00:02
In this lecture, we’re dealing
with the transport of O2 and CO2.
00:07
Our learning goals will be
to understand O2 transport
and be able to differentiate
between those modes of transport.
00:16
Also, you will be to identify the factors
that affect oxygen hemoglobin dissociation.
00:23
Furthermore, after this lecture, you’ll
be able to understand CO2 transport
and be able to differentiate
the modes of transport
as well as identify factors
that affect that transport.
00:35
So as we think about
O2 transport,
we really need to concentrate on what
the partial pressure of oxygen is.
00:44
And so there are three partial pressures
that we need to keep in mind.
00:48
PaO2, PaO2 and PVO2.
00:53
And the reason why I very much
distinguished between capital A
and small A O2, is it tells
you where to locate it.
01:01
So PaO2 is the partial pressure of
oxygen in the arterial circulation.
01:06
PAO2 is the partial
pressure of oxygen in the alveoli.
01:11
PVO2 is the partial pressure of
oxygen in the venous circulation.
01:16
And you need to remember what those
are as we walk through O2 transport.
01:22
So to give you an idea of those
numbers, the PaO2 is around 95.
01:27
The PAO2 is around 100,
and the PVO2 is around 40
millimeters of mercury.
01:34
And so those are numbers you
want to kind of keep in mind
as we walk through this
transport of oxygen.
01:43
Those numbers seem like they
are going to be very important
because these are the numbers that we
measure from an arterial blood gas.
01:52
So if were to take an arterial sample
and measure the amount of oxygen in it,
those are the numbers
that you get.
01:59
So this is a very important thing
to help us distinguish between if
someone has a hypoxemia, versus they
have a normal O2 concentration.
02:07
Those are the partial pressures.
02:11
However, partial pressure
only gives us one insight
into how much O2 is being
carried by the blood.
02:19
The other insight that we need to think
about is how much is diffused in a
gaseous form and that is really based
upon the amount of O2 solubility.
02:30
Unfortunately, O2 is
not very soluble.
02:33
So let’s go through a calculation to
edify this.
02:37
Dissolved O2 is the
partial pressure of O2
times the solubility of
O2 at body temperature.
02:44
If we go through this calculation,
it ends up that you have
less than 1 milliliter of O2
per 100 mL of blood or per
1 deciliter of blood.
02:56
So just a very small amount.
02:59
If we look on the venous side,
it’s even smaller 0.124.
03:04
So these are very, very,
very small concentrations
of oxygen in a dissolved form.
03:14
So having this amount of oxygen
only in the dissolved form is
unfortunately not compatible with life.
03:22
If you did not have someway
to carry the oxygen,
you would not be able to
transport enough blood to cells
to keep them alive via
aerobic metabolism.