Biomedical Engineering Reference
In-Depth Information
reverse reaction occurs, releasing
Oxygen in the mitochondria is consumed
with sugar to create ATP during cell respiration, as described in the next section. The myo-
globin then diffuses back to the cytosol, where the process repeats itself. The first reaction in
the cytosol is given by
O
2
and
Mb.
D
1
O
2
þ
Mb
!
MbO
2
and in the mitochondria
D
2
MbO
!
Mb
þ
O
2
which is described by the following equations that includes diffusion:
2
q
O
M
q
Mb
M
þ
B
IM
q
O
I
q
MbO
M
¼
D
1
q
O
M
q
Mb
M
K
MT
q
MbO
M
q
O
M
¼
D
1
ð
8
:
74
Þ
q
Mb
M
¼
D
q
O
M
q
Mb
M
þ
K
TM
q
Mb
T
1
q
MbO
T
K
TM
q
Mb
T
q
MbO
T
¼
D
2
q
MbO
T
þ
K
MT
q
MbO
M
q
Mb
T
¼
D
2
where
K
TM
are the diffusion transfer rates from the cytosol into the mitochondria
and the mitochondria into the cytosol, respectively;
K
MT
and
q
O
M
is the quantity of
O
2
inside the cyto-
sol;
q
Mb
M
is the quantity of
in the cytosol;
q
MbO
M
is the quantity of
2
in the cytosol;
Mb
MbO
q
MbO
T
is the quantity of
2
inside the mitochondria; and
is the quantity of
inside
MbO
q
Mb
T
Mb
the mitochondria. We assume that none of the
MbO
2
or
Mb
leaves the cell. We assume that
no
diffuses into the mitochondria.
Carbon dioxide is created in the cells during cell respiration, as discussed shortly. It then
diffuses out of the cell into the interstitial fluid and then moves to the capillaries. Once
inside the capillaries, 90 percent of the carbon dioxide moves into the red blood cell, and
10 percent dissolves into the fluid of the blood. Carbon dioxide is then transported to the
lungs.
When inside the red blood cell, carbon dioxide almost instantaneously goes through the
following reactions:
O
2
leaves the cell and no
Mb
i
1.
Approximately 70 percent of the carbon dioxide reacts with water to form carbonic acid
H
2
CO
3
H
ðÞ
ð
Þ
, using the enzyme carbonic anhydrase, and then dissociates into hydrogen
ions. These reactions occur within a fraction of a second and
HCO
3
and biocarbonate
are given by
carbonic anhydrase
!
HCO
3
þ
H
þ
2.
The hydrogen then binds with the hemoglobin in the red blood cell.
CO
þ
H
O
!
H
CO
2
2
2
3
H
þ
þ
HbH
! ð
Hb
3.
The biocarbonate diffuses out of the red blood cell, replaced by chloride ions via a
biocarbonate-chloride carrier protein in the cell membrane.
