The release of which hormone is most likely to cause a reduction in blood volume and pressure?

• A. Antidiuretic hormone
• B. Aldosterone
• C. Atrial natriuretic peptide
• D. Angiotensin II

Answer: (A)

Hormonal control of blood volume and pressure acts mainly through the kidneys and vessels to adjust salt and water balance and vascular tone. Atrial natriuretic peptide is released by atrial cells when the heart chambers are stretched from increased blood volume. It promotes natriuresis and diuresis—excreting more sodium and water in the urine—and it also dampens the renin-angiotensin-aldosterone system, which helps reduce fluid retention and vasoconstriction. The net effect is a fall in blood volume and a drop in blood pressure. By contrast, antidiuretic hormone retains water, raising volume and pressure; aldosterone increases sodium (and water) reabsorption, raising volume and pressure; and angiotensin II causes vasoconstriction and stimulates aldosterone, both increasing pressure. So the hormone most likely to decrease blood volume and pressure is atrial natriuretic peptide.