Okay, so we’ve dealt with about
40 percent of our non- volatile acids.
That still leaves 60 percent
if you’re a math wiz.
So, what do you do with here?
You have to have something else
be a part of the process.
In this case, we have NH3 and NH4 that’s going
to take care of the rest of this non- volatile acids.
So, this ammonia, ammonium
response is very important.
You utilize the same kinds of mechanisms
the sodium hydrogen ion exchanger
and what we’ll do is you’ll pump some
of the NH4 out through this exchanger.
Where does that come from? It comes from metabolism.
The NH4 comes from metabolism.
A little bit of NH3 is formed as part of this
reaction involving alpha-ketoglutarate.
NH3 is not charged enough and will be
able to move through the membrane.
NH4 has a charged and therefore has to be
exchanged through this transporter.
So, whether you use NH4, NH3 it’s not important,
that’s just how you’re getting the
molecule out across the apical membrane.
You noticed when you have made an NH4 or NH3,
a new bicarbonate is also formed.
And that gets pushed across the basolateral
membrane and reabsorbed by the blood.
Therefore, you have NH4 of being your excreted acid.
So, it doesn’t matter how you get it there,
even the NH3 by itself bind with the hydrogen ion
or kicked out an NH 4.
You will lose it as NH4.
This involves about 60 percent of your
non- volatile acids will be removed in this manner.
It’s all done in the proximal tubule.
The other important thing about NH3/NH4
is that it is highly adaptable.
If you have a chronic academia condition,
this NH3/NH4 mechanism up regulates.
You Titratable acids don’t,
they pretty much stay the way they are.
But this ability to increase
the amount of hydrogen ion
you can kick out across the
apical membrane through NH3 or NH4
can increase to help you
adopt to that environment.
So, when you think about the amount
of millimoles that we started off with,
with let’s say 70 millimoles
of non- volatile acids.
About 30 millimoles of that were taking care of
through our Titratable acids in the proximal tubule,
the distal convoluted tubule and the collecting duct.
About 15 millimoles in a proximal tubule,
about 5 millimoles in the distal convoluted tubules
and about 10 millimoles in the collecting duct.
We’re taking care of our Titratable acids.
The other 40 millimoles we’re
taking care by NH3/NH4.