La anorexia en la adolescencia

Pigmentation
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.
Many materials selectively absorb certain wavelengths of light. Materials that humans have chosen and developed for useas pigments usually have special properties that make them ideal for coloring other materials. A pigment must have a high tinting strength relative to the materials it colors. It must be stable in solid form at ambient temperatures.
For industrial applications, as well as in the arts, permanence and stability are desirable properties. Pigments that are not permanent are called fugitive. Fugitivepigments fade over time, or with exposure to light, while some eventually blacken.
Pigments are used for coloring paint, ink, plastic, fabric, cosmetics, food and other materials. Most pigments used in manufacturing and the visual arts are dry colorants, usually ground into a finepowder. This powder is added to a vehicle (or binder), a relatively neutral or colorless material that suspends thepigment and gives the paint its adhesion.
The worldwide market for inorganic, organic and special pigments had a total volume of around 7.4 million tons in 2006. Asia has the highest rate on a quantity basis followed by Europe and North America. In 2006, a turnover of 17.6 billion US$ (13 billion euro) was reached mostly in Europe, followed by North America and Asia.[1] The global demand on pigmentswas roughly US$ 20.5 billion in 2009, around 1.5-2% up from the previous year. It is predicted to increase in a stable growth rate in the coming years. The worldwide sales will increase to US$ 24.5 billion in 2015, and reach US$ 27.5 billion in 2018.[2]
A distinction is usually made between a pigment, which is insoluble in the vehicle (resulting in a suspension), and a dye, which either isitself a liquid or is soluble in its vehicle (resulting in a solution). The term biological pigment is used for all colored substances independent of their solubility. A colorant can be both a pigment and a dye depending on the vehicle it is used in. In some cases, a pigment can be manufactured from a dye by precipitating a soluble dye with a metallic salt. The resulting pigment is called a lakepigment.
In biology, a pigment is any colored material of plant or animal cells. Many biological structures, such as skin, eyes, fur and hair contain pigments (such as melanin). Animal skin coloration is often achieved with specialized cells calledchromatophores, which in animals such as the octopus and chameleon can be controlled to vary the animal's color. Many conditions affect the levels or natureof pigments in plant, animal, some protista, or fungus cells. For instance,Albinism is a disorder affecting the level of melanin production in animals.
Pigmentation is used in organisms for many biological purposes including Camouflage, Mimicry, Aposematism (warning), Sexual selection and other forms of Signalling, Photosynthesis (in plants), as well as basic physical purposes such as protectionfrom Sunburn.
Pigment color differs from structural color in that it is the same for all viewing angles, whereas structural color is the result of selective reflection or iridescence, usually because of multilayer structures. For example, butterfly wings typically contain structural color, although many butterflies have cells that contain pigment as well.
There are three basic classes ofpigments.
 Chlorophylls are greenish pigments which contain a porphyrin ring. This is a stable ring-shaped molecule around which electrons are free to migrate. Because the electrons move freely, the ring has the potential to gain or lose electrons easily, and thus the potential to provide energized electrons to other molecules. This is the fundamental process by which chlorophyll "captures" the...