potassium excretion rather than reducing it.