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.
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