Acute Renal Failure Explained Clearly by MedCram.com | 2 of 3


welcome to part two of acute renal
failure let’s little let’s review a little bit
here about what we were talking about we were talking about chem seven we have
the BUN and we’ve got the creatinine bu n stands for the blood urea nitrogen
remember it’s made in the liver it is both filtered and reabsorbed
whereas the creatinine is the end product of muscle metabolism and it is
filtered and secreted so let’s look at our nephron once again that’s the loop
of Henle that’s distal convoluted tubule
collecting duct and you’ve got the toilet down here okay and you’ve got the the a Ferentz and the efferent arteriole
and remember what we said about the U n bu n is the blood urea nitrogen it goes
through and also gets reabsorbed okay so that’s B u N and you’ve got the
creatinine cratan n’ goes does not get reabsorbed but instead goes out actually
a little bit gets secreted here okay so if you’ve got acute renal failure remember that the GFR the glomerular
filtration rate is going to go down so if that’s the case then your B UN the UN
is going to go up just because of the fact that the glomerular eighth is lower
therefore not as much as being filtered the B UN is going to go up but because
it’s going by slower because the GFR is down then
more of it is going to be reabsorbed and so it’s going to go up by even more
that’s opposed to the creatinine creatinine is going to go up why because
the GFR is low and the GFR is low because there’s a cute renal failure
going on and that means that Crichton is going to go up but it’s not going to go
up any more than that because it’s not being reabsorbed and so
what you see here is that the BU n goes up more than the Kratt name does when
you have a decrease in your GFR just based on the fact that there’s lower
flow so lower flow means higher Buick writing ratio okay so what would be a
number here that we could associate with it so normal would be for instance 15
over 1 so if the B went over cratan een if the b1 went up by more than that of
the crannium we could say for instance that this would go to a2 and a 30 okay
so the B would go up to 30 in the grant would go up to 2 so you could go up by
instead of having a 15 to 1 ratio you would have more like instead of even
30 would even go up high or go to 40 so 40 to 2 ratio which is the same as a 20
to 1 ratio so here we would see the normal ratio is 15 to 1 and it would go
up to 20 to 1 or in this case 40 over 2 and that would be from a low flow State
now what would happen here if for some reason there was a shutdown a different
type of acute renal failure at acute renal failure not because there’s less
flow coming to the glomerulus but instead because the actual tubules which
line the nephron something we call renal renal failure if they weren’t working
well what would happen is that you would still get a slow down here
because these cells are not working and the b1 would go up but it would only go
up for one reason and that’s because the GFR is low you would not get
reabsorption of this the UN and so what you would have is this would be more of
a pre renal what I mean by that is is that there is a reduction in the flow
coming here and because of that you’re getting the BU when increasing because
of the low flow and also the vun is being reabsorbed because these cells are
working so that would be a pre renal situation or in a renal situation in a
real situation these cells are not working and so if these cells are not
working the flow is going to be low as a result of that but you’re not going to
get bu and reabsorption and so it’s going to go up instead of being 50 into
one okay it’s going to go to 30 over two which is still the same 15 to one ratio
but they’re both going up but this is not going up more than that it so it
still holds the same ratio so in a renal situation where there’s a problem with
the kidney itself you hold and maintain that 15 to one ratio but when there is a
pre renal State in other words there’s not enough flow coming to the glomerulus
you’re going to get a reabsorption of the BU n preferentially and that’s going
to increase your bu and ratio to 20 to 1 okay so the bottom line here is that the
bu and the correcting ratio can kind of tell you what kind of renal failure have
is it pre renal sot mia or is it renal a zootie mia pre renal azo to me is where
there’s not enough blood coming to the kidney renal azo t Mia is where there’s
something wrong with the kidney itself if it’s 20 to 1 ratio like this you’re
thinking of pre renal sot mia if it’s still 15 to 1 ratio its renal sot mia
okay another way of looking at that is just looking at sodium and
concentration so let’s go ahead and draw our glomerulus again a little bigger
this time here’s the glomerulus the proximal convoluted tubule loop of Henle
and then out okay so pretend you’re a nephron and you’ve got two different
situations you’ve got a situation where you have a pre renal situation where
there is not enough blood coming in to the kidney and you’ve got a renal
situation where there’s a problem with the actual tubules that are supposed to
be transporting fluids and reabsorbing in a pre renal situation there’s not
enough blood coming in and you have a reduction in your GFR well the kidney
thinks that there’s not enough volume and the way the kidney regulates volume
is by reabsorbing sodium so if there’s not enough volume all the kidney is
going to do is just try to reabsorb more sodium and so what’s going to happen to
your urine that’s coming out you think it’s going to be high in sodium or low
in sodium well it’s going to be very low in sodium in a pre renal situation and
of course as sodium goes up guess what else comes with it water and so are you
going to have a lot of water in the filtrate in the urine that’s coming out
the answer is no so you’re going to be very low in sodium and very low in water
so that leaves a high concentration or a high osmolarity to the urine that’s
coming out okay let’s look at the flip side of that again here’s our Clare Ulis Oh Mary Alice proximal convoluted be a
loop of Henle and collecting tube you’ll going out to the toilet down below okay
so in this situation we’ve got a renal problem the renal problem is is that
these cells are not reabsorbing in fact none of them are reabsorbing there’s a
problem all over and so what’s the situation here here we’ve got plenty of
fluid coming to the kidneys but because these cells are not working all of that
sodium water is just going right through and out so we would expect to see a high
sodium concentration a high water concentration and therefore a low
osmolarity to the fluid and that’s in renal when there’s a problem with renal okay so let’s summarize once again make
sure everyone’s on the same page here so we’ve got the B UN okay what are some of
the points that we learned about the B UN it’s synthesized in the liver okay
it’s filtered and absorbed okay what are things that can increase it that have
nothing to do with the kidney we’ve talked about that we’ve talked about
fever we’ve talked about GI bleeding okay
there’s antibiotics that tip like tetracycline there is catabolic effects steroids all that what are some things
that can decrease it well liver failure okay and then what about proximal
convoluted tubule we see there we see that it parallels the reabsorption of
sodium and water and so we know that it’s reabsorbed okay
and so at because of that in a low flow state and a low flow state it’s going to
be really absorbed it’s going to go up okay now what about granting all right
we know that it’s the end product of muscle and that it is filtered and
secreted okay so what are some things that can increase it they have nothing
to do with the kidney function we know that it can be increased by drugs that
prevent its secretion in the kidney and that would be cimetidine and
trimethoprim what are some things that they can decrease it muscle wasting okay
and we know that it goes up in renal failure okay well let’s talk about the B
UN to creatinine ratio we know that because the B UN goes up even higher in
a low flow state that it’s usually 20 to 1 ratio if it’s pre renal pre renal
again is any reason that causes a decrease in blood flow to the kidneys
and that it’s 15 to 1 in renal okay and in renal remember is where there’s a
problem with the kidney itself and pre renal is where there’s a problem with
the amount of blood flow that’s going to the kidney okay now join me for part three for the final
wrap-up of acute renal failure thanks for joining me

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