Renal sodium handling abnormalities contribute to essential hypertension by which mechanism?

• A. They promote extracellular fluid volume expansion, increasing systemic vascular resistance and cardiac output.
• B. They decrease extracellular fluid volume.
• C. They do not affect extracellular volume.
• D. They increase potassium excretion.

Answer: (A)

The mechanism hinges on how sodium sets extracellular fluid volume. When the kidneys abnormally retain sodium, water follows to maintain osmolality, expanding the extracellular fluid volume. This increased plasma volume raises venous return and preload, which boosts cardiac output and elevates blood pressure. Over time, the elevated pressure promotes vascular remodeling and higher systemic vascular resistance, helping to sustain hypertension. So the key idea is that sodium handling abnormalities cause volume expansion, not a decrease in volume and not primarily changes in potassium excretion.