How does the counter current mechanism help in concentrating the filtrate (urine)?

How does the counter current mechanism help in concentrating the filtrate (urine)?
  1. By maintaining a concentration gradient in the medullary interstitium
  2. By transporting NaCl and urea
  3. By allowing the easy passage of water from the collecting tubule
  4. By producing a dilute urine

Solution

The presence of a concentration gradient in the medullary interstitium helps in an easy passage of water from the collecting tubule, thereby concentrating the filtrate (urine).

Asked in: NCERT

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