- [Voiceover] In order for our bodies to function properly,
the pH of our blood has to be within a fairly narrow range.
Our pH, so the pH of blood
needs to be between
seven point three five and seven point four five.
If the pH falls below seven point three five,
you're going to be diagnosed,
and you know this line is, there is kind of a gray area here
but this is what's defined by the medical community
if your pH falls below seven point three five,
you're actually diagnosed with acidosis.
Your blood is becoming too acidic.
You have too high of a
hydrogen ion concentration in your blood,
or a hydronium concentration in your blood.
If your pH, if the pH in your blood gets above
seven point four five, you're diagnosed with alkalosis.
Alkalosis. Your blood is too alkaline.
It's becoming too basic. The hydrogen concentration,
hydrogen ion concentration in your blood
is getting too low.
And so you might say, "Wow, you know this feels like
a fairly narrow range. How does blood, how does our body
put up with acidic things, acidic molecules
entering our blood, or basic molecules entering our blood.
How can it handle that without our pH,
while keeping our pH in this range right over here?"
And the answer lies in something that's also useful
for the transportation of carbon dioxide in our blood.
And this right over here, these equilibrium reactions,
we see that carbon dioxide, when you put it in the blood,
which is primarily water,
so carbon dioxide in aqueous solution, it will react.
And we have some enzymes that help this along,
but it will react to form carbonic acid.
Let me write this down. It will react to form carbonic acid,
which is a weak acid, this is carbonic adic.
And then that can dissociate to form bicarbonate.
Let me write that over here.
Bicarbonate. Bicarbonate.
And a hydrogen ion, or when we know that that would
just attach to a water molecule and become a hydronium ion.
And so, why is this useful?
Well, I said, it's actually part of
the carbon dioxide transportation in the blood because,
based on the sources I've looked at,
about five to 10 percent of your carbon dioxide
can just dissolve in the blood
and then also another, roughly, five or 10 percent
can actually be bound to hemoglobin
and be transported that way.
But the bulk of it actually needs to go through,
needs to actually be transformed, needs to react
to become carbonic acid and bicarbonate
in order to be transported.
In fact, in your blood, most of the carbon dioxide
in your blood is actually in this form right over here.
And in particular, bicarbonate.
In the sources that I look at,
80 to 90 percent of the carbon dioxide in your blood
is being transported in these forms,
and primarily as bicarbonate.
So this isn't the topic of this video,
what's a useful way to transfer, to transport carbon dioxide
in your blood, but this is how we do it.
But the topic of this video is why this is
also useful for maintaining our blood pH in this range.
Because these equilibrium reactions between
carbon dioxide, carbonic acid, and bicarbonate
this is a buffer system.
This is a buffer, this is a buffer system.
And the word "buffer," in our everyday language,
it refers to something that kind of smooths
the impact of something,
or it reduces the shock of something.
And that's exactly what's happening here.
Let's think about, remember,
these are all equilibrium reactions,
this is a weak acid, and you can even look at the different
constituents of these molecules and account for them.
You have one carbon here,
one carbon here,
one carbon there.
You have one, two, three oxygens there.
One, two, three oxygens there.
You have two hydrogens, two hydrogens, two hydrogens.
But let's just think about what if you
started dumping hydrogen ions in the blood.
So, what if you were to dump hydrogen ions,
what's going to happen?
Well, if you dump more hydrogen ions,
if this right over here increases.
Actually, let me put it this way,
if you were to just dump hydrogen ions
and if you didn't have this buffer system,
then your pH would decrease.
Your pH would go down, and if you do it enough,
your pH, you would end up with acidosis.
But lucky for us, we have this buffer system.
And so if you increase your hydrogen ion concentrations,
Le Chatelier's principle tells us,
"Hey, these equilibrium reactions
are going to move to the left."
So the more hydrogen ions you have sitting in the blood,
the more likely they're gonna bump
into the bicarbonate in just the right way
to form carbonic acid.
And the more carbonic acid that you have in the blood,
well, it's the less likely that you're going to have
the carbon dioxide reacting with the water
to form more carbonic acid.
So, as you add more hydrogen ions,
they're just going to be sopped up
by the bicarbonate.
So this equilibrium, this set of equilibrium reactions
is going to move to the left.
So you're not going to have as big effect on pH.
And similarly, if you dumped some base,
let's say, you dumped some base
in your blood right over here,
well, instead of it just making your pH go up,
and possibly give you alkalosis,
well now, the base is going to sop up the hydrogen ions,
and typically that would just make your pH go up,
but if you have these things going down,
well then, you have fewer of these to react
and have the equilibrium reaction go to the left
and so the reaction is going to move
more and more to the right.
And so this reaction, you're just gonna have more
carbon dioxide being converted to carbonic acid
being converted to bicarbonate.
This whole thing is going to move to the right.
And so it's going to be able, to some degree,
replace the lost hydrogen ions.
So this right over here's a buffer system.
It helps dampen the impact, as if you have more
hydrogen ions enter the system,
or as if you have something
sopping up all of the hydrogen ions.
And it's super important for us,
well, just being able to live.
And frankly, all mammalian systems.