Aldosterone removes acid from the blood - Renal System, Medical Video Lecture - MBBS

So in our last video,
we left off here
talking about
aldosterone and how
it works on the principal cell.
And there, kind of
the two big ideas
were losing potassium and
gaining salt and water.
So that was how it worked
on the principal cell.
And aldosterone actually works
on one other type of cell.
It has an important
job there, as well.
So let me actually
just make a little bit
of space on our canvas.
And I'll start talking about
the second type of cell.
That is the alpha
intercalated cell.
So I'm going to draw
it in yellow here.
And this is our alpha
intercalated cell.
And the main job of the
alpha intercalated cell
is to get rid of protons.
And remember that
protons are basically
our way of representing acid.
And if there's an alpha
intercalated cell,
you can probably guess that
somewhere along the line,
there's also a beta
intercalated cell.
And the beta intercalated
cell does, in many ways,
the opposite of the alpha one.
And the beta cell tries
to hold onto acid.
So here, we're going to
talk about how the blood
or body, rather,
gets rid of acid.
And in the beta cells,
in a future video,
we'll talk about how
it holds onto acid.
So here's a blood
vessel as before.
This is our
peritubular capillary.
And it's running
alongside of our cell.
And blood is going to be, in
this case, a little too acidic.
So actually, let me move
this down just a touch
so I can show you.
There we go.
So in this case,
we're going to have,
again, the basolateral surface.
And this is the
apical surface, right?
So we have our two
surfaces and just
to get you visually
oriented, I want
to make sure I just draw
another cell right here.
Just so you remember
that this is basically
where the urine is
kind of collecting.
Oops, made it too small.
So urine is collecting
on this side right here.
And we obviously have
blood on the other side.
And, in our case, let's
imagine that this blood
is getting a little too acidic.
More acidic than we would like.
So I'm going to draw
little protons here.
And there are too
many of them, right?
So it's a little too acidic.
Too many protons.
And our goal, our
blood would love
to get rid of some
of these, right?
We would love to get rid
of some of these protons
so that the blood
is less acidic.
And so, here comes into play
the alpha intercalated cell.
Now all cells are making
carbon dioxide and water.
And I say making because we're
breaking down sugar, right?
And sugar at the very core, or
at the very end of the process
is going to be turned into
carbon dioxide and water.
So all cells are making
carbon dioxide and water.
And when these molecules
within the cell meet up,
there's an enzyme here in the
alpha intercalated cell called
carbonic anhydrase.
And what this does is it helps
the carbon dioxide and water
form into protons and bicarb.
So this is bicarbonate.
HCO3 minus.
And if you actually count
it up, it all adds up.
The carbon ends up
over with the bicarb.
And the oxygens all
end up on the bicarb
and you're left with just one
lonely little proton over here.
And bicarb.
So the bicarb, I would
love if I could somehow
get that bicarb
over to the blood.
That would be fantastic, right?
Because then you can neutralize
one of those little protons.
So there happens to be
a little transporter
in the basolateral surface.
There's a little transporter.
And it basically sends
across this bicarb over here.
So this bicarb ends
up on this side.
And in exchange for doing
that, it takes on a chloride.
OK, no big deal.
So it takes on a
chloride and now
that chloride is
sitting on the inside.
We'll come back to that
chloride in just a second.
That bicarbonate, because this
is where kind of the magic
is happening, that bicarbonate
is going to bind to that proton
and they will do the reverse.
They're actually
going to go back
to water and carbon dioxide.
Right?
So they're actually
going to go back
to water and carbon dioxide.
And what have I really
accomplished here?
Well, I'm no longer
left with any bicarb
in the blood, that's fine.
But here's the cool
thing, I've actually
gotten rid of a proton, right?
Because I have water there and
I have carbon dioxide there.
And this will get, at some
point, I can breathe that out.
And water is water,
so that's great.
And so I've basically
accomplished
something really cool.
I've gotten rid of a proton
and I've gotten some water
and I've gotten carbon dioxide
which I can breathe out
through the lungs at some point
when the blood gets over there.
So this is actually
fantastic for the blood
because I've been
able to get rid
of some of that acid,
which is the whole goal.
Now if you think
about it, I've been
left with a couple of things.
I've got that chloride, which
I said I would get back to.
So let's deal with
that right now.
Happens to be a little
channel for chloride,
so chloride can just make
its way over to the blood.
Well, that's very
convenient, right?
So you can keep doing
this process and that
keeps it nice and tidy.
But you're still
stuck with a proton.
I still got this proton.
I got to figure out what
to do with this proton.
So this proton is going
to build up, right?
If I keep doing
this process, let's
say I keep driving this process,
keep driving this process.
I'm going to get lots and
lots of little protons, right?
I mean I can see how the
bicarb is going to help overall
eventually cancel all
these protons out.
But I'm going to keep building
up protons over here, right?
So for every proton I
get rid of in the blood,
I build up a proton in my cell.
So at the end of
the day, I've got
to figure out how to get rid
of these protons from the cell.
OK, so here's where
aldosterone comes into play.
We have these really
nifty little transporters.
And they do cost energy, so
they're not free of charge.
They're going to take energy.
Let me draw that in right
now, so I don't forget.
It's going to take energy,
ATP, to get this transporter
to work.
But what they'll do
is they'll basically
send a little proton
over into the urine.
And you can just
urinate that out.
So your urine will be a
little bit more acidic, sure,
but that's actually
quite helpful
because I'd rather have
urine that's acidic
and then just flush the
toilet, get rid of it,
rather than having
blood that's acidic.
Because that's a problem.
So that's one transporter that
will get the proton across.
And, actually, this transporter
is going to be driven,
it's actually going to be
working almost like overdrive
when aldosterone is around.
So now finally
we've gotten to what
aldosterone does in these cells.
It makes that transporter
work really, really well.
So you can get rid of protons.
And if you can get
rid of protons,
then this whole process is
going to work really nicely.
Now there's actually
another transporter
that gets rid of protons.
And I'll draw that right here.
And this one is actually
not going to take energy.
And you're thinking, well,
how do you get rid of protons
and not even take energy?
Well, I'm going to
first draw the proton
kind of going across.
And it took energy
the first time around,
but here we're actually going
to use something different.
We're going to use a gradient.
So you remember these cells.
Actually, let me draw it here.
These cells have a
lot of potassium.
Right?
But not too much salt.
In fact, all the salt is
sitting in the blood, right?
So I'll draw the salt sitting
over here in the blood.
Because that's the
main ion for the blood.
Now there isn't much salt
over there in the cell.
And so you can
actually allow salt in.
You'll say, all right, we'll
take a salt molecule in
and because salt wants
to get in so badly,
it actually will
drive this transporter
and will allow proton to
slip out into the urine.
So you're basically,
instead of using energy,
you're using a gradient.
And this second
transporter is also
going to be revved
up by aldosterone.
So aldosterone is really working
on these two transporters
and is going to help
you get rid of protons.
Now, there actually
happens to be
a couple of other transporters
that are important.
I'm just going to
draw them in here.
So there's another one and
this one also takes energy.
And let me draw in
the energy so we
don't forget that because
that's always important.
This one takes energy.
And this one is going
to, again, allow protons
out because that is the
whole point of all this,
is to try to get protons
out of these cells
so we can keep using them so the
alpha intercalated cell doesn't
become just a bag of acid.
And instead of sodium
coming back with it,
this time you're actually
going to use potassium.
Potassium can come back.
But now immediately you can say,
well, there's a problem here.
Potassium wouldn't
want to be in the cell.
There's a lot of
potassium already there.
And that is why this
one takes energy.
So you can already see why
this transport takes energy
whereas the one with
sodium does not.
Because potassium doesn't
want to be in the cell.
It's actually forced
to be in the cell.
And actually, that brings
up my last point, which
is that, you remember we talked
about in the principal cells,
and in fact, in all cells, we
have these sodium potassium
pumps that are on this
basolateral surface?
Remember we talked about that?
Well, in the alpha intercalated
cell, it's no different.
It also has to maintain this
sodium potassium gradient.
So it's going to
drive potassium in.
It's going to take
two potassiums in.
And it's going to force
three sodiums out.
Right?
So three sodiums are going
to get forced outside.
And that, again, takes energy.
So this is also
going to take energy.
So these are the
different transporters
in the alpha intercalated cell.
But I want you to really try
to focus on the key concept.
And the concept
here is that you're
trying to get acid
out of the blood.
And you do that by
bringing extra protons
or making extra protons
in the intercalated cell.
And you saw how that happened.
But the trick is, well,
what do you do with them?
Well, you have to dump
them into the urine.
And that's the whole concept.
Getting acid in the
urine is a process
that is either going to take
energy, like those ATP pumps,
or it's going to take some
cleverness through a gradient,
like that sodium gradient.
And two of these things,
I'll point to again,
this one and this one, are going
to be driven by aldosterone.
So that's where aldosterone
comes into play in these cells.