180
UNIT TWO
nism as eccrine glands—see merocrine glands described in
chapter 5, p. 150.) Apocrine sweat glands become active
at puberty and can wet certain areas of the skin when a
person is emotionally upset, frightened, or in pain. Apocrine
sweat glands are also active during sexual arousal. In adults,
material that accumulate, swelling and bursting the cells.
The resulting mixture of fatty material and cellular debris is
called
sebum.
Sebum is secreted into hair follicles through short ducts
and helps keep the hairs and the skin soft, pliable, and
waterproof
(f
g. 6.9)
. Acne results from excess sebum secre-
tion (Clinical Application 6.3).
Sebaceous glands are scattered throughout the skin but
are not on the palms and soles. In some regions, such as the
lips, the corners of the mouth, and parts of the external repro-
ductive organs, sebaceous glands open directly to the surface
of the skin rather than being connected to hair follicles.
Sweat
(swet)
glands,
or sudoriferous glands, are wide-
spread in the skin. Each gland consists of a tiny tube that origi-
nates as a ball-shaped coil in the deeper dermis or superF cial
subcutaneous layer. The coiled portion of the gland is closed
at its deep end and is lined with sweat-secreting epithelial
cells. The most numerous sweat glands, called
eccrine
(ek
rin)
glands,
respond throughout life to body temperature elevated
by environmental heat or physical exercise
(f g. 6.10)
. These
glands are abundant on the forehead, neck, and back, where
they produce profuse sweat on hot days or during intense
physical activity. They also release the moisture that appears
on the palms and soles when a person is emotionally stressed.
The fl uid the eccrine sweat glands secrete is carried by
a tube (duct) that opens at the surface as a
pore
(f
g. 6.11)
.
Sweat is mostly water, but it also contains small amounts of
salts and wastes, such as urea and uric acid. Thus, sweating
is also an excretory function.
The secretions of certain sweat glands, called
apo-
crine
(ap
o-krin)
glands,
develop a scent as skin bacteria
metabolize them (see F
g. 6.10). (Although these glands are
currently called apocrine, they secrete by the same mecha-
FIGURE 6.11
Light micrograph of the skin showing an eccrine
sweat gland with its duct extending to a pore (30×).
Hair
Sebaceous
gland
Hair follicle
FIGURE 6.9
A sebaceous gland secretes sebum into a hair follicle,
shown here in oblique section (300×).
Duct of eccrine
sweat gland
Pore
Sebaceous
gland
Eccrine sweat
gland
Dermal
papilla
Sebaceous
gland
Duct
Hair shaft
Hair
follicle
Eccrine
sweat
gland
Apocrine
sweat
gland
Pore
FIGURE 6.10
Note the diF
erence in location of the ducts of the
eccrine and apocrine sweat glands.
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