Question

Explain how the osmolarity of the filtrate changes (be quantitative) as it moves through the sections of the nephron becoming urine

Answer 1

- the osmolarity of filtrate changes from PCT to CD like I mentioned below.:-

In the proximal convoluted tubule (PCT) the osmolarity is nearly 300 mOsmol .

- As the filtrate moves down the descending loop of henle , water is absorbed by osmosis and the tubular fluid reaches equilibrium with the surrounding interstitial fluid of the renal medulla, which is very Hypertonic about two to four time more osmolarity of the original glomerular filtrate. In the descending loop of henle the osmolarity of the filtrate is 400mOsml. In the hairpin loop the filtrate concentrated to maximum osmolarity of about 1000 mOsmol.

- Again when the filtrate moves upwards towards the distal convoluted tubule. Now again the filtrate gets diluted.

- In the ascending loop of henle sodium , potassium , chloride are absorbed largely . As this segment is impermeable to water the tubular fluid become diluted as it go up to the Distal convoluted tubule.

- The osmolarity again becomes about 300 mOsmol in the DCT. At the collecting duct the osmolarity of urine becomes around 200 mOsmol. This dilution is due to more absorption of sodium chloride.

Hopefully it helps. Thanks.