Question:medium
Tubuloglomerular feedback control is useful for the regulation of which one of the following?
Tubuloglomerular feedback control is useful for the regulation of which one of the following?
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Think of the macula densa and juxtaglomerular apparatus and the one renal variable they keep constant.
Updated On: Jun 23, 2026
- GFR
- Plasma sodium
- Plasma volume
- Determining tubular secretion
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The Correct Option is A
Solution and Explanation
Step 1: The kidney protects its filtration rate using a built-in loop called tubuloglomerular feedback, so the variable being controlled is the glomerular filtration rate.
Step 2: A specialised patch of distal tubule epithelium, the macula densa, lies against the afferent arteriole inside the juxtaglomerular apparatus and continuously monitors the salt content of fluid passing by.
Step 3: If too much filtrate is being produced, the macula densa releases adenosine, which opens calcium channels and tightens the afferent arteriole, while angiotensin II tightens the efferent arteriole. The net effect dials filtration back toward baseline.
Step 4: Sodium concentration, circulating volume, and secretion of solutes are not the direct targets of this loop; they merely shift as filtration changes. Hence the answer is GFR.
\[\boxed{\text{GFR}}\]
Step 2: A specialised patch of distal tubule epithelium, the macula densa, lies against the afferent arteriole inside the juxtaglomerular apparatus and continuously monitors the salt content of fluid passing by.
Step 3: If too much filtrate is being produced, the macula densa releases adenosine, which opens calcium channels and tightens the afferent arteriole, while angiotensin II tightens the efferent arteriole. The net effect dials filtration back toward baseline.
Step 4: Sodium concentration, circulating volume, and secretion of solutes are not the direct targets of this loop; they merely shift as filtration changes. Hence the answer is GFR.
\[\boxed{\text{GFR}}\]
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