Concentrating ability of kidney is impaired if:

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.