Counter Current & Urine Concentration — NEET Biology
📚 Practice ConceptA counter current mechanism operates between the two limbs of the loop of Henle and those of vasa recta (capillary parallel to Henle's loop). The filtrate gets concentrated as it moves down the descending limb but is diluted by the ascending limb. Electrolytes and urea are retained in the interstitium by this arrangement. DCT and collecting duct concentrate the filtrate about four times, i.e., from 300 mOsmolL⁻¹ to 1200 mOsmolL⁻¹, an excellent mechanism of conservation of water. Urine is stored in the urinary bladder till a voluntary signal from CNS carries out its release through urethra, i.e., micturition. Skin, lungs and liver also assist in excretion.
Assertion (A): The filtrate undergoes concentration changes as it moves through the loop of Henle. Reason (R): The filtrate gets diluted as it moves down the descending limb but is concentrated by the ascending limb.
View solution & NCERT explanation
Correct answer: C — If assertion is true but reason is false.
NCERT states “The filtrate gets concentrated as it moves down the descending limb but is diluted by the ascending limb.” The Assertion is true - filtrate concentration does change in the loop. The Reason reverses the effects - descending limb concentrates (due to water loss), ascending limb dilutes (due to salt loss without water). This tests understanding of the counter-current mechanism.
What does NCERT say about counter current mechanism operates?
Has this concept appeared in NEET?
Which chapter is this from?
Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
176/180MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.