Vitamin A in human body
The term vitamin A is generally used to refer to a group of compounds that possess the biological activity of all-trans retinol.
Vitamin A is a fat soluble vitamin. It is found only in animals, although a number of plants contain carotene, from which vitamin A can be produced in the body once the plants contain carotene are eaten.
The main physiological active forms of vitamin A are retinaldehyde and retinoic acid, both of which are derive from retinol.
Retinaldehyde functions in the visual system as the prosthetic group of the opsins, while retinoic acid modulates gene expression and tissue differentiation, acting by way of nuclear receptors.
Vitamin A may be formed in the body from the yellow pigments (containing carotene) of many fruits and vegetables, especially carrots.
Vitamin A is converted to light sensitive pigments in receptor cells of the retina, the light sensitive layer of the eye.
Vitamin A is also required for healthy reproduction and lactation. Vitamin A helps form and maintain healthy teeth, mucous membranes, skeletal and soft tissues and skin.
This vitamin also required for resistance to infection. One of its physiological functions is the formation and maintenance do epithelial tissue, which contributes to the body immune system. Scientists claim that vitamin A is ‘the anti-infective vitamin,’ enabling body surfaces to act as a barriers to invading micro-organism and toxins.
Epithelial cells (those cells present in the lining of body cavities and in the skin and glands) require vitamin A.
Lack of vitamin A in the diet will result in the drying up of the body cells which could lead to dermatitis, dry hair or night blindness.
