dreamfyre
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What goes the sodium ions to diffuse into the descending limb? and what cause them to move out at the bottom of the ascending limb. Is it because of the sodium concentration gradient out side - so when he water leaves the inside has more sodium then outside? also at the DCT that is found in the cortex, which isnt in the salty medulla, so what cause water to move out of there, is that just because water potential of the capillary is lower than the filtrate?? please answer all of these questions thanks
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macpatgh-Sheldon
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Hi,

The main forces that allow humans to reabsorb over 95% of the water filtered into the urine compartment in the glomerulus are the differences in permeability to sodium and to water in the thin descending limb of the loop of Henle and the thick ascending limb of the loop of Henle.

The permeability to water is much greater in the descending limb, so water accumulates around the ascending limb - vice versa for sodium i.e. the permeabiliy to sodium is much greater in the ascending limb than in the descending limb. (MEMORY AID: salt (sodium sort of) is heavier than water so remember that sodium tends to accumulate downward due to gravity so goes into dscending limb - water, being lighter imagineit rising i.e. into the ascending limb haha ONLY A MEMORY TACTIC - NOT A FACT!!)

With the flow of "urine" in its correct direction i.e. from descending limb (the first part of loop of Henle immediately after proximal convolute tubule) towards the ascending limb (the later part just before the distal convoluted tubule), the above movements of sodium and water result in the so-called "Counter-current mechanism", whereby there is always (meaning throughout the length of the loop of Henle) a water potential gradient encouraging outward (out of urine compartment into the interstitium of the renal medulla) i.e. there is throughout the loop of Henle a higher water potential inside the lumen of the loop than outside it, so WATER COMES OUT OF THE loop of Henle AND EVENTUALLY BACK INTO THE BLOOD in massive amounts.

The normal GFR (glomerular filtration rate is 180 litres/day, but we do not p**s () nearly that much, otherwise we would be doing nothing else haha no eating, no going out, no school, just one room in every house - the loo !!!!!.

To understand the above better, look at the diagram below, which I have scanned specially for you.

ENJOY BIOLOGY it is fab!!

M (Specialist Biology tutor [alias Sheldon!])

Name:  Loop of Henle function.jpg
Views: 243
Size:  415.6 KB
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dreamfyre
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(Original post by macpatelgh)
Hi,

The main forces that allow humans to reabsorb over 95% of the water filtered into the urine compartment in the glomerulus are the differences in permeability to sodium and to water in the thin descending limb of the loop of Henle and the thick ascending limb of the loop of Henle.

The permeability to water is much greater in the descending limb, so water accumulates around the ascending limb - vice versa for sodium i.e. the permeabiliy to sodium is much greater in the ascending limb than in the descending limb. (MEMORY AID: salt (sodium sort of) is heavier than water so remember that sodium tends to accumulate downward due to gravity so goes into dscending limb - water, being lighter imagineit rising i.e. into the ascending limb haha ONLY A MEMORY TACTIC - NOT A FACT!!)

With the flow of "urine" in its correct direction i.e. from descending limb (the first part of loop of Henle immediately after proximal convolute tubule) towards the ascending limb (the later part just before the distal convoluted tubule), the above movements of sodium and water result in the so-called "Counter-current mechanism", whereby there is always (meaning throughout the length of the loop of Henle) a water potential gradient encouraging outward (out of urine compartment into the interstitium of the renal medulla) i.e. there is throughout the loop of Henle a higher water potential inside the lumen of the loop than outside it, so WATER COMES OUT OF THE loop of Henle AND EVENTUALLY BACK INTO THE BLOOD in massive amounts.

The normal GFR (glomerular filtration rate is 180 litres/day, but we do not p**s () nearly that much, otherwise we would be doing nothing else haha no eating, no going out, no school, just one room in every house - the loo !!!!!.

To understand the above better, look at the diagram below, which I have scanned specially for you.

ENJOY BIOLOGY it is fab!!

M (Specialist Biology tutor [alias Sheldon!])

Name:  Loop of Henle function.jpg
Views: 243
Size:  415.6 KB
thanks a lot
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