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U N I T 1
Cell and Tissue Function
Wound healing involves the restoration of the integrity of injured tissue.The healing
of skin wounds, which are commonly used to illustrate the general principles of
wound healing, is generally divided into three phases: (1) the inflammatory phase,
(2) the proliferative phase, and (3) the wound contraction and remodeling phase.
Each of these phases is mediated through cytokines and growth factors.
U N D E R S T A N D I N G
Wound Healing
Epidermis
Dermis
Fat
Clot
Neutrophil
Fibrin
Inflammatory Phase.
The
inflammatory phase begins at the
time of injury with the formation
of a blood clot and the migration of
phagocytic white blood cells into the
wound site. The first cells to arrive,
the neutrophils, ingest and remove
bacteria and cellular debris. After
24 hours, the neutrophils are joined
by macrophages, which continue to
ingest cellular debris and play an
essential role in the production of
growth factors for the proliferative
phase.
1
Blood vessel
Epithelial
cells
Granulation
tissue
Fibroblast
Macrophage
Proliferative Phase.
The pri-
mary processes during this phase
focus on the building of new tissue
to fill the wound space. The key cell
during this phase is the
fibroblast,
a
connective tissue cell that synthesizes
and secretes the collagen, proteo-
glycans, and glycoproteins needed
for wound healing. Fibroblasts also
produce a family of growth factors
that induce angiogenesis (growth of
new blood vessels) and endothelial
cell proliferation and migration. The
final component of the proliferative
phase is epithelialization, during
which epithelial cells at the wound
edges proliferate to form a new
surface layer that is similar to that
which was destroyed by the injury.
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