from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Either of two yellow to red retinal pigments, formed by oxidation of vitamin A alcohols. Also called retinal2.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Either of two carotenoid pigments found in the retina and produced from vitamin A; retinal
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. either of two yellow to red retinal pigments formed from rhodopsin by the action of light
Sorry, no etymologies found.
Nevertheless in that period, after dissecting retinas from 300 frogs, he found that rhodopsin on stimulation with light yielded both the protein opsin and a compound he called "retinene" (now "retinaldehyde") that in turn yielded vitamin A (now called retinol).
Retinene can exist in two forms, different in molecular shape, called cis-retinene and trans-retinene.
In the dark, trans-retinene changes into cis-retinene and joins opsin once more to form the rhodopsin.
If the diet is deficient in vitamin A, the body's stores eventually give out and retinene is not replaced as it is lost.
Vitamin A, which is more stable, is, however, easily converted into retinene, so that the vitamin A stores of the body can be called upon to replace the constant dribbling loss of this visual pigment.
In the presence of light, cis-retinene is converted to trans-retinene and, if it already makes up part of the rhodopsin molecule, it falls off, leaving the largely colorless opsin behind.
The shape of cis-retinene is such that it can combine with opsin to form rhodopsin, whereas trans-retinene cannot.