Haemostasis
is promoted rapidly after injury when platelets released from blood
at the wound site bind to freshly exposed tissue components. These cells
contain many chemicals that act as messenger molecules responsible for
initiating blood coagulation, inflammation and wound healing. For healing
one of the most important molecules released is Platelet Derived Growth
Factor (PDGF) which attracts neutrophils and monocytes from the blood
and fibroblasts from adjacent dermis into the wound site by a process
known as chemotaxis. These cells then initiate the healing process.
The importance of PDGF is emphasised by the fact that it was one of
the first pharmaceutical products developed as a wound treatment from
our knowledge of the healing process and is now available for topical
application to enhance wound healing (Nagai, 2002).
Inflammation
following injury is a normal part of healing but it rapidly resolves
and is followed by a cell proliferation phase. Fibroblasts at the wound
site are stimulated by PDGF and other growth factors to proliferate
and produce extracellular matrix (ECM) as a component of granulation
tissue. The presence of functional ECM is required to allow keratinocyte
migration from the wound edge and re-epithelialise the wound surface
with eventual scar formation.
Many
growth factors and other proteins known as cytokines are involved in
regulating the healing process (Moore, 2001). They are synthesised by
all cell types present and once released in an active form bind to receptors
on other cells to control their activity. This raises the possibility
that they may be used for therapeutic interventions as demonstrated
for PDGF. Conversely, because they act in complex networks any disruption
to the network may delay healing.
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