Long loop of Henle?

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I thought I understood the human kidney and its function, but I'm having trouble solving problems when it comes to applying the knowledge.
For example, Kangaroo rats have nephrons with long loops of Henle to increase their survival in desert.

I'm having trouble understand the concept behind it. Can someone explain the mechanism for this please?
Thanks!

Descending loop absorb water even without ADH(which only works at the end of distal convoluted tubule and collecting duct).

so the longer it is, the more water will be absorbed.

The only thing that I still don't understand is that ascending is the opposite so if
it descends for 1 foot and absorb 10g of water, shouldn't we regain 10g when it's ascending?
so in this scenario, I don't think we can say the urine got concentrated, since it became diluted back to original.

Originally Posted by joonkimdds

Descending loop absorb water even without ADH(which only works at the end of distal convoluted tubule and collecting duct).

so the longer it is, the more water will be absorbed.

The only thing that I still don't understand is that ascending is the opposite so if
it descends for 1 foot and absorb 10g of water, shouldn't we regain 10g when it's ascending?

Exactly! That's what I'm talking about. I was thinking in the same way-- how is it possible to have more water absorved in descending loop while it doesnt lose in ascending loop?

Water is also reabsorbed in the collecting duct. Thus the urine is more concentrated at the end.

You don't regain water in the ascending loop, you lose salts. What you regain is the low osmolarity.

Longer loop = more water resorbed in the descending loop.

Originally Posted by LoLPoPs

I thought I understood the human kidney and its function, but I'm having trouble solving problems when it comes to applying the knowledge.
For example, Kangaroo rats have nephrons with long loops of Henle to increase their survival in desert.

I'm having trouble understand the concept behind it. Can someone explain the mechanism for this please?
Thanks!

Let's review the structure and the function of the loop of Henle:
The descending arm is where water resorption takes place. The ascending loop is where salt resorption takes place. The fact that salt is actively absorbed into the medulla maintains a higher concentration of solute in the medulla compared to solute concentration in the descending loop, allowing continuous water resorption.
So, how does a long loop of Henle contribute to survival of Kangaroo rats?
These animals never drink water throughout their lives. So, they need to be very efficient in terms of water conservation. Increasing the length of loop of Henle allows more salt resorption into the medulla, which will in turn promote more efficient water absorption (Higher concentration of salt in the medulla contributes to a greater osmotic pressure, which results in greater water resorption). Finally, the fact that the descending arm is longer provides a greater surface area for water resorption (Very similar that increasing the length of the digestive track results in more efficient nutrient resorption). This is why a longer loop of Henle is crucial for the survival of Kangaroo rats.

Originally Posted by LoLPoPs

I thought I understood the human kidney and its function, but I'm having trouble solving problems when it comes to applying the knowledge.
For example, Kangaroo rats have nephrons with long loops of Henle to increase their survival in desert.

I'm having trouble understand the concept behind it. Can someone explain the mechanism for this please?
Thanks!

Basically, the longer your loop of Henle, the bigger the osmotic gradient that is setup between the kidney's cortex and medulla. The higher your osmolarity is at the depth of your medulla, the higher the maximum osmalirty of the excreted urine. (Even if the inner medulla's osmalirty is 1200 (like in humans, I think), no matter how high your ADH levels are (how much water you reabsorb), you can't have a urine more concentrated than 1200 osmo because the water reabsorption is passive and not active. However, in animals that have adapted to deserts, like this kangaroo rat I guess, the inner medulla has a much higher osmolarity, therefore, they're able to produce urine that is much more concentrated and conserve more water than humans would be able to.

Originally Posted by Shinpe

Basically, the longer your loop of Henle, the bigger the osmotic gradient that is setup between the kidney's cortex and medulla. How high your osmolarity is at the depth of your medulla, the higher the maximum osmalirty of the excreted urine. (Even if the inner medulla's osmalirty is 1200 (like in humans, I think), no matter how high your ADH levels are (how much water you reabsorb), you can't have a urine more concentrated than 1200 osmo because the water reabsorption is passive and not active. However, in animals that have adapted to deserts, like this kangaroo rat I guess, the inner medulla has a much higher osmolarity, therefore, they're able to produce urine that is much more concentrated and conserve more water than humans would be able to.

Is that what it is? Kangaroo rat? I've read about some neat little rodent that can live off only the H2O they get from metabolism. They have loops of Henle so long that they reach down into the renal pelvis.

Originally Posted by UCB05

Is that what it is? Kangaroo rat? I've read about some neat little rodent that can live off only the H2O they get from metabolism. They have loops of Henle so long that they reach down into the renal pelvis.

Yup kangaroo rats. I actually use their kidney epithelium cells (PTK2) for my research. Random fact, but these cells are frequently used in mitosis studies because they don't round up like most other cells do during mitosis (makes seeing the whole process easier on a microscope).

Originally Posted by joonkimdds

Descending loop absorb water even without ADH(which only works at the end of distal convoluted tubule and collecting duct).

so the longer it is, the more water will be absorbed.

The only thing that I still don't understand is that ascending is the opposite so if
it descends for 1 foot and absorb 10g of water, shouldn't we regain 10g when it's ascending?
so in this scenario, I don't think we can say the urine got concentrated, since it became diluted back to original.

also just to note, i read in one of the destroyer explanations last night (88) that the cells of the ascending loop are impermeable to water.

Originally Posted by Kneecoal

also just to note, i read in one of the destroyer explanations last night (88) that the cells of the ascending loop are impermeable to water.

way to be, nicole! - exactly what i was going to throw in this thread.

Originally Posted by Kneecoal

also just to note, i read in one of the destroyer explanations last night (88) that the cells of the ascending loop are impermeable to water.

In the Kaplan course, I just tell everyone to remember that "water only flows downhill", and this helps you remember that only the descending loop is permeable to water. It really helps me remember it as well.