MSc Medical Biochemistry, Ph.D,.
6C beta-ionine ring with 11C polyprenoid side chain with
alternate double bonds.
Provitamin–beta carotene [Retinal+Retinal]
Active forms 1.Retinol
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.
primary causes [dietary]
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
Toxicity produces headache , nausea , vomitings
, liver damage alterations in the skin and mucous
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.
closes Na+ channels in rod cell membrane
hyper polarization of rod cell membrane
generation of nerve impulse to visual cortex
plants - Ergosterol Ergocalciferol [D2]
Active form in animals is calcitriol
2. animal sources; fish liver oils eggs
3. plant sources
4. food fortification ; milk butter
200-400 IU day
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
Synthesis of vit-D
Regulation of synthesis by Ca and PO4.
Low calcium stimulates PTH secretion which
activates 1- hydroxylase
Vit-D plays a major role in regulation of calcium
and phosphate levels by mainly acting on 3
Intestine ; increases absorption of Ca and PO4
Bone ; increases deposition of CaPO4 thus
increasing mineralization of bones .
Kidneys ; reabsorbs Ca and decreases Ca
Adults ------ Osteomalacia
hyper-vitaminosis D causes toxic effects
like de-mineralization , hyper-calcemia ,
renal calculi etc.