Question

The glomerular filtrate in the loop of Henle gets concentrated in the descending and then gets diluted in the ascending limbs. Explain.

Answer 1

Descending limb of Henle's loop:

The descending limb of Henle's loop is more permeable to water and almost impermeable to electrolytes. As a result, filtrate gets concentrated as it moves down the descending limb of Henle's loop

Ascending limb of Henle's loop:

The ascending limb of Henle's loop is impermeable to water but permeable to electrolytes. As a result, the filtrate gets diluted as it moves up the ascending limb of Henle's loop.

Process involved:

• The ascending limb of the loop of Henle is impermeable to water but permeable to ions like $K^{+},C{l}^{-},N{a}^{+}$ and it is partially permeable to urea. Thus, the filtrate becomes hypertonic to blood plasma.
• In the thick ascending limb of the loop of Henle, $N{a}^{+},K^{+},C{a}^{+},M{g}^{+}andC{l}^{-}$ are reabsorbed, making the filtrate hypotonic to blood plasma and diluted as compared to descending limb.
• This concentrates the filtrate as it moves down. The ascending limb is impermeable to water but allows the transport of electrolytes.
• Therefore, as the concentrated filtrate passes through the ascending limb, it gets diluted due to the passage of electrolytes to the medullary fluid