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does ADH increases the permeability of the distal tubule to water?


early distal tubule--is called cortical diluting segment. Like the thick ascending limb the early distal tubule reabsorbs NaCl but is IMPERMEABLE to water.Consequently the tubular fluid is further diluted.

In the late distal tubule water permeability is increase by ADH. Water is reabsorbedfrom the tubule until the osmolarity of the late distal tubule equal that of the surrounding interstitial fluid: 300mOsm/L -TF/P =1

extra-in the Collecting duct Osmolarity is high near 1200mOsm/L because ADH increases water permeability in this area --TF/P is greater then 1
Always remember that the late distal tubule and collecting ducts are permeable to water in the presence of ADH

Hope this helps -- TF stands for Tubular Fluid-P stands for plasma


thanx, for the explanation.
i knew that ADH increases the permeability. but i am abit getting confused. i had read from a book that ADH increases water resorbtion or retention in the collecting tubule due to osmotic gradient created in the medulla by the counter current meccanism. this means that it does not directly act on the permeability per se?
does that make sense? or it is because i am feeling sleepy


Bolo, I think what u read was correct.Because ADH also increases the permeablity of urea along with the permeability of water increasing the osmolarity of the interstitium.
Hope that makes sense

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