CHAPTER 13
Integumentary System
249
Figure 13-6A.
Keratinocytes in stratum spinosum, thin skin.
EM,
3
7,097 (left);
3
12,390 (right)
The
stratum spinosum
gets its name from the many small processes that seem to join neighboring cells with one another. The basis for
these spines is obvious in this transmission electron micrograph. Each cell is joined to its neighbors by numerous
maculae adherens
(
desmosomes
), and the spines refl ect the persistence of these connections after some cell shrinkage has occurred during processing of
the tissue. The electron dense tuft of material evident on either side of each desmosome is a bundle of
tonof laments
anchored into
the
attachment plaques
at the cytoplasmic faces of the desmosomes. The desmosomes and tonoF lament bundles are numerous and
more easily seen in the higher magniF cation view in the right-hand panel. As indicated by the extensive
euchromatin
in the nuclei of
these cells, the
keratinocytes
are actively synthesizing proteins, most prominently subunits of
keratin f laments
, which will function
in establishing a tough, impermeable barrier layer at the surface of the skin.
Desmosomes
Desmosomes
Desmosomes
Desmosomes
Keratin filaments
Keratin filaments
Keratin filaments
Keratin
Keratin
filaments
filaments
Keratin
filaments
Desmosomes
Desmosomes
Desmosomes
Melanin
granules
Melanin
Melanin
granules
granules
Melanin
granules
Euchromatin
Euchromatin
Euchromatin
Heterochromatin
Heterochromatin
Heterochromatin
Keratinocyte
Keratinocytes in
stratum spinosum
A
CLINICAL CORRELATION
Figure 13-6B.
Basal Cell Carcinoma.
H&E,
3
50
Basal cell carcinoma
is the most common form of malig-
nant skin neoplasm. It originates from the basal layer
of epidermis and often occurs on sun-exposed areas.
Basal cell carcinoma rarely metastasizes and is usually
non–life-threatening if addressed early. Local invasion
may damage surrounding tissues causing cosmetic con-
cerns. Genetics and long-term exposure to ultraviolet
light and arsenical compounds contribute to the dis-
ease. Clinically, basal cell carcinoma appears as pearly
white nodules or waxy bumps on the face or neck with
telangiectatic blood vessels. Subtypes of basal cell car-
cinoma include
nodular
,
superf cial
,
pigmented
, and
f brosing
. Histologic features include a
lobular growth
pattern
of malignant basal cells with
peripheral pali-
sading
and retraction of lobules from the surrounding
stroma. Treatment includes surgical
excision, cryosur-
gery, curettage, and electrodessication.
B
Peripheral
palisading
Lobe of basal cell
carcinoma with
squamous
diffentiation
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