Which hormone produced by the heart atria serves as a direct chemical antagonist to the renin-angiotensin-aldosterone system by causing vasodilation and reducing blood pressure?

Answer and explanation

Correct answer: C. Atrial Natriuretic Factor (ANF)

  1. Step 1: When systemic blood pressure or venous blood volume returning to the heart rises, the walls of the cardiac atria are stretched.
  2. Step 2: In response to this mechanical stretch, atrial cardiomyocytes release the peptide hormone Atrial Natriuretic Factor (ANF).
  3. Step 3: ANF binds to receptors on vascular smooth muscle, causing vasodilation and a rapid decrease in systemic blood pressure.
  4. Step 4: It also acts on the kidneys to promote sodium excretion (natriuresis) and inhibits the secretion of renin and aldosterone, thereby counteracting the RAAS.
Answer
Atrial Natriuretic Factor (ANF)
Why not the others: 'Angiotensin II' is a potent vasoconstrictor that elevates blood pressure and stimulates aldosterone; 'Antidiuretic Hormone (ADH)' stimulates renal water reabsorption and vasoconstriction; 'Aldosterone' causes renal sodium retention to increase blood volume.

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