I am a high school student and I am a little confused in 2 things related to our urinary system:
We know in our kidneys a countercurrent mechanism exists due to which there is a steep gradient of osmolarity is observed as we go deep inside the medulla and due to which water gets reabsorbed from the descending limb of Henle's loop into the ascending limb of vasa recta but due to the countercurrent of vasa recta osmolarity of blood doesn't changes but as collecting duct descends deep into the medulla it also loses water. Where does this water get drained? Does it get absorbed into a blood vessel? I don't think so because if the blood is also moving down with the collecting duct then it should also lose water as osmolarity increases as we go down.
We know that ADH increases the water reabsorption from the distal parts of nephron via aquaporins but if more aquaporins are there the collecting duct should pass urine of 1200mosml osmolarity, shouldn't it? and in that case will the concentration gradient in the medulla be maintained? if yes then how? I am not able to imagine how our kidney would behave if blood of increased osmolarity get into it.