00:02
So now let's talk
about oxygen transport
and let's really talk about
how we are actually transporting
these oxygen molecules
in our blood.
00:12
This occurs in two ways.
00:14
First we have a little bit
dissolved in our blood plasma,
but most of our oxygen
is actually going
to be bound to iron
on our hemoglobin molecules
found in our red blood cells.
00:31
So each hemoglobin molecule
is actually composed
of four polypeptide chains.
00:37
And each of these chains contain
an iron containing heme group
and is the heme groups
that are going to
carry the oxygen
so each hemoglobin molecule
can carry four oxygen molecules.
00:53
When oxygen is loaded
onto the hemoglobin
we refer to it as oxyhemoglobin.
01:01
When the oxygen is released
from the hemoglobin.
01:04
We refer to it as reduced
hemoglobin or deoxyhemoglobin.
01:12
So the loading and the unloading
of oxygen is going to be
facilitated by changes
in the shape of the
hemoglobin molecule.
01:21
The oxygen binds and the
hemoglobin changes shape
thus increasing the
affinity for oxygen.
01:28
However, when oxygen is released
the hemoglobin is
going to change shape
and decrease the
affinity for oxygen.
01:38
When we have a hemoglobin,
we're all for heme groups
are carrying oxygen
we refer to that
as fully saturated.
01:48
When all four heme groups
are not carrying oxygen however,
we refer to that hemoglobin
as partially saturated.
01:58
So the rate of
unloading and loading
of oxygen is going
to be regulated
in order to ensure that we have
adequate delivery of
oxygen to our cells.
02:10
Multiple factors are
going to influence
this hemoglobin saturation
the most important
of that being the partial
pressure of oxygen.
02:20
However, there are other
factors that can also affect
the saturation including
temperature, the blood pH,
the partial pressure
of carbon dioxide,
and also concentrations
of a molecule
known as
bisphosphoglycerate or BPG
which reduces the affinity
of hemoglobin for our
certain molecules.
02:43
So now let's look
at how this works in
different parts of the body.
02:47
So in arterial blood
the partial pressure
of oxygen is 100
and there is a
about a 20 percent
oxygen volume
compared to the blood.
02:57
So 20 milliliters of oxygen
per 100 milliliters of blood.
03:03
Are hemoglobin molecules are
going to be 98 percent saturated.
03:09
Because of this 98
percent saturation,
further increases in our
partial pressure of oxygen
will actually produce
a minimal effect
on oxygen binding
because there's just nowhere
for these oxygen molecules to go
because it's already
pretty much saturated.
03:28
In contrast, in our venous blood
the partial pressure
of oxygen is much lower
at 40 millimeters of mercury
and because of this it
contains a lower volume
of oxygen at 15%.
03:44
Even still,
at this lower partial pressure
our hemoglobin is still
about 75 percent saturated.
03:52
We also have what's
known as a venous reserve
which are oxygen molecules
that are going to remain
in our venous blood.
04:00
So although we consider venous
blood to be deoxygenated.
04:04
There is still a low level of
oxygen found in that blood.
04:11
So if we look at the
dissociation curves for this
what we find is
that at sea level,
there's plenty of oxygen,
and the partial
pressure in the lungs
is going to be about a hundred
and the saturation is
going to be about 98%.
04:29
This however changes
when we move to
higher altitudes.
04:33
And the reason why is
because at higher altitudes,
the partial pressure
of oxygen is lower,
and because of that
when we breathe in that air
the partial pressure
of oxygen is less
at about 80 instead of at a 100.
04:49
However, even though this
partial pressure is lower,
the hemoglobin is still
about 95 percent saturated.
04:57
So this is why we
can climb a mountain
and still be able to
breathe pretty adequately
until we get two parts
where the oxygen
levels are too low.
05:08
So now let's compare
resting tissue
to metabolically active tissue.
05:14
So in our resting tissue,
the partial pressure of
oxygen is going to be
about 40 millimeters of mercury
or 75 percent
saturated hemoglobin.
05:26
However, and are
metabolically active tissue
are partial pressure of
oxygen is even lower.
05:33
The reason why it's lower is
because we're actually
using this oxygen
in order to undergo these
metabolic processes,
so we're undergoing
cellular respiration
and we're soaking up
all of that oxygen.
05:48
This is okay up until a point
when we get to a partial
pressure of about 20
our hemoglobin is
only going to be about
forty percent saturated.
05:59
And that is because
we have released about
35% of our oxygen
into the tissues for use.
06:06
And so we have a lot
less oxygen occupying
our hemoglobin molecules.
06:13
So other factors
that can influence
hemoglobin saturation
include things like temperature,
the concentration
of H+ molecules,
which affects pH,
the partial pressure
of carbon dioxide,
and the bisphosphate
glycerate molecule
that modifies the
structure of hemoglobin.
06:32
All of these factors can result
in a decrease and hemoglobins
affinity for oxygen.
06:40
These effects usually take place
and are systemic capillaries,
and these enhancements
and our unloading
of oxygen molecules
causes a shift in our oxygen
hemoglobin dissociation curves
to the right.
06:58
A decrease in these factors.
07:00
However,
would shift the curve to the left
thus decreasing
oxygen and unloading
from our hemoglobin.
07:10
BPG our bisphosphoglycerate is
produced by our red blood cells
during the process
of glycolysis.
07:18
The levels of BPG
are going to rise
when oxygen levels are low
and when these levels rise,
this is going to cause a
lot more oxygen unloading.
07:32
As our cells metabolize
glucose several things happen.
07:36
First when they're using oxygen.
07:39
This is going to increase
the partial pressure
of carbon dioxide
as well the concentration
of H+ molecules
and our blood capillaries
is also going to increase
an increase in the H+ molecules
leads to a decrease
in our blood pH,
or it makes our
blood more acidic
also known as acidosis.
08:04
This plus increasing
the partial pressure
of carbon dioxide
is going to cause the
hemoglobin oxygen bond
to weaken
and this is referred
to as the Bohr effect
and this is going to
lead to oxygen unloading.
08:22
Another thing that happens
as we metabolize glucose
is heat production.
08:27
Heat production and
our active tissues
are going to directly
as well as indirectly
decrease our
hemoglobins affinity
for oxygen molecules,
again,
increasing the oxygen unloading
from the hemoglobin.