CHAPTER 13
Integumentary System
247
Thin Skin
Figure 13-4A.
Thin skin, scalp.
H&E,
3
25; inset
3
84
Thin skin
covers the entire body surface except for the palms of
the hands and the soles of the feet. Thin skin has a thin epidermis,
largely because its stratum corneum is much reduced compared to
that of thick skin. In contrast to thick skin, thin skin contains
hair
follicles
and their associated
sebaceous glands
. This section shows
the
epidermis
and
dermis
of the skin and a deeper layer of sub-
cutaneous tissue called the
hypodermis
. The hypodermis is a layer
of loose connective tissue, which contains
adipose tissue
, nerves,
arteries, and veins. The nerves give off branches, which provide the
various types of sensory and autonomic nerve endings in the dermis.
Pacinian corpuscles
, sensory receptors that respond to vibration
stimuli, are found in the hypodermis of both thin and thick skin.
They are found in many regions of the body but are more numerous
in the tips of the F ngers and toes than in other areas (±ig. 13-1). The
hypodermis serves as a transition layer, providing the dermis with a
fl exible attachment to the underlying muscles and other structures.
Sebaceous
Sebaceous
glands
glands
Sebaceous
glands
Arrector
Arrector
pili muscles
pili muscles
Arrector
pili muscles
Duct of the
Duct of the
sweat glands
sweat glands
Duct of the
sweat glands
Skin
Skin
Skin
Epidermis
Epidermis
Epidermis
Dermis
Dermis
Dermis
Hypodermis
Hypodermis
Hypodermis
Pacinian
Pacinian
corpuscle
corpuscle
Pacinian
corpuscle
Hair
Hair
follicles
follicles
Hair
follicles
Adipose
Adipose
tissue
tissue
Adipose
tissue
Eccrine
Eccrine
sweat
sweat
glands
glands
Eccrine
sweat
glands
A
Figure 13-4B.
Thin skin.
Elastic F ber stain,
3
142; inset
3
487
The epidermis of
thin skin
consists of four layers, including
the
stratum basale
,
stratum spinosum
,
stratum granulosum
, and
stratum corneum
. (The stratum lucidum is absent in thin skin.)
The
stratum granulosum
is very thin, often only a single cell layer,
and it is not easily distinguished in thin skin. The
stratum cor-
neum
is thin but varies in thickness from region to region. This
section is stained with an elastic F
ber stain, which shows the elas-
tic F
bers in the dermis. These F
bers become very F
ne toward the
epidermis. The dermis contains type I collagen F
bers and elas-
tic F
bers, which give the skin fl
exibility and strength. The
inset
shows a few very F
ne F
bers called
oxytalan ±
bers
. The elastic
F bers can be classiF
ed into three types based on their
micro±
-
bril
and
elastin
content: (1)
elastic ±
bers
, the largest F bers, con-
taining predominantly elastin; (2)
elaunin ±
bers
, intermediate
in size, containing small amounts of amorphous elastin; and (3)
oxytalan ±
bers
, the smallest F
bers, containing only microF brils.
Oxytalan
Oxytalan
fibers
fibers
Oxytalan
fibers
Elastic fibers
Elastic fibers
Elastic fibers
Stratum basale
Stratum basale
Stratum basale
Elaunin fibers
Elaunin fibers
Elaunin fibers
Stratum
spinosum
Stratum corneum
B
Figure 13-4C.
Stratum corneum, thin skin.
Elastic F
ber stain,
3
284
Fine grooves (sulci cutis)
and
elevated areas (cristae cutis)
are the basis of
the varying surface contours characteristic of speciF c areas of both thin skin
and thick skin. The orientation of the grooves varies from region to region.
±ingerprints (
dermatoglyphics
) are a good example of a skin pattern, which
is distinctive. The top layer of the epidermis, the
stratum corneum
, is com-
posed of several layers of fl attened and corniF ed keratinocytes. These cells
have no nuclei and are F lled with
keratin
, which helps to stabilize the cells
against physical stress. This layer of cells is constantly sloughed off and
replaced by differentiating cells from beneath. In this section, the extensive
spaces between the dead cells of the stratum corneum are artifacts of speci-
men preparation. Some of the
cuboidal cells
in the
stratum basale
are stem
cells capable of cell division. Some cells derived by division of the stem cells
remain in the stratum basale as stem cells and some begin differentiation
in the stratum spinosum.
Keratinocytes
undergo an orderly sequence of
differentiation (
keratinization
) and cell death (
apoptosis
) as they move up
toward the surface of the epidermis.
Collagen
Collagen
fibers
fibers
Collagen
fibers
Cuboidal cells
Cuboidal cells
in stratum basale
in stratum basale
Cuboidal cells
in stratum basale
Elastic
Elastic
fibers
fibers
Elastic
fibers
Capillary
Capillary
Capillary
Keratinocytes
Keratinocytes
in stratum
in stratum
spinosum
spinosum
Keratinocytes
in stratum
spinosum
Sulci cutis
Sulci cutis
Sulci cutis
Stratum corneum
Stratum corneum
Stratum corneum
Crista cutis
Crista cutis
Crista cutis
C
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