Sophie.cerys
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The markscheme for a question about reabsorption in the proximal convoluted tubule says:

"Water follows by osmosis so concentration of, ions/nitrogenous waste/urea/remaining substances, increases;"

I don't understand why the addition of water would cause the concentration of ions to increase?? Surely it would decrease?
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Jpw1097
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(Original post by Sophie.cerys)
The markscheme for a question about reabsorption in the proximal convoluted tubule says:

"Water follows by osmosis so concentration of, ions/nitrogenous waste/urea/remaining substances, increases;"

I don't understand why the addition of water would cause the concentration of ions to increase?? Surely it would decrease?
In the proximal tubule, sodium, potassium, bicarbonate, calcium, etc. ions are reabsorbed via many different mechanisms. Water follows these ions out of the tubule and into the interstitium/peritubular capillaries. Since water leaves the proximal tubule, the osmolality/concentration of the filtrate (i.e. what’s LEFT in the tubule) increases.
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