P arts o f th e nail • Figure 4.5
Sagittal plane
Nail root
is the portion that
is not visible
Cuticle
is stratum
corneum of
epidermis
Lunula
is thick, white
part of nail
Nail body
is the visible
portion of the
nail
Nail matrix
is the proximal portion of the nail root.
It contains dividing cells, which
produce new nail cells.
Free edge
extends past
the finger or toe
Nail bed
Epidermis
Dermis
Phalanx
(finger
bone)
Sagittal section showing internal detail
Nails Are Composed
of Keratinized Dead Cells
Nails are plates of tightly packed, hard, dead, keratinized
cells of the epidermis. Functionally, nails help us grasp and
manipulate small objects, provide protection to the ends of
the fingers and toes, and allow us to scratch various parts
of the body. Each nail consists of several parts, or regions:
nail body, nail root,
and
nail matrix
(Figure 4.5). Dividing
cells within the nail matrix become keratinized as the nail
grows outward. The average growth of fingernails is about
1
mm (0.04 inch) per week.
Various portions of nails have different colors. For ex-
ample, the nail body is pink because the blood vessels of
the underlying skin partially show through. The free edge
is white because it extends past the tip of the finger or
toe, and there is no underlying tissue. Finally, the lunula
(LOO-nyu-la) is white because the nail is too thick in this
region for any blood vessels to show through.
Artificial nails have become popular in recent years.
Although these acrylic nails can enhance the appearance,
they are not without hazards. The adhesives used to attach
these nails are toxic and can cause inflammation of the
nail bed. Fungal infections are also common. If the chemi-
cal adhesives damage the nail root, ridges and peeling of
the nail layers may be seen on the nail surface. Occasion-
ally, the nail may even separate from the nail bed, leading
to a loss of the nail.
CONCEPT CHECK
1.
What
causes hair color?
2.
Where
are eccrine sweat glands located, and
what do they do?
3.
What
are the parts of the nail?
Accessory Structures Provide Protection and Help Regulate Body Temperature 99
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