246
UNIT 3
Organ Systems
Figure 13-3A.
Thick skin, palm.
H&E,
3
34;
inset
3
116
The skin can be classif ed into
thick skin
and
thin skin
based on
the thickness oF the epidermis.
Thick skin
has a thick epidermis
(400–600
μ
m) with f ve distinct cell layers. The
stratum
corneum
is extremely thick in this skin. Thick skin covers the palms oF
the hands and soles oF the Feet. Thick skin has abundant eccrine
sweat glands and lacks hair Follicles. The epidermis is a stratif ed
squamous epithelium. Because it is an avascular tissue (no direct
blood supply), nutrients are delivered to the tissue by fl uid diFFu-
sion From the dermis (connective tissue). The dermis is composed
oF a superf cial
papillary layer,
a layer oF loose connective tissue,
and a deeper
reticular layer,
which is a thick layer oF dense irregu-
lar connective tissue. This section shows thick epidermis
containing
the duct oF an
eccrine sweat gland
.
Duct of eccrine
Duct of eccrine
sweat gland
sweat gland
Duct of eccrine
sweat gland
Duct of eccrine
Duct of eccrine
sweat gland
sweat gland
Duct of eccrine
sweat gland
Stratum
Stratum
corneum
corneum
Stratum
corneum
Epidermis
Epidermis
Epidermis
Reticular
Reticular
layer
layer
Reticular
layer
Papillary
Papillary
layer
layer
Papillary
layer
Dermis
Dermis
Dermis
A
Figure 13-3B.
Layers of the epidermis, palm.
H&E,
3
68;
insets
3
422
The
epidermis
oF thick skin has f ve layers. (1) The
stratum basale
contains a single layer oF cuboidal/tall cuboidal cells (
stem cells
)
and sits upon the basement membrane. This layer Forms a dividing
line between the epidermis and dermis (
dotted line
). (2) The
stra-
tum spinosum
contains 5 to 10 layers oF polyhedral keratinocytes,
fl attened toward the surFace. These cells are also called
prickle
cells
. (3) The
stratum granulosum
contains three to f ve layers oF
fl attened keratinocytes f lled with keratohyaline granules, which
appear dark blue here. (4) The
stratum lucidum
is a very thin layer
containing extremely fl attened and tightly packed keratinocytes
f lled with keratin f laments. Their nuclei are beginning to be elimi-
nated. (5) The
stratum corneum
is a layer oF dead, nonnucleated
cells, which Form the most superf cial layer oF the skin. Cells in this
layer are constantly sloughed oFF and replaced by new cells.
Dermal
Dermal
papilla
papilla
Dermal
papilla
Epidermal
Epidermal
rete ridge
rete ridge
Epidermal
rete ridge
Stratum
Stratum
corneum
corneum
Stratum
corneum
Stratum
Stratum
lucidum
lucidum
Stratum
lucidum
Stratum
Stratum
granulosum
granulosum
Stratum
granulosum
Stratum
Stratum
spinosum
spinosum
Stratum
spinosum
Stratum
Stratum
basale
basale
Stratum
basale
Papillary
Papillary
layer
layer
Papillary
layer
Dermis
Dermis
Dermis
Reticular
Reticular
layer
layer
Reticular
layer
Stratum
Stratum
granulosum
granulosum
Stratum
granulosum
Stratum
Stratum
spinosum
spinosum
Stratum
spinosum
Stratum
Stratum
lucidum
lucidum
Stratum
lucidum
B
Figure 13-3C.
Dermal papilla, palm.
H&E,
3
272; inset
3
192
The border between the epidermis and dermis (
dotted white line
) is
expanded into Folds. The
dermis
is a connective tissue layer, which
contains
blood vessels
,
nerves
, and
sensory receptors
(
free nerve
endings
and
Meissner corpuscles
). The portion oF the epidermis
that projects into the dermis is termed the
epidermal rete ridge
, and
the portion oF the dermis that projects into the epidermis is called
the
dermal papilla
. This unique Feature increases the contact area
between these two layers, preventing the epidermis From detaching
From the dermis. The dermal papilla contains loose connective tis-
sue that includes many capillaries, Free nerve endings, and encapsu-
lated sensory receptors.
Meissner corpuscles
are shown here. The
nerve f bers cannot be seen in H&E stains; demonstration oF nerve
f bers requires special stains (±ig. 13-1; see also Chapter 7, “Ner-
vous Tissue,” ±ig. 7-8A,B). Meissner corpuscles are responsible For
discriminative touch and are more numerous in thick skin such
as at the tips oF the f ngers. These receptors help us to distinguish
between, For example, diFFerent coins by touch alone.
C
Dermal
Dermal
papilla
papilla
Dermal
papilla
Meissner
Meissner
corpuscle
corpuscle
Meissner
corpuscle
Meissner
Meissner
corpuscles
corpuscles
Meissner
corpuscles
Epidermal
Epidermal
rete ridge
rete ridge
Epidermal
rete ridge
Dermis
Dermis
Dermis
Thick Skin
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