Vitamins
n Vitamins are organic compounds required by the body in trace amounts to perform specific functions.Functions of vitamin A
a. Visual cycle (retinal)
O Vitamin A is a component of the visual pigments (rhodopsin) of rod in
the retina
O Rod cells are responsible for vision in dim light (night vision)
O Rhodopsin consists of 11-cis retinal bound to the protein opsin.ProvitaminA(?-carotene)
n It is the plant precursor of vitamin A
n It consists of two molecules of retinal linked at
their aldehydes
n In humans ?-carotene has only about one sixth the activity of retinol.Sources of vitamin A
n VitaminA(retinal,retinol)
n Are present only in animal tissue e.g. Liver, milk
fat and egg
n ?-carotene(precursorofvit.A)
n Present in dark green vegetables and orange
vegetables & fruits.n Whenneeded,itisreleasedandtransportedto extra-hepatic tissues by the plasma retinol-binding protein (RBP).n They regulate synthesis of many body compounds (bone, skin, nerves, brain, blood, etc..)
n They prevent nutritional deficiency diseases and allow optimal health at all ages.n Storage: adipose tissues
n Overdosage symptoms: yellow coloration of skin

 Absorption & storage
n VitaminAisabsorbedwithfatintheintestineand secreted into chylomicrons which reach blood.Vitamin A function
n Important functions:
n Maintenance of healthy epithelium
n Retinol and retinoic acid are required for the growth, differentiation, and maintenance of epithelial cells.Recommended dietary allowance (RDA)
n 1ugofretinol=6ugof?-carotene=5IU
n Thedailyrequirementisabout5000IUofretinol.Retinol retinal
2.n TheyincludevitamincandvitaminsB.3.4.