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U N I T 1 3
Integumentary Function
Like hair, nails are the end product of dead cells that are
pushed outward from the nail matrix. Unlike hair, nails
grow continuously rather than cyclically, unless perma-
nently damaged or diseased. The epithelium of the fold
of skin that surrounds the nail consists of the usual layers
of skin. The stratum corneum forms the
eponychium
or
cuticle. The nearly transparent nail plate provides a useful
window for viewing the amount of oxygen in the blood,
and providing a view of the color of the blood in the der-
mal vessels. Changes or abnormalities of the nail can also
serve to help diagnose skin or systemic diseases.
Manifestations of Skin
Disorders
No two skin disorders look exactly alike. Their appear-
ance varies according to the causative agent, location,
skin color, and many other factors, and may be further
influenced by excessive scratching, secondary infection,
or the effects of self-treatment. Nevertheless, most skin
disorders have some common characteristics that can be
used to describe them. This section of the chapter covers
lesions and rashes, pigmentary skin disorders, pruritus,
dry skin, and variations in dark skin.
Lesions and Rashes
The term
lesion
refers to a traumatic or pathologic loss
of normal tissue continuity, structure, or function. Skin
lesions may occur as primary lesions arising in previ-
ously normal skin, or they may develop as secondary
lesions resulting from other disease conditions. Figure
45-8 illustrates various types of skin lesions.
Rashes
are temporary eruptions of the skin, such as
those associated with childhood diseases, heat, diaper
irritation, or drug-induced reactions. The components
of a rash often are referred to as lesions.
Lesions and rashes may range in size from a fraction
of a millimeter (e.g., the pinpoint spots of petechiae)
to many centimeters (e.g., pressure ulcer). They may
be blanched (white), erythematous (reddened), hemor-
rhagic or purpuric (containing blood), or pigmented
(colored). A
macule
is a small (
≤
1.0 cm in diameter) flat
spot, such as a freckle; a
papule
is an elevated (
≥
1.0 cm)
superficial lesion.
Plaques
are elevated lesions (
≥
1 cm),
often formed by the coalescence of papules.
Nodules
are
solid marblelike lesions (>0.5 cm) that are deeper and
firmer than a papule. A
wheal
is a somewhat irregular,
relatively transient area of localized skin edema, such
as a mosquito bite.
Lichenification
is a thickened and
leathery roughening of the skin with increased visibility
of the normal skin furrows and excoriations caused by
scratching.
Blisters
are circumscribed elevations of the skin
caused by fluid under or within the epidermis.
Pustules
are circumscribed pus-filled elevations of the skin.
Vesicles
are small (<1.0 cm in diameter) and
bullae
are
large (1.0 cm or larger in diameter) fluid-filled blisters
(see Fig. 45-8). Friction blisters most commonly occur
on the palmar and plantar surfaces of the hands and
feet where the skin is constantly exposed to mechanical
trauma, such as from shoes and household tools and
appliances.
An
erosion
is a loss of the superficial epidermis, the
surface of which is moist but does not bleed. An
ulcer
is
a skin defect in which there has been loss of the epider-
mis and papillary layer of dermis. It may extend into the
subcutaneous tissue, and often occurs in pathologically
damaged tissue.
A
callus
is a hyperkeratotic plaque of skin that devel-
ops because of chronic pressure or friction. It represents
hyperplasia of the dead keratinocytes that make up the
stratum corneum. Increased cohesion between cells
results in hyperkeratosis and decreased skin shedding. A
callus may be filed down but is likely to recur if pressure
continues in the localized area.
Corns
(helomas) are small, well-circumscribed, coni-
cal, keratinous thickenings of the skin. They usually
appear on the toes from rubbing or ill-fitting shoes. The
corn may be either hard (heloma durum) with a central
hard, horny core, or soft (heloma molle), as commonly
seen between the toes. They may appear on the hands
as an occupational hazard. The hard tissue at the center
of the corn looks like a funnel with a broad top and a
pointed bottom, hence the name “corn.” Corns on the
feet often are painful, whereas corns on the hands may
be asymptomatic. Corns may be abraded or surgically
removed, but they recur if the causative agent is not
removed.
Pigmentary Skin Disorders
Pigmentary skin disorders involve the melanocytes. In
some cases, there is an absence of melanin production, as
in vitiligo or albinism. In other cases, there is an increase
in melanin or some other pigment, as in melasma. In
either case, the emotional impact can be devastating.
SUMMARY CONCEPTS
■■
Skin appendages, including the sweat glands,
sebaceous glands, hair follicles, and nails, are
derived from outgrowths of the epidermal
epithelium during development.
■■
The skin glands are exocrine glands. Eccrine
sweat glands secrete sweat directly onto the skin
surface, whereas the apocrine sweat glands and
sebaceous glands release an oily secretion into
hair follicles.
■■
A hair is a keratin filament arising from a hair
follicle, whereas a nail is a hardened keratinized
plate emerging from a germinal region called the
nail matrix.
