skin

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A section through the skin. The tough, dead cells of the outer epidermal surface (corneal layer) (credit: © Merriam-Webster Inc.)

Surface covering of the body that protects it and receives external sensory stimuli, consisting of an epidermis over a thicker dermis. The epidermis contains cells involved in immune defenses, sensory receptors, pigment cells, and keratin-producing cells. The last harden and migrate to the surface to form a dead, relatively dry outer layer of horny tissue that constantly sloughs away. The dermis contains sensory nerves and blood vessels within connective tissue. Collagen and elastin fibres give skin its tough, elastic quality. Cells scattered through it produce its components and take part in immune and other skin responses. A fat layer under the dermis provides nutritional storage, cushioning, and insulation. Skin disorders range from dermatitis and acne to skin cancer. Changes in skin colour (e.g., jaundice) or texture may be clues to systemic disorders. dermatology; hair; integument; nail; perspiration; sebaceous gland; sweat gland.

For more information on skin, visit Britannica.com.

Creating a new appearance on a graphical interface (GUI). See skin.

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The first line of defence against disease and physical damage, the skin is a complex organ containing different types of tissue.

The surface layer consists of dead, keratin-containing cells which swell in response to moisture and are shed daily. Given time, this layer thickens and hardens in response to friction. If friction is excessive, burns, blisters, and corns can develop. One aim of training is to harden the skin gradually so that it can withstand the forces experienced during activity. This is particularly important in martial arts which use parts of the body to inflict blows.

Beneath the outer layer, lie the living cells of the epidermis, protecting the body from injury and invasion from parasites. This layer also helps to prevent dehydration. Epidermal cells are continually dividing to replace dead cells lost from the surface. Since these cells have such a short lifespan, signs of nutritional deficiency develop quickly and skin condition is a good reflection of inner health. Clear, moist, glowing skin usually indicates that a person is healthy and well nourished.

The middle layer of the skin, the dermis or corium, contains cells with a black pigment, melanin. Melanin shields the underlying layers from the potentially damaging effects of ultraviolet radiation. Also in the dermis, sensory receptors and nerves inform the body of changes in body temperature. They enable a person to respond, sometimes defensively, to pressure, touch, and pain. The dermis is well supplied with blood vessel and sweat glands. These, combined with the action of erectile hairs, form part of the temperature-regulating system in the body. Sebaceous glands associated with the hair secrete oils which keep the skin moist and contribute to waterproofing. The dermis is the region in which wrinkles originate.

The deepest layer in the skin is the subcutaneous layer containing the stores of fat which many people spend much effort and time trying to reduce.

A well-balanced diet with plenty of fluid intake, regular aerobic exercise, and moderate exposure to sunlight can help to maintain a healthy skin. Nutrient deficiencies may cause dryness, roughness, wrinkling, and slow healing of wounds. Particularly important dietary components are the essential fatty acids and vitamins, particularly A, C, E, niacin, and riboflavin, but in developed countries deficiencies of these nutrients are very rare. See also chafing; eczema; and sun-protection factor.

v. To remove the skin of food before or after cooking. Skinning is done for a variety of reasons including appearance, taste and diet. Foods that are often skinned include poultry, fish and game.

The skin is the largest organ of the human body, exceeding two square metres in area in the average adult. Whilst it is rarely more than 2 mm in thickness, the skin plus subcutaneous fat may weigh 9 kg — approximately 14% of the body weight. The primary function of skin is to act as a physical barrier between the organism and its external environment, preventing water loss in dry conditions, hydration in humid or aquatic environments, and access to the body by microbes, and screening the harmful effects of ultraviolet rays of the sun. The skin also plays an important role in transmitting signals from the external environment and in regulating body temperature. The structure of skin confers mechanical strength, enabling it to withstand considerable physical insults, and when it is breached, it exhibits an amazing power of regeneration and repair.The epidermis, the outer layer of the skin, is a multi-layered epithelium approximately 0.1 mm thick, although there are great variations, such as on the palms and soles, where it may reach 1.4 mm. (The underlying dermis is about 3 mm thick.) The major cell type of the epidermis is the keratinocyte, so named because of the protein keratin, which it synthesizes in abundance. The epidermis is in a state of constant turnover, with keratinocytes being generated by mitosis (cell division) in a basal layer adjacent to the underlying dermis, and daughter cells passing outward toward the skin surface through successive stages of differentiation, characterized by dramatic changes in shape and size (see figure). After leaving the basal layer, the cells become large and polyhedral (spinous), and are joined to adjacent cells by complex structures called ‘desmosomes’, which are like spot welds. This spinous layer may be several cells thick, with the cells becoming increasingly flattened before they form the granular layer and then ultimately the cornified horny outer layer, in which the cells lose most of their internal structures including their nuclei and essentially become dead packages of compacted keratin coated with lipid. Cell-to-cell adhesive processes degenerate and the dead cells are eventually shed from the skin surface. It takes 26-42 days for a cell to transit from the basal layer to the outer horny layer, and a further 14 days before being shed, so the epidermis can completely replace itself within two months. The rate of epidermal cell turnover is normally strictly controlled, but a number of diseases are characterized by epidermal hyperproliferation. In psoriasis, for example, the rate may be increased twenty-fold.

The keratin proteins within the keratinocytes are fundamental to the protective functioning and integrity of the skin. The mixture of compacted fibrous keratins in the outer horny layer (the word, ‘keratin’ is derived from the Greek keratos, meaning horn) is highly stable, inert, hard, waterproof, and resistant to physical insult, and therefore is ideally suited to act as a protective layer. The dehydrated nature of the horny surface layer together with an acidic environment due to various secretions, makes it an inhospitable environment for microorganisms. That this outer surface of dead, keratin-rich cell layers is important in regulating water loss or skin saturation in humid conditions and infection can be demonstrated by removal of the outer layers by successive stripping with sellotape. The resulting denuded skin surface is highly permeable to water and susceptible to infection by a number of microorganisms. Defects in keratins have now been identified as having a causal role in a number of skin disorders.

Other cell types within the epidermis include melanocytes, Langerhan cells, and Merkel cells. The melanocytes are confined to the basal cell layer, are highly dendritic (i.e. they have many branching extensions, like nerve cells), and synthesize the pigment melanin, which moves into surrounding keratinocytes, via the dendritic processes, in small packages termed melanosomes. The Langerhan cells appear to be involved in immunological monitoring of the skin, while the Merkel cells are associated with sensory perception.

The layers and components of the skin. Right: the full thickness; left, the epidermis only
(Click to enlarge)

Hair While in most animals hair and fur plays an important role in heat conservation, in humans its primary function is in sexual attraction. The keratinous hairs cover the whole body surface except the palms and soles, and are present as either ‘terminal’ hair characterized by that of the scalp, or ‘vellus’ hair such as the very fine short body hairs. Hair fibres arise as a result of cell division within the hair follicles, which go through a cyclical pattern of active growth, regression, and a resting phase. The rate of hair growth varies depending upon body site: eyebrow hair, for example, grows much faster than the scalp hair rate of about 0.33 mm per day. Loss of hair in males (male pattern baldness) is essentially inherited and androgen-dependent: from the second decade, following multiple growth cycles, the terminal hairs gradually convert to fine vellus hairs. Other types of baldness (alopecia) may occur due to infection or immunological disorders.

Sebaceous glands are sac-like structures that arise from an epithelial outgrowth of the hair follicle outer root sheath, and are composed of a single cell type, the sebocyte. The gland produces an oily ‘sebum’ secretion, of unknown function. The glands remain immature until puberty, and it is the secretion of sebum that is associated with pubertal acne. This is a chronic inflammation of the hair follicle and sebaceous gland (pilosebaceous unit) characterized by pustules, comedones (blackheads), cysts, and scars, and it affects most adolescents. Treatments may include anti-androgens, retinoids, or antibiotics.

Sweat glands are of two types. Eccrine sweat glands are distributed over almost all of the body surface (2-4 million in total), but they are particularly numerous on the palms, soles, axillae, and forehead. The eccrine sweat gland is a simple unbranched tube which runs from the epidermal surface deep into the dermis, where it develops into a coiled structure. These glands are responsible for the secretion of large amounts of sweat, particularly during strenuous exercise or heat stress, when up to 10 litres a day may be produced; evaporation of the sweat cools the body. Elevated sweat production may also be stimulated by emotion or the consumption of spicy food. Apocrine sweat glands differ from the eccrine in that the gland ducts discharge into the lumen of a hair follicle; also they are confined mainly to the underarms, and the genital area in women. Their secretion is probably of limited functional significance, but as a result of bacterial action it is responsible for body odour.

Wound healing

Skin has an amazing ability to heal wounds, but the rate of healing is dependent upon the severity of the wound. Superficial wounds may be repaired rapidly by simple migration of keratinocytes over the defect. Deeper wounds involve blood coagulation, inflammation, re-epithelialization, wound contraction, and new tissue synthesis and remodelling. These processes have been optimized for rapid wound closure, thus preventing fluid loss and infection, but usually at the expense of subsequent function and cosmetic appearance by the formation of scar tissue. Some large wounds, such as severe burns, may be assisted in their healing response by grafts, or by the use of keratinocyte sheets — grown in the laboratory from keratinocytes derived from biopsies of the patient's own skin. Much research effort is currently devoted to accelerating wound healing and reducing scar formation.

Sun exposure

Exposure of the skin to non-ionizing ultraviolet emissions of the sun is unavoidable, but the effect of such exposure is dependent upon both skin type and the length of exposure. Skin is classified as a certain type depending upon its susceptibility to burn, ranging from type I for very fair skin which burns easily and never tans, to type VI-black negroid skin. Within the spectrum of sunlight, ultraviolet B (UVB, 290-320 nm wavelength) causes sunburn, while both UVB and UVA (320-400 nm) will induce pigmentation. UVB is predominantly absorbed by the outer horny layer, allowing only about 10% to reach the dermis, while all UVA penetrates the epidermis to reach the dermis. Exposure to UVA (the predominant wavelength used in sunbeds) is therefore likely to be a major contributor to connective tissue damage in the dermis, resulting in the features of aged, wrinkled skin. More seriously, sun exposure is a major cause of skin cancer (see below).

Sun exposure does have some benefits, such as promoting the synthesis of vitamin D3 from its precursor in the skin, while stimulation of tanning has a protective effect from subsequent sun exposure. Many psoriasis patients also exhibit a marked improvement in their disease following sun exposure.

Ageing

Aged sun-protected skin is characterized by a general laxity, thinning, and the presence of numerous fine wrinkles. The skin becomes less elastic, is greatly reduced in its tensile strength, and exhibits a diminished ability to resist various insults such as injury, infection, and irritants. Chronic sun exposure induces substantial photoageing characterized by a coarse leathery texture, loss of elasticity, deep wrinkles, yellowish colouration, and the presence of numerous irregular pigmented lesions including actinic keratoses. While the youth of today may regard a deep tan as attractive, in their later years they will undoubtedly suffer the consequences of their actions. A more sinister consequence of prolonged sun exposure is the greatly increased incidence of both benign and malignant tumours.

Skin diseases

In the UK, skin diseases account for approximately 10% of patient visits to general practitioners and 6% of hospital outpatient referrals, and this, combined with the fact that they are the most prevalent cause of occupational absence, has substantial economic implications. In addition, many skin diseases, such as those that are debilitating or particularly apparent and extensive, can have serious psychological effects. Some of the more common skin complaints include urticaria (an eruption characterized by usually itchy weals and swelling), acne, viral warts, infections (bacterial, viral or fungal such as ringworm and athlete's, foot), eczema/dermatitis, rashes, and psoriasis. Psoriasis affects approximately 2% of the population in Europe and North America, and is characterized by well demarcated, inflammatory red plaques topped by silvery scales; it is a major medical problem, causing anxiety and distress, and can be debilitating in severe cases. Although our knowledge of the disease has progressed greatly in recent years, the primary cause of the excessive epidermal proliferation which underlies psoriasis has eluded major worldwide research efforts.

Tumours

Tumours of the skin may be benign or malignant. Benign epidermal tumours such as ‘seborrheic keratoses’ are extremely common. Malignant skin tumours are much the commonest type of cancer overall. Excess exposure, particularly of pale Caucasian skin to ultraviolet irradiation in the form of sunlight, is currently recognized as the major cause of skin cancers, of which the most frequent are basal cell carcinomas (rodent ulcers), squamous cell carcinomas, and malignant melanoma. Basal cell carcinomas are most frequently found on the faces of middle-aged or elderly patients and do not spread to other parts of the body, whereas squamous cell carcinomas may spread. Both of these tumour types are derived from keratinocytes, and are usually treated by simple excision. Malignant melanomas are derived from epidermal melanocytes, and frequently arise from pre-existing pigmented lesions such as moles. The incidence has increased dramatically over the last two decades and this is the most lethal of all skin cancers, spreading rapidly to other organs. If caught at an early stage, however, the prognosis is good, and, due to public education campaigns, the use of sun screens has become more prevalent, and patients are presenting at the clinic much earlier.

Cosmetics

Cosmetics play an important role in skin protection, either as moisturizers or sunscreens, but many are simply used to promote attractiveness, to mask unwanted smells, or to impart pleasant smells and camouflage skin defects. Many contain so-called active ingredients which may alleviate the damage inflicted by sun exposure such as anti-wrinkle creams, or skin lightening creams, or artificial tanning creams. However, a number of cosmetic preparations may elicit a reaction in some people resulting in either irritant dermatitis or allergic sensitivity and contact urticaria.

— Mike Edward, Rona Mackie

Bibliography

• MacKie, R. M. (1997). Healthy skin — the facts. Oxford University Press, Oxford.
• MacKie, R. M. (1996). Clinical dermatology, 4th ed. Oxford University Press, Oxford

See also body decoration, body odours, hair, sun and the body, sweating; temperature regulation.

noun

1. The tissue forming the external covering of the body: epidermis, integument. See surface/depth.
2. A thin outer covering of an object: lamina, membrane, sheath, sheathing. See surface/depth.
3. The outer covering of a fruit: peel, rind. See surface/depth.

verb

1. To remove the skin of: decorticate, pare, peel, scale¹, strip¹. See put on/take off.
2. To furnish with a covering of a different material: clad, cover, face, sheathe, side. See surface/depth.
3. To exploit (another) by charging too much for something: fleece, overcharge. Slang clip¹, gouge, nick, rip off, scalp, soak. Idioms: make someone pay through the nose, take someone for a ride, take someone to the cleaners. See honest/dishonest.

Idioms beginning with skin:
skin deep
skin of one's teeth
skin off one's nose
skin alive
skin and bones

See also beauty is only skin deep; by the skin of one's teeth; get under someone's skin; jump out of one's skin; make one's flesh creep (skin crawl); more than one way to skin a cat; no skin off one's nose; save one's bacon (skin); soaked to the skin; thick skin.

Definition: outer covering, especially of animate
Antonyms: body, core, interior, middle

v

Definition: remove outer covering
Antonyms: cover

A non-load-bearing exterior wall; often composed of prefabricated panels; also see curtain wall.

The external tissue that covers the body. As the body's largest organ (it makes up about one twenty-fifth of an adult's weight), the skin serves as a waterproof covering that helps keep out pathogens and protects against temperature extremes and sunlight. The skin also contains special nerve endings that respond to touch, pressure, heat, and cold. The skin has an outer layer, or epidermis, and a layer immediately below, called the dermis.

The outer covering and largest organ of the body. It serves as a protective barrier against microorganisms, helps shield delicate tissues underneath from mechanical and other injuries, insulates against heat and cold, and helps eliminate body wastes. It guards against ultraviolet radiation by producing a protective pigment and it helps produce vitamin D. Its sense receptors detect pain, cold, heat, touch and pressure.
The skin consists of an outer cellular, avascular epidermis, and an inner fibrous corium (dermis, true skin) resting upon a hypodermis of fat and panniculus muscle.
See also cutaneous, epidermal, epidermis.

Basic structure of the skin. By permission from McCurnin D, Poffenbarger EM, Small Animal Physical Diagnosis and Clinical Procedures, Saunders, 1991

• s. appendages — see hair, claw, hoof, horn, chestnut (1), ergot2, dewclaw, comb, wattle, spur (3), pad, footpad, beak, feather (1), cere, scale, fin, antler, bristle (1), wool, mohair, cashmere, angora.
• s.-associated lymphoid tissues (SALT) — see skin-associated lymphoid tissue.
• autoimmune s. disease — see autoimmune, pemphigus, lupus erythematosus.
• s. biopsy — removal of a small section of skin for histopathological examination. See also keyes punch.
• s. cancer — include squamous cell carcinoma, papilloma and fibropapilloma, intracutaneous cornifying epithelioma (keratoacanthoma), basal cell tumors and tumors of the adnexa, perianal gland and hair follicles.
• congenital absence of s. — see epitheliogenesis imperfecta.
• s. depigmentation — see hypopigmentation.
• s. emphysema — see subcutaneous emphysema.
• s. fold thickness — a measure of obesity in humans but not a valid indicator in dogs or cats as the skin lifts off the subcutaneous tissue.
• s. fungal infection — see dermatomycosis, dermatophytosis.
• s. gangrene — death of tissue and usually involves dermis, epidermis and subcutaneous tissue, e.g. severe saddle galls, heat burns, chemical burns, Claviceps purpurea poisoning. The affected area is cold and bluish in color. This changes to black and the area begins to lift at the edges and to dry out.
• s. inflammation — see dermatitis.
• s. leukosis — occurs in marek's disease. Called also cutaneous lymphosarcoma.
• s.-maggot fly — see cordylobia anthropophaga.
• s. memory — see mnemodermia.
• s. receptor — cutaneous sensory endorgans.
• s. resiliency test — see skin tenting test (below).
• s. tag — see fibrovascular papilloma.
• s. tension lines — see tension line.
• s. tenting test — a fold of skin is picked up and then quickly let go. The amount that it will stretch is an indication of its extensibility. The speed with which it returns to a normal position is determined by the degree of hydration of the skin and subcutaneous tissue and the amount of fat in the subcutaneous tissue, e.g. in an animal that is 10 to 12% dehydrated the skin fold will not disappear until 20 to 45 seconds have elapsed.

  Tenting of the skin in a dehydrated cow. By permission from Blowey RW, Weaver AD, Diseases and Disorders of Cattle, Mosby, 1997

• s. test — application or intradermal injection of a substance to the skin to test the body's reaction to it. Such a test detects an animal's sensitivity to such allergens as dust and pollen, or to preparations of microorganisms believed to be the cause of a disorder.
— There are several types of skin tests, including the patch test, the scratch test, and the intradermal test.
• s. wool — scoured wool from a fellmonger.

The tough, supple cutaneous membrane that covers the entire surface of the body. It is the largest organ of the body and is composed of five layers of cells. See also stratum, stratum basale, stratum corneum, stratum granulosum, stratum lucidum, stratum spinosum.

• Tissue, Fiber, and Integumentary System - skin: outer covering, containing dermis and epidermis
• Aspects and Components of Appearance - skin: smooth outer covering of body, forming complexion on face
• Airframe and Engines - skin: panels of metal riveted in place to cover fuselage
• Parts of Ships, Sails, and Equipment - skin: outer surface of hull
• Contraception and Fertility - skin: Slang. condom

For the article about skin in humans, see human skin.

For other uses, see Skin (disambiguation).

Skin
A diagram of human skin.

A close up picture of a rhinoceros skin.

Skin is the soft outer covering of vertebrates. Other animal coverings such as the arthropod exoskeleton or the seashell have different developmental origin, structure and chemical composition. The adjective cutaneous means "of the skin" (from Latin cutis, skin). In mammals, the skin is the largest organ of the integumentary system made up of multiple layers of ectodermal tissue, and guards the underlying muscles, bones, ligaments and internal organs.^[1] Skin of a different nature exists in amphibians, reptiles, and birds.^[2] All mammals have some hair on their skin, even marine mammals which appear to be hairless. The skin is one of the most important parts of the body because it interfaces with the environment and is the first line of defense from external factors. For example, the skin plays a key role in protecting the body against pathogens^[3] and excessive water loss.^[4] Its other functions are insulation, temperature regulation, sensation, and the production of vitamin D folates. Severely damaged skin may heal by forming scar tissue. This is often discoloured and depigmented. The thickness of skin also varies from location to location on an organism. In humans for example, the skin located under the eyes and around the eyelids is the thinnest skin in the body at 0.5 mm thick, and is one of the first areas to show signs of aging such as "crows feet" and wrinkles. The skin on the palms and the soles of the feet is 4 mm thick and the thickest skin in the body.

Fur is dense hair. Primarily, fur augments the insulation the skin provides but can also serve as a secondary sexual characteristic or as camouflage. On some animals, the skin is very hard and thick, and can be processed to create leather. Reptiles and fish have hard protective scales on their skin for protection, and birds have hard feathers, all made of tough β-keratins. Amphibian skin is not a strong barrier to passage of chemicals and is often subject to osmosis. For example, a frog sitting in an anesthetic solution could quickly go to sleep.

Contents 1 Functions 2 Mammalian skin layers 2.1 Epidermis 2.2 Basement membrane 2.3 Dermis 2.3.1 Papillary region 2.3.2 Reticular region 2.4 Hypodermis 3 In fish and amphibians 4 In birds and reptiles 5 Mechanics 6 Human uses and culture 7 Detailed cross section 8 See also 9 References

Functions

Skin performs the following functions:

1. Protection: an anatomical barrier from pathogens and damage between the internal and external environment in bodily defense; Langerhans cells in the skin are part of the adaptive immune system.^[3][4]
2. Sensation: contains a variety of nerve endings that jump to heat and cold, touch, pressure, vibration, and tissue injury (see somatosensory system and haptic perception).
3. Heat regulation: increase perfusion and heatloss, while constricted vessels greatly reduce cutaneous blood flow and conserve heat. Erector pili muscles are significant in animals.
4. Control of evaporation: the skin provides a relatively dry and semi-impermeable barrier to fluid loss.^[4]
5. Storage and synthesis: acts as a storage center for lipids and water
6. Absorption: oxygen, nitrogen and carbon dioxide can diffuse into the epidermis in small amounts; some animals use their skin as their sole respiration organ (in humans, the cells comprising the outermost 0.25–0.40 mm of the skin are "almost exclusively supplied by external oxygen", although the "contribution to total respiration is negligible")^[5]
7. Water resistance: The skin acts as a water resistant barrier so essential nutrients aren't washed out of the body. The nutrients and oils that help hydrate our skin are covered by our most outer skin layer, the epidermis. This is helped in part by the sebaceous glands that release sebum, an oily liquid. Water itself will not cause the elimination of oils on the skin, because the oils residing in our dermis flow and would be affected by water without the epidermis. ^[6]

Mammalian skin layers

(See also:  image rotating (1.1 mb) )
Optical coherence tomogram of fingertip, depicting stratum corneum (~500 µm thick) with stratum disjunctum on top and stratum lucidum (connection to stratum spinosum) in the middle. At the bottom superficial parts of the dermis. Sweatducts are clearly visible.^{[citation needed]}

Dermis
The distribution of the bloodvessels in the skin of the sole of the foot. (Corium – TA alternate term for dermis – is labeled at upper right.)
A diagrammatic sectional view of the skin (click on image to magnify). (Dermis labeled at center right.)
Gray's	subject #234 1065
MeSH	Dermis
Dorlands/Elsevier	Skin

Mammalian skin is composed of two primary layers:

• the epidermis, which provides waterproofing and serves as a barrier to infection; and
• the dermis, which serves as a location for the appendages of skin;

Epidermis

Main article: Epidermis (skin)

The epidermis is composed of the outermost layers of the skin. It forms a protective barrier over the body's surface, responsible for keeping water in the body and preventing pathogens from entering, and is a stratified squamous epithelium,^[7] composed of proliferating basal and differentiated suprabasal keratinocytes. The epidermis also helps the skin regulate body temperature.^{[citation needed]}

Keratinocytes are the major cells, constituting 95% of the epidermis^[7], while Merkel cells, melanocytes and Langerhans cells are also present. The epidermis can be further subdivided into the following strata or layers (beginning with the outermost layer)^[8]:

• Stratum corneum
• Stratum lucidum (only in palms and soles)
• Stratum granulosum
• Stratum spinosum
• Stratum germinativum (also called the stratum basale)

Keratinocytes in the stratum basale proliferate through mitosis and the daughter cells move up the strata changing shape and composition as they undergo multiple stages of cell differentiation to eventually become anucleated. During that process keratinocytes will become highly organized, forming cellular junctions (desmosomes) between each other and secreting keratin proteins and lipids which contribute to the formation of an extracellular matrix and provide mechanical strength to the skin^[9]. Keratinocytes from the stratum corneum are eventually shed from the surface (desquamation).

The epidermis contains no blood vessels, and cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the dermis.

Basement membrane

Main article: basement membrane

The epidermis and dermis are separated by a thin sheet of fibers called the basement membrane, and is made through the action of both tissues. The basement membrane controls the traffic of cells and molecules between the dermis and epidermis but also serves, through the binding of a variety of cytokines and growth factors, as a reservoir for their controlled release during physiological remodeling or repair processes^[10].

Dermis

Main article: Dermis

The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis provides tensile strength and elasticity to the skin through an extracellular matrix composed of collagen fibrils, microfibrils, and elastic fibers, embedded in proteoglycans^[9].

It harbors many Mechanoreceptors (nerve endings) that provide the sense of touch and heat. It also contains the hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels. The blood vessels in the dermis provide nourishment and waste removal from its own cells as well as for the epidermis.

The dermis is tightly connected to the epidermis through a basement membrane and is structurally divided into two areas: a superficial area adjacent to the epidermis, called the papillary region, and a deep thicker area known as the reticular region.

Papillary region

The papillary region is composed of loose areolar connective tissue. This is named for its fingerlike projections called papillae, that extend toward the epidermis. The papillae provide the dermis with a "bumpy" surface that interdigitates with the epidermis, strengthening the connection between the two layers of skin.

Reticular region

The reticular region lies deep in the papillary region and is usually much thicker. It is composed of dense irregular connective tissue, and receives its name from the dense concentration of collagenous, elastic, and reticular fibers that weave throughout it. These protein fibers give the dermis its properties of strength, extensibility, and elasticity. Also located within the reticular region are the roots of the hair, sebaceous glands, sweat glands, receptors, nails, and blood vessels.

Hypodermis

Main article: Hypodermis

The hypodermis is not part of the skin, and lies below the dermis. Its purpose is to attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves. It consists of loose connective tissue and elastin. The main cell types are fibroblasts, macrophages and adipocytes (the hypodermis contains 50% of body fat). Fat serves as padding and insulation for the body. Another name for the hypodermis is the subcutaneous tissue.

Microorganisms like Staphylococcus epidermidis colonize the skin surface. The density of skin flora depends on region of the skin. The disinfected skin surface gets recolonized from bacteria residing in the deeper areas of the hair follicle, gut and urogenital openings.

In fish and amphibians

The epidermis of fish and of most amphibians consists entirely of live cells, with only minimal quantities of keratin in the cells of the superficial layer. It is generally permeable, and, in the case of many amphibians, may actually be a major respiratory organ. The dermis of bony fish typically contains relatively little of the connective tissue found in tetrapods. Instead, in most species, it is largely replaced by solid, protective bony scales. Apart from some particularly large dermal bones that form parts of the skull, these scales are lost in tetrapods, although many reptiles do have scales of a different kind, as do pangolins. Cartilaginous fish have numerous tooth-like denticles embedded in their skin, in place of true scales.

Sweat glands and sebaceous glands are both unique to mammals, but other types of skin gland are found in other vertebrates. Fish typically have a numerous individual mucus-secreting skin cells that aid in insulation and protection, but may also have poison glands, photophores, or cells that produce a more watery, serous fluid. In amphibians, the mucus cells are gathered together to form sac-like glands. Most living amphibians also possess granular glands in the skin, that secrete irritating or toxic compounds.^[11]

Although melanin is found in the skin of many species, in reptiles, amphibians, and fish, the epidermis is often relatively colourless. Instead, the colour of the skin is largely due to chromatophores in the dermis, which, in addition to melanin, may contain guanine or carotenoid pigments. Many species, such as chameleons and flounders may be able to change the colour of their skin by adjusting the relative size of their chromatophores.^[11]

In birds and reptiles

Main article: Reptile scales

The epidermis of birds and reptiles is closer to that of mammals, with a layer of dead keratin-filled cells at the surface, to help reduce water loss. A similar pattern is also seen in some of the more terrestrial amphibians, such as toads. However, in all of these animals there is no clear differentiation of the epidermis into distinct layers, as occurs in humans, with the change in cell type being relatively gradual. The mammalian epidermis always possesses at least a stratum germinativum and stratum corneum, but the other intermediate layers found in humans are not always distinguishable. Hair is a distinctive feature of mammalian skin, while feathers are (at least among living species) similarly unique to birds.^[11]

Birds and reptiles have relatively few skin glands, although there may be a few structures for specific purposes, such as pheromone-secreting cells in some reptiles, or the uropygial gland of most birds.^[11]

Mechanics

Main article: Soft tissue

Skin has a soft tissue mechanical behavior when stretched. The intact skin is prestreched (i.e. has residual stress) like neoprene wetsuits around the diver's body. When deep cuts are made on the skin, it retracts, widening the slice hole.

Human uses and culture

The term "skin" may also refer to the covering of a small animal, such as a sheep, goat (goatskin), pig, snake (snakeskin) etc. or the young of a large animal.

The term hides or rawhide refers to the covering of a large adult animal such as a cow, buffalo, horse etc.

Skins and hides from different animals are used for clothing, bags and other consumer products, usually in the form of leather, but also furs.

Skin from sheep, goat and cattle was used to make parchment for manuscripts.

Skin can also be cooked to make pork rind or crackling.

Dutch artist Jalila Essaïdi is trying to create bulletproof skin.^[12]

Detailed cross section

Skin layers, of both hairy and hairless skin

See also

Wikimedia Commons has media related to: Human skin

Look up skin in Wiktionary, the free dictionary.

• List of cutaneous conditions
• Acid mantle
• Callus – thick area of skin
• Cutaneous structure development
• Hair – including hair follicles in skin
• Intertriginous
• Moult
• Meissner's corpuscle
• Pacinian corpuscle
• Rawhide
• Role of skin in locomotion
• Superficial fascia
• Potential of embryonic stem cells to reconstitute a skin.^[13]

References

1. ^ "Skin care" (analysis), Health-Cares.net, 2007
2. ^ Alibardi L. (2003). Adaptation to the land: The skin of reptiles in comparison to that of amphibians and endotherm amniotes. J Exp Zoolog B Mol Dev Evol. 298(1):12–41. PMID 12949767
3. ^ ^{a b} Proksch E, Brandner JM, Jensen JM. (2008).The skin: an indispensable barrier. Exp Dermatol. 17(12):1063–72. PMID 19043850
4. ^ ^{a b c} Madison KC. (2003). Barrier function of the skin: "la raison d'être" of the epidermis. J Invest Dermatol. 121(2):231-41. doi:10.1046/j.1523-1747.2003.12359.x PMID 12880413
5. ^ Stücker, M., A. Struk, P. Altmeyer, M. Herde, H. Baumgärtl & D.W. Lübbers (2002). The cutaneous uptake of atmospheric oxygen contributes significantly to the oxygen supply of human dermis and epidermis.PDF Journal of Physiology 538(3): 985–994. doi:10.1113/jphysiol.2001.013067
6. ^ McCracken, Thomas (2000). New Atlas of Human Anatomy. China: Metro Books. pp. 1–240. ISBN 1-58663-097-0. 
7. ^ ^{a b} McGrath, J.A.; Eady, R.A.; Pope, F.M. (2004). Rook's Textbook of Dermatology (7th ed.). Blackwell Publishing. pp. 3.1–3.6. ISBN 978-0-632-06429-8. 
8. ^ The Ageing Skin – Structure. pharmaxchange.info. March 3, 2011
9. ^ ^{a b} Breitkreutz, D; Mirancea, N; Nischt, R (2009). "Basement membranes in skin: Unique matrix structures with diverse functions?". Histochemistry and cell biology 132 (1): 1–10. doi:10.1007/s00418-009-0586-0. PMID 19333614. 
10. ^ Iozzo, RV (2005). "Basement membrane proteoglycans: From cellar to ceiling". Nature reviews. Molecular cell biology 6 (8): 646–56. doi:10.1038/nrm1702. PMID 16064139. 
11. ^ ^{a b c d} Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 129–145. ISBN 0-03-910284-X. 
12. ^ Human skin strengthened with spider silk can stop a bullet (2:16). Reuters (2011-09-20)
13. ^ "Reconstituted Skin from Murine Embryonic Stem Cells". Current Biology 13 (10): 849–853. 2003. doi:10.1016/S0960-9822(03)00296-3. 

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - hud, skind, skræl, beklædning
v. tr. - flå, tage skindet af, pille, skrabe
v. intr. - danne hud
adj. - hud-

idioms:

• all skin and bone    ikke andet end skind og ben
• by the skin of one's teeth    med nød og næppe
• get under a person's skin    irritere nogen, gøre nogen interesseret i en
• make one's skin crawl    give gåsehud
• no skin off my nose    det er mig ligemeget
• save one's (own) skin    redde skindet
• skin alive    flå levende
• skin deep    overfladisk
• skin diving    sportsdykning, dykning med frømandsudstyr
• skin graft    hudtransplantation
• skin test    hudprøve
• with a whole skin    helskindet

Nederlands (Dutch)
huid, vel, schil, vlies, schillen, villen, afstropen, schaven iemand irriteren zich te pletter schrikken

Français (French)
n. - peau, (Culin) peau, pelure, revêtement (d'un avion), (US) paluche, pince (fam), papier à cigarette
v. tr. - (Culin) dépecer, s'écorcher, (US) plumer (fam), (US) scalper
v. intr. - se recouvrir de peau, se cicatriser, se dépêcher
adj. - de la peau

idioms:

• by the skin of one's teeth    de justesse, l'échapper belle
• get under a person's skin    taper sur les nerfs de qn
• keep a whole skin    être indemne, être sain et sauf, sans une écorchure
• make one's skin crawl    donner la chair de poule à qn
• no skin off my nose    (je) m'en balance!
• save one's own skin    sauver sa peau
• skin alive    écorcher (qn) vif
• skin and bone    qui n'a que la peau et les os
• skin deep    superficiel
• skin diving    plongée sous-marine
• skin graft    greffe de la peau
• skin test    cuti-réaction
• skin up    s'écorcher
• sleep in a whole skin    bien dormir

Deutsch (German)
n. - Haut, Fell, Schlauch, Schale, Pelle
v. - häuten, schälen, aufschürfen
adj. - geschält, gehäutet

idioms:

• by the skin of one's teeth    mit knapper Not
• get under a person's skin    jmdm. auf die Nerven gehen
• keep a whole skin    mit heiler Haut davonkommen
• make one's skin crawl    eine Gänsehaut bekommen lassen
• no skin off my nose    das braucht mich nicht zu kratzen
• save one's own skin    seine eigene Haut retten
• skin alive    jmdn. lebendig braten
• skin and bone    Haut und Knochen
• skin deep    oberflächlich
• skin diving    Tauchen
• skin graft    Hauttransplantation
• skin test    Hauttest
• skin up    eine Haschischzigarette machen
• sleep in a whole skin    fliehen (mit Verletzungen)

Ελληνική (Greek)
n. - δέρμα, επιδερμίδα, πέτσα, πετσί, τουλούμι, φλούδα, εξωτερική επιφάνεια, περίβλημα, καϊμάκι, μεμβράνη (πολυγράφου), πόσθη, (αργκό) προφυλακτικό, λάστιχο (αυτοκινήτου), τσιγκούνης
v. - αποφλοιώνω, γδέρνω, καταληστεύω, χαρατσώνω

idioms:

• all skin and bone    πετσί και κόκαλο
• by the skin of one's teeth    μόλις και μετά βίας
• get under a person's skin    κερδίζω τη συμπάθεια, γίνομαι ενοχλητικός
• make one's skin crawl    προξενώ ρίγη φρίκης
• no skin off my nose    κάτι εντελώς αδιάφορο
• save one's (own) skin    σώζω το τομάρι μου
• skin alive    γδέρνω ζωντανό
• skin deep    επιφανειακός, επιδερμικός, επιπόλαιος, ρηχός, ξώπετσος
• skin diving    κατάδυση χωρίς αναπνευστική συσκευή
• skin graft    (ιατρ.) μεταμόσχευση δέρματος, δερματικό μόσχευμα
• skin test    δοκιμασία αλλεργικής αντίδρασης
• with a whole skin    σώος και αβλαβής

Italiano (Italian)
scorticare, spellare, sbucciare, pelare, scalfire, pelle, buccia, pellicola

idioms:

• by the skin of one's teeth    per un pelo
• get under a person's skin    irritare
• jump out of one's skin    morire dallo spavento
• no skin off my nose    non è affar mio
• save one's (own) skin    scamparla
• skin alive    scorticar vivo
• skin deep    superficiale
• skin diving    nuoto subacqueo libero
• skin graft    trapianto cutaneo
• skin test    esame cutaneo
• with a whole skin    intatto

Português (Portuguese)
n. - pele (f), odre (m), tünica (f), corsta (f), pergaminho (m)
v. - cicatrizar, esfolar, enganar

idioms:

• by the skin of one's teeth    por uma margem (f) mínima
• get under a person's skin    interessar ou preocupar ou irritar alguém
• jump out of one's skin    ficar muito surpreso
• no skin off my nose    algo indiferente
• save one's (own) skin    salvar sua própria pele
• skin alive    esfolar, repreender severamente
• skin deep    superficial, ilusório
• skin diving    pesca (f) submarina
• skin graft    enxerto (m) de pele
• skin test    teste (m) alérgico
• with a whole skin    sair de uma situação sem se machucar

Русский (Russian)
кожа, жизнь, "шкура", мех животного, пергамент, бурдюк, кожура, оболочка, верхний или наружный слой, обшивка судна, сдирать шкуру, очищать от кожуры, ободрать кожу, покрывать тонким слоем, кожей, зарубцовываться, линять (о животных), стягивать тесную одежду, обворовать, ободрать как липку, взбираться, давать нагоняй

idioms:

• by the skin of one's teeth    едва (еле-еле, чудом) спастись
• get under a person's skin    раздражать кого-л., действовать кому-л. на нервы, сидеть у кого-л. в печенках
• jump out of one's skin    быть вне себя
• no skin off my nose    меня это ни с какого боку не касается
• save one's (own) skin    спасать свою шкуру
• skin alive    живьем сдирать кожу, живого места не оставить, спустить шкуру, нанести сокрушительный удар
• skin deep    поверхностный, неглубокий, скоропроходящий
• skin diving    подводное плавание без специального костюма с аквалангом
• skin graft    делать пересадку кожи
• skin test    кожная проба
• with a whole skin    уцелеть, спасти свою шкуру

Español (Spanish)
n. - piel, cutis, tez, cáscara, cascarilla, película, membrana
v. tr. - desollar, despellejar, pelar, estafar, mondar, cubrir, despojar
v. intr. - cubrirse, despojarse, cicatrizarse, mudar la piel
adj. - de piel, de la piel, cutáneo

idioms:

• by the skin of one's teeth    por un pelo, al último momento
• get under a person's skin    irritar a una persona
• keep a whole skin    escapar estando herido
• make one's skin crawl    poner los pelos de punta
• no skin off my nose    me da lo mismo, no me va ni me viene
• save one's own skin    salvar el pellejo, salvar su propio pellejo
• skin alive    desollar vivo
• skin and bone    que no tiene más que la piel y los puros huesos, estar en los huesos
• skin deep    superficial
• skin diving    buceo, submarinismo
• skin graft    injerto de piel
• skin test    cutirreacción, dermorreacción
• skin up    liar un porro, armar un cigarrillo de marihuana
• sleep in a whole skin    escapar estando herido

Svenska (Swedish)
n. - hud, skinn, skal, hinna, vinsäck
v. - flå, dra av huden på, skrapa av, skinna, klå, spöa

中文（简体）(Chinese (Simplified))
皮肤, 皮, 剥...的皮, 在...上植皮, 去...的壳, 擦破...上的皮肤, 植皮, 结成皮, 愈合, 脱皮, 皮的, 皮肤的, 有关皮肤的, 裸露的, 裸体的, 色情的

idioms:

• all skin and bone    极瘦
• by the skin of one's teeth    好不容易, 侥幸
• get under a person's skin    激怒某人
• make one's skin crawl    使汗毛直竖, 起鸡皮疙瘩
• no skin off my nose    跟某人毫不相干
• save one's (own) skin    保护自己, 使自己免遭杀害
• skin alive    活剥皮, 严斥
• skin deep    肤浅的, 皮毛的, 轻微的, 表面的
• skin diving    赤身潜水
• skin graft    补皮术, 表皮移植
• skin test    皮肤反应测验
• with a whole skin    未受伤地, 安然无恙地

中文（繁體）(Chinese (Traditional))
n. - 皮膚, 皮
v. tr. - 剝...的皮, 在...上植皮, 去...的殼, 擦破...上的皮膚
v. intr. - 植皮, 結成皮, 癒合, 脫皮
adj. - 皮的, 皮膚的, 有關皮膚的, 裸露的, 裸體的, 色情的

idioms:

• all skin and bone    極瘦
• by the skin of one's teeth    好不容易, 僥倖
• get under a person's skin    激怒某人
• make one's skin crawl    使汗毛直豎, 起雞皮疙瘩
• no skin off my nose    跟某人毫不相干
• save one's (own) skin    保護自己, 使自己免遭殺害
• skin alive    活剝皮, 嚴斥
• skin deep    膚淺的, 皮毛的, 輕微的, 表面的
• skin diving    赤身潛水
• skin graft    補皮術, 表皮移植
• skin test    皮膚反應測驗
• with a whole skin    未受傷地, 安然無恙地

한국어 (Korean)
n. - (사람의) 피부, 구두쇠, (과일 따위의) 껍질
v. tr. - 껍질을 벗기다, 엄하게 꾸짖다, (가죽 따위로) 덮다
v. intr. - (상처 따위에) 딱지가 생기다, 빠져 나오다, 기어오르다
adj. - 피부의, 나체의, (잡지 등이) 누드를 다루는

idioms:

• by the skin of one's teeth    겨우, 간신히 도망치다
• get under a person's skin    ~를 성나게 하다, 애타게 하다, 흥미를 갖게 하다
• make one's skin crawl    남을 오싹하게 하다
• with a whole skin    무사히

日本語 (Japanese)
n. - 皮膚, 肌, 皮, 毛皮, 皮袋, 薄い膜, 上皮, 殻, 外側を覆う薄い板, 外被, 表皮
v. - 皮をはぐ, 皮をむく, 皮膚をすりむく, からだましとる

idioms:

• all skin and bone    全身骨と皮ばかりの
• by the skin of one's teeth    かろうじて
• gold-beater's skin    ゴールドビーターズスキン
• make one's skin crawl    ぞっとする
• no skin off my nose    痛くもかゆくもない, 無関係
• skin alive    生皮をはぐ, こっぴどくしかる, さんざんやっ付ける
• skin deep    わずかな
• skin diving    スキンダイビング
• skin graft    皮膚移植, 植皮用の皮膚片
• skin someone alive    生皮をはぐ, 苦しめる
• skin test    皮膚試験

العربيه (Arabic)
‏(الاسم) جلد أو بشرة, ألمحتال (فعل) يستحث, يقشر يسيطر عليه‏

עברית (Hebrew)
n. - ‮עור, קליפה, קרום, נאד, חמת, משטח חיצוני, מסגרת‬
v. tr. - ‮פשט עור, שרט, רימה, עשק, הציגו ככלי ריק‬
v. intr. - ‮הגליד, העלה קרום‬
adj. - ‮פורנוגרפי‬

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