The reasoning: high total flow, hypoxic medulla
Renal blood flow ≈ 1.1–1.25 L/min (20–25% of CO); renal plasma flow ≈ 600–650 mL/min; renal O₂ consumption is high but arteriovenous O₂ difference is small — flow is set by filtration needs, not metabolism. >90% of flow goes to the cortex; the medulla receives < 10% via vasa recta, and countercurrent O₂ shunting leaves medullary PO₂ ≈ 10–20 mmHg while the medullary thick ascending limb (TAL) and S3 proximal segments have high O₂ demand — the anatomical basis of ischaemic and toxic acute tubular injury.