Microvascular Beds - Biofluidmechanics: An Introduction to Fluid Mechanics Macrocirculation and Microcirculation - page 200

other probability statements come into play. For instance, they will state if any portion of
the cell that is expressing adhesion molecules comes within one cell diameter from the
vessel wall, then there is some probability for adhesion to the vessel wall to occur. The
adhesion between the cell and the vessel wall is then typically modeled as a spring, so
that if the fluid forces exceed the spring's elastic capacity, the bond between the cell and
the wall will break. However, once the cell is attached to the wall, there is also some prob-
ability that states how likely it will be for other cell membrane adhesion molecules to
adhere to other wall adhesion proteins. As more connections are made, the capacity of the
system increases. Once the adhesion between the membrane protein and the wall becomes
stable (e.g., there are multiple connections), it is then modeled with an on/off probability,
which states how likely the cell will maintain the connection. This process is summarized
in the following flow chart ( Figure 6.7 ), and examples are discussed in Chapter 13.

Criteria for
adhesion molecule
expression is met

Does criteria persist?

YES NO

Cells do not
express adhesion
molecules

Multiple cells
express adhesion
molecules

Do cells come within a
diameter of the wall?

YES NO

Continue within
the fluid phase

Adhesion probability

Is the adhesion stable?

YES NO

Cells shear off the
wall

Multiple cellular
connections

FIGURE 6.7 Flow chart for cell-wall interaction modeling. There is a certain predetermined probability that is
associated with each step in the flow chart. Also, the first step in the flow chart can continually change and is
reversible, making this flow chart not a direct path from beginning to end.