ABSTRACT
Physiology This vitamin exists in several forms that are interconverted. Retinol (vitamin A1) is a primary alcohol and is present in the tissues of animals and marine fishes; 3-dehydroretinol (vitamin A2) is present in freshwater fish; retinoic acid shares some but not all of the actions of retinol. Carotene is provitamin A and is readily converted into retinol in the body. Vitamin A has many physiological functions (Figure 35.1). Its deficiency retards growth and development, and causes night blindness, keratomalacia, dry eyes and keratinization of the skin. Dietary sources of vitamin A include eggs, fish liver oil, liver, milk and vegetables.
