In SIAD, which hormones are inhibited or increased to regulate extracellular fluid?

• A. Aldosterone increased; ANP decreased
• B. Aldosterone inhibited; ANP increased
• C. Aldosterone unchanged; ANP unchanged
• D. Aldosterone decreased; ANP decreased

Answer: (B)

The key idea is how the body counteracts water retention in SIAD by adjusting the aldosterone–ANP axis. In SIAD, excess ADH drives water retention and expands extracellular fluid. To counter this, aldosterone is reduced, which lowers sodium and water reabsorption, and ANP is increased due to atrial stretch from the expanded volume, promoting natriuresis and diuresis. This combination helps decrease extracellular fluid volume back toward normal. So, the statement describing inhibited aldosterone and increased ANP best fits the physiological response.