Question

Renin secretion from the juxtaglomerular apparatus is stimulated in response to:

• A. Elevated sodium delivery to the macula densa
• B. Elevated renal perfusion pressure
• C. Reduced renal perfusion pressure
• D. Increased extracellular fluid volume

Hint:

The JG baroreceptor fires renin when it senses LOW pressure/stretch.

Answer 1

The Correct Option is C

Step 1: Triggers of renin release. Renin is released by juxtaglomerular (granular) cells of the afferent arteriole in response to three signals: (i) the renal baroreceptor sensing low afferent arteriolar/perfusion pressure, (ii) decreased NaCl delivery sensed by the macula densa, and (iii) sympathetic (beta₁) stimulation.

Step 2: Apply to options. A fall in renal perfusion pressure (e.g., hypovolemia, hypotension, renal artery stenosis) reduces stretch of the JG baroreceptor and increases renin - option 3 is correct.

Step 3: Why the others are wrong. Elevated sodium at the macula densa inhibits renin (tubuloglomerular feedback), so option 1 is wrong. Elevated perfusion pressure and an increased ECF/blood volume both suppress renin, so options 2 and 4 are wrong.

Key fact: Renin rises when renal perfusion pressure, distal NaCl delivery fall, or sympathetic drive increases - here, reduced renal perfusion pressure.