DefinitionThis section has been translated automatically.
Nails, also known as nail plates, are descendants of the epidermis, which only occur in primates.
Nail plate: The nail plate is a (dead) keratin product (see below keratin) of the epidermis and consists of transversely curved horny plates (nail plate) with a longitudinal linear structure and is located on the dorsal side of the finger and toe end phalanges. Physiologically, the nail plate does not contain melanin in Caucasians (see melanonychia). It consists of corneocytes without nuclei which adhere firmly to each other. It is transparent so that the nail bed, which is well supplied with blood, can shine through pink. The nail matrix consists of a dense network of nucleated keratinocytes and is no longer transparent.
The matrix formation (onychisation) is a keratinisation which, in contrast to the keratinisation of the epidemic of the skin surface (epidermisation), takes place without the formation of keratohyalin granules. It is thus similar to the (tricholemmal) keratinization of the hair root (see epidermis; see keratinization, cf. keratinization of the hair. The formation of keratohyalin granules is therefore a pathological process for the nail matrix.
Nail bed: The nail bed consists of the epithelial hyponychium and the connective tissue part of the nail bed. The connective tissue of the nail bed is firmly attached to the periosteum of the distal phalanx.
The lower layer of the nail plate is a cornification product of the hyponychium. Hyponychium and nail plate are firmly fused together.
Nail root: The proximal end of the nail plate (nail root) originates from an epidermal intrusion (nail pocket = sinus with nail matrix). The part of the hyponychium which is placed in the nail pocket is called nail matrix.
The invisible epithelium which lies dorsally on the nail plate in the nail pocket is called eponychium.
A fine, non-sensitive, keratinized membrane slides from this epithelium onto the nail plate, closing the nail pocket dorsally and thus taking over an important function - the cuticle or perionychium (also called perionyx).
The nail matrix extends from the proximal end of the nail pocket to a visible crescent-shaped bright zone of the lunula (nail moon) and produces the dorsal and middle layer of the nail plate.
Laterally and proximally, the nails are surrounded by a skin fold, the so-called "nail wall" (also nail fold or paronychium).
General informationThis section has been translated automatically.
Nail growth: Nails grow at different rates depending on age (childhood nails grow significantly faster than old people's nails) and location (toenails grow more slowly than fingernails). Nail growth in healthy people is about 0.05-0.12 cm per week. See also nail diseases. A complete fingernail is thus formed in 4-6 months. The toenails need 2-3 times the time (about 12-18 months for a complete outgrowth).
Nail thickness: The nail plate consists of 100 to 150 layered horn cells. Their thickness ranges from 0.05 (infants) to 0.75 mm (adults).
Nail diseases: Various congenital or acquired diseases can cause considerable thickening ( pachyonychia) of the nail plate (see also onychogrypose, scleronychia, onychomycosis). Furthermore, circumscribed or complete thinning, pathological discoloration or subsidence of the nail plate can occur.