Nail

Anatomy

In anatomy, a nail is a horny epidermal derivative that covers the dorsal tip of the fingers and toes of humans and most primates, and consists of of a flattened, slightly curved translucent plate of the protein keratin that forms largely from dividing cells in the base, and attaches to and slides over a nail bed. In humans, nails are the largest skin appendages (Haneke 2006), homologous to vertebrate claws and hooves, and made of the same protein found in hair, skin, and horns.

scratch pick up objects

decoration of toenails and fingernails for aesthetic purposes dates at least as far back as Ancient Egypt (

Parts of the nail unit

Fingernails

Toenails

The nail unit, for both fingernails and toenails, is made up of several different structures (Levit and Boissy 2001; ND 2005:

• Germinal matrix or nail root. Much of this is under the nail fold at the base of the nail plate and thus is not seen, although the distal end is seen in most people as represented by the distal end of the lunula. This is formed from thick epithelium and consists of mostly matrix cells, which differentiate into the nail plate.
• Lunula. This is the whitish, half-moon or crescent shape structure visible in the human thumb and big toe.
• Nail plate. This is the hard, translucent, flattended portion, composed of keratin, with the proximal area white (lunula), the middle portion firmly adhering to and sliding over the nail bed, and the distal portion the free edge.
• Free edge. The free edge pis the part of the nail plate that extends past the finger, which is no longer attached to the nail bed.
• Nail frame (perionychium). The perionychium or paronychial edge is the skin of the finger or toe that overlies the nail plate on the sides.
• Cuticle (eponychium). The eponychium or cuticle is the fold of tissue at the proximal end of the nail, connecting the skin and the nail plate, and overlaping the nail plate at the base of the nail, providing a waterproof barrier.
• Hyponychium. This is the attachment between the skin of the finger or toe and the distal end of the nail, which also provides a waterproof barrier.
• Nail fold. This is the skin that on the three sides of the nail that frames the nail.
• Nail bed. The nail bed is the adherent connective tissue that underlies the nail plate, often colloquially referred to as the "quick." The nail plate adheres to this bed and flows over it.

In common usage the word nail usually refers to the nail plate only.

Nail growth

The matrix or root is about 4 to 9 millimeters long in humans, with most under the nail fold (Levit and Boissy 2001). The distal end is visible in most people as the lunula in the thumbs and big toes. Consisting mostly of matrix cells, the matrix gives rise to the nail plate and the nail bed.

The nail plate in humans is about 0.6 millimeters to 1 millimeter in thickness (Levit and Boissy 2001). It is dorsally smooth. The nail bed adheres tightly to the ventral surface of the nail plate and slides along the nail plate via longitudinal folds and grooves formed by a nail bed horny layer. The nail plate has large onychocytes in the deeper portion of the nail plate and smaller ones near the dorsal surface (Levit and Boissy 2001). The nail plate is composed of keratins believed to be held in place by a surrounding globular matrix proteins with a high concentration of cystine disulfide bonds. the nail matrix cells differentiate into the nail plate by broadening, flattening, and nuclear fragmentation and get accumulation of cytoplasmic microfibrils. Nail plate rigidity not dependent on calcium, as in boines, but rather sulfur bonds of scystgine.

Nail plate "consists of clsoely packed, fully keratinized, multilayer lamellae of cornified cells."

Nails grow at an average rate of 3 millimetres a month ^[1] Fingernails require 3 to 6 months to regrow completely. Toenails require 12 to 18 months. Actual growth rate is dependent upon age, season, exercise level, and hereditary factors. And contrary to popular belief, they do not continue to grow after death, the skin dehydrates and tightens giving the illusion that the nails grow, the same goes for hair.

This growth record can show the history of recent health and physiological imbalances, and has been used as a diagnostic tool since ancient times.^[2] Major illness will cause a deep groove to form across the nails. Miscoloration, thinning, thickening, brittleness, splitting, grooves, Mees' lines, small white spots, receded lunula, clubbing (convex), flatness, spooning (concave) can indicate illness in other areas of the body, nutrient deficiencies, drug reaction or poisoning, or merely local injury. Nails can also become thickened (onychogryphosis), loosened (onycholysis), infected with fungus (onychomycosis) or degenerative (onychodystrophy); for further information see nail diseases. +

Health and care

Long, manicured nails are a fashion statement.

Nails can dry out, just like skin. They can also be infected: toe infections, for instance, can be caused or exacerbated by dirty socks, specific types of aggressive exercise, tight footwear and walking unprotected in an unclean environment.^{[citation needed]}

Manicures and pedicures are health and cosmetic procedures to groom, trim, and paint the nails and manage callouses. They require various tools such as cuticle scissors, nail scissors, nail clippers, and nail files.

Nail tools used by different people may transmit infections. Regarding nail tools such as files, "If they're used on different people, these tools may spread nail fungi, staph bacteria or viruses", warns Rick Lopes, a spokesperson for the California Board of Barbering and Cosmetology.^[3] In fact, over 100 bacterial skin infections in 2000 were traced to footbaths in nail salons. To avoid this, new improved contactless tools can be used, for example, gel and cream cuticle removers instead of cuticle scissors.

Biting

Biting the nails often indicates internal tension, stress, boredom, hunger, or it may simply be a habit.

Nail biting can result in the transportation of germs that are buried under the surface of the nail into the mouth. It may also cause excessive or abnormal wear of tooth enamel^{[citation needed]}.

Culture

Empress Dowager Cixi displays long fingernails which reflect her high position in Qing China.

In western culture, long nails are a symbol of femininity, while short nails are a symbol of masculinity. Nail decoration is usually limited to females.

In some Asian cultures men may also grow long fingernails, or only the nail on the little finger, to show that they do not do much manual labor, but instead work in an office setting.

In the 19th century in the Balkans, white-collar workers, such as clerks, grew their fingernails long to distinguish them from people in lower classes who worked with their hands.

Some guitar players, notably classical and fingerstyle players, will purposely grow long nails on the hand they use to pluck the strings. Their longer nails serve as small, easily-maneuverable guitar picks. For some serious musicians, daily nail care can become a mark of pride and dedication.

In comparison, pianists must keep their nails trimmed short to avoid clicking noises on the keys and avoid dangerous situations where in fast passages the nail may be caught under a key and rip off, and most string players, such as violinists and guitarists, must keep at least the nails on their fretting hand short to allow the strings to be fingered correctly.

Fashion

Someone whose occupation is to cut any type of nail, apply artificial nails and care for nails is sometimes called a nailist. The place where a nailist works may be called a nail salon or nail shop (also "nailshop").

Painting the nails with nail polish (also known as nail lacquer) is a common practice dating back to at least 3000 B.C.E.

Ornamented fake nails are sometimes used to display designs, such as stars or sparkles, on nails. They are also used to make nails look longer.

Medical test

Health care and pre-hospital care providers (paramedics) often use the fingernail beds as a cursory indicator of distal tissue perfusion of individuals who may be in shock. However, this test is now accepted as reliable in young children only.^{[citation needed]}

Procedure: briefly depress the fingernail bed gently with a finger. This will briefly turn the nailbed white; the normal pink colour should be restored within a second or two. Delayed return to pink colour can be an indicator of certain shock states such as hypovolemia.^{[citation needed]}

See also

• Leukonychia
• Nail disease
• Hangnail

References

ISBN links support NWE through referral fees

• Blakemore, C., and S. Jennett. 2001. The Oxford Companion to the Body. New York: Oxford University Press. ISBN 019852403X.

• Haneke, E. 2006. Onychocosmeceuticals. Journal of Cosmetic Dermatology 5(1): 95-100.

• Levit, E. K., and R. E. Boissy, R. E. 2001. Chapter 6. Basic science of the nail unit. In R. K. Freinkel, and D. T. Woodley. The Biology of the Skin. New York: Parthenon Pub. Group. ISBN 1850700060.

• Haneke E (2006). Surgical anatomy of the nail apparatus.. Dermatol Clin 24 (3): 291-6. PMID 16798426.

1. ^  Toenail Definition - Medicine.net
2. ^  American Academy of Dermatology - Nail Health
3. ^  Nails Guide - Nail Health

Integumentary system

Skin • Sweat glands • Sebaceous glands • Hair (Hair follicle) • Nails

Skin
Epidermis (Stratum corneum, Stratum lucidum, Stratum granulosum, Stratum spinosum, Stratum germinativum/basale)

Dermis • Subcutis

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