question on the kidney

[ToothFairy423]

hi guys, need your input, thanx!!

Kaplan, in a practice exam, has a question where the explanation basically says that NaCl is actively transported from the loop of henle to the medulla, and water passively follows.

from my bio book (campbells), this is what they say,
descending loop is impermeable to salt, only permeable to water
ascending loop is impermeable to water, only salt can pass.

so basically what kaplan is saying seems to be true for the collecting duct, but not the loop of henle, right, since both water and salt cannot pass together in the loops?? it seems to be an error on kaplans part, but i wanted confirmation of it, so your input will help. thanks!

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[fouyboy]

Descending Loop of Henle:
passive diffusion of water out to medulla
impermeable to salt
-> since the medulla is hypertonic to the descending.

Ascending Loop of Henle:
Impermeable to water
Salt is ACTIVELY transported FROM the ascending loop of henle TO the medulla.
-> since the descending loop is now more concentrated due to the diffusion of water in the descending loop of henle, salt must be actively transported.

Campbell is correct, Kaplan from what you said wasnt too clear on the location of the nephron.

Hope that helps

fouyboy

hi guys, need your input, thanx!!

Kaplan, in a practice exam, has a question where the explanation basically says that NaCl is actively transported from the loop of henle to the medulla, and water passively follows.

from my bio book (campbells), this is what they say,
descending loop is impermeable to salt, only permeable to water
ascending loop is impermeable to water, only salt can pass.

so basically what kaplan is saying seems to be true for the collecting duct, but not the loop of henle, right, since both water and salt cannot pass together in the loops?? it seems to be an error on kaplans part, but i wanted confirmation of it, so your input will help. thanks!

 

[ToothFairy423]

Descending Loop of Henle:
passive diffusion of water out to medulla
impermeable to salt

Ascending Loop of Henle:
Impermeable to water
Salt is ACTIVELY transported FROM the ascending loop of henle TO the medulla.

Campbell is correct, Kaplan from what you said wasnt specific on the location of the nephron.

Hope that helps

fouyboy

either way, water cannot follow salt and passively diffuse out, in the loop of henle right? water can only passively follow salt in the collecting duct right?

 

[fouyboy]

either way, water cannot follow salt and passively diffuse out, in the loop of henle right? water can only passively follow salt in the collecting duct right?

Right. Lets reason with some thinking. If water in the ascending loop of henle were allowed to cross the membrane, then wouldnt the water diffuse into the ascending loop of henle from the medulla? Thus, because this doesnt happen, the ascending loop of henle must be impermeable to water.

 

[fouyboy]

either way, water cannot follow salt and passively diffuse out, in the loop of henle right? water can only passively follow salt in the collecting duct right?

My orginal post had an error, the one above

 

[ToothFairy423]

Right. Lets reason with some thinking. If water in the ascending loop of henle were allowed to cross the membrane, then wouldnt the water diffuse into the ascending loop of henle from the medulla? Thus, because this doesnt happen, the ascending loop of henle must be impermeable to water.

well if you really want to break it down, water would not necessarily diffuse into the loop of henle from the medulla. the thin segment of the ascending loop, that is located in the inner medulla, has a higher osmolarity than the interstitial fluid, so nacl actually passively diffuses out, which means, IF it were permeable to water, then yes, water would actually move from the medulla into the loop of henle. what you are saying is that NaCl is actively pumped out, meaning there is a higher concentration of NaCl outside the filtrate, how is it then possible then water would diffuse into the loop of henle?

in the outer medulla, in the thicker segment of the ascending loop, the solution (due to the passive diffusion of nacl) now has become more dilute than the interstitial fluid. it is here where nacl has to be ACTIVELY pumped out. therefore, if it were permeable to water, water would actually move from the loop of henle, to the filtrate.

all in all, hopefully I dont need to know this crap in THIS much detail