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why is urea reabsorbed?

hi i was revising homeostasis and my notes and text books say urea is reabsorbed but not why so i was wondering if anyone could tell me please.

Thanks in advance!

Reply 1

Cirsium

19

Are you sure that's what they say?? Really REALLY sure?? because I am positive that no urea is reabsorbed unless it is talking about in the glomerulus in which case it is VERY badly worded!!

Reply 2

Golden Maverick

4

K2theJ

hi i was revising homeostasis and my notes and text books say urea is reabsorbed but not why so i was wondering if anyone could tell me please.

Thanks in advance!

Urea is filtered by the glomerulus and most of it is reabsorbed in the nephron. This depends on how much water is reabsorbed - for example when much water is being reabsorbed urea is also reabsorbed more to help with water retention.

Just remember some urea is still excreted, and this excretion is enough. :smile:

Reply 3

idiopathic

15

Bekaboo

Are you sure that's what they say?? Really REALLY sure?? because I am positive that no urea is reabsorbed unless it is talking about in the glomerulus in which case it is VERY badly worded!!

The original poster was correct :eek:

Up to half of the urea in the filtrate even, (initially absorbed in the glomeruli) is reabsorbed back into the blood as urea is a relatively small molecule and can easily and passively diffuse down its concentration gradient. I think it's due to the efferent arteriole having a lower urea concentration (which is due to the urea being absorbed out of the affererent arteriole), and subsequently the filtrate has a higher concentration.

Reply 4

Revenged

15

Bekaboo

Are you sure that's what they say?? Really REALLY sure?? because I am positive that no urea is reabsorbed unless it is talking about in the glomerulus in which case it is VERY badly worded!!

Dont worry... for our exam board, Edexcel, we get the marks for saying that urea is waste product and is not reabsorbed - so you'd get the marks for saying that... Don't worry that it isn't actually what happens, but it is much easier to understand

Reply 5

Golden Maverick

4

endeavour

The original poster was correct :eek:

Up to half of the urea in the filtrate even, (initially absorbed in the glomeruli) is reabsorbed back into the blood as urea is a relatively small molecule and can easily and passively diffuse down its concentration gradient. I think it's due to the efferent arteriole having a lower urea concentration (which is due to the urea being absorbed out of the affererent arteriole), and subsequently the filtrate has a higher concentration.

It's rebsorbed in the proximal tubule as you say through the leaky epithelium with many other solutes. It is actually secreted into the loop of Henle, and then reabsorbed with water in the last parts of the collecting duct. It can't pass through tight epithelia though, it needs channels or leaky borders.

Reply 6

K2theJ

OP

thanks for all your help!!

why is urea reabsorbed?

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