nail (anatomy) nail (anatomy) a nail is a flattish claw-like plate at the tip of the fingers and toes which is characteristically found on all primates. nails correspond to the claws found in other animals. fingernails and toenails are made of a tough protective protein called alpha-keratin, which is a polymer. alpha-keratin is found in the hooves, claws, and horns of vertebrates. this article uses anatomical terminology.naila gorilla's fingernailsdetailssystemintegumentary systemidentifierslatinunguismeshd009262ta98a16.0.01.001ta27065thh3.12.00.3.02001 fma54326anatomical terminology structure human nailsfingernailstoenails a. nail plate; b. lunula; c. root; d. sinus; e. matrix; f. nail bed; g. hyponychium; h. free margin. the nail consists of the nail plate, the nail matrix and the nail bed below it, and the grooves surrounding it. parts of the nail the matrix, sometimes called the matrix unguis, keratogenous membrane, nail matrix, or onychostroma, is the active tissue (or germinal matrix) that generates cells, which harden as they move outward from the nail root to the nail plate. it is the part of the nail bed that is beneath the nail and contains nerves, lymph and blood vessels. the matrix produces 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 bone determines if the nail plate is flat, arched, or hooked. the matrix will continue to produce cells as long as it receives nutrition and remains in a healthy condition. 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. the lunula ("small moon") is the visible part of the matrix, the whitish crescent-shaped base of the visible nail. the lunula can best be seen in the thumb and may not be visible in the little finger. the lunula appears white due to a reflection of light at the point where the nail matrix and nail bed meet. the nail bed is the skin beneath the nail plate. it is the area of the nail on which the nail plate rests. nerves and blood vessels found here supply nourishment to the entire nail unit. like all skin, it is made of two types of tissues: the dermis and the epidermis. the epidermis is attached to the dermis by tiny longitudinal "grooves" called matrix crests (cristae matricis unguis). in old age, the nail plate becomes thinner, and these grooves become more visible. the nail bed is highly innervated, and removal of the nail plate is often excruciatingly painful as a result. the nail sinus (sinus unguis) is where the nail root is; i.e. the base of the nail underneath the skin. it originates from the actively growing tissue below, the matrix. the nail plate (corpus unguis) sometimes referred to as the nail body, is the visible hard nail area from the nail root to the free edge, made of translucent keratin protein. several layers of dead, compacted cells cause the nail to be strong but flexible. its (transverse) shape is determined by the form of the underlying bone. in common usage, the word nail often refers to this part only. the nail plate is strongly attached to the nail bed and does not contain any nerves or blood vessels. the free margin (margo liber) or distal edge is the anterior margin of the nail plate corresponds to the abrasive or cutting edge of the nail. the hyponychium (informally known as the "quick") 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. 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. eponychium together, the eponychium and the cuticle form a protective seal. the cuticle is the semi-circular layer of 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. they are continuous, and some references view them as one entity; in this classification, the names eponychium, cuticle, and perionychium are synonymous. it is the cuticle (nonliving part) that is removed during a manicure, but the eponychium (living part) should not be touched due to risk of infection. the eponychium is a small band of living cells (epithelium) that extends from the posterior nail wall onto the base of the nail. 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. the perionyx is the projecting edge of the eponychium covering the proximal strip of the lunula. the nail wall (vallum unguis) is the cutaneous fold overlapping the sides and proximal end of the nail. the lateral margin (margo lateralis) lies beneath the nail wall on the sides of the nail, and the nail groove or fold (sulcus matricis unguis) are the cutaneous slits into which the lateral margins are embedded. paronychium the paronychium is the soft tissue border around the nail, and paronychia is an infection in this area. the paronychium is the skin that overlaps onto the sides of the nail plate, also known as the paronychial edge. the paronychium is the site of hangnails, ingrown nails, and paronychia, a skin infection. hyponychium the hyponychium is the area of epithelium, particularly the thickened portion, underlying the free edge of the nail plate. it is sometimes called the "quick", as in the phrase "cutting to the quick". function a healthy fingernail has the function of protecting the distal phalanx, the fingertip, and the surrounding soft tissues from injuries. it also serves to enhance precise delicate movements of the distal digits through counter-pressure exerted on the pulp of the finger. the nail then acts as a counter-force when the end of the finger touches an object, thereby enhancing the sensitivity of the fingertip, although the nail itself has no nerve endings. finally, the nail functions as a tool enabling a so-called "extended precision grip" (e.g., pulling out a splinter in one's finger), and certain cutting or scraping actions. growth the growing part of the nail is under the skin at the nail's proximal end under the epidermis, which is the only living part of a nail. in mammals, the growth rate of nails is related to the length of the terminal phalanges (outermost finger bones). thus, in humans, the nail of the index finger grows faster than that of the little finger; and fingernails grow up to four times faster than toenails. in humans, fingernails grow at an average rate of approx. 3.5 mm (0.14 in) a month, whereas toenails grow about half as slowly (approx. average 1.6 mm (0.063 in) a month). fingernails require three to six months to regrow completely, and toenails require twelve to eighteen months. actual growth rate is dependent upon age, sex, season, exercise level, diet, and hereditary factors. the longest female nails known ever to have existed measured a total of 8.65 m (28 ft 4.5 in). contrary to popular belief, nails do not continue to grow after death; the skin dehydrates and tightens, making the nails (and hair) appear to grow. permeability the nail is often considered an impermeable barrier, but this is not true. in fact, it is much more permeable than the skin, and the composition of the nail includes 7–12% water. this permeability has implications for penetration by harmful and medicinal substances; in particular cosmetics applied to the nails can pose a risk. water can penetrate the nail as can many other substances including paraquat, a fast acting herbicide that is harmful to humans, urea which is often an ingredient in creams and lotions meant for use on hands and fingers, and several fungicidal agents such as salicylic acid, miconazole branded monistat, natamycin; and sodium hypochlorite which is the active ingredient in common household bleach (but usually only in 2–3% concentration). clinical significance main article: nail disease thumbnail of the right hand with cuticle (left) and hangnail (top) healthcare and pre-hospital-care providers (emts or paramedics) often use the fingernail beds as a cursory indicator of distal tissue perfusion of individuals who may be dehydrated or in shock. however, this test is not considered reliable in adults. this is known as the crt or blanch test. the fingernail bed is briefly depressed to turn the nail-bed white. when the pressure is released, the normal pink colour should be restored within a second or two. delayed return to pink color can be an indicator of certain shock states such as hypovolemia. nail growth record can show the history of recent health and physiological imbalances, and has been used as a diagnostic tool since ancient times. deep, horizontally transverse grooves known as "beau's lines" may form across the nails (horizontal, not along the nail from cuticle to tip). these lines are usually a natural consequence of aging, although they may result from disease. discoloration, thinning, thickening, brittleness, splitting, grooves, mees' lines, small white spots, receded lunula, clubbing (convex), flatness, and 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 degenerate (onychodystrophy). a common nail disorder is an ingrowing toenail (onychocryptosis). dna profiling is a technique employed by forensic scientists on hair, fingernails, toenails, etc. health and care a set of professional nail care tools the best way to care for nails is to trim them regularly. filing is also recommended, as to keep nails from becoming too rough and to remove any small bumps or ridges that may cause the nail to get tangled up in materials such as cloth. bluish or purple fingernail beds may be a symptom of peripheral cyanosis, which indicates oxygen deprivation. nails can dry out, just like skin. they can also peel, break, and be infected. toe infections, for instance, can be caused or exacerbated by dirty socks, specific types of aggressive exercise (long-distance running), tight footwear, and walking unprotected in an unclean environment. common organisms causing nail infections include yeasts and molds (particularly dermatophytes). nail tools used by different people may transmit infections. standard hygiene and sanitation procedures avoid transmission. in some cases, gel and cream cuticle removers can be used instead of cuticle scissors. nail disease can be very subtle and should be evaluated by a dermatologist with a focus in this particular area of medicine. however, most times it is a nail stylist who will note a subtle change in nail disease. inherited accessory nail of the fifth toe occurs where the toenail of the smallest toe is separated, forming a smaller "sixth toenail" in the outer corner of the nail. like any other nail, it can be cut using a nail clipper. effect of nutrition biotin-rich foods and supplements may help strengthen brittle fingernails. a few small studies support biotin supplement use to that effect. one study in 35 people with brittle fingernails found that 2.5 mg of biotin per day for six weeks to seven months improved symptoms in 63% of participants. vitamin a is an essential micronutrient for vision, reproduction, cell and tissue differentiation, and immune function. vitamin d and calcium work together in cases of maintaining homeostasis, creating muscle contraction, transmission of nerve pulses, blood clotting, and membrane structure. a lack of vitamin a, vitamin d, or calcium can cause dryness and brittleness. insufficient vitamin b12 can lead to excessive dryness, darkened nails, and rounded or curved nail ends. insufficient intake of both vitamin a and b results in fragile nails with horizontal and vertical ridges. some over-the-counter vitamin supplements such as certain multivitamins and biotin may help in growth of strong nails, although this is quite subjective. both vitamin b12 and folate play a role in red blood cell production and oxygen transportation to nail cells. inadequacies can result