Assertion: A decrease in blood flow to the atria of the heart can cause the release of Atrial Natriuretic Factor (ANF) which cause vasodilation.

Reason: Angiotensin II, being a powerful vasoconstrictor, increases the glomerular blood pressure and thereby GFR and also activates the adrenal cortex to release Aldosterone.

Assertion (A) is false and Reason (R) is true.

The correct answer is Option (4)- Assertion (A) is false and Reason (R) is true.

The JGA plays a complex regulatory role. A fall in glomerular blood flow/glomerular blood pressure/GFR can activate the JG cells to release renin which converts angiotensinogen in blood to angiotensin I and further to angiotensin II. Angiotensin II, being a powerful vasoconstrictor, increases the glomerular blood pressure and thereby GFR. Angiotensin II also activates the adrenal cortex to release Aldosterone. Aldosterone causes reabsorption of Na⁺ and water from the distal parts of the tubule. This also leads to an increase in blood pressure and GFR. This complex mechanism is generally known as the Renin-Angiotensin mechanism. An increase in blood flow to the atria of the heart can cause the release of Atrial Natriuretic Factor (ANF). ANF can cause vasodilation (dilation of blood vessels) and thereby decrease the blood pressure. ANF mechanism, therefore, acts as a check on the renin-angiotensin mechanism.