Answer about the loop of Henle. Which limb is permeable to water and almost impermeable to…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Answer about the loop of Henle.
- Which limb is permeable to water and almost impermeable to electrolytes?
- Which limb lets electrolytes out, and why does its filtrate become dilute?
- Is the filtrate more concentrated at the tip of the loop or at the start of the descending limb?
- Is the fluid that enters the DCT more or less concentrated than the plasma?
Need a reminder? The key ideaShow
The osmolarity of the interstitial fluid rises from mOsmol/L in the cortex to about mOsmol/L in the inner medulla. The descending limb is permeable to water. The ascending limb is impermeable to water and lets electrolytes out. The vasa recta runs beside the loop in a counter current. Only water leaves the collecting duct, so the amount of solute stays the same: is constant.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The descending limb.
Step 2. (b) The ascending limb. It is impermeable to water, so the electrolytes that leave it are not followed by water, and the filtrate becomes more dilute.
Step 3. (c) At the tip. Water has left the descending limb all the way down, so the filtrate there is the most concentrated.
Step 4. (d) Less concentrated. The ascending limb diluted it.
Answer: (a) descending; (b) ascending, because salt leaves and water does not; (c) at the tip; (d) less concentrated.
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