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Follicular structure
The total number of hair follicles
for an adult human is estimated at 5
million with 1 million on the head
of which 100,000 alone cover the
scalp (Szabo 1958). In humans, the
only external regions of skin devoid
of hair follicles are the palms of
the hands and soles of the feet. The
basic hair follicle structure
remains essentially the same
throughout the range of mammalian
species with modifications for
specialized functions. The hair
follicle can be recognized as a
separate entity within the skin with
formation and maintenance based on
interaction between dermal and
epidermal components.
Under the influence of the DP,
epidermal cell differentiation
during anagen produces a keratinized
hair fiber and associated products.
The source epidermal cells, called
matrix cells, that lie in the
immediate vicinity of the dermal
papilla are a living, actively
proliferating group of cells which
differentiate and become keratinized
to form the hair cortex (Co) and
surrounding hair cuticle (Hc) of the
hair shaft at the center of which is
situated the medulla (M). Cells
Around the hair shaft comprise the
inner root sheath (IRS) which can be
divided into three layers the
cuticle (Cu), Huxley layer (Hu) and
Henle layer (He) based on structure,
patterns of keratinization and
incorporation of a product called
trichohyalin. The IRS breaks down at
the level of the sebaceous gland to
leave only the hair cortex and
surrounding cuticle to protrude
above the epidermis.
Diagram showing the main
differentiated layers in a mature
anagen hair follicle. The hair
follicle penetrates the dermal layer
of the skin composed of fibroblast
cells and collagen connective tissue
interspersed with blood vessels,
sweat glands and sensory nerves. The
bulb region sits just above the
subcutaneous (adipose fat) tissue
layer.
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A Hair Loss
B Type of hair loss
C What causes hair loss
D Sign and symptoms
E Introduction to skin and
biology
F Follicular structure
G Dermal papilla
H Hair fiber
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