M.Prasad NaiduMSc Medical Biochemistry, Ph.D,.

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

CH3

CH3H3CCH3

CH2OH

CH3

VITAMIN A (RETINOL)

RDA: 0.7 mg

Poly isoprenoid side chain

Retinol Retinal retinoicacid All-trans Retinal A1 common in circulation.

11cis- Retinal form is present in rhodopsin. Active forms are heat stable and light

sensitive.

Sources Animal –marine fish liver oils Plant - mango\papaya\carrot RDA – 1000 ug \ day 1 RE = 1ug of retinol = 0.6 ug of betacarotene

FUNTIONS 1. Retinal and Retinol vision 2. Retinoic acid – cell differentiation

glycoprotein synthesis reproduction.

3.Beta-carotene- Anti-oxidant

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.

WALDS

VISUAL CYCLE

primary causes [dietary] secondarycauses[malabsorption] Results in Night blindness Conjunctival xerosis Bitots spots Corneal xerosis keratomalasia Blindness

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.

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.

meta-rhodopsin

Transducin Transducin [A]

PDE PDE [A] CGMP

GMP

Decreased CGMP closes Na+ channels in rod cell membrane

hyper polarization of rod cell membrane generation of nerve impulse to visual cortex

Structure plants - Ergosterol Ergocalciferol

[D2] Active form in animals is calcitriol

UV

Sources 1. sunlight 2. animal sources; fish liver oils \ eggs 3. plant sources 4. food fortification ; milk\ butter

RDA 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 liver.

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 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.

Deficiency Children ---Rickets Adults ------ Osteomalacia

Toxicity hyper-vitaminosis D causes toxic

effects like de-mineralization , hyper-

calcemia , renal calculi etc.

Laboratory findings Hypochromic microcytic

anemia ferritin ( 30 to 300

Nanogm/ml) serum iron (50 to175

µgm/dl) TIBC (300 to 350 µgm/dl) transferrin (200 to 400

mg/dl)

Spoon-shaped nails (koilonychia)

Dental fluorosis