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    i understand ultrafiltration
    but was wondering if anybody could summarise the following stages

    Reabsorption (wt is reabsorbed and from where to where and how)
    Loop Of Henle (generally i dont understand):confused:

    thanks a lot
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    Reabsorption happens in proximal convulated tubule, selective reabsorption of useful products are reabsorbed back into the blood stream i.e. glucose by active transport

    Loop of henle has 2 limbs: Water leaves the descending limb of the loop by osmosis, and Na+ and Cl- ions diffuse into the loop.
    Opposite for ascending limb. This maintains a concentration gradient and water is therefore absorbed into the blood through the capillary network.

    The longer the loop of henle, the more water is reabsorbed back into blood and therefore urine is more concentrated!

    Hope thaT HELPS
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    this is a great resource for the kidney here it looks simplistic at first, but if you explore it thoroughly it's really usefull!
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    reapsorption of salt and water also occurs in the distal convoluted tubule and collecting duct, according to the actions of aldosterone and ADH respectively

    edit: Look! a shiney diagram!

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    Selective reabsorption occurs in the PCT.
    Useful substances are reabsorbed, such as water, glucose, amino acids, vitamins.

    • Water (65%) is reabsorbed by osmosis.
    • Glucose, amino acids, and vitamins are cotransported by Na+. What happens is that the cell basement membrane (of cells lining the PCT) pump Na+ actively into the blood supply, this lowers the conc of Na+ inside the cell....therefore creating a conc gradient between the cells and the lumen of the tubule. Thus, Na+ diffuses down its conc gradient into the cell, via protein channels which specifically transport Na+ and another substance such as glucose, amino acids or vitamins. (Na+ basically gives them a piggy back)
    • Urea (suprise!) is also reabsorbed, about 50% of it infact


    Where as, creatinine + uric acid are actively secreted into the tubule, by the surrounding cells
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    (Original post by Dipz)
    Loop Of Henle (generally i dont understand):confused:

    thanks a lot
    Right, is easier to start with the ascending the limb.
    Its impermeable to water, but Na+, Cl- are actively pumped out into the medulla of the kidney....thus giving it a very high salt conc.

    In the descending limb, water moves into the medulla by osmosis, because its very salty in the medulla, and therefore has a low water potential.
    Also, at the same time Na+ Cl- diffuses into the descending limb because there is such a high conc of salt in the medulla.

    Thus when the filtrate reaches the top of the ascending limb, its more dilute because of the loss of water in the descending limb.

    The loop of Henle is a counter current multiplier

    try drawing a diagram, its much easier to see!
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    Reabsorption of glucose i know we have to know this for my spec, i dunno what board etc ur on but here u go!

    Glucose enters the cells of the first convoluted tubule by facilitated diffusion
    it is then actively pumped out of the cells into intercellular spaces (in order to maintain a diffusion gradient between the cells and the filtrate)
    The glucose now in the intercellular spaces enters capillaries by diffusion and is carried away in the blood.
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    (Original post by ~*Sar*~)
    Reabsorption of glucose i know we have to know this for my spec, i dunno what board etc ur on but here u go!

    Glucose enters the cells of the first convoluted tubule by facilitated diffusion
    it is then actively pumped out of the cells into intercellular spaces (in order to maintain a diffusion gradient between the cells and the filtrate)
    The glucose now in the intercellular spaces enters capillaries by diffusion and is carried away in the blood.
    Is that all you need to know? You dont have to know about Na+ cotransporting? lucky! lol
    Wot exam board are you doing?
 
 
 
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