252
UNIT 3
Organ Systems
Accessory Structures
Figure 13-9A.
Sebaceous gland, thin skin (scalp).
H&E,
3
35;
inset
3
66
Sebaceous glands
are found in thin skin, usually associated with hair
follicles. They are most numerous in the skin of the scalp and face.
Sebaceous glands are classiF ed as
simple branched acinar glands
(see
Chapter 3, “Epithelium and Glands”). The secretory cells are lipid-
producing cells, arranged into several acini, which open into a short
duct. Usually, the ducts of sebaceous glands empty their oily secre-
tion, called
sebum
, into a
hair follicle
(±ig. 13-1); however, the ducts
sometimes open directly onto the surface of the skin. Sebaceous glands
release their products by
holocrine secretion
, that is, by the disintegra-
tion of entire cells. Sebum lubricates the skin and coats and protects
hair shafts from becoming brittle. The
inset
shows an acinus of a seba-
ceous gland and a nearby
arrector pili muscle
. Arrector pili muscles
are bundles of sympathetically innervated smooth muscle cells that
span between hair follicles and the papillary layer of the dermis. They
contract to stand the hair up in response to cold or fear (±ig. 13-1).
Sebaceous gland
Sebaceous gland
duct
duct
Sebaceous gland
duct
Hair
Hair
follicle
follicle
Hair
follicle
Sebaceous glands
Sebaceous glands
Sebaceous glands
Sebaceous glands
Sebaceous glands
Sebaceous glands
Arrector pili
Arrector pili
muscle
muscle
Arrector pili
muscle
A
Figure 13-9B.
Eccrine sweat gland, thin skin (scalp).
H&E,
3
248
Eccrine (merocrine) sweat glands
can be found in both thin and thick
skin over most of the body. They are more numerous in the palms
and soles. Eccrine sweat glands produce a clear watery product called
sweat
. These glands are simple glands in which the secretory cells are
arranged into coiled tubules. These glands have long unbranched, but
coiled, ducts, which are lined by two layers of cuboidal cells and open
directly onto the surface of the skin. Sweat consists mainly of water
(99%), some ions (K
+
, Na
+
, and Cl
), waste, and metabolic prod-
ucts. Releasing sweat onto the surface of the skin helps adjust body
temperature as well as aiding in the excretion of metabolic wastes.
The secretory units of eccrine sweat glands contain three cell types.
(1)
Dark cells
are pyramid-shaped cells containing dark secretory
granules. These cells lie toward the lumen of the tubule. (2)
Clear
cells
are also pyramid shaped and have no secretory granules, but
have ultrastructural features of ion pumping cells. They are located
toward the basement membrane. (3)
Myoepithelial cells
are not
secretory cells. They are spindle-shaped contractile cells, which help
to push secretory products into and along the lumen.
Eccrine sweat glands
Eccrine sweat glands
Duct of eccrine
Duct of eccrine
sweat gland
sweat gland
Duct of eccrine
sweat gland
Eccrine sweat glands
B
Figure 13-9C.
Apocrine sweat gland, labia.
H&E,
3
248
Apocrine sweat glands
are simple coiled tubular glands like the
eccrine sweat glands, but their
lumens
are larger (about 10 times
larger than those of the eccrine sweat glands) and their ducts empty
into the superF
cial regions of the hair follicles. The
secretory cells
of
the apocrine glands release their products by shedding part of their
apical cytoplasm; this is called
apocrine secretion
. The tubules of the
glands are lined by cuboidal or columnar epithelial cells, depending
on the secretory stage. These glands are infl
uenced by hormones and
start to function at puberty. They are also called
sexual scent glands
.
They are restricted in location to some speciF
c regions of thin skin,
such as the axilla, the areola (nipple), and the perianal and genital
areas. Their product is a viscous, thick, milky fl
uid that contains pro-
tein, ammonia, lipids, and carbohydrates. These secretory fl
uids are
odorless when they are released but may have an axillary body odor
after degradation by bacteria.
Secretory cells
Secretory cells
(cuboidal cells)
(cuboidal cells)
Secretory cells
(cuboidal cells)
Lumen of the
Lumen of the
apocrine
apocrine
sweat gland
sweat gland
Lumen of the
apocrine
sweat gland
Secretion
Secretion
inside lumen
inside lumen
Secretion
inside lumen
C
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