Biomedical Engineering Reference
In-Depth Information
B
CR
B
AC
q
O
A
q
O
C
q
O
R
H
B
CA
B
RC
Alveoli
Capillaries
Red Blood Cell
FIGURE 8.16
The diffusion of oxygen from the alveoli into the red blood cell.
alveoli,
q
O
C
be the quantity of
O
2
in the capillaries, and
q
O
R
be the quantity of
O
2
in the red
blood cells. The equation that describes the movement of oxygen is given by
q
O
A
¼
B
CA
q
O
C
B
AC
q
O
A
q
O
C
¼
B
AC
q
O
A
þ
B
RC
q
O
R
B
CA
q
O
C
B
CR
q
O
C
q
O
R
¼
B
CR
q
O
C
B
RC
q
O
R
ð
8
:
71
Þ
Once inside the red blood cell, oxygen then binds with hemoglobin
H
ðÞ
, forming oxyhe-
moglobin
. This is a reversible reaction that allows oxygen to be taken up by the red
blood cell and released into the tissues. The binding of
ð
Þ
HbO
8
2
with hemoglobin allows 100
times more oxygen in the blood than if it had just dissociated into the blood. The overall
chemical reaction is
O
Hemoglobin has four polypeptide subunits (proteins), with each polypeptide subunit
attached to a heme group. Each heme group can bind with a molecule of
O
2
:
The four
molecules of
do not simultaneously react with heme groups but occur
in four steps, with each step facilitating the next step. Figure 8.17 illustrates the five states
of hemoglobin based on the number of
O
2
that bind to
Hb
O
2
molecules bound to it, ranging from 0 to 4. Let
q
H
0
be the quantity of
Hb
,
q
H
1
be the quantity of
HbO
2
, and so on, up to
q
H
4
be the quantity
of
Equation (8.72) describes the chemical reactions that take place to create the
oxyhemoglobin:
Hb
O
8
:
q
H
0
¼
K
q
H
1
K
q
H
0
q
O
R
10
01
q
H
1
¼
K
q
H
0
q
O
R
þ
K
q
H
2
K
q
H
1
K
q
H
1
q
O
R
q
H
2
¼
K
12
q
H
1
q
O
R
þ
K
32
q
H
3
K
21
q
H
2
K
23
q
H
2
q
O
R
ð
8
:
72
Þ
01
21
10
12
q
H
3
¼
K
q
H
2
q
O
R
þ
K
q
H
4
K
q
H
3
K
q
H
3
q
O
R
23
43
32
34
q
H
4
¼
K
34
q
H
3
q
O
R
K
43
q
H
4
K
01
q
O
R
K
12
q
O
R
K
23
q
O
R
K
34
q
O
R
q
H
2
q
H
0
q
H
1
q
H
3
q
H
4
H
K
10
K
32
K
43
K
21
FIGURE 8.17
The five states of hemoglobin.
