Tissue Engineering - Introduction to Biomedical Engineering - page 312

or in mathematical terms:

dX
dt ¼ I

d X a X þ m X

ð 6 : 9 Þ

¼ I ð d þ a m Þ X

where are the rates of differentiation, apoptosis, and replication, respectively.

This equation can be rewritten as

d , a , and m

dX
dt þ kX ¼ I

, ð 6 : 10 Þ

where k ¼ d þ a - m ,t ¼ 1/k. The parameter k is the reciprocal of the time constant t that

characterizes the dynamics of changes in the number of cells of type X . It is therefore

evident that the ratios of m / d , a / m are the key dimensionless groups that determine the

overall cell production in tissue.

6.2.8 Cellular Communications
How Do Cells Communicate?
Cells in tissues communicate with one another in three principal ways (Figure 6.18).

1. They secrete soluble signals, known as cyto and chemokines.
2. They touch each other and communicate via direct cell-cell contact.
3. They make proteins that alter the chemical microenvironment (ECM).

FIGURE 6.18 Cell and extracellular matrix (ECM) protein interactions. From [13].