Corpus: Nail

Nails' are skin appendages formed on the end phalanges of fingers and toes with a mechanical protective function.

In surgery, nails usually refer to metal pins for osteosynthesis, see nail (surgery).

Overview[Bearbeiten]

Anatomically speaking, nails are circumscribed formations of cornea. The nail substance is a thick corneal plate consisting of keratin scales arranged like roof tiles. The thickness depends on age: In babies, the nails are approx. 0.05 to 0.1 mm thick, in adults approx. 0.7 to 1 mm.

As nails occur on the hands and feet, a distinction is made between

• Fingernails (Ungues digiti manus)
• Toenails or toenails (Ungues digiti pedis)

To designate individual nails, they are numbered systematically:

• Unguis digiti manus 1, Unguis digiti manus 2 etc.
• Unguis digiti pedis 1, Unguis digiti pedis 2 etc.

Toenails and fingernails do not differ in their basic anatomical structure.

Structure[Bearbeiten]

A distinction is made between the nail in detail:

• Nail plate
  • Nail root (radix unguis): concealed part of the nail plate, located in the nail pocket
  • Nail body (corpus unguis): exposed part of the nail plateReferenzfehler: Für ein <ref>-Tag fehlt ein schließendes </ref>-Tag.

Contrary to popular belief, nails do not grow post-mortem. The apparent nail growth after death is caused by a shrinkage of the surrounding tissue.

Permeability[Bearbeiten]

The keratin of the nails is more permeable to moisture than the surrounding skin. The nail substance itself consists of about 7-12% water. Prolonged exposure to moisture therefore leads to swelling of the nail plate. Chemicals, but also drugs, can also penetrate the nail substance in this way.

Function[Bearbeiten]

In addition to their mechanical protective function for the end phalanx of the finger, the nails also have a tactile function. They form an abutment for the palpating fingertips and thus enable a more differentiated perception of pressure and surface texture. They are also a tool that allows the finger force to be concentrated on a small area. This application of force via the nails is used for actions such as scratching, tearing or peeling fruit.

Furthermore, nails have a cosmetic significance in various civilisations that should not be underestimated (nail polish, nail extensions).

Changes in the colour and shape of the nails occur in a variety of diseases. Important colour changes are

• white (leukonychia),
• green (chloronychia),
• yellow (yellow nail syndrome) or
• black nail discolouration (melanonychia).

A thickening of the nail plate is known as scleronychia or pachyonychia, a severe shortening as brachyonychia.

Some nail changes allow diagnostic conclusions to be drawn about systemic diseases. Examples of this are spotted nails in psoriasis, frosted glass nails in chronic inflammatory bowel diseases or watch glass nails in chronic cardiopulmonary diseases.

Widespread diseases of the nail are onychomycosis (nail fungus) and unguis incarnatus. Trauma to the nail leads to a subungual haematoma and nail detachment (onycholysis). Bacterial nail infections are also clinically relevant.

The partial or complete absence of one or more nails is known as anonychia, while nails that are too small are known as microonychia.

Brittle and soft fingernails are usually more of a cosmetic problem, which may be due to a lack of biotin, but are usually the result of repeated applications of nail polish and nail polish remover.