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Jai Ganesh

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Registered: 2005-06-28

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Scales

Scales

Summary

Scales are a visible peeling or flaking of outer skin layers. These layers are called the stratum corneum.

Causes

Scales may be caused by dry skin, certain inflammatory skin conditions, or infections.

Examples of disorders that can cause scales include:

* Eczema
* Fungal infections such as ringworm or tinea versicolor
* Psoriasis
* Seborrheic dermatitis
* Pityriasis rosea
* Discoid lupus erythematosus, an autoimmune disorder
* Genetic skin disorders called ichthyoses

Home Care

If your health care provider diagnoses you with dry skin, you'll likely be recommended the following self-care measures:

* Moisturize your skin with an ointment, cream, or lotion 2 to 3 times a day, or as often as needed.
* Moisturizers help lock in moisture, so they work best on damp skin. After you bathe, pat your skin dry then apply your moisturizer.
* Bathe only once a day. Take short, warm baths or showers. Limit your time to 5 to 10 minutes. Avoid taking hot baths or showers.
* Instead of regular soap, try using gentle skin cleansers or soap with added moisturizers.
* Avoid scrubbing your skin.
* Drink plenty of water.
* Try over-the-counter cortisone creams or lotions if your skin is inflamed.

If your provider diagnoses you with a skin disorder, such as an inflammatory or fungal disease, follow instructions on home care. This may include using a medicine on your skin. You may also need to take a medicine by mouth.

When to Contact a Medical Professional

Call your provider if your skin symptoms continue and self-care measures aren't helping.

What to Expect at Your Office Visit

Your provider will perform a physical exam to look closely at your skin. You may be asked questions such as when the scaling began, what other symptoms you have, and any self-care you've done at home.

You may need blood tests to check for other conditions.

Treatment depends on the cause of your skin problem. You may need to apply medicine to the skin, or take medicine by mouth.

Alternative Names

Skin flaking; Scaly skin; Papulosquamous disorders; Ichthyosis

Details

In zoology, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopterans (butterflies and moths), scales are plates on the surface of the insect wing, and provide coloration. Scales are quite common and have evolved multiple times through convergent evolution, with varying structure and function.

Scales are generally classified as part of an organism's integumentary system. There are various types of scales according to the shape and class of an animal.

Fish scales

Main article: Fish scale
Fish scales are dermally derived, specifically in the mesoderm. This fact distinguishes them from reptile scales paleontologically. Genetically, the same genes involved in tooth and hair development in mammals are also involved in scale development.

Cosmoid scales

True cosmoid scales can only be found on the Sarcopterygians. The inner layer of the scale is made of lamellar bone. On top of this lies a layer of spongy or vascular bone and then a layer of dentine-like material called cosmine. The upper surface is keratin. The coelacanth has modified cosmoid scales that lack cosmine and are thinner than true cosmoid scales.

Ganoid scales

Ganoid scales can be found on gars (family Lepisosteidae), bichirs, and reedfishes (family Polypteridae). Ganoid scales are similar to cosmoid scales, but a layer of ganoin lies over the cosmine layer and under the enamel[clarification needed]. Ganoin scales are diamond shaped, shiny, and hard. Within the ganoin are guanine compounds, iridescent derivatives of guanine found in a DNA molecule. The iridescent property of these chemicals provide the ganoin its shine.

Placoid scales

Placoid scales are found on cartilaginous fish including sharks and stingrays. These scales, also called denticles, are similar in structure to teeth, and have one median spine and two lateral spines. The modern jawed fish ancestors, the jawless ostracoderms and later jawed placoderms, may have had scales with the properties of both placoid and ganoid scales.

Leptoid scales

Leptoid scales are found on higher-order bony fish. As they grow they add concentric layers. They are arranged so as to overlap in a head-to-tail direction, like roof tiles, allowing a smoother flow of water over the body and therefore reducing drag. They come in two forms:

* Cycloid scales have a smooth outer edge, and are most common on fish with soft fin rays, such as salmon and carp.
* Ctenoid scales have a toothed outer edge, and are usually found on fish with spiny fin rays, such as bass and math.

Reptilian scales

Reptile scale types include: cycloid, granular (which appear bumpy), and keeled (which have a center ridge). Scales usually vary in size, the stouter, larger scales cover parts that are often exposed to physical stress (usually the feet, tail and head), while scales are small around the joints for flexibility. Most snakes have extra broad scales on the belly, each scale covering the belly from side to side.

The scales of all reptiles have an epidermal component (what one sees on the surface), but many reptiles, such as crocodilians and turtles, have osteoderms underlying the epidermal scale. Such scales are more properly termed scutes. Snakes, tuataras and many lizards lack osteoderms. All reptilian scales have a dermal papilla underlying the epidermal part, and it is there that the osteoderms, if present, would be formed.

Many reptiles possess large scales not supported by osteoderms known as feature scales. The green iguana possesses large feature scales on the ventral sides of its neck, and dorsal spines not supported by osteoderms. Many extinct non-avian dinosaurs such as Carnotaurus and Brachylophosaurus are known to possess feature scales from skin impressions.

Avian scales

Birds' scales are found mainly on the toes and metatarsus, but may be found further up on the ankle in some birds. The scales and scutes of birds were thought to be homologous to those of reptiles, but are now agreed to have evolved independently, being degenerate feathers.

Carcharodontosaurid theropod dinosaur Concavenator, is known to have possessed these feather-derived tarsal scutes.

Mammalian scales

An example of a scaled mammal is the pangolin. Its scales are made of keratin and are used for protection, similar to an armadillo's armor. They have been convergently evolved, being unrelated to mammals' distant reptile-like ancestors (since therapsids lost scales), except that they use a similar gene.

On the other hand, the musky rat-kangaroo has scales on its feet and tail. The precise nature of its purported scales has not been studied in detail, but they appear to be structurally different from pangolin scales.

Anomalures also have scales on their tail undersides.

Foot pad epidermal tissues in most mammal species have been compared to the scales of other vertebrates. They are likely derived from cornification processes or stunted fur much like avian reticulae are derived from stunted feathers.

Arthropod scales

Butterflies and moths - the order Lepidoptera (Greek "scale-winged") - have membranous wings covered in delicate, powdery scales, which are modified setae. Each scale consists of a series of tiny stacked platelets of organic material, and butterflies tend to have the scales broad and flattened, while moths tend to have the scales narrower and more hair like. Scales are usually pigmented, but some types of scales are iridescent, without pigments; because the thickness of the platelets is on the same order as the wavelength of visible light the plates lead to structural coloration and iridescence through the physical phenomenon described as thin-film optics. The most common color produced in this fashion is blue, such as in the Morpho butterflies.

Some types of spiders also have scales. Spider scales are flattened setae that overlay the surface of the cuticle. They come in a wide variety of shapes, sizes, and colors. At least 13 different spider families are known to possess cuticular scales, although they have only been well described for jumping spiders (Salticidae) and lynx spiders (Oxyopidae).

Some crustaceans such as Glyptonotus antarcticus have knobbly scales. Some crayfish have been shown to use antennal scales that are activated in rapid response movements.

Insect Scale

Scales are present on the bodies of various insects. A notable example are the Lepidoptera, the insect order comprising moths and butterflies, which have scales on their wings and on the head, parts of the thorax and abdomen, and parts of the genitalia. The name is derived from Ancient Greek scale and wing.

The Trichoptera (caddisflies) which are a sister group of the Lepidoptera have scales, but also possess caudal cerci on the abdomen, a feature absent in the Lepidoptera. Beetles of family Dermestidae also commonly have scales.

Morphology

The morphology of scales has been studied by Downey & Allyn (1975) and scales have been classified into three groups, namely:

* Hair-like or piliform.
* Blade-like or lamellar.
* Other variable forms.

Primitive moths (non-Glossata and Eriocranidae) have 'solid' scales which are imperforate, i.e., they lack a lumen.

Structure

Though there is great diversity in scale form, they are structured similarly. The body or 'blade' of a typical scale consists of an upper and lower lamina. The surface of the lower lamina is smooth whereas the structure of the upper lamina is structured and intricate. Scales are attached to the substrate by a stalk or 'pedicel'. The scales cling somewhat loosely to the wing and come off easily without harming the insect.

Colour

The colouration of butterfly wings is created by the scales which are pigmented with melanins that give them blacks and browns, but blues, greens, reds and iridescence are usually created not by pigments but the microstructure of the scales. This structural coloration is the result of coherent scattering of light by the photonic crystal nature of the scales.

Function

Scales play an important part in the natural history of Lepidoptera. Scales enable development of vivid or indistinct patterns which help the organism protect itself by concealment and camouflage, mimicry and warning. Besides providing insulation, dark patterns on wings provided by dark colour scales would allow sunlight to be absorbed and thus probably have a role to play in thermoregulation. Bright and distinctive colour patterns in butterflies which are distasteful to predators help communicate their aposematism (toxicity or inedibility) thus preventing a predator from preying on it. In Batesian mimicry, wing colour patterns help edible Lepidopterans mimic inedible models while in Müllerian mimicry inedible butterflies resemble each other to reduce the numbers of individuals sampled by predators.

Scales possibly evolved initially for providing insulation. Scales on the thorax and other parts of the body probably contribute to maintaining the high body temperatures required during flight. The 'solid' scales of basal moths are however not as efficient as those of their more advanced relatives as the presence of a lumen adds air layers and increases the insulation value.

Young adults of myrmecophilous Lepidoptera escape from ant's nests by virtue of the deciduous waxy scales with which they are covered when born. These scales rub off and stick on the ants as they make their way out of the nest after hatching.

Scales greatly reduce fatalities among Lepidoptera after flying into spiderwebs. The detachable scales pull away freely and enable the insect to escape. Thomas Eisner tested spiderwebs' effectiveness by dropping various insects onto the webs. Moths were consistently able to escape, and all left impact spots where scales had stuck to the web.

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