Lancien
Forum Newbie
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Question1:
Which has the greatest renal clearance: Inulin or Creatinin?
Question2:
Could any one please explain the difference between secretiion-excretion-and reabsorption?
Thank you
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Matesul
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| mildus
Forum Guru
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First of all:
You have blood (plasma + blood cells) in glomerulus. By filtration through filtration membrane, from blood, you get a part of plasma which comes to tubule (tubular fluid).
Tubular fluid is then reabsorbed, secreted and excreted.
Reabsorbtion means that part (99 %) of tubular fluid is coming back to blood in order to be saved not excreted (Re means again).
Secretion means that some substances which remained in blood after filtration, can be transported from blood to tubular fluid, in order to be excreted.
Excretion means that fluid which remained after reabsorption and secretion, is thrown out from the body through the urethra.
A substance can be filtered, reapsorbed, secreted and excreted. But, not all the substances undergo all these processes. So there can be several cases:
1. Some substances aren't filtered at all (proteins)
2. Some are filtered, then not reabsorbed (and not secreted), then excreted (inulin)
3. Some are filtered, then extra secreted (but not reapsorbed), and then excreted (kreatinin)
Clearance of inulin shows GFR (about 125 ml/min) because inulin is filtered and not reapsorbed and not secreted, and it is excreted by urin. So, inulin concentration in urine is equal to that in plasma! That is why inulin shows the GFR!
Clearance of kreatinin is higher than clearance of inulin because kreatinin is even secreted! (filtered, not reapsorbed, secreted and excreted). This means that kreatinin concentration in urine is higher than its concentration in plasma, and its clearance is higher than clearance of inulin, so it is not so good to show GFR. But, kreatinin has two characteristics which are the main reason why it is calculated in clinical practise to show GFR instead of inulin. The reasons are: 1. kreatinin is endogenous substance so doesn't have to be infused 2. I have already said that kreatinin clearance is higher than that of inulin, but plasma concentration of inulin isn't so strictly measured (we get slightly higher value), so in the end we know that kreatinin clearance is approximately equal to GFR
And there is a substance PAH which shows renal plasma flow and renal blood flow. It is filtered, not reapsorbed, then remained PAH is secreted, and in the end, excreted.
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| kaira
Forum Senior
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thnx mildus
gr8 explanation!!
kaira
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| Lancien
Forum Newbie
Topics: 4
Posts: 21
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Thank you very much mildus.You explained it all.
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Matesul
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