This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: DNB 2018, Subject name: Physiology
Dilution segment in nephrom is: 
Select and explain. 
A. Ascending LOH, B. Descending LOH, C. Collecting tubule, D. Proximal tubule
A: Ascending LOH
Answer: A: Ascending LOH 
Explanation: The thick LOH is viually impermeable to H20, but large amounts of Na, Cl & other ions are actively transpoed from the tubule into the medullary interstitium. Thus, fluid in thick ascending loop becomes very dilute and k/a diluting segment of the nephron. Proximal tubules: = 65% of the filtered electrolytes is reabsorbed here, along with water ( osmosis & aquaporin - 1). Descending LOH: Water absorbed AQP - 1 much less permeable to Na & urea; there by increasing the osmolarity.