VitaminA and its defeciency

VITAMINS
Vitamin A
Vitamin A plays an important role in development, epithelial proliferation, keratinization, and the transduction of visual images by the retina. Vitamin A is a fat-soluble vitamin found only in the animal kingdom. It is obtained in the diet through consumption of liver, fish, and other animal products. After absorption. Vitamin A also may be obtained in the diet through metabolism of carotenoids found in fruits and vegetables.
VITAMIN A DEFICIENCY
The principal causes of vitamin A deficiency are inadequate diet , fat malabsorption, and liver disease. Deficiency effects the visual system, the immune system, and the skin. Vitamin A deficiency has been associated with increased childhood mortality. It is known to cause night blindness and disease of the conjunctiva,sclera ( white patches representing shed corneal epithelium), and cornea .
Vitamin A deficiency is a leading cause of blindness, especially in children, throughout the developing world.
Vitamin A deficiency also has been shown to reduce immunity in a number of ways. Production of antibodies to bacteria becomes impaired. Natural killer cell number and function are decreased. Activity against viral infections (such as measles and HIV) and parasites is also diminished.
Severely malnourished persons with vitamin A deficiency exhibit skin changes termed dermomalacia. The skin over large areas of the body is dry, wrinkled, and covered with fine scales.
Vitamin A deficiency is assessed by measurement of the serum retinol level. Treatment of vitamin A deficiency with administration of 100,000 to 300,000 IU/day of retinol rapidly corrects some visual disturbances, although corneal ulcers are permanent. Skin changes respond over a period of weeks to months.