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M.Prasad Naidu MSc Medical Biochemistry, Ph.D,. 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 Vitamin- A
Poly isoprenoid side chain RDA: 0.7 mg
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. Vitamin A
Sources Animal –marine fish liver oils Plant - mango\papaya\carrot • RDA – 1000 ug \ day 1 RE = 1ug of retinol = 0.6 ug of betacarotene Vitamin A
FUNTIONS • Retinal and Retinol vision • 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
FUNCTIONS OF VIT A WALDS VISUAL CYCLE
primary causes [dietary] secondarycauses[malabsorption] Results in Night blindness Conjunctival xerosis Bitots spots Corneal xerosis keratomalasia Blindness Defeciency
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 Visual cycle
Decreased CGMP closes Na+ channels in rod cell membrane hyper polarization of rod cell membrane generation of nerve impulse to visual cortex VISUAL CYCLE
Structure plants - Ergosterol Ergocalciferol [D2] Active form in animals is calcitriol Vitamin D UV
Sources 1. sunlight 2. animal sources; fish liver oils \ eggs 3. plant sources 4. food fortification ; milk\ butter RDA 200-400 IU \ day 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. Vitamin D
Synthesis of vit-D • Regulation of synthesis by Ca and PO4. • Low calcium stimulates PTH secretion which activates 1- hydroxylase Vitamin D
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. functions
Deficiency Children ---Rickets Adults ------ Osteomalacia Vitamin D
Toxicity hyper-vitaminosis D causes toxic effects like de-mineralization , hyper-calcemia , renal calculi etc. Vitamin D
Iron deficiency anemia • 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)
