Knowing Vitamin A

Vitamin A is a vitamin which is needed by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal. This molecule is absolutely necessary for both scotopic and color vision. Vitamin A also functions in a very different role, as an irreversibly oxidized form retinoic acid, which is an important hormone-like growth factor for epithelial and other cells.

In foods of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate, which is converted to an alcohol (retinol) in the small intestine. The retinol form functions as a storage form of the vitamin, and can be converted to and from its visually active aldehyde form, retinal. The associated acid (retinoic acid), a metabolite which can be irreversibly synthesized from vitamin A, has only partial vitamin A activity, and does not function in the retina or some essential parts of the reproductive system.

All forms of vitamin A have a beta-ionone ring to which an isoprenoid chain is attached, called a retinyl group. This structure is essential for vitamin activity. The orange pigment of carrots – beta-carotene – can be represented as two connected retinyl groups, which are used in the body to contribute to vitamin A levels. Alpha-carotene and gamma-carotene also have a single retinyl group which give them some vitamin activity. None of the other carotenes have vitamin activity. The carotenoid beta-cryptoxanthin possesses an ionone group and has vitamin activity in humans. http://en.wikipedia.org/wiki/Vitamin_A

Both comments and pings are currently closed.

 

Comments are closed.

 

Resources

Hi dear friends and visitors!! thanks for visiting me here!! Have a great and blessed day!!




WANT TO EXCHANGE LINK WITH ME? READ HERE FIRST

Extras

All photographs used on this site, including thumbnails, are the Author's property and are ©copyright. Please do not use our photos without our permission. If you wish to use one of our photos on your personal website or blog, please send us the link to the page where it is being used and the photo must be linked back to this site. We hope that you respect the Authors' request. Thank you for your respect and understanding!

Copyright © 2013 Health, Food and Travel | All Rights Reserved

Blog Design by Simple Blog MakeOver