This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
[{'content': 'Mechanism that does not contribute to counter current multiplier in nephron \nSelect and explain. \nA. Active transport of sodium and chloride out of thick ascending limb of LOH, B. Water reabsorption in thin descending limb of LOH, C. Sodium reabsorption out of thin descending limb of LOH, D. Urea concentration in collecting duct', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ref. Guyton. 13th edition. Page. 435\nCountercurrent multiplication in the kidneys is the process of using energy to generate an\xa0osmotic gradient\xa0that enables you to reabsorb water from the tubular fluid and produce concentrated urine.\n\xa0\nThe three segments of the loops of Henle have different characteristics that enable countercurrent multiplication.\n\nThe\xa0thin descending\xa0limb is passively permeable to both water and small solutes such as sodium chloride and urea. The tubular fluid becomes steadily more concentrated or hyperosmotic (compared to blood) as it travels down the thin descending limb of the tubule.\nThe\xa0thin ascending\xa0limb is passively permeable to small solutes, but impermeable to water, which means water cannot escape from this part of the loop. The tubular fluid becomes steadily more dilute or hyposmotic as it moves up the ascending limb of the tubule.\nThe\xa0thick ascending\xa0limb actively reabsorbs sodium, potassium and chloride. this segment is also impermeable to water, which again means that water cannot escape from this part of the loop. This segment is sometimes called the “diluting segment”', 'role': 'assistant'}]