Biomedical Engineering Reference
In-Depth Information
Tissue Function (homeostasis)
Tissue Formation (developmental biology)
Tissue Repair (wound healing)
Cellular Fate
Processes
1. Cell Replication
2. Cell Differentiation
3. Cell Death
4. Cell Motion
5. Cell Adhesion
3
2
1
4
5
FIGURE 6.13
Tissue dynamics. The three dynamic states of tissues and the underlying cellular fate processes.
These processes are illustrated in Figure 6.13. What is known about each one of these
processes will be briefly described in the following sections, with particular emphasis on
quantitative and dynamic descriptions. The processes contribute to three dynamic states
at a tissue level:
1.
Histogenesis:
The maturational lineages of cells derived from a tissue's stem cell
compartment. A tissue's overall functions are the net sum of contributions from all the
cells within the maturational lineages of a tissue.
2.
Tissue formation:
The formation of tissue has been characterized by studies comprising the
field of developmental biology. Tissues vary in their proportion of stem cells, diploid
cells, and polyploid cells, depending on age. The tissue, when isolated from young
donors (e.g., infants) will have tissues with maturational lineages skewed toward the
young cells in the lineage (stem cells, diploid somatic cells), whereas those from geriatric
donors will have tissues skewed toward the later stages of the lineage (polyploid cells).
This phenomenon is the explanation for why tissues procured from young donors have
greater expansion potential ex vivo and are probably going to have greater potential for
most forms of cell therapy programs.
3.
Tissue repair:
Repair of damaged tissues involves production of cells from the stem cell
compartment, proliferation of the cells, and their differentiation into the fully mature
cells. The repair process can also involve migration of cells, if need be, to a site of
damage.
The preceding dynamic processes involve interplay among many different cell types.
The cells communicate and coordinate their efforts through the principal cellular processes
shown in Figure 6.13. The biology and dynamics of these processes are discussed in detail
in Section 6.3.4.
Tissue Histogenesis
All tissues are dynamic. For instance, tissue dynamics can be illustrated by comparing
the cell numbers that some organs produce over a lifetime to the total number of cells in
the human body. As stated before, the human bone marrow produces about 400 billion
myeloid cells daily in a homeostatic state. Over a 70-year lifetime, the cell production from
