Biology · Excretory Products and Their Elimination · NEET
Atrial Natriuretic Factor (ANF) is a peptide hormone released by the atrial wall of the heart when blood flow to the atria increases (that is, when blood pressure or blood volume rises). ANF causes vasodilation (widening of blood vessels), which lowers blood pressure. Memory hook: ANF is the "brake" on high BP, and it works opposite to the renin-angiotensin-aldosterone system, which is the "accelerator."
When blood pressure rises, the atrial wall of the heart releases ANF, which causes vasodilation and lowers blood pressure. ANF acts as a check on the renin-angiotensin-aldosterone system.
Your doubts, answered
Is ANF released when blood pressure goes up or down?
ANF is released when blood pressure or blood volume goes UP. NCERT says an increase in blood flow to the atria of the heart causes the release of ANF. So a fall (decrease) in BP does NOT release ANF. This is the exact point NEET 2017 tested. Renin, aldosterone and ADH are the ones released when BP falls.
Does ANF raise or lower blood pressure?
ANF lowers blood pressure. It causes vasodilation, meaning the blood vessels become wider. Wider vessels mean less resistance, so blood pressure drops. Think of it this way: BP is already high, so the body sends ANF to bring it back down.
How is ANF different from aldosterone?
They do opposite jobs, so they are antagonistic. Aldosterone (from the renin-angiotensin pathway) causes reabsorption of Na+ and water, which raises blood pressure. ANF causes vasodilation and lowers blood pressure. One is the accelerator (aldosterone raises BP), the other is the brake (ANF lowers BP).
Why is ANF called a check on the renin-angiotensin mechanism?
When BP falls, the renin-angiotensin-aldosterone system raises it back up. If BP then rises too much, ANF is released to bring it back down through vasodilation. Because ANF opposes and balances that system, NCERT says the ANF mechanism acts as a check on the renin-angiotensin mechanism.
Where exactly is ANF secreted from?
ANF is secreted by the atrial wall of the heart, not by any kidney part. It is a peptide hormone. The heart is not a classic endocrine gland, but its atrial tissue still secretes this hormone. NEET matching questions often pair Heart with ANF.
⚠️ The NEET trap ✗ A decrease in blood pressure or volume triggers the release of ANF along with renin, aldosterone and ADH. ✓ A decrease in BP triggers renin, aldosterone and ADH (to raise BP), but it does NOT release ANF. ANF is released when BP INCREASES, to lower it back down. 🧠 ANF is the odd one out: the other three conserve water and push BP up; ANF alone pushes BP down. If BP falls, ANF stays quiet.
Real NEET questions
NEET 2017
A decrease in blood pressure/volume will not cause the release of
A · Renin
B · Atrial Natriuretic Factor ✓
C · Aldosterone
D · ADH
Solution: A fall in BP/volume triggers renin (from JG cells), then angiotensin II and aldosterone, plus ADH, all to conserve water and raise BP. ANF works oppositely: it is released only when blood flow/volume to the atria INCREASES, causing vasodilation to lower BP. So a decrease in BP will not release ANF.
NEET 2020
Which of the following would help in prevention of diuresis?
A · Atrial natriuretic factor causes vasoconstriction
B · Decrease in secretion of renin by JG cells
C · More water reabsorption due to undersecretion of ADH
D · Reabsorption of Na+ and water from renal tubules due to aldosterone ✓
Solution: Diuresis means increased urine output, so preventing it means conserving water. Aldosterone causes reabsorption of Na+ and water from the distal tubule, retaining water and preventing diuresis. Option A is wrong because ANF causes vasodilation, not vasoconstriction; B means less aldosterone (more water loss); C is self-contradictory since low ADH increases urine.
NEET 2023 Phase 1
Which of the following statements are correct? A. An excessive loss of body fluid switches off osmoreceptors. B. ADH facilitates water reabsorption to prevent diuresis. C. ANF causes vasodilation. D. ADH causes increase in blood pressure. E. ADH is responsible for decrease in GFR.
A · A and B only
B · B, C and D only ✓
C · A, B and E only
D · C, D and E only
Solution: B is true (ADH reabsorbs water, preventing diuresis). C is true (ANF causes vasodilation). D is true (ADH raises BP by its constrictory effect). A is false (fluid loss activates, not switches off, osmoreceptors). E is false (ADH raises BP and so increases, not decreases, GFR). Correct: B, C and D.
Solved Excretory Products and Their Elimination NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
ANF stands for Atrial Natriuretic Factor. It is a peptide hormone from the atrial wall of the heart that lowers blood pressure.
Is ANF part of the current NEET syllabus?
ANF appears in the Excretory Products chapter and in Chemical Coordination. Even though some editions mark the heart-hormone list as reduced, ANF has appeared in recent NEET papers (2017, 2020, 2023), so learn it fully.
What does ANF do to blood vessels?
ANF causes vasodilation, meaning it widens the blood vessels. Wider vessels lower the resistance to blood flow, which decreases blood pressure.
Which hormone is antagonistic to ANF?
Aldosterone is antagonistic to ANF. Aldosterone raises blood pressure by reabsorbing Na+ and water, while ANF lowers blood pressure through vasodilation.
When is ANF released?
ANF is released when blood flow, volume or pressure to the atria increases. Its job is to bring high blood pressure back down.
