33. Unit of activity
International units (I.U.)
• 0.3 µg of retinol = 1 I.U.
• Daily requirement
• Adult Male And Female
• 3000 I.U. /day
33
34. Unit of activity
International units (I.U.)
• Recommended Allowance
• 5000 I.U./ day
• Higher In
Growing Children, Pregnant Women
, Lactating Mothers
and
HEPATIC DISEASE
34
45. MECHANISM OF ACTION OF VITAMIN
“A”
• Retinoic acid …. Binds with
high affinity to specific proteins
in the nucleus of target tissues
• Activated retinoic acid-receptor
complex interacts with nuclear
chromatin…..
45
46. MECHANISM OF ACTION OF VITAMIN
“A”
• Stimulation of retinoid-
specific RNA synthesis
• Mediation of physiologic
functions
46
47. Role of vitamin A
•VISION (RETINAL)
•REPRODUCTION
• GROWTH AND CELL
DIFFERENTIATION
47
48. Role of vitamin A
•MAINTENANCE OF
EPITHELIAL TISSUES
• CONTROL OF KERATIN
PRODUCTION
48
49. Role of vitamin A
• RETINOIC ACID
Mediates Most Of The Actions
Except Vision
49
50. Role of vitamin A
• Retinoid X receotors form
dimers with vitamin D and
thyroid hormone receptors
• So deficiency of vitamin A
impairs vitamin D and thyroid
hormone function
50
56. Functions of vit.A
• In the pigment epithelium
of the retina
• ALL-TRANS-RETINOL
• Isomerized to
11-cis-RETINOL
• Oxidized to
• 11-cis-RETINALDEHYDE
56
58. Functions of vit.A
• The aldehyde group of retinal
Reacts With Amino group of
Lysine Residue in opsin,
forming the holo-protein
RHODOPSIN.
• Rhodopsin has light absorbing
property
• Even dim light can break
rhodopsin 58
64. • the absorption of light by
rhodopsin
• isomerization of the
retinaldehyde from 11-cis to
all-trans, and a conformational
change in opsin.
• release of retinaldehyde
from the protein
64
65. • the initiation of a nerve
impulse.
• series of conformational
changes
• formation of metarhodopsin
II,
initiates a guanine nucleotide
amplification cascade and
then a nerve impulse.
65
66. • Final Step Is Hydrolysis of
RHODOPSIN
• Release ALL-TRANS-
RETINALDEHYDE And OPSIN
• Key To Initiation Of The Visual
Cycle Is The Availability Of 11-
cis-Retinaldehyde, And Hence
Vitamin A. 66
67.
68. • In Deficiency,
Both The Time Taken To Adapt
To Darkness And The Ability
To See In Poor Light Are
Impaired
68
72. Vitamin A Deficiency Is The Most Important
Preventable Cause Of Blindness
Earliest Sign Of Deficiency
Loss Of Sensitivity To
Green
Light
followed by
Impairment To Adapt To Dim
Light
followed by
NIGHT BLINDNESS 72
73. Vitamin A Deficiency Is The Most Important
Preventable Cause Of Blindness
Keratinization
Of Cornea
Leading To
Permanent
Blindness 73
74. Role in the Regulation of Gene Expression and
Tissue Differentiation
• Control Of Cell
Differentiation And
Turnover
• Regulate
Growth,Development, And
Tissue Differentiation
74
75. Role in the Regulation of Gene Expression and
Tissue Differentiation
• Retinol
Essential for normal
reproduction
Supporting spermatogenesis
in the male
preventing fetal resorption
in the female 75
76. Role in the Regulation of Gene Expression and
Tissue Differentiation
Control The Expression
Of The
Gene For Keratin
In Most Epithelial
Tissues Of The Body
76
77. Role in the Regulation of Gene Expression and
Tissue Differentiation
Retinoic Acid
Binds To
Nuclear Receptors
That Bind To Response
Elements Of DNA And
Regulate The Transcription
Of Specific Genes 77
81. Vitamin A deficiency is the most
important preventable cause of
blindness
• More prolonged deficiency leads to
xerophthalmia
keratinization of the cornea and
blindness
81
85. SKIN AND MUCOSAL CELLS
FUNCTION AS A BARRIER AND
FORM THE BODY'S FIRST LINE
OF DEFENSE AGAINST
INFECTION.
• RETINOL AND ITS METABOLITES
ARE REQUIRED TO MAINTAIN THE
INTEGRITY AND FUNCTION OF
EPITHELIAL CELLS
85
91. Important Role In
Differentiation Of Immune System Cells
CENTRAL ROLE IN THE
DEVELOPMENT
AND
DIFFERENTIATION
of white blood cells
such as
LYMPHOCYTES 91
92. Important Role In
Differentiation Of Immune System Cells
EVEN MILD DEFICIENCY
LEADS TO INCREASED
SUSCEPTIBILITY TO
INFECTIOUS DISEASES
92
94. • Red capsule 200000 IU (60 mg RE) 12-59
months of age , blue capsule 100000 IU (30
mg RE) 6-11 months of age twice yearly
(WHO RECOMMENDATION)
• SIDE EFFECTS bulging of open fontanelles in
younger infants
• Nausea / vomitting , headache in older
children
99. Vitamin A Is Toxic In Excess
• Limited Capacity To
Metabolize Vitamin A
• Excessive Intakes Lead To
Accumulation Beyond The
Capacity Of Binding
Proteins
99
100. Vitamin A Is Toxic In Excess
Hypervitaminosis A
• Unbound Vitamin A Causes
• Membrane lysis
• Tissue damage
100
101. Vitamin A Is Toxic In Excess
Hypervitaminosis A
Caused By
Overconsumption Of
Preformed Vitamin A
Not Carotenoids
101
104. Vitamin A Is Toxic In Excess
Hypervitaminosis A
Preformed Vitamin A
Rapidly Absorbed
Slowly Cleared
From The Body
104
105. One ounce of
polar bear
liver contains
enough
vitamin A
(retinol) to kill
a person!
106. Vitamin A Is Toxic in Excess
hypervitaminosis A
Symptoms
• Central Nervous System
Increased intracranial
pressure
• Headache
• Nausea
• Ataxia
And
• Anorexia 106
107. Vitamin A Is Toxic in Excess
hypervitaminosis A
• LIVER
Hepatomegaly
• CALCIUM HOMEOSTASIS
Thickening Of The Long Bones
Hypercalcemia
And
Calcification Of Soft Tissues
107
108. Vitamin A Is Toxic in Excess
hypervitaminosis A
• SKIN
excessive drynes
desquamation
and
alopecia
108
