Question

What effect does the presence of ANF have on the body?

• A. It increases the production of renin
• B. It increases the excretion of sodium and water
• C. It stimulates the production of aldosterone
• D. It stimulates the production of angiotensin

Answer 1

Answer: (B)

It increases the excretion of sodium and water

• Cyclic GMP is a cyclic nucleotide, Guanosine 3', 5' cyclic monophosphate or cGMP. It functions as a second messenger in certain cells including those of intestinal linings, heart, blood vessels, brain and the collecting ducts of the kidneys.
• The cGMP is produced by guanylate cyclase. In mammals, guanylate cyclase is activated by the binding of the hormone atrial natriuretic factor or ANF, which is released by cells in the atrium of the heart when increased blood volume stretches the atrium. Carried in the blood to the kidney,
• ANF activates guanylate cyclase in cells of the collecting ducts, and the resulting rise in cGMP triggers increased renal excretion of sodium and consequently of water.
• Water loss reduces the blood volume, countering the stimulus that initially led to ANF secretion. Vascular smooth muscles also have an ANF receptor- guanylate cyclase, upon binding to the receptor, ANF causes vessel relaxation (i.e., vasodilation) which reduces the blood pressure.

So, the correct answer is option B.