Retinol (redirected from Polar bear liver)

retinol: see Vitamin A under vitamin.

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vitamin A

 also called retinol

Fat-soluble alcohol, most abundant in fatty fish and especially in fish-liver oils. It is not found in plants, but many vegetables and fruits contain beta-carotene (see carotene), which is readily converted in the body to vitamin A. It functions directly in vision, especially night vision. A derivative, retinaldehyde, is a component of the visual pigments, including rhodopsin, in the retina. Humans require vitamin A in very small amounts. Unlike carotenes, it is toxic in large amounts and is readily destroyed by exposure to heat, light, or air.

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retinol [′ret·ən‚ȯl]

(biochemistry)

vitamin A

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Retinol 

(also called axerophthol or vitamin A), an isoprenoid whose chemical formula is C₂₀H₃₀O. Retinol is soluble in nonpolar organic solvents, insoluble in water, and has a melting point of 63°–64°C. In animals and man, it is converted from the carotene in food and stored mainly in the liver; it is particularly abundant in the liver of whales and fish and in fish oil.

The most important biological function of retinol is its participation in the form of retinal in the visual process. A retinol deficiency results in impairment of twilight vision (night blindness, or nyctalopia) and in injury to epithelial tissue, as in xe-rophthalmia. An excess of retinol causes a variety of metabolic disturbances, an accumulation of retinol in the hydrophobic fraction of cell membranes, and destruction of these membranes. Retinol is commercially synthesized from β-ionone. Retinol is sometimes called vitamin A₁; its dehydro derivative C₂₀H₂₈O is called vitamin A₂. Retinal₁ and retinal₂ are distinguished accordingly.