Figure 22.20
The amount of oxygen carried by hemoglobin
depends on the P
O
2
(the amount of oxygen) available locally.
This relationship ensures optimal oxygen pickup and delivery.
20
40
60
80
100
0
20
40
60
80
100
0
Percent O
2
saturation of hemoglobin
P
O
2
(mm Hg)
In the tissues of other organs,
where P
O
2
is low (40 mm Hg), Hb
is less saturated (75%) with O
2
.
This axis tells you the relative
amount (partial pressure) of
O
2
dissolved in the fluid
surrounding the Hb.
In the lungs, where P
O
2
is high
(100 mm Hg), Hb is almost
fully saturated (98%) with O
2
.
The oxygen-hemoglobin dissociation curve will
help you understand how the properties of
hemoglobin (Hb) affect oxygen binding in the
lungs and oxygen release in the tissues.
This axis tells you how much
O
2
is bound to Hb. At 100%,
each Hb molecule has 4 bound
oxygen molecules.
If more O
2
is present,
more O
2
is bound.
However, because of
Hb’s properties (O
2
binding strength
changes with saturation),
this is an S-shaped curve,
not a straight line.
Hemoglobin
Oxygen
FOCUS
The Oxygen-Hemoglobin Dissociation Curve
830
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