While flowing through a specific segment 'A' of the nephron, the osmolarity of the filtrate gradually increases from 300 mOsmol L ⁻¹ to 1200 mOsmol L ⁻¹ . Subsequently, as it flows through segment 'B', the osmolarity decreases from 1200 mOsmol L ⁻¹ to 200 mOsmol L ⁻¹ . Identify the structural segments A and B along with the primary reason for these changes.

Step-by-step solution

The descending limb of Henle's loop (Segment A) is permeable to water but almost impermeable to electrolytes. As the filtrate moves down this segment, water moves out into the medullary interstitium, concentrating the filtrate from 300 mOsmol L ⁻¹ to 1200 mOsmol L ⁻¹ . The ascending limb of Henle's loop (Segment B) is impermeable to water but allows the transport of electrolytes (actively or passively). As the concentrated filtrate passes upward, electrolytes pass into the medullary fluid, diluting the filtrate dow