About vitamin afat-soluble vitamin, treatment of vitamin a deficiency.mechanism of action of vitamin avitamin a is required for a variety of physiological functions in the body such as: - 1).proper functioning of retina and formation of pigment rhodopsin during dark adaptation. 2).promotes differentiation and maintains structural integrity of epithelia over the body and also retard the malignancies of epithelial structures.3).promotes mucous secretion. 4).inhibits keratinization, 5). maintains proper bone growth, 6).maintenance of spermatogenesis, 7).supports foetal development, 8).improves resistance to infection. it is required for proper antibody response, normal lymphocyte proliferation and killer cell function.