Vitamin A Three forms i. Retinol (OH) - Alcohol form: Most active, transported form ion the body ii. Retinal (HCHO) - Aldehyde form iii. Retinoic acid (COOH) - Carboxylic acid Vitamin A stored I liver as retinyl esters Retinoids: Synthetic form of Vitamin A CarotenoidsPro Vitamin AVitamin A Beta carotene2 Retinal molecules Retinol (Vitamin A) and retinoic acid Important Vitamin A sources: Eggs, butter, white milk, fish liver has retinol esters. Cod liver, shark liver oil are good sources of Vitamin A Herbivores: Vitamin A from carotenoids from plant Carnivores: Vitamin A from animal tissues especially liver Bile and pancreatic enzymes are important for Vitamin A absorption More than 90% of body’s Vitamin A stored in liver Vitamin A has anticancer properties Rhodopsin or visual purple, three iodopsins in cone cells have Vitamin A Rhodopsin is most light sensitive pigment obtained from Vitamin A (Retinol) Iodopsins are responsible for specific colours in bright light George Wald: Nobel Prize for elucidating visual process Vitamin A deficiency causes squamous metaplacia Major target of Vitamin A is eye. Deficiency causes night blindness or nyctalopia observed mainly in cattle and horse Chronic nyctalopia leads to Xerophthalmia (dryness of eye) which is hyperkeratinisation of cornea Dryness of cornea is xerosis Biot’s spot is keratin debris in small opaque plaque Keratomalacia is roughening, softening or destruction of cornea Special nodules are pathegnomonic of hypovitaminosis A also with coryza and respiratory infections produce nutritional roup in birds Squamous metaplasia is most important effect is on urinary tract. Vitamin A deficiency in males causes urolithiasis. In females due to less constricted urethra effect ts of urolithiasis is less. Vitamin A deficiency causes Infertility in bovines Vitamin A deficiency causes foetal mal formations and cause sterility in males Vitamin A deficiency causes increased CSF pressure so convulsions occur Vitamin A deficiency causes still birth and abortion Vitamin A is toxic in excess doses Keratitis is inflammation of cornea Chronic Respiratory Disease (air saculitis) in poultry is caused by Mycoplasma + E. coli, IB Important component of Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). NAD is important in dehydrogenases involved in metabolism of fat, carbohydrate and proteins. NADP is important in dehydrogenization of HN pathway
