Biomedical Engineering Reference
In-Depth Information
J
v
[m/sec]
10
-8
6
×
4
J
vwb
2
0
-2
J
vwa
-4
-6
0
50
100
c
si
[mol/m
3
]
FIGURE 8.6
Relations:
J
vwa
=
f
(
c
si
) and
J
vwb
=
f
(
c
si
), for human erythrocytes. (Reprinted
from publication, Kargol, A., Przestalski, M., and Kargol, M.,
Cryobiol.
, 50,
2005.
c
2005, with permission from Elsevier.)
For these relationships to have any physiological significance one must
identify possible mechanisms for changes of these parameters for a give ery-
throcyte. To that end we recall the mechanistic definition of the reflection
coecient, equation (8.45):
σ
=
L
pa
L
p
where
L
pa
is the filtration coecient of permeable pores of the equivalent
membrane (Figure 8.7).
According to this definition any change in the number of permeable or
impermeable pores due, for instance, to gating of ion channels or blockage of
aquaporins and other pores contributing to this transport, not only changes
the filtration coecient of the erythrocyte membrane but also its reflec-
tion coecient. It then affects water influx and eux across the membrane
(Figure 8.8).
8.6.2 Distribution of Pore Sizes
Another aspect of passive transport across porous membranes is the determi-
nation of the pore sizes. In previous sections we implicitly assumed knowledge
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