This document discusses vitamin A, including its structures, functions, sources, requirements, and clinical uses. It notes that vitamin A is a fat-soluble vitamin that includes retinol and provitamin A carotenoids. It is essential for vision, reproduction, growth, and epithelial tissue maintenance. The document outlines the absorption and transport of vitamin A in the body as well as its mechanisms of action on gene expression. It also covers vitamin A functions in visual cycles, epithelial cells, and reproduction, along with its sources, requirements, deficiency symptoms, and uses to treat conditions like acne and psoriasis. Risks of excessive intake like hypervitaminosis A and potential side effects of isotretinoin are

1. Vitamins (Lippincott
biochemistry)
Muhammad Anwaar Ahmad (MBBS 1st year 2016)
Sahara medical college Narowal, Lahore

2. Vitamin A(Retinol & B-carotenes)
 It is a fat soluble vitamin.
 Retinoids family of molecule related to dietary retinol(Vit-A) essential for
+Vision +Reproduction
+growth +maintenance of epithelial tissue.
 Play a role in immune function.
OH Oxidation
 Retinal Retinol Retinoic acid

3. Structure of Vit-A
(Retinal __ Retinol__ Retinoic acid __ B-Carotene)
 Retinol: primary Alcohol containing a B-ionone ring with unsaturated side chain.
e.g ; Retinol is found in animal tissue as retinyl ester + long chain FAs.
 Retinal: Aldehyde derived from oxidation of retinol.
Retinol interconvert able Retinal
 Retinoic Acid: derived from Oxidation of Retinal.
Retinal oxidation Retinoic Acid
 B-Carotene: plant food contain B-Carotene , which can be cleaved in small
intestine yield two molecules of Retinal.
B-Carotene 2-Retinal

4. Absorption & transport of vit-A
(transport to liver , release from liver)
 Transport to liver: retinyl ester present in diet &
hydrolyzed in intestinal mucosa relese retinol & FFAs.
Retinyl ester(DIET) hydrolyzed intestinal mucosa Retinol+FFAs
 Retinyl ester contained in chylomicron remnants &
store in liver.
 Release from liver: Retinol released from liver to
tissue by plasma retnol-binding-protein(RBP).
Chylomicron
Remnant
Retinyl
ester
Retinol
(peripheral
tissues)

5. Mechanism of action of vit-A
(Target Tissue)
 Retinol is oxidized in to retinoic acid ,which bind to retinoic acid receptors(RARs).
 Activated retinoic acid receptor stimulates responsive genes reselt in control
specific protein for several physiological function.
e.g Retinoids control expression of the gene for keratin in epithelial tissue of body.

6. Function of vit-A
(Visual cycle , maintenance of epithelial cell , Reproduction)
 Visual cycle: RETINA
 Maintenance of epithelial cell:
 Vit-A is essential for differentiation of
Epithelial tissues & mucus secretion & support
Body barrier-based defence against pathogens.
 Reproduction:
 Retinol & retinal are essential for reproduction ,
supporting spermatogenesis in male & prevent
fetal reabsorption in female.
All trans
retinol
All trans
retinyl
ester
11-cis
retinol
11-cis
retinol
+Opsin
Rhodopsin
-Opsin (light)
All trans
retinal

7. Distribution/sources of Vit-A
(carotenoid , vit-A)
 Kidney, liver, cream, butter & egg yolk (good sources for vit-A)
 Yellow, orange & Dark green vegetables & fruits (good sources for carotenoid)
 Carotenoids are precursors of vit-A.

8. Requirement for Vit-A
(Dietary Requirment of vit-A “RDA")
(Retinol activity equivalents “RAEs”)
 RDA for Adult Male: 900 RAEs.
 RDA for Adult Female: 700 RAEs.
 1 RAEs = 1 µg retinol = 12 µg carotene =24 other carotenoids.
1 RAEs
1 µg retinol
12 µg carotene
24 other
carotenoids

9. Clinical Indication
(Dietary deficiency , Acne & Psoriasis)
 Retinol & Retinyl ester used to treated patient having vit-A deficiency .
 Night blindness, difficulty to see in dim light are early symptoms
 Prolong deficiency cause loss of visual cell , also sever lead to xerophthalmia.
 Xerophthalmia pathological dryness of conjunctiva & cornea caused by increased
keratin synthesis.
 Xerophthalmia result in corneal ulceration & ultimate in blindness due to formation
of opaque scar tissue.
 500,000 child are blind in each year due to deficiency of vit-A.
 Acne & Psoriasis are treated with retinoic acid .
 Causes of acne are Darier disease (keratosis follicularis), skin aging are treated All
trans retinoic acid as well as benzoyl peroxide & antibiotics.

10. Toxicity of Retinoids
(Hypervitaminosis-A , Brain tumor , Isotretinoin)
Hypervitaminosis A: excessive intake of vit-A .
 Normal amount of retinol = 7.5 mg/day (if exceeding cause hypervitaminosis)
 Early signs reflected in skin are;
 Dry & pruritic (due to decrease keratin synthesis)
 Liver become enlarge
 CNS rise intracranial pressure cause Brain tumor
 Vit-A promotes Bone growth ,however it associated with decrease bone mineral density
& increased risk of fracture.
Isotretinoin: drug ,an isomer of retinoic acid .
 Absolute contraindicated in women & child bearing potential .
 Treated with isotretinoin leads to hyperlipidemia with increase TAGs & cholesterol .
 Providing concern to increased rick of cardiovascular disease.

11. THANKS
.