As filtrate passes through the loop of Henle, salt is reabsorbed ...

Question

As filtrate passes through the loop of Henle, salt is reabsorbed and concentrated in the interstitial fluid of the medulla. This high solute concentration in the medulla enables nephrons to
a. excrete the maximum amount of salt.
b. neutralize toxins that might be found in the kidney.
c. excrete a large amount of water.
d. reabsorb water from the filtrate very efficiently.

Accepted Answer

Hi everyone, Welcome back, let's look at our next question. It says which portion of the Effron is impermeable to water? Well we're thinking about the different portions of the saffron and which are permeable or impermeable to water. It's helpful to kind of recall the structure of the ephron from our content videos and I'm just posting a very simplified diagram here to help us think through the different parts. So as we think about those different portions, um we see we've got the proximal to bill up here and this area has kind of the primary area of reabsorption of both salt and salute small molecules and water. Um You see a decrease in volume and that's because those salt, small molecules are being re absorbed and by osmosis, water is following them as well. Salt salts and water being reabsorbed. So this area is definitely permeable to water. So when we look at choice, a proximal convoluted tubules, that's not going to be our answer. Now let's look at this loop of henley, both the descending limb and the ascending limb. And as we're thinking about what's going on with water there, we want to recall that as we go down this loop, we're going deeper into the medulla of the kidney and the solute concentration is increasing as we go down, creating that gradient. And so let's think about what is causing that to increase as we move down. Well, the descending limb, we should see solute concentration concentration increasing and that happens because we don't have salts leaving, but we have water being re absorbed, so water is leaving salts are staying in, we have increasing solute concentration as you go down the descending limb. So let's look over here, descending limb loop of Henley's Choice C. So we can eliminate that. Now as we go up the ascending limb we're going to be going up again and concentration will be decreasing. And there's two ways you can decrease solid concentration. Either have solid roots leaving or have water coming in, but we don't want water coming back in, we're trying to re absorb water as things are moving through the Effron. So the that is managed by the ascending limb is impermeable to water with the end result that the volume remains the same as no water is coming in or out. But saul utes are being reabsorbed, essentially diluting your concentration there. So the ascending limb loop of Henley, which is choice B is our correct answer. That's the portion of the rahn that's impermeable to water as a means of keeping that volume constant. And finally, just to be thorough, Choice D is the distal convoluted tubules. This region here and this region has variable permeability to water. That's the region where control is exerted to help maintain constant osmolarity of the blood. So it can become more or less permeable to water salts of water more or less coming in or out, as part of that control system um involving hormones and keeping blood osmolarity constant, adjusting blood pressure. So that definitely has to be permeable to water and is not the correct answer. So again, which portion of the net front is impermeable to water? Choice be the ascending limb loop of Henle. E. See you in the next video.

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