What is the primary function of the vasa recta in maintaining urinary concentrating ability?
- A Serving as a countercurrent exchanger that passively traps solute and prevents washout of the medullary gradient ✓
- B Actively transporting sodium into the inner medulla to build the corticomedullary gradient
- C Providing the source of urea recycled into the inner medullary interstitium via UT-A1
- D Secreting renin in response to low medullary interstitial tonicity
Correct answer: A. Serving as a countercurrent exchanger that passively traps solute and prevents washout of the medullary gradient
Explanation
The vasa recta behave as passive countercurrent exchangers: descending vessels lose water and gain solute while ascending vessels reverse this exchange, so the hypertonic medullary interstitium is preserved despite continuous blood flow. They are not the multiplier; the loops of Henle generate the gradient. Active transport occurs in the nephron epithelium, not the vessel wall, and renin comes from juxtaglomerular cells of the afferent arteriole in the cortex.
Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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