Environmental Engineering Reference
In-Depth Information
FiguRe .
Time.course.of.diffusion.equilibrium.across.the.intestinal.epithelium.
where:
dn
1
/
dt
.
=..Rate. of. solute. lux. from. gastrointestinal. (GI). tract. to. GI. epithelial.
cell
dn
2
/
dt
.
=..Rate. of. solute. lux. from. GI. epithelial. cell. to. the. central.
compartment
A
GI
.
=.Cellular.surface.presented.to.the.GI.tract
A
CC
.
=.Cellular.surface.presented.to.the.central.compartment
.
[
C
]
GI
.
=.Solute.concentration.within.the.GI.tract
.
[
C
]
IC
.
=.Solute.concentration.in.the.GI.epithelium.cell
.
[
C
]
CC
.
=.Solute.concentration.within.the.central.compartment
While.data.are.available.to.determine.the.relations.of.
D
mem
.vs..
V
.and.
P
v=0
.vs..
k
ow
,.
one.problem.with.this.approach.in.relation.to.nanomaterials.is.the.lack.of.compa-
rable.data.related.to.the.permeability.to.materials.in.an.appropriate.size.range..While.
irst. principal. thermodynamics. suggests. that. if. the. original. relations. are. accurate,.
the.relation.between.
P
.and.
V
.should.hold.through.the.nanoparticle.range;.the.relation.
between.
P
V=0
.and.
k
ow
.is.in.fact.a.structure/activity.relationship.and.may.not.be.valid.
in.extrapolation.to.such.large.particle.sizes..This.data.gap.must.be.illed.to.under-
stand.the.potential.absorption.and.hence.toxicity.of.ingested.nanomaterials.
9.2.2 e
ndOCytOsis
Endocytosis.refers.to.the.process.of.cellular.transport.without.requiring.transmem-
brane.diffusion..It.usually.involves.the.activation.of.a.membrane.receptor.that.results.
in.the.invagination.and.separation.of.a.membrane.vessel.within.which.the.activating.
material. is. contained.. The. cell,. in. effect,. engulfs. the. particle.. For. nanomaterials,.
