Vitamin A is fat soluble vitamin formed in the body from precursors, yellow pigments of plants (alpha, beta and gamma carotene).
Vitamin A is required for vision. Epithelial cells (those cells present in the lining) of body cavities and in the skin and glands) require vitamin A.
The form of vitamin A required in vision is 11-cis-retinal. On the retina, the initiating event of vision occurs when a photon of light excites a molecule so 11-cis-retinal that is covalently bound to the protein opsin.
Vitamin A seems to be essential for maintenance of the integrity of the rods because on prolonged depletion of the vitamin the outer segments of the rods lose their opsin resulting in their eventual disintegration.
A shortage of vitamin A results in inadequate formation of rhodopsin, the pigment mediating low- intensity.
Vitamin A required for vision
