biochemical function , clinical manifestation of vitaminA

1. •Dr. Jaswant Kaur
Assistant professor
Department Biochemistry

6. Daily requirement of Vitamin A
The recommended daily allowance (RDA) of
Vitamin A for children = 400–600 μg/day, for
men = 750–1000 μg/day,
• For women = 750 μg/day pregnancy = 1000
μg/day.
• quirement of Vitamin A

7. Dietary Sources
• Animal sources :- milk, butter, cream, cheese,
egg yolk and liver. Fish liver oils (cod liver oil
and shark liver oil)
• Vegetable sources contain the yellow pigment
beta carotene.
• Carrot contains significant quantity of beta
carotene. Papaya, mango, pumpkins and
green leafy vegetables (spinach, amaranth) are
other good sources of vitamin A activity.

8. Active form of viatmin A

9. Interconversion of vitamin A molecules.

10. Vitamin A metabolism.

11. Wald’s visual cycle

12. Mechanism of Dark Adaption

13. Dark adaption mechanism
• Person shifts from bright light to dim area- leads
difficulty in seeing .
Due to resynthesis of rhodopsin & vision is
improved.
• Increased in Vit. A deficiency.
• Red light bleaches rhodopsin to a lesser extent.
photosensitive cells
• Rods cones
( for dim light vision) ( bright light & color vision)

14. • Vision
• Visual cycle
• Rods are for Vision in Dim Light
• Cones are for Color Vision
• Other Biochemical Functions
• Gene Regulation
• Immunological System
• Reproductive System
• Anti-oxidant Property
• Effect on Skin

15. Cont.

16. Deficiency manifestation of Vit. A
• Night Blindness or Nyctalopia
• Bitot’s Spots
• Xerophthalmia
• Keratomalacia
• Preventable Blindness
• Skin and Mucous Membrane Lesions growth retardation
reduced immunity against infections.

17. • Deficiency of vitamin A: Deficiency leads to a variety of
disorders of the eyes and this affect the vision, some of the
disorders are –
• 1)Night blindness: The person cannot see the objects in
dim light and in nights.
• Bitot’s spot:- seen as greenish white triangular
plaques adherent to conjuctiva.
2)Xeropthalmia : conjuctiva becomes dry, thick, wrinkled.
• Losses its transperancy.
• Dryness spreads to cornea.
3) Keratomalacia ( softening of the cornea) :- Xeropthalmia
persists for long time , leads Keratomalacia .
Occur degeneration of corneal epithelium

18. Bitot spots
Keratomalacia.

19. • 4)Skin become scaly, rough and is covered
with papillae (Small eruptions).
• 5)Reproductive functions may also be
effected in vitamin ‘A’ deficiency.
• National Institute of Nutrition, Hyderabad
has evolved a method giving a large dose
(5 – 6 drops) of Vitamin-A once in six
months to prevent blindness in children

20. Hypervitaminosis A or toxicity
• Excessive intake can lead to toxicity since the
vitamin is stored.
• Symptoms of toxicity are anorexia, irritability,
headache, drowsiness and vomiting, increased
intracranial tension.
• Sometimes swelling over long bones (bony
exostosis) may occur with painful bones.
Enlargement of liver is also seen in children

21. Objectives
• List the different active forms of vitamin A
State the dietary sources and RDA in children,
adults, pregnancy and lactation
• Explain the role of vitamin A in vision and
Wald’s visual cycle
• Describe the deficiency manifestations of
vitamin A .