Diseases of the Nails

Abstract

The nail unit (unguis, onyx=nail) consists of four epidermal structures: nail matrix, nail bed,hyponychium,and the proximal nail fold. The bony phalanx is part of the nail apparatus. The nail sits between the proximal and lateral nail grooves,which are invaginations of the corresponding nail folds. Size and shape of the distal bone, the nail plate, and the periungual tissue make up the final form of the nail. The nail plate is produced by the nail matrix, which extends 3-6 mm under the proximal nail fold; its distal part is visible as a white semicircular structure, the lunula. The proximal nail fold is attached to the nail plate, usually sealing this cul-de-sac. The nail plate continually slides over the nail bed to which it is firmly attached. The nail bed is richly vascularized and contains glomus organs. The nail plate is translucent, revealing the pink-colored nail bed. Transmission of radiation depends on the wave length and thickness of the nail plate. Approximately less than 1%-3% of UV B, some 5%-10% of UV A, but 10%-20% of visible light pass through a normal nail plate. Distal to the nail bed is the hyponychium, which represents an extension of the epidermis under the nail plate and ends at the distal groove.