A

thumb.

The nail is a convex skin structure located in the distal regions of the fingers. Animal nails can have various shapes, elongated and sharp, like the claws of some reptiles, birds and mammals, or highly developed, covering the fingers on which they walk, like the hooves of ungulates.

Nails are made up primarily of hardened dead cells that contain keratin, a fibrous protein that the body produces naturally.

The rate of nail growth varies from finger to finger and from person to person. Fingernails grow at an average rate of 0.1 mm/day (1 mm every 10 days or about 3 mm per month). Fingernails take 4 to 5 months to fully regrow. Toenails take 6 to 7 months to fully grow back. The exact rhythm depends on age, the season of the year, the amount of calcium, the exercises done and hereditary factors.

If not trimmed, nails can grow quite long. Fingernails grow four times faster than toenails.

Examination of the appearance of the nails has been frequently used in the past as a diagnostic tool for various diseases or physiological imbalances.

Anatomy

Anatomy of a human nail

• Body or lamina ungueal. It's the cornea structure we usually know as nail; the hard and translucent portion composed of keratin.
• Matrix or root. It is the part where the ungueal body originates, located under the skin at its bottom.
• Lúnula. It is the whiteish part in the form of medialuna that is observed almost always at the base of the ungueal body. The lining is the end of the matrix and, therefore, the visible part of the living nail, although it is not seen on all fingers. The rest of the ungueal body consists of dead cells.
• Ungueal milk. It is the adhesive connective tissue below the ungueal body and connects with the finger.
• Hiponiquio. It is the tissue located below the free edge of the ungueal body. It is a waterproof seal that protects the ungueal bed from infections.
• Paroniquio. It is the narrow strip of the skin fold to the sides of the ungueal body.
• Eponiquio. It is the narrow strip of the skin fold that seems to end at the base of the ungueal body. Sometimes the term is confused with cuticle or stepfather. The first term refers to the group of cells that make up the outer lining of an organism, among others that of the eponyquium. The second term is equivalent to a skin, and is reserved to refer to a small piece of skin that rises from the immediate flesh to the fingernails.

Together, the eponychium and cuticle form a protective seal. The cuticle is the semi-circular layer of almost invisible dead skin cells that "stick out" 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 see them as a single entity; in this classification, the names cuticle eponychium and perionychium are synonymous. It is the cuticle (non-living part) that is removed during a manicure, but the eponychium (living part) should not be touched due to the risk of infection. The eponychium is a small band of living cells (epithelium) that extends from the posterior wall of the nail to the nail bed. The eponychium is the end of the proximal fold that folds in on itself to shed an epidermal layer of skin over the newly formed nail plate. [ contradictory ] The perionyx is the projecting edge of the eponychium that covers the proximal strip of the lunula.

The nail wall (vallum unguis) is the skin fold that overlies the sides and proximal end of the nail. The lateral margin (margo lateralis) lies under the nail wall on the sides of the nail, and the nail groove or nail fold (sulcus matricis unguis) are the cutaneous grooves into which the lateral margins embed.

Functions

A healthy nail protects the distal phalanx, fingertip, and surrounding soft tissue from injury. It also serves to enhance the delicate and precise movements of the distal fingers through counter pressure exerted on the pulp of the finger. [2] The nail then acts as a counterforce when the fingertip touches an object, thus enhancing the sensitivity of the fingertip, even though the nail itself has no nerve endings. Finally, the nail works as a tool that allows the so-called "extended precision grip" (eg, picking a splinter out of your finger) and certain cutting or scraping actions.

Growth

The growing part of the nail is found under the skin at the proximal end under the epidermis, which is the only living part of a nail.

In mammals, nail growth rate 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 about 3.5 mm. per month, while toenails grow about half as fast, averaging about 1.6 mm per month. Fingernails require three to six months to fully regrow, and fingernails feet twelve to eighteen months. Actual growth rate depends on age, sex, season, exercise level, diet, and hereditary factors. The longest known female fingernails measure a total of 8.65 m. Contrary to popular belief, fingernails do not continue to grow after death; dehydrated and tight skin, making nails (and hair) appear to grow.

One function of the nail plate is permeability: water loss through the nail is as high as through the palm of the hand. The nail, together with the adjacent tissue and the fingertips, constitute a functional unit as an organ of touch and a prehensile organ that enables such important functions for the life of the human being such as scratching and tickling, thus becoming a emotional resource.

It is convenient that, before doing any activity or function with the nails, they are subject to extreme care for good hygiene. He has taken to the habit of biting his nails in times of stress.

Another important use of fingernails is in music. In many plucked string instruments the nails are used, the difference in sound being remarkable with respect to the pick. In these cases the nails are allowed to grow and are given a specific shape.

Nails also serve as a decorative element, covering the surface with synthetic nail polishes and small artificial fragments.

Permeability

The nail is often considered a waterproof barrier, but this is not true. In fact, it is much more permeable than the skin and the composition of the nail includes between 7 and 12% water. This permeability has implications for the penetration of noxious 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 hand and finger creams and lotions, and various agents. fungicides such as Monistat brand miconazole salicylic acid, natamycin; and sodium hypochlorite, which is the active ingredient in common household bleach but usually only at a concentration of 2% to 3%.

Health and care

Nails can be as dry as skin. Manicures and pedicures are cosmetic treatments to give your nails a good look. This is done with a variety of tools, such as cuticle scissors, nail scissors, nail clippers, and files. Leaving aside merely aesthetic treatments, when there is a nail problem in the nails, a health specialist should be consulted, such as a dermatologist, or a podiatrist (if the problem occurs in the toenails). Nails can improve their condition if they are attached to or put in contact with minerals which, when in contact with them, can give them greater hardness and nutrition.^{[citation required]}

Toe infections can come from dirty socks, certain types of strenuous exercise, walking barefoot, and exposing the feet. The nails can lead to a deformity based on blows and scratches.^{[citation needed]}

Disorders

In the hands

Structural alterations

• The ointment (built nail)
• Uña de spoon (coiloniquia)
• Rotary Uña (onicolisis)
• Uña astillada (onicorrexis)
• Laminated Uña (onicosquisis)
• Punctured pineapple (noise stitch)
• Picketing in laminas (psoriasis)
• Long pineapples (doliconiquia)
• Small farms (small farms)

Chromatic alterations

• White field (leuconiquia)
• Black Uña (nigroniquia)
• Coloring type oil stain (psoriasis)

Periuncheal changes

• Padrastro
• Panadizo

• Nails (onicomicosis)

On the feet

Most of the nail conditions of the hands can also occur in the feet, but also, due to their special characteristics and the aggression of footwear, there are other alterations that occur exclusively in the toenails:

• Uña thick (onicodistrophy)
• Uña en garra (onicogrifosis)
• Incarnated Uña (onicocriptosis)
• Fungal infection of the nails (onicomycosis)

Onychophagy

The action of eating or biting the nails is called onychophagia, it is a psychological disorder and it is not totally healthy, since the nails contain bacteria that, when they come into contact with the mouth, can cause diseases such as sepsis, which is a harmful immune response of the body to a bacterial invasion. Such defense causes internal inflammation and leads to organ damage, which can lead to death.

A person with nail biting is very likely to develop paronychia, an infection contracted by contact between the teeth and the skin that protects and surrounds the nails.

Evolution in Primates

Nails are a distinctive feature of the order of the primates.

The nail is an unguis, that is, a keratin structure at the end of a finger. Other examples of nails include the hoof and claw. Primate nails and the hooves of running mammals evolved from the claws of earlier animals. Unlike the nails, the claws are usually curved ventrally (downward in animals) and compressed to the sides. They serve a multitude of functions, including climbing, digging, and fighting, and have undergone numerous adaptive changes in different animal taxa. The claws are pointed at their ends and are made up of two layers: a thick, deep layer and a hardened surface layer that serves a protective function. The underlying bone is a virtual cast of the overlying horny structure and is therefore the same shape as the claw or fingernail. Compared to claws, nails are flatter, less curved, and do not extend much beyond the tips of the fingers. The ends of the nails usually consist only of the hardened "surface" and they are not pointed like claws.

With only a few exceptions, primates retain plesiomorphic (original, 'primitive') hands with five digits, each equipped with a nail or claw. For example, nearly all living strepsirrhine primates have nails on all fingers except the second toe, which is equipped with a grooming claw. Tarsiers have a grooming claw on the second and third toes. Less well known, a grooming claw is also found on the second pedal toe of owl monkeys (Aotus), marmosets (Callicebus), and possibly other New World monkeys. The needle-clawed bushbaby (Euoticus) has keeled nails (the thumb and first and second toes have claws) with a central ridge ending in a needle-like point.

A study of the fingertip morphology of four species of small-bodied New World monkeys indicated a correlation between increased foraging on small branches and:

1. Expanded apical pads (toe pins),
2. Developed epidermal creams (dactillary footprints),
3. widened distal parts of distal phalanges (bones of the tip of the fingers), and
4. Reduced flexor and extenders (areas of insertion of the finger muscles into the bones).

This suggests that while claws are useful on large-diameter branches, broad fingertips with nails and epidermal ridges were required for habitual locomotion on small-diameter branches. It also indicates that the keel-shaped nails of Callitrichines (a family of New World monkeys) are a derived postural adaptation rather than a retained ancestral condition.