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U N I T 1 3
Integumentary Function
moving between the two layers. It is also a major site
of immunoglobulin and complement deposition in skin
disease.
Most of the structures of the basal membrane zone
are produced by cells of the epidermis. The basal lam-
ina is the zone’s primary organizational structure. Its
layers include the lamina lucida, lamina densa, and
hemidesmosome (Fig. 45-5). The
lamina lucida
con-
sists of fine anchoring filaments and a cell adhesion
glycoprotein, called
laminin,
which plays a role in the
organization of the macromolecules in the basement
membrane zone and promotes attachment of cells to
the extracellular matrix. The
lamina densa
contains
an adhesive called
type IV collagen
as well as lam-
inin. It is important in dermal–epidermal attachment.
The hemidesmosome is similar in structure to half a
desmosome, and serves as an attachment site for the
dermis and epidermis. Bundles of tonofibrils, epider-
mal fibers similar to keratin filaments, converge and
terminate in the hemidesmosomes. Because they form
a continuous link between the intracellular tonofibrils
of the epidermis and the extracellular basement mem-
brane, the hemidesmosomes are also thought to be
involved in relaying signals between the epidermis and
dermis.
The basement membrane zone is often involved in
skin disorders that cause bullae or blister formation.
One of these disorders, bullous pemphigoid, is a blis-
tering disease caused by antibodies against basement
membrane proteins. The blisters of bullous pemphi-
goid are large and tense and may appear on skin that
otherwise looks normal. The thighs and flexor ten-
dons are most commonly affected. The disease is self-
limited but chronic, and the person’s general health is
unaffected.
Appendages of the Skin
Skin appendages are derived from outgrowths of epider-
mal epithelium during development. They include the
eccrine and apocrine sweat glands, sebaceous glands,
hair follicles, and nails.
Sweat and Sebaceous Glands
Two types of exocrine glands originate in the dermis
and release their products onto the skin surface. These
are sweat (or sudoriferous) glands and sebaceous glands
(commonly referred to as oil glands).
There are two types of sweat glands: eccrine and apo-
crine. Eccrine sweat glands are simple tubular structures
that originate in the dermis and open directly to the skin
surface. They are numerous (several million), vary in den-
sity, and are located over the entire body surface. Their
purpose is to transport sweat to the outer skin surface
to regulate body temperature. Apocrine sweat glands are
less numerous than eccrine sweat glands. They are larger
and located deep in the dermal layer. They open through
a hair follicle, even though a hair may not be present, and
are found primarily in the axillae and groin. The major
difference between the two types of sweat glands is that
SUMMARY CONCEPTS
■■
The skin is a complex organ that forms the
major barrier between the internal and external
environments. It consists of two primary layers, the
epidermis and the dermis; is richly innervated with
pain, temperature, and touch receptors; and plays
an essential role in fluid and electrolyte balance.
■■
The outer epidermis, which is avascular, is
composed of four to five layers of stratified
squamous epithelial cells, predominantly
keratinocytes.The keratinocytes are formed in the
deepest layer of the epidermis and migrate to the
skin surface to replace cells that are lost during
normal skin shedding.
■■
The dermis is a connective tissue layer that
separates the epidermis from the underlying
subcutaneous fat layer. It contains the blood
vessels and nerve fibers that supply the
epidermis, as well as sensory receptors for pain,
temperature, and touch.
■■
The basement membrane zone is a layer of
intercellular and extracellular matrices that serves
as an interface between the dermis and the
epidermis. It not only cements the epidermis to
the dermis, but also serves as a selective filter for
molecules moving between the two layers.
Tonofilaments
Attachment plaque
Plasma membrane
Subdesmosomal
dense plate
Anchoring filaments
Anchoring
fibrils
Microfibrils
Dermis
Basement
membrane
zone
Hemidesmosome
Lamina
lucida
Lamina
densa
Epidermis
FIGURE 45-5.
The dermal–epidermal interface and layers
of the basement membrane zone. (Adapted from Storm
CA, Elder DE.The skin. In: Rubin R, Strayer DS, eds. Rubin’s
Pathology: Clinicopathologic Foundations of Medicine. 6th ed.
Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &
Wilkins; 2012:1116.)
