158
UNIT 2
Covering, Support, and Movement of the Body
5
Te wall of a hair follicle is composed of an outer
peripheral
connective tissue sheath
(or
fibrous sheath
), derived from the
dermis; a thickened basal lamina called the
glassy membrane
;
and an inner
epithelial root sheath
, derived mainly from an
invagination of the epidermis (Figure 5.5). Te epithelial root
A
hair papilla
, a nipple-like bit of dermal tissue, protrudes
into the hair bulb. Tis papilla contains a knot of capillaries that
supplies nutrients to the growing hair and signals it to grow. Ex-
cept for its location, this papilla is similar to the dermal papillae
underlying other epidermal regions.
Hair shaft
Arrector
pili
Sebaceous
gland
Hair root
Hair bulb
(a) Diagram of a cross section of a hair within its follicle
(b) Photomicrograph of a cross section of a
hair and hair follicle (100
m
)
(d) Photomicrograph of longitudinal view
of the hair bulb in the follicle (160
m
)
(c) Diagram of a longitudinal view of the expanded hair
bulb of the follicle, which encloses the matrix
Epithelial root sheath
External root sheath
Internal root sheath
Epithelial root sheath
External root sheath
Internal root sheath
Peripheral
connective tissue
(fibrous) sheath
Follicle wall
Hair matrix
Melanocyte
Hair papilla
Subcutaneous
adipose tissue
Medulla
Cortex
Peripheral
connective tissue
(fibrous) sheath
Follicle wall
Cuticle
Cuticle
Glassy membrane
Cortex
Medulla
Glassy membrane
Hair
Hair root
Figure 5.5
Skin appendages: Structure of a hair and hair follicle.
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