vitamin A

a complete presentation on vit. A

1. Vitamin A ZARAFSHAN DEPT:HUMAN NUTRITION AND DIETETICS 1 11/16/2019

2. VITAMIN A Vitamin A consists of Retinol from animal source & B-carotene from plant source. The term ‘Retinoid’ include both natural and synthetic form of VIT.A . RDA Infants = 400-500 mcg Children = 400-600 mcg Adults = 700-900 mcg Pregnancy = 750-770 mcg Lactation = 1200-1300 mcg 2

3. SOURCES ANIMAL: Liver, egg, butter, cheese, whole milk, fish, meat. Fish liver oil is the richest natural source of retinol. PLANTS: Green leafy vegetables and fruits. FORTIFID FOODS: Food fortified with Vit. A such as margarine , banaspati . 3

4. FUNCTIONS Helps in vision Role in gene expression Necessary for healthy skin Helps in mucous membrane Act as anti-oxidant Support growth Helps in reproduction 4

5. Digestion & Absorption Vit. A are available in the form of retinyl esters, which is hydrolyzed to retinol and fatty acid by pancreatic hydrolases and release as a components of chylomicrons. The absorption of retinol requires the presence of bile salt Once absorbed, retinyl esters are reformed in intestinal cells. After absorption conversion of carotenoids into retinol occurs in liver . 5

6. Transport and Storage of Vitamin A Liver stores 90% of vitamin A in the body. Transported via chylomicrons from intestinal cells to lymphatic tissue & then to liver for storage. Transported from the liver to target tissue as retinol via retinol-binding protein. RBP attaches to specific receptors present on the surface of tissue , that permit retinol to enter . Then carried to the site where vitamin is needed. 6

7. Role in Vision Retina contain two types receptors cells , cones (specialized for color & bright light) and rods (for dim light or night vision). The 11-cis retinal (vit. A) occur in retina, it combines with a protein namely opsin to form a conjugated protein molecule called rhodopsin , responsible for night vision. Rhodopsin is sensitive to light, it bleached & break down into opsin and all trans-retinal & the person unable to see. The trans-retinal is converted back into 11 cis-retinal & re-enter into the cycle. 7

8. Visual cycle 8

9. Vitamin A Deficiency Vitamin A deficiency is a lack of vitamin A in humans. It is common in developing countries but rarely seen in developed countries. Contain ocular and extra ocular diseases. Ocular contain: night blindness, conjunctival xerosis, corneal xerosis, bitot spots and Keratomalacia. 9

10. 1.Night blindness Caused by the lack of vit. A. It is the inability to see dim light. Cloudy area is formed in the lens of the eye. Condition may get worse if vit. A is not taken. 10

11. 2.CONJUNCTIVEL XEROSIS Caused by vit.A deficiency Conjuctive becomes dry and roughed It appears muddy and wrinkled . 3. CORNEAL XEROSIS Caused by vit.A deficiency Cornea become dry, dull and non wettable . and eventually opaque in very serious stage. 11

12. 4 . Bitot’s Spots Cause by vit.A deficiency. Triangular, white or yellowish foamy spots on the either side of cornea . 5 . Keratomalacia Caused by vit.A deficiency. It is the liquefaction of the cornea. The cornea may become soft and may burst open. 12

13. Extra-ocular Diseases Extra ocular contains g rowth retardation , intestinal infections & follicular hyperkeratosis Follicular hyperkeratosis is a skin condition characterized by excessive development of keratin in hair follicles and normal skin will be replaced by keratinized one. 13

14. Causes of vitamin A deficiency Inadequate intake of vitamin A . Fats malabsorption. Liver disorders. Excess alcohol consumption can deplete vitamin A. Iron deficiency can affect vitamin A uptake. 14

15. Hypervitaminosis A Hypervitaminosis A occurs when the maximum limit for liver stores of vit.A is exceeded. Symptoms : Nausea Skin peeling Birth defects Increased liver size Vomiting Headache Increased respiratory & intestinal infection 15

16. Treatment 16

17. References Essentials of bio-chemistry volume two ,by Hafeezullah Khan and Mansoor Khan. 17

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