A student imagines a kidney in which the blood of the medulla runs in one direction only…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student imagines a kidney in which the blood of the medulla runs in one direction only. It goes down a straight vessel and then leaves, so it does not form a counter current with the loop. The loop of Henle is normal.
- What would the blood do to the NaCl that the ascending limb puts into the medulla?
- What would happen to the salty gradient?
- What would you expect for the volume and the concentration of the urine?
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 blood would carry the NaCl away from the medulla, because it leaves without returning it.
Step 2. (b) The gradient would become much weaker. The medulla would be less salty with depth.
Step 3. (c) Less water could leave the collecting duct, so the urine would be larger in volume and less concentrated.
Answer: (a) the blood carries the salt away; (b) the gradient falls; (c) more urine, less concentrated.
Watch out. This is a prediction from the text, not a measured result.
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