Now.. I want to tell you about the other kind of Vitamin, on the last post, I've told you about Vitamin C... And now I will tell you about Vitamin A...
Vitamin A is a group of unsaturated nutritional organic compounds, that includes retinol, retinal, retinoic acid, and several provitamin A carotenoids, among which beta-carotene is the most important. Vitamin A has multiple functions: it is important for growth and development, for the maintenance of the immune system and good vision. Vitamin A is needed by the retina of the eye in the form of retinal, which combines with protein opsin to form rhodopsin the light-absorbing molecule, that is necessary for both low-light (scotopic vision) and color vision. Vitamin A also functions in a very different role as an irreversibly oxidized form of retinol known as 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 retinol (chemically an alcohol) 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 that can be irreversibly synthesized from vitamin A, has only partial vitamin A activity, and does not function in the retina for the visual cycle. Retinoic acid is used for growth and cellular differentiation.
All forms of vitamin A have a beta-ionone ring to which an isoprenoid chain is attached, called a retinyl group. Both structural features are 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.
Health Benefit Of Vitamin A
Vitamin A Is important for vision
When we look at objects, light is reflected from the object and enters the eye, striking a tissue located in the back of the eye. This tissue is known as the retina. When light strikes the retina, retinol is converted to retinal, which is then shuttled to rods – the cells that help you to see in the dark. In rod cells, retinal binds to a protein called opsin. As a result, opsin changes shape and causes nerve impulses to be generated. These nerve impulses then carry messages to the brain regarding the objects in our visual field. Retinal is then converted back to retinol, ending the visual cycle.
A hallmark of vitamin A deficiency is night blindness – an impaired ability to see in low light conditions. This is because with a reduced availability of retinol, the nerve impulses necessary for our brain to interpret visual information are hindered.
Vitamin A Regulates Genes
Our genes hold the code for vital proteins needed to carry out the body’s day to day functions. Thus, when these proteins are needed, the genetic code needs to be transcribed. However, gene transcription is highly regulated. This includes when it occurs and how fast it occurs. The retinoic acid form of Vitamin A helps to regulate the rate of gene transcription.
Vitamin A Supports the Immune System
The skin and the lining that covers the digestive, respiratory and urinary tracts are important components of the immune system. They are your body’s first barrier against infection. The retinol form of vitamin A is responsible for maintaining the function of the cells that make up these barriers. Vitamin A is also needed for the formation and activation of white blood cells.
Vitamin A Is Important for Red Blood Cell Production
All blood cells are developed from stem cells. Vitamin A facilitates the specialization of stems into red blood cells. Vitamin A also allows iron to be incorporated into hemoglobin – the oxygen carrying component of red blood cells.
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