Biologie de la peau
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Epidermal appendages

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Nails (Nails)

Sunday 25 September 2011

The nail is mainly composed of the hard nail plate arising from a matrix. The shape of the nail is very variable in different persons; it is roughly rectangular and flat in shape; The nail bed has a pink color that can be seen because of the transparency of the plate and its extensive vascular network.

A whitish crescent -shaped lunula projecting from under the proximal nail folds is observed in the thumbs, uncommonly in the other fingers and in the large toenails. The lunula is the more distal portion of the matrix and determines the shape of the free edge of the nail plate. Its color is due in part to the effect of light scattered by the nucleated cells of the matrix and in part to the thick layer of the epithelial cells making up the matrix.

As the nail plate emerges from the matrix, its lateral and proximal borders are enveloped by folds of skin termed lateral and proximal nail folds. The skin underlying the free end of the nail is referred to as the hyponichium and is contiguous with the skin on the tip of the finger.

In humans, nails grow at an average rate of 3 mm a month. The growths of fingernails and toenails have different speeds. Complete regrowth of fingernails require 3 to 6 months while complete toenail regrowth needs 12 to 18 months. The growth rate is related to the length of the terminal phalanges; the nail of the little finger grows slower than the nail of the index finger. They grow faster in summer than in the other season. Contrary to popular belief, they do not continue to grow after death; it is the severe postmortem drying and shrinking of the soft tissue around the nail plate that give the illusion of a nail growth.

The main functions of the nails are to protect the end of the digit and to help in grasping objects.



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