The nails
The
structure of the nail and nail bed is shown in Fig. 13.19. The hard keratin of
the nail plate is formed in the nail matrix, which lies in an invagination of
the epidermis (the nail fold) on the back of the terminal phalanx of each
digit. The matrix runs from the prox-imal end of the floor of the nail fold to
the distal margin of the lunule. From this area the nail plate grows forward
over the nail bed, ending in a free margin at the tip of the digit.
Longitudinal ridges and grooves on the under surface of the nail plate dovetail
with similar ones on the upper surface of the nail bed. The nail bed is capable
of producing small amounts of keratin which contribute to the nail and which
are responsible for the ‘false nail’ formed when the nail matrix is obliterated
by surgery or injury. The cuticle acts as a seal to protect the potential space
of the nail fold from chemicals and from infection. The nails provide strength
and protection for the terminal phalanx. Their presence helps with fine touch
and with the handling of small objects.
The
rate at which nails grow varies from person to person: fingernails average
between 0.5 and 1.2 mm per week, while toenails grow more slowly. Nails grow
faster in the summer, if they are bitten, and in youth. They change with ageing
from the thin, occasionally spooned nails of early childhood to the duller,
paler and more opaque nails of the very old. Longitudinal ridging and beading
are particularly common in the elderly.
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