What is the effect of Renal Artery Stenosis (RAS) on the kidney?

Renal Artery Stenosis (RAS) significantly affects kidney function by triggering the renin-angiotensin-aldosterone system (RAAS). When the renal arteries become narrowed, it leads to reduced blood flow to the kidneys. In response to this perceived low blood flow or low blood pressure, the kidneys release renin. Renin is an enzyme that converts angiotensinogen, released by the liver, into angiotensin I. This is subsequently converted into angiotensin II, which is a potent vasoconstrictor, causing blood vessels to narrow, increasing blood pressure, and stimulating the release of aldosterone from the adrenal glands. Aldosterone promotes sodium and water retention, which further helps to normalize blood pressure but also increases the workload on the kidneys.

This cascade of effects can lead to further complications such as hypertension and can compromise kidney function over time. Therefore, option B correctly identifies the pathophysiological response initiated by renal artery stenosis.