In acute tubular necrosis, which segment of the nephron is MOST commonly affected in ischemic injury?
A. Glomerular filtration barrier
B. Thin descending limb of loop of Henle
C. Proximal convoluted tubule and thick ascending limb of loop of Henle
D. Distal convoluted tubule and collecting duct
Explanation
Segmental Vulnerability in Ischemic ATN
Key Point
The proximal convoluted tubule (PCT) and thick ascending limb (TAL) of the loop of Henle are the most metabolically active segments and therefore most susceptible to ischemic injury in ATN.
Why These Segments Are Vulnerable
Table
Segment
Metabolic Demand
Vulnerability
Reason
Proximal tubule
Very high
Highest
Active reabsorption of glucose, amino acids, ions; high Na⁺-K⁺-ATPase activity
Thick ascending limb
Very high
Highest
Active Na⁺-K⁺-2Cl⁻ cotransport; no aquaporins; oxygen-dependent
Distal tubule
Moderate
Lower
Some active transport but less than PCT/TAL
Collecting duct
Low-moderate
Lower
Primarily water reabsorption (ADH-dependent)
Thin limb
Very low
Lowest
Passive transport only
High-YieldNEET PG
The proximal tubule accounts for 65% of oxygen consumption in the kidney despite being only 5% of renal mass. This makes it exquisitely sensitive to hypoxia.
Ca²⁺ influx → activation of proteases and phospholipases
5.
Cell death → necrosis and apoptosis
Clinical Pearl
The proximal tubule is the first to show injury and the first to recover. This is why ATN is potentially reversible—the basement membrane remains intact and epithelial cells can regenerate from surviving basal cells.
Mnemonic: High-Risk Segments = PTAL
Proximal tubule (highest metabolic demand)
Thick ascending limb (active transport-dependent)
Active reabsorption zones
Low oxygen tolerance
Practice similar questions
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.
