Concentration of the filtrate (and the final urine) takes place in the medulla o

Question

Concentration of the filtrate (and the final urine) takes place in the medulla of the kidney. At the turn in the nephron's loop, the concentration of the filtrate is about 1200 mOsm, but in the distal convoluted tubule the concentration is only about 100 mOsm. a. What causes the filtrate to become so dilute when it reaches the DCT? ??? Given the information above, in the absence of ADH, what would the approximate concentration of the final urine be (in mOsm)? b. se mosm c. What part of the nephron is responsible for determining the concentration of the final urine?

Explanation / Answer

a. In the presence of ADH, distal convulated tubule and collecting duct become permeable to water resulting in water reabsorption and final concentration of urine. When dilute urine is formed due to low ADH as in this case, the interstitial fluid is less than 1200 and therefore DCT becomes less concentrated and urine osmolarity decreases 100 mOsm/l (1200-100=100)

b. In the absence of ADH , DCT is almost impermeable to water and fails to reabsorb water and continues to reabsorb solutes and further dilutes the urine. Soo the concentration will be 0 (100-100=0) mOsm/l.

c. Its collecting duct.

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