CHAPTER 13
Integumentary System
253
CLINICAL CORRELATION
Figure 13-10C.
Androgenetic Alopecia.
H&E,
3
50.
Androgenetic alopecia
is the most common form of hair
loss, affecting 30% to 40% of the adult population.
Males and females have a similar incidence in developing
this type of hair loss, characterized by varying degrees of
partial hair thinning from the vertex and frontal areas of
the scalp. In females, it rarely leads to total baldness. In
males, the cause is both
genetic
and
androgen dependent
.
Patients usually have higher levels of 5-alpha-reductase
and androgen receptors.
5-alpha-reductase
increases
production of
dihydrotestosterone
, which binds to the
androgen receptors in susceptible follicles to trigger the
genes to miniaturize the follicles and weaken hair growth.
Treatment options include the oral medication
f
nasteride
and topical solutions of minoxidil. This cross section
of scalp tissue shows variation in hair follicle size with
miniaturized ±ollicles
and the absence of infl
ammation.
Miniaturized
follicle
C
D. Cui /T. Yang
Hair medulla
Connective
tissue sheath
Hair cuticle
Inner root
sheath
Outer root
sheath
Hair cortex
Blood vessel
Blood vessel
Blood vessel
Hair medulla
Hair medulla
Hair medulla
Hair cuticle
Hair cuticle
Hair cuticle
inner root sheath
inner root sheath
Inner root sheath
outer root sheath
outer root sheath
Outer root sheath
Hair cortex
Hair cortex
Hair cortex
Connective
Connective
tissue sheath
tissue sheath
Connective
tissue sheath
A
Figure 13-10A.
Hair ±ollicle.
H&E,
3
95
A cross section of a hair follicle is shown on the
left
and a photomicrograph of a cross section of a hair follicle from the scalp on
the
right
. The structures of the hair follicle containing a hair shaft include (from inside to outside) the
hair medulla
(thin core of the
hair shaft), the
hair cortex
(keratinized cells surrounding the medulla), the
hair cuticle
(outermost layer of the hair shaft), the
inner
root sheath
(cellular sheath that extends from the hair bulb and surrounds and grows along with the hair), the
outer root sheath
(a cellular sheath which is a continuation of the epidermis), and the
connective tissue sheath
(
dermal root sheath
).
Figure 13-10B.
Hair ±ollicles, thin skin (scalp).
H&E,
3
78; inset
3
172
Hair ±ollicles
are the structures that produce the hair and maintain
hair growth. They are cellular structures extending from the epider-
mis into the dermis or hypodermis. The basal region of the hair fol-
licle forms a balloon-shaped structure called the
hair bulb
, which is
composed of the hair root and the dermal papilla. The
hair root
con-
tains melanocytes and a group of epithelial cells called the
matrix
or
germinal matrix
. These cells are capable of cell division and give
rise to the
inner root sheath
and to the hair. The epithelial cells form
a cap around the
dermal papilla
(
hair papilla
). The dermal papilla
contains capillaries and nerve F
bers that supply the hair follicle. The
interaction between the hair bulb and dermal papilla induces hair fol-
licle differentiation and the growth of the hair. The photomicrograph
shows a longitudinal section of hair follicles. The
inset
shows
melanin
granules
, which give color to the hair. The melanin granules are pro-
duced by melanocytes in the hair bulb.
Inner root
Inner root
sheath
sheath
Inner root
sheath
Outer root
Outer root
sheath
sheath
Outer root
sheath
Matrix
Matrix
Matrix
Melanin
Melanin
granules
granules
Melanin
granules
Connective
Connective
tissue sheath
tissue sheath
Connective
tissue sheath
Hair root
Hair root
Hair root
Dermal papilla
Dermal papilla
(hair papilla)
(hair papilla)
Dermal papilla
(hair papilla)
Hair
Hair
bulb
bulb
Hair
bulb
B
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