70
UNIT 2
Basic Tissues
Figure 4-14A.
Dense irregular connective tis-
sue, thin skin.
H&E,
3
193
This is
dense irregular connective tissue
in the
dermis of thin skin. The epidermis is composed of
epithelial tissue
; the dermis is composed of dense
irregular connective tissue and lies beneath the
epidermis. “Dense” refers to the high abundance
of collagen F
bers (but fewer cells) compared to
loose connective tissue. “Irregular” indicates that
the orientation of the F
ber bundles is in many dif-
ferent directions (or randomly oriented bundles).
This type of connective tissue contains mostly
col-
lagen f bers
with a lesser number of other F
bers
such as elastic F
bers. The skin has a thick layer
of dense irregular connective tissue, with F
bers
arranged in various directions to resist stretching
forces in any direction. Dense irregular connective
tissue is prominent in the dermis of the skin, mam-
mary glands, and capsules of many organs.
CLINICAL CORRELATION
Figure 4-14C.
Hypertrophic Scars and Keloids.
H&E,
3
53
Hypertrophic scars
and
keloids
are disorders caused by
accumulation of
excessive
amounts of
collagen
deposited
in the skin by
hyperproli±eration
of
f broblasts
. They often
occur after burns, radiation injury, or surgical procedures.
Hypertrophic scars
appear raised, are characterized by red-
ness, and usually remain within the margins of the original
wound. There is a tendency for spontaneous regression
over time. If the scar tissue grows beyond the boundaries
of the original wound and does not regress, it is called a
keloid
. A keloid is more severe and more difF
cult to treat
than a hypertrophic scar. Treatments of hypertrophic scars
and keloids include cryosurgery (freezing), laser surgery,
and steroid injections. This photomicrograph is a keloid
on the earlobe; the collagen F
bers appear thicker and
denser,
forming
thick bands
. The number of
f broblasts
is
increased.
C
Thick collagen
bands
Increased
fibroblasts
Collagen
fibers
Dense irregular
connective tissue
Epithelium
Epithelium
Epithelium
A
D. Cui
B
Collagen fiber
Ground substance
Elastic fiber
Fibroblast
Figure 4-14B.
A representation o± dense irreg-
ular connective tissue.
The background represents
ground substance
.
Collagen f bers
are represented by randomly
arranged, thick, pink bundles, and
elastic f bers
are
indicated by thinner dark lines. A few
f broblasts
are scattered sparsely among these F bers. Most col-
lagen and elastic F bers are produced by F broblasts.
Maintaining the normal metabolism of collagen is
very important to the body.
Malfunctioning collagen can cause a series of con-
nective tissue diseases such as
Ehlers-Danlos syn-
drome
(see Table 4-1). Overproduction of collagen
in the dermis of the skin can cause
hypertrophic
scars
or
keloids
(±ig. 4-14C).
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