Bohr effect vs. Haldane effect | Human anatomy and physiology | Health & Medicine | Khan Academy

So we've talked a little bit
about the lungs and the tissue,

and how there's an interesting
relationship between the two

where they're trying to
send little molecules back

and forth.

The lungs are trying to
send, of course, oxygen out

to the tissues.

And the tissues are
trying to figure out

a way to efficiently
send back carbon dioxide.

So these are the
core things that

are going on between the two.

And remember, in terms
of getting oxygen across,

there are two major
ways, we said.

The first one, the easy one
is just dissolved oxygen,

dissolved oxygen in
the blood itself.

But that's not the major way.

The major way is when oxygen
actually binds hemoglobin.

In fact, we call that HbO2.

And the name of that
molecule is oxyhemoglobin.

So this is how the
majority of the oxygen

is going to get
delivered to the tissues.

And on the other side,
coming back from the tissue

to the lungs, you've got
dissolved carbon dioxide.

A little bit of carbon
dioxide actually, literally

comes just right in the plasma.

But that's not the majority of
how carbon dioxide gets back.

The more effective ways of
getting carbon dioxide back,

remember, we have this
protonated hemoglobin.

And actually
remember, when I say

there's a proton
on the hemoglobin,

there's got to be some bicarb
floating around in the plasma.

And the reason that works is
because when they get back

to the lungs, the proton, that
bicarb, actually meet up again.

And they form CO2 and water.

And this happens because
there's an enzyme called

carbonic anhydrase inside
of the red blood cells.

So this is where the carbon
dioxide actually gets back.

And of course,
there's a third way.

Remember, there's
also some hemoglobin

that actually binds
directly to carbon dioxide.

And in the process, it forms
a little proton as well.

And that proton can
go do this business.

It can bind to a
hemoglobin as well.

So there's a little
interplay there.

But the important ones I want
you to really kind of focus in

on are the fact that
hemoglobin can bind to oxygen.

And also on this
side, that hemoglobin

actually can bind to protons.

Now, the fun part
about all this is

that there's a
little competition,

a little game going on here.

Because you've got,
on the one side,

you've got hemoglobin
binding oxygen.

And let me draw it twice.

And let's say this top one
interacts with a proton.

Well, that protons going to want
to snatch away the hemoglobin.

And so there's a little
competition for hemoglobin.

And here, the oxygen gets
left out in the cold.

And the carbon dioxide does
the same thing, we said.

Now, we have little hemoglobin
bound to carbon dioxide.

And it makes a proton
in the process.

But again, it leave
oxygen out in the cold.

So depending on whether
you have a lot of oxygen

around, if that's the kind
of key thing going on,

or whether you have a lot
of these kinds of products

the proton or the
carbon dioxide.

Depending on which one you
have more of floating around

in the tissue in the
cell, will determine

which way that reaction goes.

So keeping this
concept in mind, then I

could actually step
back and say, well,

I think that oxygen is affected
by carbon dioxide and protons.

I could say, well, these two,
carbon dioxide and protons,

are actually
affecting, let's say,

are affecting the, let's say,
the affinity or the willingness

of hemoglobin to bind,
of hemoglobin for oxygen.

That's one kind of
statement you could

make by looking at that
kind of competition.

And another person come
along and they say,

well, I think oxygen
actually is affecting,

depending on which one,
which perspective you take.

You could say, oxygen is
affecting maybe the affinity

of hemoglobin for the
carbon dioxide and proton

of hemoglobin for
CO2 and protons.

So you could say it
from either perspective.

And what I want to point
out is that actually,

in a sense, both
of these are true.

And a lot of times we
think, well, maybe it's

just saying the
same thing twice.

But actually, these are
two separate effects.

And they have two
separate names.

So the first one, talking about
carbon dioxide and protons,

their effect is called
the Bohr effect.

So you might see that
word or this description.

This is the Bohr effect.

And the other one, looking at
it from the other prospective,

looking at it from
oxygen's perspective,

this would be the
Haldane effect.

That's just the name
of it, Haldane effect.

So what is the Bohr effect
and the Haldane effect?

Other than simply saying
that the things compete

for hemoglobin.

Well, let me actually bring
up a little bit of the canvas.

And let's see if I
can't diagram this out.

Because sometimes I think a
little diagram would really

go a long way in
explaining these things.

So let's see if I can do that.

Let's use a little graph and see
if we can illustrate the Bohr

effect on this graph.

So this is the partial
pressure of oxygen,

how much is dissolved
in the plasma.

And this is oxygen
content, which is to say,

how much total oxygen
is there in the blood.

And this, of course,
takes into account

mostly the amount of oxygen
that's bound to hemoglobin.

So as I slowly increase the
partial pressure of oxygen,

see how initially,
not too much is

going to be binding
to the hemoglobin.

But eventually as a few
of the molecules bind,

you get cooperativity.

And so then, slowly the
slope starts to rise.

And it becomes more steep.

And this is all because
of cooperativity.

Oxygen likes to bind where other
oxygens have already bound.

, And then it's
going to level off.

And the leveling off
is because hemoglobin

is starting to get saturated.

So there aren't too many
extra spots available.

So you need lots and lots of
oxygen dissolved in the plasma

to be able to seek out and
find those extra remaining

spots on hemoglobin.

So let's say we
choose two spots.

One spot, let's say,
is a high amount

of oxygen dissolved
in the blood.

And this, let's
say, is a low amount

of oxygen dissolved
in the blood.

I'm just kind of choosing
them arbitrarily.

And don't worry about the units.

And if you were to think
of where in the body

would be a high
location, that could

be something like
the lungs where

you have a lot of oxygen
dissolved in blood.

And low would be, let's say,
the thigh muscle where there's

a lot of CO2 but not so much
oxygen dissolved in the blood.

So this could be two
parts of our body.

And you can see that.

Now, if I want to figure
out, looking at this curve

how much oxygen is being
delivered to the thigh,

then that's actually
pretty easy.

I could just say, well, how much
oxygen was there in the lungs,

or in the blood vessels
that are leaving the lungs.

And there's this much
oxygen in the blood

vessels leaving the lungs.

And there's this much
oxygen in the blood

vessels leaving the thigh.

So the difference, whenever
oxygen is between these two

points, that's the amount of
oxygen that got delivered.

So if you want to figure out
how much oxygen got delivered

to any tissue you can simply
subtract these two values.

So that's the oxygen delivery.

But looking at this, you
can see an interesting point

which is that if you wanted to
increase the oxygen delivery.

Let's say, you wanted
for some reason

to increase it, become more
efficient, then really,

the only way to
do that is to have

the thigh become more hypoxic.

As you move to the
left on here, that's

really becoming hypoxic,
or having less oxygen.

So if you become more
hypoxic, then, yes, you'll

have maybe a lower point
here, maybe a point like this.

And that would mean a
larger oxygen delivery.

But that's not ideal.

You don't want your
thighs to become hypoxic.

That could start
aching and hurting.

So is there another way to
have a large oxygen delivery

without having any
hypoxic tissue,

or tissue that has a low
amount of oxygen in it.

And this is where the Bohr
effect comes into play.

So remember, the
Bohr effect said

that, CO2 and protons
affect the hemoglobin's

affinity for oxygen.

So let's think of a situation.

I'll do it in green.

And in this situation, where
you have a lot of carbon dioxide

and protons, the
Bohr effect tells us

that it's going to be harder
for oxygen to bind hemoglobin.

So if I was to sketch
out another curve,

initially, it's going to
be even less impressive,

with less oxygen
bound to hemoglobin.

And eventually, once the
concentration of oxygen

rises enough, it will
start going up, up, up.

And it does bind
hemoglobin eventually.

So it's not like it'll
never bind hemoglobin

in the presence of carbon
dioxide and protons.

But it takes longer.

And so the entire curve
looks shifted over.

These conditions of high
CO2 and high protons,

that's not really
relevant to the lungs.

The lungs are thinking,
well, for us, who cares.

We don't really have
these conditions.

But for the thigh,
it is relevant

because the thigh
has a lot of CO2.

And the thigh has
a lot of protons.

Again, remember, high
protons means low pH.

So you can think
of it either way.

So in the thigh, you're going
to get, then, a different point.

It's going to be on the green
curve not the blue curve.

So we can draw it at
the same O2 level,

actually being down here.

So what is the O2 content in the
blood that's leaving the thigh?

Well, then to do it
properly, I would say, well,

it would actually be over here.

This is the actual amount.

And so O2 deliver is actually
much more impressive.

Look at that.

So O2 delivery is increased
because of the Bohr effect.

And if you want to know exactly
how much it's increased,

I could even show you.

I could say, well, this
amount from here down to here.

Literally the vertical
distance between the green

and the blue lines.

So this is the extra oxygen
delivered because of the Bohr

effect.

So this is how the Bohr effect
is so important at actually

helping us deliver
oxygen to our tissues.

So let's do the same thing,
now, but for the Haldane effect.

And to do this, we actually
have to switch things around.

So our units and our axes
are going to be different.

So we're going to have the
amount of carbon dioxide there.

And here, we'll do carbon
dioxide content in the blood.

So let's think through
this carefully.

Let's first start
out with increasing

the amount of carbon
dioxide slowly but surely.

And see how the content goes up.

And here, as you increase
the amount of carbon dioxide,

the content is kind of
goes up as a straight line.

And the reason it
doesn't take that S

shape that we had
with the oxygen

is that there's no cooperativity
in binding the hemoglobin.

It just goes up straight.

So that's easy enough.

Now, let's take two
points like we did before.

Let's take a point,
let's say up here.

This will be a high amount
of CO2 in the blood.

And this will be a low
amount of CO2 in the blood.

So you'd have a low amount,
let's say right here,

in what part of the tissue?

Well, low CO2, that
sounds like the lungs

because there's not
too much CO2 there.

But high CO2, it
probably is the thighs

because the thighs like
little CO2 factories.

So the thigh has a high
amount and the lungs

have a low amount.

So if I want to look at the
amount of CO2 delivered,

we'd do it the same way.

We say, OK, well, the
thighs had a high amount.

And this is the amount of
CO2 in the blood, remember.

And this is the amount
of CO2 in the blood when

it gets to the lungs.

So the amount of CO2 that
was delivered from the thigh

to the lungs is the difference.

And so this is how
much CO2 delivery

we're actually getting.

So just like we had O2 delivery,
we have this much CO2 delivery.

Now, read over the
Haldane effect.

And let's see if we can actually
sketch out another line.

In the presence of high
oxygen, what's going to happen?

Well, if there's a
lot of oxygen around,

then it's going to change
the affinity of hemoglobin

for carbon dioxide and protons.

So it's going to allow less
binding of protons and carbon

dioxide directly
to the hemoglobin.

And that means that you're
going to have less CO2

content for any given amount
of dissolved CO2 in the blood.

So the line still is a straight
line, but it's actually,

you notice, it's kind
of slope downwards.

So where is this relevant?

Where do you have
a lot of oxygen?

Well, it's not really
relevant for the thighs

because the thighs don't
have a lot of oxygen.

But it is relevant
for the lungs.

It is very relevant there.

So now you can actually say,
well, let's see what happens.

Now that you have high
O2, how much CO2 delivery

are you getting?

And you can already see it.

It's going to be more because
now you've got this much.

You've got going all
the way over here.

So this is the new
amount of CO2 delivery.

And it's gone up.

And in fact, you can even
show exactly how much

it's gone up by, by simply
taking this difference.

So this difference right
here between the two,

this is the Haldane effect.

This is the visual way
that you can actually

see that Haldane effect.

So the Bohr effect and
the Haldane effect, these

are two important
strategies our body

has for increasing the
amount of O2 delivery and CO2

delivery going back and
forth between the lungs

and the tissues.