Factors Affecting Hb-O

2

Affinity

Changes in Hb-O

2

affinity of the oxygen

saturation curve

.

%

saturation

100

0

PO

2

, mm Hg

25

50

75

100

Hb + add back 2,3 BPG

tissue PO

2

lung PO

2

Hb "stripped"

of 2,3 BPG

2,3-Bisphosphoglyceric acid has important physiological

consequences

2,3 BPG alters O

2

affinity

2,3-Bisphosphoglycerate

(BPG) [2,3-

Diphosphoglyceric acid

(DPG)]

Hb-O

2

Dissociation Curves

pH = 7.4, 7.2,
7.0 P

CO2

= 40

P

CO2

= 25, 40,

55 pH = 7.4

The Hb-O

The Hb-O

2

2

dissociation curve is highly non-

dissociation curve is highly non-

linear in the physiological range of values of

linear in the physiological range of values of

P

P

O2

O2

(40-100 mmHg).

(40-100 mmHg).

P

50

= 26

mmHg (P

CO2

=

40 mmHg &
pH = 7.4)

Effect of
pH

Effect of
PCO

2

Effect of
temperatur
e

PCO

2

effect is the same as the

pH effect

(Bohr Effect: covered
later)

CO

2

+ H

2

O  H

2

CO

3

 H

+

+

HCO

3

-

Biochemical & functional differences of Fetal

Hemoglobin

advantag
e

Expression of Hb differs

during development

Fetal red blood cells have a higher
oxygen affinity than do maternal red
cells, because the



hemoglobin has a

lower affinity for BPG than does adult 

hemoglobin, making fetal red cells
behave like adult red cells “stripped” of
BPG.

Hb-oxygen dissociation

curve

hemoglobin

myoglobin

Active
cell

m

l

O

2

/1

0

0

m

l

b

lo

o

d

0

5

1
0

1
5

2
0

Tissues

3 ml/100
ml

17 ml/100
ml

Let’s compare Hemoglobin and

Myoglobin