The term carotene (also carotin, from the Latin carota, "carrot") is used for many related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but in general cannot be made by animals (with the exception of some aphids and spider mites which acquired the synthesizing genes from fungi). Carotenes are photosynthetic pigments important for photosynthesis. Carotenes contain no oxygen atoms. They absorb ultraviolet, violet, and blue light and scatter orange or red light, and (in low concentrations) yellow light. Carotenes are responsible for the orange colour of the carrot, after which this class of chemicals is named, and for the colours of many other fruits, vegetables and fungi (for example, sweet potatoes, chanterelle and orange cantaloupe melon). Carotenes are also responsible for the orange (but not all of the yellow) colours in dry foliage. They also (in lower concentrations) impart the yellow coloration to milk-fat and butter. Omnivorous animal species which are relatively poor converters of coloured dietary carotenoids to colourless retinoids have yellowed-coloured body fat, as a result of the carotenoid retention from the vegetable portion of their diet. The typical yellow-coloured fat of humans and chickens is a result of fat storage of carotenes from their diets. Carotenes contribute to photosynthesis by transmitting the light energy they absorb to chlorophyll. They also protect plant tissues by helping to absorb the energy from singlet oxygen, an excited form of the oxygen molecule O2 which is formed during photosynthesis.
Pleural thickening is an increase in the bulkiness of one or both of the pulmonary pleurae. Causes
Pleural plaques
Pleural plaques are patchy collections of hyalinized collagen in the parietal pleura. They have a holly leaf appearance on X-ray. They are indicators of asbestos exposure, and the most common asbestos-induced lesion. They usually appear after 20 years or more of exposure and never degenerate into mesothelioma. They appear as fibrous plaques on the parietal pleura, usually on both sides, and at the posterior and inferior part of the chest wall as well as the diaphragm. See also
Pleural disease


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