2. VITAMIN- A
Structure
6C beta-ionine ring with 11C polyprenoid side chain with
alternate double bonds.
Provitamin–beta carotene [Retinal+Retinal]
Active forms 1.Retinol
2.Retinal
3.Retinoic acid
5. VITAMIN A
Retinol Retinal retinoicacid All-trans Retinal
common in circulation.
11cis- Retinal form is present in rhodopsin.
Active forms are heat stable and light sensitive.
6. VITAMIN A
Sources
Animal –marine fish liver oils
Plant - mangopapayacarrot
RDA – 1000 ug day
1 RE = 1ug of retinol = 0.6 ug of betacarotene
9. WALDS VISUAL CYCLE
The Cyclic events that occur in the process
of vision is visual cycle. .
Rhodopsin is a photoreceptor present in
retinal rod cells.
Rhodopsin is a conjugated protein with 11-cis
retinal and protein opsin.
13. .
Toxicity of vit-A is either due to
1. over-dosage of vit-A supplements
2. excess dietary intake [
As vitamin A is not excreted from the body it
isccumulated in liver producing toxic
effects
Toxicity produces headache , nausea , vomitings
, liver damage alterations in the skin and mucous
membranes etc.
14. .
Vit-A can be used to treat diseases where
epithelial surface is damaged.
Retinoic acid acts on cell differentiation and
growth therefore used as a drug.
It is used to treat diseases like Measles,
Acne, Psoriasis , Leukemia etc.
18. VISUAL CYCLE
Decreased CGMP
closes Na+ channels in rod cell membrane
hyper polarization of rod cell membrane
generation of nerve impulse to visual cortex
21. VITAMIN D
Sources
1. sunlight
2. animal sources; fish liver oils eggs
3. plant sources
4. food fortification ; milk butter
RDA
200-400 IU day
22. VITAMIN D
Digestion absorption transport
Digested and absorbed in small intestine
using bile salts .
Vit-D is transported from intestine to
circulation by chylomicrons and stored in the
liver.
23. VITAMIN D
Synthesis of vit-D
Regulation of synthesis by Ca and PO4.
Low calcium stimulates PTH secretion which
activates 1- hydroxylase
24. FUNCTIONS
Vit-D plays a major role in regulation of calcium
and phosphate levels by mainly acting on 3
different organs.
Intestine ; increases absorption of Ca and PO4
Bone ; increases deposition of CaPO4 thus
increasing mineralization of bones .
Kidneys ; reabsorbs Ca and decreases Ca
excretion.