00:01
Now you also have a few other
mechanisms to get hydrogen ions
out of this apical membrane
in the proximal tubule.
00:12
So, we talked about the sodium hydrogen
ion exchanger and that was very important
for eventually binding into bicarbonate.
00:21
You also have a secondary hydrogen ion transporter,
which is a hydrogen ion pump or ATPase.
00:29
So, this HATPase will also push hydrogen
ions across the apical membrane.
00:36
No, why is this going to be an important process?
Well, remember that a certain portion of the acid
that you took in by a non-volatile acids,
you are going to have to excrete the
hydrogen ion and make a new bicarb.
00:53
So, with the Titratable acids
is one of the ways that occurs.
00:57
So, let’s take phosphate as our example.
01:00
So, phosphate will be coming
down the renal tubule,
and you noticed phosphate
has a negative charge on it.
01:08
So, this is HPO4, 2-.
01:14
You will kick out hydrogen ion
from the hydrogen ion exchanger
or form the V type hydrogen ion pump.
01:22
It will bind then to phosphate. Once it’s
bound as phosphate, you can urinate it out.
01:32
So, this is how you can remove a hydrogen ion,
is you push it across the apical membrane,
have it bind to something and then,
have it be removed from the system.
01:45
You don’t have it bind to bicarb, why?
Because you want to reabsorb bicarb.
01:50
But phosphate, you can get rid
of some of your phosphate.
01:53
But you have to reabsorb your bicarb
so you don’t urinate out your bicarb,
you bind it rather to one of these Titratable acids.
02:03
The hydrogen ions that then
will be left will be in a bound form.
02:10
You may ask, how low can you get
your pH of your urine?
They say about 4,4 is about
the lowest pH of your urine.
02:20
but that could be anywhere from 4,4 up to
whatever is in the blood, maybe 7,4 or so forth.
02:27
So, that’s kind of your
range of pH of your urine.
02:32
You noticed that phosphate
has a pK of around 6,8.
02:36
This becomes important because it’s kind a maximally
bind hydrogen ions at it’s pK which is 6,8.
02:45
So, you can utilize this
when your pH is very close to 7.
02:51
Some of the other Titratable acids such as
urate and creatinine, these have a lower pK.
02:58
Therefore, the pH of the urine has to be lower
Before you’re going to be able to
utilize these two great extent.
03:06
You also have lactate and pyruvate but those pH’s
are actually, or pK’s are below the normal pH
That you can obtain in the urine.
03:15
So, these are less important. So, they have very
minor roles because of the lower pK values.
03:21
In or with Titratable acids, you can,
or make new bicarb in the proximal tubule,
the distal convoluted tubule and the collecting duct.
03:33
You make about 40 percent of your new bicarb using
titratable acids, phosphate, urate, and creatinine.
03:43
Which one are you going to use? Depends upon
the pH of the urine and it’s pK value.
03:50
So, if we look at something like a pH
range here for something like phosphate
has a wide pH range, so you can utilize
that throughout many different pH’s of the urine.
04:02
Something like creatinine, is a little bit tighter.
And so, you can’t always use creatinine
to bind those hydrogen ions
to be able to urinate them out.