Define the Functions of Vitamin A?

Vitamin A (retinol) is an essential nutrient needed in small amounts by humans for the normal functioning of the visual system, growth and development, and maintenance of epithelial cellular integrity, immune function, and reproduction. While we discuss the major functions of vitamin A, it is important to note  &at primary vitamin A deficiency (VAD) may give rise to more than one secondary  effects which can of tell be recognized in the form of clinical signs and symptoms  most important  being ocular manifestations grouped under 'xerophthamia. In addition to the specific signs and symptoms of xerophthamia and the risk of irreversible blindness, nonspecific symptoms include increased morbidity  and mortality, poor reproductive health, increased risk of anaemia, and contributions  o depressed growth and development.