- Human pathology

Home > E. Pathology by systems > Skin > Nails > nail


Monday 25 March 2019

Adj. ungueal


Definition : A nail is a horn-like envelope covering the tips of the fingers and toes in most primates and a few other mammals. Nails are similar to claws in other animals. Fingernails and toenails are made of a tough protective protein called alpha-keratin. This protein is also found in the hooves and horns of different animals.

The nail consists of :
- the nail plate
- the nail matrix
- the nail bed below it,
- the grooves surrounding it.

The nail unit comprises the nail plate, the surrounding soft tissues, and their vasculature and innervation based upon the distal phalanx.

The nail plate is a laminated keratinized structure lying on the nail matrix (15-25%), the nail bed with its distal onychodermal band (75-85%), and the hyponychium at its free edge.

The distal part of the matrix, the lunula characterized by its half-moon shape, can be observed in some digits.

The nail plate is embedded by the proximal and lateral folds.

From the proximal nail fold, the cuticle (also known as the eponychium), adheres to the superficial surface of the proximal nail plate.

The nail unit possesses a complex and abundant vascular network to ensure adequate blood supply.

Finally, both the periungual soft tissues and the nail folds are innervated.

The nail is a platelike, keratinous, translucent structure that consists of highly specialized epithelial cells.

The nail grows from a deep groove in the dermis of the skin.

All nail growth occurs at the nail’s base, where the specialized cells that make up the nail’s plate are produced; these cells are pushed forward as new cells form behind them.

The nail plate is also attached to the underlying, richly vascularized nail bed , which supplies the plate with necessary nutrients. The cells at the front edge of the nail plate die and turn white as they lose contact with the nail bed.

The whitish, crescent-moon-shaped part of the nail, known as the lunula, is also not attached to the underlying nail bed.