CHAPTER 3
Epithelium and Glands
41
Figure 3-13A.
Stratif ed squamous epithelium, palm
o± the hand (thick skin).
H&E,
3
78; inset
3
96
Thick
skin
(palms and soles) and
thin
skin
(most other
body surfaces) are covered by
keratinized stratif
ed
squamous epithelium
. Skin includes epidermis (stratiF
ed
squamous epithelium) and dermis (connective tissue).
The top layer of the keratinized stratiF
ed squamous epi-
thelium consists of dead cells (corneocytes), which lack
nuclei. This tough
keratinized layer
resists friction and
is impermeable to water. The cells of outer layers of the
epithelium are fl
attened, and the middle and most basal
layers of cells are more polyhedral or cuboidal. Only the
cells in the deepest layer are in contact with the basement
membrane. Note that the interface between the epithe-
lium and the underlying connective tissue is expanded
by unique features, such as dermal papillae and rete
ridges throughout most of the stratiF
ed squamous epi-
thelium. The
white dashed line
indicates the depth of
the epithelial layer (epidermis) and the boundaries of
the dermal papilla and rete ridge.
Rete
Rete
ridge
ridge
Keratinized
Keratinized
dead cells
dead cells
Epidermis
Epidermis
of the skin
of the skin
Epidermis
of the skin
Keratinized
dead cells
Stratified
Stratified
squamous
squamous
epithelium
epithelium
(keratinized)
(keratinized)
Stratified
squamous
epithelium
(keratinized)
Dermal papilla
Rete
ridge
Dermis of the skin
Dermis of the skin
Connective
Connective
tissue
tissue
Basement
Basement
membrane
membrane
Dermis of the skin
(Connective tissue)
(Connective tissue)
Basement
membrane
Connective
tissue
(Connective tissue)
A
D. Cui
Keratinized dead cells
(stratum corneum)
Connective tissue
Basal
cuboidal
cell
Basement
membrane
Squamous
cell
B
CLINICAL CORRELATION
Figure 3-13C.
Psoriasis.
Psoriasis
is a common chronic
infl
ammatory skin
disease typically characterized by pink- to salmon-
colored plaques with silver scales and sharp margins.
T lymphocyte– mediated immunologic reactions
are
believed to cause the clinical features. Symptoms and
signs include itching, joint pain, nail pitting, and nail
discoloration. Pathologic examinations reveal a thick-
ened epidermis caused by increased epidermal cell
turnover and extensive overlying
parakeratotic scales
.
Neutrophils may migrate into the epidermis from
dilated capillaries to form
microabscesses
(within the
parakeratotic area of the
stratum corneum layer
of
the epidermis) and
micropustules
(within the
stratum
granulosum
and
spinosum layers
of the epidermis) as
shown in this illustration.
D. Cui
Inflammatory
connective tissue
Micropustules
Dilated capillary
Microabscesses
Piled
parakeratotic
scales
Stratum
corneum
Stratum
granulosum
Stratum
Spinosum
C
Figure 3-13B.
Stratif
ed squamous epithelium in thin
skin.
H&E,
3
207
Stratif
ed squamous epithelium
that covers thin skin is
similar to that of thick skin, although its
superf cial ker-
atinized layer
(
stratum corneum
) is much thinner than in
thick skin. Keratinized stratiF
ed squamous epithelium is
composed of several layers of cells. The superF
cial lay-
ers are formed by dead cells whose nuclei and cytoplasm
have been replaced with
keratin
. Under the keratinized
layer is the
squamous cell layer
; these cells are fl
at. The
intermediate layers contain cells that are polyhedral.
The cells close to the
basement membrane
are
cuboidal
in shape and are called
basal cells
; they are
stem cells
that are continuously dividing and migrating from the
basal layer toward the surface as they differentiate.
Stratif
ed Squamous Epithelium (Keratinized)
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