Vitamin - A
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Biochemistry of Vitamin A. Chemistry, RDA, Functions, Deficiency manifestations.
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Vitamin - A
- 3. H i s t o r y The discovery of vitamin A may have started from research dating back 1816. In 1912, an English biochemist Frederick Gowland Hopkins found unknown factors present in milk that were required to aid growth in rats. (Nobel Prize in 1929) In 1917, Elmer McCollum and his colleagues discovered one of these substances while researching the role of dietary fats. In 1918, these “accessory factors” were described as “fat soluble” and in 1920, they were referred to as vitamin A.
- 4. • Vitamin A occurs in two forms in food Retinoids Retinol Retinal Retinoic acid Carotenes α- carotene β- carotene γ- carotene
- 7. Retinyl esters Beta-carotene Retinol Retinal Retinoic acid (most) (some)
- 11. One ounce of polar bear liver contains enough vitamin A (retinol) to kill a person!
- 12. The daily requirement of vitamin A is expressed as retinol equivalents [RE] 1000 RE MEN 800 RE WOMEN 1RE = 1 μg retinol, 2 μg of β-carotene in oil, 12 μg of "dietary" β- carotene 3.3 IU of retinol
- 15. HEALTH VISION 01 REPRODUCTION 03 CELL GROWTH & DIFFERENTIATION 04 05 EPITHELIAL INTEGRITY 02 SUPPORT THE IMMUNE SYSTEM 06 ANTIOXIDANTS 07 GLYCOPROTEIN SYNTHESIS (β –carotenes) VITAMIN A FUNCT IONS 7
- 18. Photoreceptor cells in the retina Photosensitive pigment RHODOPSINRODS Opsin 11-Cis retinal
- 19. Rhodopsin cycle comprises two distinct events Bleaching of rhodopsin & generation of nerve impulse Regeneration of rhodopsin
- 24. Vision Cycle
- 25. Photoreceptor cells in the retina Required for vision in daylight and colour identification PorphyropsinIodopsinCynopsin CONES
- 26. Dark Adaptation • Torsten Wiesel -1981 Nobel prize. • Bright light depletes stores of rhodopsin in rods. • After few minutes rhodopsin is resynthesized & vision improved. • This period called -Dark Adaptation Time. • Increased in vitamin A deficiency.
- 28. • Retinoic acid is necessary for cellular differentiation • Important for… • Embryo development, • Gene expression • Retinoic acid influences production, structure, and function of epithelial cells that line skin and mucus cells.
- 31. • Deficiency leads to decreased resistance to infections • Supplementation may decrease severity of infections in deficient person
- 34. Night Blindness • Lack of vitamin A causes night blindness or inability to see in dim light. • night blindness occurs as a result of inadequate pigment in the retina. • It also called tunnel vision.
- 35. Bitot’s Spot • These are foamy & whitish cheese-like tissue spots that develop around the eye ball, causing severe dryness in the eyes. • These spots do not affect eye sight in the day light.
- 36. Conjunctival Xerosis • Conjunctiva becomes dry and non wettable. • Instead of looking smooth shiny it appears muddy &wrinkled.
- 37. Keratomalacia • One of the major cause for blindness in India. • Cornea becomes soft and may burst • The process is rapid • If the eye collapses vision is lost.
- 38. Other Symptoms of VAD • Alteration of skin and mucous membrane • Hepatic dysfunction • Headache • Drowsiness • Peeling of skin about the mouth and elsewhere
- 40. Impaired dark adaptation time Decreased vitamin A in plasma Decreased RBP in plasma
- 41. Over ingestionCauses Bone and joint pain Anorexia Hair loss Headache Hepato- megaly Weight loss
- 42. 47 of 43 Thank you
Editor's Notes
- A. History.It was first recognized as an essential nutritional factor by Elmer McCollum in 1915 and then isolated from fish-liver oil by Holmes in 1917. On account of its established role in the visual process, it is often called as antixerophthalmic factor or the “bright eyes” vitamin. It was first synthesized in 1946 by Milas.
- Organ Meats (Liver), Cod Liver Oil Cheese, Milk products Carrot juice Sweet Potato with peel Tomato Pumpkin Spinach Turnip Green Mixed Green leafy vegetables
- Vitamin A originates in marine algae, and then passes up the food chain to reach the large carnivorous animals. Toxic levels of vitamin A may accumulate in the livers of a wide range of creatures such as Polar bears, seals, porpoises, dolphins, sharks, whales, Arctic foxes and huskies. Even a small meal of southern Australian seal liver, say 80g, may produce illness in man. Most of the foods recommended as source of vitamin A contain well below the toxic levels of vitamin A, but one– Halibut liver oil– contains dangerously high amounts of vitamin A. As regards the vitamin A contents of polar animals, one can see that, in reality, very little quantities of livers of these animals are required to kill a human being : 30–90 g of polar bear liver or halibut liver, 80–240 g of bearded seal liver and 100-300 g of Antarctic husky liver is enough to kill a human being.
- Normal plasma vitamin 20 to 80 µg/100ml