This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Excretory System (Kidney, Bladder) Acid-Base Balance, Subject name: Physiology
[{'content': 'Concentrating ability of kidney is impaired if: \nSelect and explain. \nA. There is damage to the glomerulus, B. There is excess secretion of ADH, C. There is vigorous activity of Na+-K+-pump, D. Blood flow through the vasa recta is increased substantially', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Concentrating ability of kidney is based on two factors: Creating hyperosmolarity of medullary interstitium, Role of ADH (reabsorbs H2O & concentrate urine) To achieve hyperosmolarity in medullary interstitium, by 15% juxta-medullary nephrons, two things come into effect Counter current multiplier mechanism occur at thick ascending loop of Henle. It is permeable to solutes & impermeable to H2O. So, it removes solutes, & interstitium becomes hyperosmolar / hypeonic Counter current exchange mechanism: Hypeonicity is created by counter-current multiplier mechanism. It is maintained by vasa recta by viue of their sluggish blood flow.', 'role': 'assistant'}]