Nail (anatomy) – Wikipedia, the free encyclopedia

For the nail on a bird's beak, see Beak#Nail. "Toenail" redirects here. For the construction technique, see Toenailing.

A nail is a horn-like envelope covering the tips of the fingers and toes in humans, most non-human 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 keratin. This protein is also found in the hooves and horns of different animals. The mammalian nail, claw, and hoof are all examples of unguis [plural ungues]. The nail also reaches a temperature of 90 degrees F.[1] (See image 4 of the scorpion.)

The nail consists of the nail plate, the nail matrix and the nail bed below it, and the grooves surrounding it.[2]

The matrix, sometimes called[3] the matrix unguis, keratogenous membrane, nail matrix, or onychostroma, is the tissue (or germinal matrix) which the nail protects.[4] It is the part of the nail bed that is beneath the nail and contains nerves, lymph and blood vessels.[5] The matrix is responsible for producing cells that become the nail plate. The width and thickness of the nail plate is determined by the size, length, and thickness of the matrix, while the shape of the fingertip itself shows if the nail plate is flat, arched or hooked.[6] The matrix will continue to grow as long as it receives nutrition and remains in a healthy condition.[5] As new nail plate cells are made, they push older nail plate cells forward; and in this way older cells become compressed, flat, and translucent. This makes the capillaries in the nail bed below visible, resulting in a pink color.[7]

The lunula ("small moon") is the visible part of the matrix, the whitish crescent-shaped base of the visible nail.[8] The lunula can best be seen in the thumb and may not be visible in the little finger.

The nail bed is the skin beneath the nail plate.[8] Like all skin, it is made of two types of tissues: the deeper dermis, the living tissue which includes capillaries and glands, and the epidermis, the layer just beneath the nail plate, which moves toward the finger tip with the plate. The epidermis is attached to the dermis by tiny longitudinal "grooves"[6] called matrix crests (cristae matricis unguis).[4] In old age, the nail plate becomes thinner so that these grooves become more visible.[6]

The nail sinus (sinus unguis) is where the nail root is;[4] i.e. the base of the nail underneath the skin. It originates from the actively growing tissue below, the matrix.[5]

The nail plate (corpus unguis)[4] is the hard part of the nail, made of translucent keratin protein. Several layers of dead, compacted cells cause the nail to be strong but flexible.[6] Its (transverse) shape is determined by the form of the underlying bone.[6] In common usage, the word nail often refers to this part only.

The free margin (margo liber) or distal edge is the anterior margin of the nail plate corresponding to the abrasive or cutting edge of the nail.[4] The hyponychium (informally known as the "quick")[10] is the epithelium located beneath the nail plate at the junction between the free edge and the skin of the fingertip. It forms a seal that protects the nail bed.[5] The onychodermal band is the seal between the nail plate and the hyponychium. It is just under the free edge, in that portion of the nail where the nail bed ends and can be recognized in fair-skinned people by its glassy, greyish colour. It is not visible in some individuals while it is highly prominent on others.[6]

Together, the eponychium and the cuticle form a protective seal. The cuticle is the semi-circular layer of non-living, almost invisible dead skin cells that "ride out on" and cover the back of the visible nail plate while the Eponychium is the fold of skin cells that produces the cuticle. It is the cuticle that is removed during a manicure, but the Eponychium should not be touched due to risk of infection.[7] The eponychium is a the small band of living cells (epithelium) that extends from the posterior nail wall onto the base of the nail.[4] The eponychium is the end of the proximal fold that folds back upon itself to shed an epidermal layer of skin onto the newly formed nail plate.[contradictory]. The perionyx is the projecting edge of the eponychium covering the proximal strip of the lunula.[4]

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Nail (anatomy) - Wikipedia, the free encyclopedia