Which cardiac hormone acts as a physiological antagonist to the Renin-Angiotensin-Aldosterone System (RAAS) by promoting natriuresis and vasodilation?

Answer and explanation

Correct answer: C. Atrial Natriuretic Factor (ANF)

  1. Step 1: An increase in blood volume or venous return causes stretch of the atria of the heart.
  2. Step 2: In response to atrial distension, atrial myocytes synthesize and release Atrial Natriuretic Factor (ANF / ANP).
  3. Step 3: ANF acts as a potent vasodilator, dilates afferent renal arterioles, increases GFR, and inhibits the secretion of renin and aldosterone.
  4. Step 4: It promotes the excretion of sodium () in urine (natriuresis) and water diuresis, reducing blood volume and blood pressure, thus checking the RAAS.
Answer
Atrial Natriuretic Factor (ANF)
Why not the others: 'Erythropoietin (EPO)' is a peptide hormone produced by renal peritubular cells that stimulates erythropoiesis in bone marrow; 'Aldosterone' is a steroid hormone from the adrenal cortex that promotes retention (the primary effector of RAAS); 'Thyroxine' regulates basal metabolic rate.

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