It may occurs in two main ways –
i)
Healing of clean surgical
incision ( with less infection ) of primary union or union by first intention .
ii)
Healing of a gaping wound or
secondary union or healing by secondary intension .
1.. Primary union – here , the tissues are
approximated by surgical sutures or tapes and healing occyurs without
significant bacterial contamination and minimal tissue loss .
The sequence are like …
a)
The incision causes death of
tissue at the time of incision , dermal adnexa 9 accesssory organs ) and
connective tissue cells The space is immediately filled up by a scant amount of
clotted blood .
b)
Within 24 Hrs , the
characteristic changes of acute inflammatory response appear in the subepithelial
connective tissue in the margins of the incision . The inflammatory cells are
mainly neutrophils . The epidermis at its cut edge thickened as a result of
mitotic activity of the basal cells and within 24 to 48 Hours , spurs of
epithelial cells from the both edges
along the cut margings as well as beneath the surface scab to fuse in the midline and thus produce a
continuous but thin epithelial layer within 24 to 48 Hrs .
c)
By 3rd day the
neutrophils have largely disappeared and are replaced by monocytes busily
scavenging necrotic debris and removing red cells and fibrin . There are solid
buds seen sprouting margin . They progress and meet one another .After that their
furthergrowth stop because of contact inhibition . These buds become canalized
and all these form a capillary network . in the sealed space . Fibroblast
invade the capillary tube and they lay down collagen tissue ./ While this
connective tissue response is taking place , epithelial cells proliferation and
differentiation continue thickening the epidermal covering layer .
d)
BY 5TH day , the
whole incisional space with loose vascularised fibroblastic connective tissue
rich in groundsurface . this whole thing is like red granule and known as
granulation tissue . Vascularisation is maximum at these days . epidermis
usually recovers its normal thickness and differentiation of surface cells
yields a mature epidermal architecture with surface keratinisatiion .
e)
During the 2nd week
, there is continued accumulation of collagen and proliferation of fibrioblast
within the incisional onnective tissue . The cellular connective tissue which
fills the incision begins to compress the thin waled newly formed capillary
channel . At this time devascularis starts . The surface scab generally shed
during this week .
f)
By one mon the ,
devascularisation is mostly complete . The blood vessel loose their lumina and
endothelial ccells migrate to the nearest patent capillary . the fibroblast
becomes flattened and eventually the area becomes acellular . Thus the inside
wound is replaced by a narrow linear scar to b e transformed into acellular ,
avacular , pale , collagenous scar . The dermal appendages are permanently loss
.
2.. Secondary union –
a)
The wound is filled up by blood
clot and acute inflammatory reactions
start . There are plenty of inflammatory exudates with plenty of neutrophils
and pyogenic micro-organisms . Gradually , there is liquefaction of the tissue
by autolytic and leucolytic ferments . It is followed by macrophage invasion
and scavenging process will start .
b)
Ingrowth of granulation tissue
occurs from below and from the sides of wound cavity . They are very vascular and bleed severely when injured .
the mechanism of development of fibroblastic vascular system bears full resemblance
with that of primary union . It ends in the formation of collagen tissue and
ultimately in formation of scar .
c)
Surface epithelium grows verty
early pahse of repair ( within 48 Hrs ) and in the same manner as that of
primary union .
d)
The most important feature in
secondary healing which differentiate it from the primary healing is the
phenomenon of wound contraction which occurs in large surface wound ., It can
only occur in those sites where skin is mobile . the margin of the wound are
laterally drawn together . The exact mechanism of wound contraction is obscure
. It may be that the fibrioblasts exert considerable pull while laying down
collagen .
