SlideShare a Scribd company logo
1 of 30
Aamir Ali Khan
M.Phil Biochemistry
Head of pathology department
Northwest institute of health sciences
Vitamin A is a generic term for a group of lipid soluble
compounds related to retinol.
 Retinol is often referred to as preformed vitamin A.
It is found only in animal sources, mainly as retinyl esters and in
food supplements.
Beta-carotene and other carotenoids that can be converted to
vitamin A by an enzymatic process in the body are referred to as
provitamin A.
They are found only in plant sources
Retinal, the oxidized metabolite of retinol, is required
for the process of vision
Retinoic acid, another vitamin A metabolite, is
considered to be responsible for all non-visual
functions of vitamin A
Retinoic acid combines with specific nuclear receptor
proteins which bind to DNA and regulate the expression of
various genes, thereby influencing numerous physiological
processes
Retinoic acid is therefore classified as a hormone
Receptor cells in the retina of the eye (rod cells) contain a light-
sensitive pigment called rhodopsin, which is a complex of the
protein opsin and the vitamin A metabolite retinal .
 The light-induced disintegration of the pigment triggers a cascade
of events which generate an electrical signal to the optic nerve.
Rhodopsin can only be regenerated from opsin and vitamin A.
Rod cells with this pigment can detect very small amounts of light,
making them important for night vision.
In the pigment epithelium of the
retina, all-trans -retinol is
isomerizes to 11-cis–retinol and
oxidized to 11-cis-retinaldehyde.
This reacts with a lysine residue in
opsin, forming the holoprotein
rhodopsin
The absorption of light by rhodopsin causes isomerization of
the retinaldehyde from 11-cis to all trans, and a
conformational change in opsin. This results in the release of
retinaldehyde from the protein and the initiation of a nerve
impulse.
The key to initiation of the visual cycle is the availability of
11-cis retinaldehyde, and hence vitamin A .
In deficiency, both the time taken to adapt to darkness and
the ability to see in poor light are impaired.
The many different types of cells in the body perform highly
specialized functions. The process whereby cells and tissues
become “programmed” to carry out their special functions is called
differentiation. Through the regulation of gene expression, retinoic
acid plays a major role in cellular differentiation.
Vitamin A is necessary for normal differentiation of epithelial
cells, the cells of all tissues lining the body, such as skin, mucous
membranes, blood vessel walls and the cornea
In vitamin A deficiency, cells lose their ability to differentiate
properly
Retinoic acid plays an important role in reproduction
and embryonic development, particularly in the
development of the spinal cord and vertebrae, limbs,
heart, eyes and ears
Vitamin A is required for the normal functioning of the
immune system and therefore helps to protect against
infections in a number of ways. It is essential in maintaining
the integrity and function of the skin and mucosal cells, which
function as a mechanical barrier and defend the body against
infection .
Vitamin A also plays a central role in the development and
differentiation of white blood cells, such as lymphocytes,
killer cells and phagocytes, which play a critical role in the
defense of the body against pathogens
Absorption and body stores
Vitamin A is absorbed in the upper part of the small intestine. Pro-
vitamin A carotenoids can be cleaved into retinol via an enzymatic
process. Preformed vitamin A occurs as retinyl esters of fatty acids. They
are hydrolyzed and retinol is absorbed into intestinal mucosal cells (i.e.
enterocytes). After re-esterification it is incorporated into chylomicrons,
excreted into lymphatic channels, delivered to the blood and transported to
the liver.
Vitamin A is stored in the liver as retinyl esters; stores are enough for one
to two years in most adults.
Carotenes are not absorb 100 %
1ug of retinol is taken as equivalent to 6ug of beta carotene
For vitamin A absorption, cellular retinol binding protein II
is necessary
Vitamin is then reestirified within the mucosal cells of the
small intestine where absorb with chylomicrons
Bile salts help in carotene and vitamin A absorption
Eye changes
“Xerophthalmia” bitot’s spots of cornea
“Keratomalacia” cornea becomes dull and
insensitive.
Cilia are lost and respiratory tract infections take place
Vitamin A increases immunity.
Xerosis (dryness) and scaling of hair follicles (Hair loss
with skin shedding)
Growth retardation
Deformed skull bones may result nerve degeneration and
paralysis
Defective formation of the tooth enamel takes place
Lipocytes of liver cells store it in the form of esters
Retinoic acid is transported by albumin in plasma
Headache, nausea, vomiting, drowsiness, peeling of skin,
anorexia, dry itchy skin, alopecia, cracking of the lips and
painful areas over bones
May be hepatomegaly, splenomegaly, hypothyroidism,
leucopenia, anemia, bleeding tendency because of
hypoprothrombinemia, high ALP
Vitamin D is a fat-soluble vitamin. Vitamin D is not found in many
foods.
Foods that naturally contain significant amounts of vitamin D are fatty
fish and eggs.
To increase intake of vitamin D, foods have been fortified.
Milk is the most commonly consumed products that are fortified with
vitamin D. Juices, breakfast cereals, breads, and yogurt are also fortified
with vitamin D.
Cholecalciferol is a form of vitamin D made naturally by the body when
the skin is exposed to sunlight. However, most people do not get enough
sunlight to satisfy their daily recommended intake through sunlight,
especially in the winter.
7-Dehydrocholesterol, undergoes a nonenzymic reaction on
exposure to ultraviolet light, yielding previtamin D.
This undergoes a further reaction over a period of hours to
form the vitamin itself, Cholecalciferol, which is absorbed
into the blood stream.
The recommendations are 200 IU from birth to 50 years of
age, 400 IUs from 51-70 years age, and 600 IUs for 71+ years
of age.
These recommendations meet the minimum requirements,
mostly based on bone health
In the liver, Cholecalciferol, which has been synthesized in
the skin or derived from food, is hydroxylated to form the 25-
hydroxy derivative calcidiol.
 This is released into the circulation bound to a vitamin D
binding globulin which is the main storage form of the
vitamin.
In the kidney, calcidiol undergoes either 1-hydroxylation to
yield the active metabolite 1,25-dihy-droxyvitamin D
(calcitriol) or 24-hydroxylation to yield an inactive
metabolite, 24,25-dihydroxyvitamin D(24-hydroxycalcidiol).
Ergocalciferol from fortified foods undergoes similar
hydroxylation's to yield calcitriol.
Fish, including salmon and tuna are excellent
sources.
Egg also contains vitamin D, the highest
concentration is in the yolk
The main function of vitamin D is in the control of calcium
homeostasis, and in turn vitamin D metabolism is regulated
by factors that respond to plasma concentrations of calcium
and phosphate
Calcitriol acts to reduce its own synthesis by inducing the
24-hydroxylase and repressing the 1-hydroxylase in the
kidney. Its principal function is to maintain the plasma
calcium concentration.
Calcitriol achieves this in three ways: it increases intestinal
absorption of calcium, reduces excretion of calcium, and
mobilizes bone mineral.
In addition, calcitriol is involved in insulin secretion,
synthesis and secretion of parathyroid and thyroid hormones,
inhibition of production of interleukin by activated T
lymphocytes and of immunoglobulin by activated B
lymphocytes, differentiation of monocyte precursor cells, and
modulation of cell proliferation. In its actions, it behaves like
a steroid hormone, binding to a nuclear receptor protein.
The two main forms of calcium in supplements are
carbonate and citrate.
Calcium carbonate is more commonly available and
inexpensive.
Both forms are absorbed well by the body, but individuals
with low levels of stomach acid may absorb citrate better.
Carbonate is absorbed better when taken with food but
citrate is unaffected by the presence of food.
There are two forms available for vitamin D supplements,
D2 (Ergocalciferol) and D3 (Cholecalciferol).
Vitamin D2 is made by the conversion of a sterol found in
plants and yeast.
Unlike calcium these two forms are not equal in absorption.
Vitamin D3 is metabolized differently than D2 and research
shows it is more effective in raising serum concentrations of
the active form of vitamin D and is also able to maintain
higher levels for longer.
 Probably the most well understood function that Vitamin D
has is in the absorption of calcium from the small intestine.
When vitamin D is inadequate, calcium from the diet is
poorly absorbed.
Another well characterized and important role of vitamin D
is to maintain appropriate levels of calcium and phosphate in
the blood to ensure proper bone formation, mineralization,
growth, and repair.
Vitamin D has other roles that have been less well
characterized. It is thought to improve muscle strength and
immune function and reduce inflammation.
Deficiency (Complication)
People at risk for vitamin D deficiency include breast fed
infants, older adults, people with limited sun exposure, people
with dark skin, and people with fat malabsorption.
People age 50 and older are at increased risk of developing
vitamin D deficiency because as they age the skin looses its
ability to synthesize vitamin D as efficiently and the kidneys
also convert less to its active form
People with darker skin have more pigment melanin which
reduces the skin’s ability to produce vitamin D after sun
exposure.
Prolonged inadequate intake of vitamin D will lead to impaired
bone metabolism.
In children, under mineralization of bone causes soft and
deformed bones and can lead to the condition known as rickets.
When children developed rickets, their legs were too weak to hold
their weight, resulting in bowed legs, which often persisted into
adulthood.
Osteomalacia is the adult form of rickets, and leads to impaired
mobility and bone fractures
Osteoporosis, a condition that leads to weak and porous bones.
In the vitamin D deficiency disease rickets, the bones of
children are under mineralized as a result of poor absorption
of calcium.
Similar problems occur in adolescents who are deficient
during their growth.
Osteomalacia in adults results from demineralization of bone
in women who have little exposure to sunlight, often after
several pregnancies.
Although vitamin D is essential for prevention and treatment
of Osteomalacia in the elderly, there is little evidence that it is
beneficial in treating osteoporosis.
Some infants are sensitive to intakes of vitamin D as low as
50 µg/d, resulting in an elevated plasma concentration of
calcium.
This can lead to contraction of blood vessels, high blood
pressure, and calcinosis, the calcification of soft tissues.
Although excess dietary vitamin D is toxic, excessive
exposure to sunlight does not lead to vitamin D poisoning
because there is a limited capacity to form the precursor 7-
dehydrocholesterol and to take up Cholecalciferol from the
skin
Vitamin a and vitamin d

More Related Content

What's hot

What's hot (20)

Vitamin A
Vitamin AVitamin A
Vitamin A
 
Vit d
Vit dVit d
Vit d
 
Vitamins
VitaminsVitamins
Vitamins
 
Vitamins
VitaminsVitamins
Vitamins
 
Vitamin e
Vitamin eVitamin e
Vitamin e
 
Fat soluble vitamin (A,D,E,K)
Fat soluble vitamin (A,D,E,K)Fat soluble vitamin (A,D,E,K)
Fat soluble vitamin (A,D,E,K)
 
Minerals: Macro and Micro
Minerals: Macro and MicroMinerals: Macro and Micro
Minerals: Macro and Micro
 
Vitamin A
Vitamin AVitamin A
Vitamin A
 
Vitamin a presentation, Vitamin A Deficiency, Vitamin A toxicity
Vitamin a presentation, Vitamin A Deficiency, Vitamin A toxicityVitamin a presentation, Vitamin A Deficiency, Vitamin A toxicity
Vitamin a presentation, Vitamin A Deficiency, Vitamin A toxicity
 
Vitamin d
Vitamin dVitamin d
Vitamin d
 
Vitamin A and D
Vitamin A and DVitamin A and D
Vitamin A and D
 
Vitamin k
Vitamin kVitamin k
Vitamin k
 
Vitamins -Biochemistry /Biotechnology
Vitamins -Biochemistry /BiotechnologyVitamins -Biochemistry /Biotechnology
Vitamins -Biochemistry /Biotechnology
 
Vitamin E and vitamin k
Vitamin E and vitamin kVitamin E and vitamin k
Vitamin E and vitamin k
 
Vitamins
VitaminsVitamins
Vitamins
 
Vitamins
VitaminsVitamins
Vitamins
 
Vitamin A
Vitamin AVitamin A
Vitamin A
 
Water Soluble Vitamins
Water Soluble VitaminsWater Soluble Vitamins
Water Soluble Vitamins
 
Vitamins and minerals
Vitamins and minerals Vitamins and minerals
Vitamins and minerals
 
Vitamin D
Vitamin DVitamin D
Vitamin D
 

Similar to Vitamin a and vitamin d

Fat soluble vitamins- structure, rda, functions, sources, deficiency, hypervi...
Fat soluble vitamins- structure, rda, functions, sources, deficiency, hypervi...Fat soluble vitamins- structure, rda, functions, sources, deficiency, hypervi...
Fat soluble vitamins- structure, rda, functions, sources, deficiency, hypervi...
akash mahadev
 

Similar to Vitamin a and vitamin d (20)

14.1.ppt
14.1.ppt14.1.ppt
14.1.ppt
 
Vitamins 36-42
Vitamins 36-42Vitamins 36-42
Vitamins 36-42
 
Vitamins Likhith K
Vitamins Likhith KVitamins Likhith K
Vitamins Likhith K
 
Vitamins (fat and water soluble)
Vitamins (fat and water soluble)Vitamins (fat and water soluble)
Vitamins (fat and water soluble)
 
Fat Soluble Vitamins
Fat Soluble VitaminsFat Soluble Vitamins
Fat Soluble Vitamins
 
Fat soluble vitamins- structure, rda, functions, sources, deficiency, hypervi...
Fat soluble vitamins- structure, rda, functions, sources, deficiency, hypervi...Fat soluble vitamins- structure, rda, functions, sources, deficiency, hypervi...
Fat soluble vitamins- structure, rda, functions, sources, deficiency, hypervi...
 
VITAMINS.pptx
VITAMINS.pptxVITAMINS.pptx
VITAMINS.pptx
 
13 14. vitamins and minerals
13 14. vitamins and minerals13 14. vitamins and minerals
13 14. vitamins and minerals
 
Different roles of fat soluble vitamins
Different roles of fat soluble vitaminsDifferent roles of fat soluble vitamins
Different roles of fat soluble vitamins
 
Fad soluble vitamins
Fad soluble vitaminsFad soluble vitamins
Fad soluble vitamins
 
Fat Soluble Vitamins..pptx
Fat Soluble Vitamins..pptxFat Soluble Vitamins..pptx
Fat Soluble Vitamins..pptx
 
Vitamins UNIT-7 biochemistry and clinical pathology, D.Pharm 2nd year.pptx
Vitamins UNIT-7 biochemistry and clinical pathology, D.Pharm 2nd year.pptxVitamins UNIT-7 biochemistry and clinical pathology, D.Pharm 2nd year.pptx
Vitamins UNIT-7 biochemistry and clinical pathology, D.Pharm 2nd year.pptx
 
Fat soluble vitamins ppt 3.pptx
Fat soluble vitamins ppt 3.pptxFat soluble vitamins ppt 3.pptx
Fat soluble vitamins ppt 3.pptx
 
Vitamins ppt presented by Ankit Boss Golden Heart
Vitamins ppt  presented by Ankit Boss Golden HeartVitamins ppt  presented by Ankit Boss Golden Heart
Vitamins ppt presented by Ankit Boss Golden Heart
 
presentation on vitamin
presentation on vitaminpresentation on vitamin
presentation on vitamin
 
Vit a,d l1, l2
Vit a,d  l1, l2Vit a,d  l1, l2
Vit a,d l1, l2
 
Vitamin A
Vitamin AVitamin A
Vitamin A
 
4. vitamins
4. vitamins4. vitamins
4. vitamins
 
Fat Soluble Vitamins
Fat Soluble VitaminsFat Soluble Vitamins
Fat Soluble Vitamins
 
Fat Soluble Vitamins
Fat Soluble VitaminsFat Soluble Vitamins
Fat Soluble Vitamins
 

More from Dr. Aamir Ali Khan

More from Dr. Aamir Ali Khan (20)

Paternity testing in forensic science.pptx
Paternity testing in forensic science.pptxPaternity testing in forensic science.pptx
Paternity testing in forensic science.pptx
 
drug of abuse.pptx
 drug of abuse.pptx drug of abuse.pptx
drug of abuse.pptx
 
Toxicology and Toxicological Evidence.pptx
 Toxicology and Toxicological Evidence.pptx Toxicology and Toxicological Evidence.pptx
Toxicology and Toxicological Evidence.pptx
 
Asphyxiants.pptx
Asphyxiants.pptxAsphyxiants.pptx
Asphyxiants.pptx
 
Analysis of Bodily Fluids.pptx
Analysis of Bodily Fluids.pptxAnalysis of Bodily Fluids.pptx
Analysis of Bodily Fluids.pptx
 
Blood Stains.pptx
Blood Stains.pptxBlood Stains.pptx
Blood Stains.pptx
 
Forensic detection of seminal stains.pptx
Forensic detection of seminal stains.pptxForensic detection of seminal stains.pptx
Forensic detection of seminal stains.pptx
 
Forensic Sample Collection and Preservation.pptx
Forensic Sample Collection and Preservation.pptxForensic Sample Collection and Preservation.pptx
Forensic Sample Collection and Preservation.pptx
 
Cell and cellular transport system
Cell and cellular transport systemCell and cellular transport system
Cell and cellular transport system
 
Nucleotide
NucleotideNucleotide
Nucleotide
 
Lipid chemistry
Lipid chemistryLipid chemistry
Lipid chemistry
 
Protein digestion and absorption
Protein digestion and absorptionProtein digestion and absorption
Protein digestion and absorption
 
Digestion of carbohydrates
Digestion of carbohydratesDigestion of carbohydrates
Digestion of carbohydrates
 
Antigen antibody reactions
Antigen antibody reactions Antigen antibody reactions
Antigen antibody reactions
 
Tolerance Auto-immune Diseases and Tumor Immunity
Tolerance Auto-immune Diseases and Tumor ImmunityTolerance Auto-immune Diseases and Tumor Immunity
Tolerance Auto-immune Diseases and Tumor Immunity
 
Hypersensitivity
HypersensitivityHypersensitivity
Hypersensitivity
 
The complement system new
The complement system newThe complement system new
The complement system new
 
Enzymes
EnzymesEnzymes
Enzymes
 
Hormone action
Hormone actionHormone action
Hormone action
 
Nutrition and dietetics
Nutrition and dieteticsNutrition and dietetics
Nutrition and dietetics
 

Recently uploaded

Spellings Wk 4 and Wk 5 for Grade 4 at CAPS
Spellings Wk 4 and Wk 5 for Grade 4 at CAPSSpellings Wk 4 and Wk 5 for Grade 4 at CAPS
Spellings Wk 4 and Wk 5 for Grade 4 at CAPS
AnaAcapella
 
Personalisation of Education by AI and Big Data - Lourdes Guàrdia
Personalisation of Education by AI and Big Data - Lourdes GuàrdiaPersonalisation of Education by AI and Big Data - Lourdes Guàrdia
Personalisation of Education by AI and Big Data - Lourdes Guàrdia
EADTU
 
SPLICE Working Group: Reusable Code Examples
SPLICE Working Group:Reusable Code ExamplesSPLICE Working Group:Reusable Code Examples
SPLICE Working Group: Reusable Code Examples
Peter Brusilovsky
 

Recently uploaded (20)

Spellings Wk 4 and Wk 5 for Grade 4 at CAPS
Spellings Wk 4 and Wk 5 for Grade 4 at CAPSSpellings Wk 4 and Wk 5 for Grade 4 at CAPS
Spellings Wk 4 and Wk 5 for Grade 4 at CAPS
 
e-Sealing at EADTU by Kamakshi Rajagopal
e-Sealing at EADTU by Kamakshi Rajagopale-Sealing at EADTU by Kamakshi Rajagopal
e-Sealing at EADTU by Kamakshi Rajagopal
 
Improved Approval Flow in Odoo 17 Studio App
Improved Approval Flow in Odoo 17 Studio AppImproved Approval Flow in Odoo 17 Studio App
Improved Approval Flow in Odoo 17 Studio App
 
UChicago CMSC 23320 - The Best Commit Messages of 2024
UChicago CMSC 23320 - The Best Commit Messages of 2024UChicago CMSC 23320 - The Best Commit Messages of 2024
UChicago CMSC 23320 - The Best Commit Messages of 2024
 
Trauma-Informed Leadership - Five Practical Principles
Trauma-Informed Leadership - Five Practical PrinciplesTrauma-Informed Leadership - Five Practical Principles
Trauma-Informed Leadership - Five Practical Principles
 
Observing-Correct-Grammar-in-Making-Definitions.pptx
Observing-Correct-Grammar-in-Making-Definitions.pptxObserving-Correct-Grammar-in-Making-Definitions.pptx
Observing-Correct-Grammar-in-Making-Definitions.pptx
 
Book Review of Run For Your Life Powerpoint
Book Review of Run For Your Life PowerpointBook Review of Run For Your Life Powerpoint
Book Review of Run For Your Life Powerpoint
 
ANTI PARKISON DRUGS.pptx
ANTI         PARKISON          DRUGS.pptxANTI         PARKISON          DRUGS.pptx
ANTI PARKISON DRUGS.pptx
 
Supporting Newcomer Multilingual Learners
Supporting Newcomer  Multilingual LearnersSupporting Newcomer  Multilingual Learners
Supporting Newcomer Multilingual Learners
 
ĐỀ THAM KHẢO KÌ THI TUYỂN SINH VÀO LỚP 10 MÔN TIẾNG ANH FORM 50 CÂU TRẮC NGHI...
ĐỀ THAM KHẢO KÌ THI TUYỂN SINH VÀO LỚP 10 MÔN TIẾNG ANH FORM 50 CÂU TRẮC NGHI...ĐỀ THAM KHẢO KÌ THI TUYỂN SINH VÀO LỚP 10 MÔN TIẾNG ANH FORM 50 CÂU TRẮC NGHI...
ĐỀ THAM KHẢO KÌ THI TUYỂN SINH VÀO LỚP 10 MÔN TIẾNG ANH FORM 50 CÂU TRẮC NGHI...
 
FICTIONAL SALESMAN/SALESMAN SNSW 2024.pdf
FICTIONAL SALESMAN/SALESMAN SNSW 2024.pdfFICTIONAL SALESMAN/SALESMAN SNSW 2024.pdf
FICTIONAL SALESMAN/SALESMAN SNSW 2024.pdf
 
Including Mental Health Support in Project Delivery, 14 May.pdf
Including Mental Health Support in Project Delivery, 14 May.pdfIncluding Mental Health Support in Project Delivery, 14 May.pdf
Including Mental Health Support in Project Delivery, 14 May.pdf
 
Personalisation of Education by AI and Big Data - Lourdes Guàrdia
Personalisation of Education by AI and Big Data - Lourdes GuàrdiaPersonalisation of Education by AI and Big Data - Lourdes Guàrdia
Personalisation of Education by AI and Big Data - Lourdes Guàrdia
 
Stl Algorithms in C++ jjjjjjjjjjjjjjjjjj
Stl Algorithms in C++ jjjjjjjjjjjjjjjjjjStl Algorithms in C++ jjjjjjjjjjjjjjjjjj
Stl Algorithms in C++ jjjjjjjjjjjjjjjjjj
 
SPLICE Working Group: Reusable Code Examples
SPLICE Working Group:Reusable Code ExamplesSPLICE Working Group:Reusable Code Examples
SPLICE Working Group: Reusable Code Examples
 
Basic Civil Engineering notes on Transportation Engineering & Modes of Transport
Basic Civil Engineering notes on Transportation Engineering & Modes of TransportBasic Civil Engineering notes on Transportation Engineering & Modes of Transport
Basic Civil Engineering notes on Transportation Engineering & Modes of Transport
 
24 ĐỀ THAM KHẢO KÌ THI TUYỂN SINH VÀO LỚP 10 MÔN TIẾNG ANH SỞ GIÁO DỤC HẢI DƯ...
24 ĐỀ THAM KHẢO KÌ THI TUYỂN SINH VÀO LỚP 10 MÔN TIẾNG ANH SỞ GIÁO DỤC HẢI DƯ...24 ĐỀ THAM KHẢO KÌ THI TUYỂN SINH VÀO LỚP 10 MÔN TIẾNG ANH SỞ GIÁO DỤC HẢI DƯ...
24 ĐỀ THAM KHẢO KÌ THI TUYỂN SINH VÀO LỚP 10 MÔN TIẾNG ANH SỞ GIÁO DỤC HẢI DƯ...
 
VAMOS CUIDAR DO NOSSO PLANETA! .
VAMOS CUIDAR DO NOSSO PLANETA!                    .VAMOS CUIDAR DO NOSSO PLANETA!                    .
VAMOS CUIDAR DO NOSSO PLANETA! .
 
How To Create Editable Tree View in Odoo 17
How To Create Editable Tree View in Odoo 17How To Create Editable Tree View in Odoo 17
How To Create Editable Tree View in Odoo 17
 
MOOD STABLIZERS DRUGS.pptx
MOOD     STABLIZERS           DRUGS.pptxMOOD     STABLIZERS           DRUGS.pptx
MOOD STABLIZERS DRUGS.pptx
 

Vitamin a and vitamin d

  • 1. Aamir Ali Khan M.Phil Biochemistry Head of pathology department Northwest institute of health sciences
  • 2. Vitamin A is a generic term for a group of lipid soluble compounds related to retinol.  Retinol is often referred to as preformed vitamin A. It is found only in animal sources, mainly as retinyl esters and in food supplements. Beta-carotene and other carotenoids that can be converted to vitamin A by an enzymatic process in the body are referred to as provitamin A. They are found only in plant sources
  • 3. Retinal, the oxidized metabolite of retinol, is required for the process of vision Retinoic acid, another vitamin A metabolite, is considered to be responsible for all non-visual functions of vitamin A
  • 4. Retinoic acid combines with specific nuclear receptor proteins which bind to DNA and regulate the expression of various genes, thereby influencing numerous physiological processes Retinoic acid is therefore classified as a hormone
  • 5. Receptor cells in the retina of the eye (rod cells) contain a light- sensitive pigment called rhodopsin, which is a complex of the protein opsin and the vitamin A metabolite retinal .  The light-induced disintegration of the pigment triggers a cascade of events which generate an electrical signal to the optic nerve. Rhodopsin can only be regenerated from opsin and vitamin A. Rod cells with this pigment can detect very small amounts of light, making them important for night vision.
  • 6. In the pigment epithelium of the retina, all-trans -retinol is isomerizes to 11-cis–retinol and oxidized to 11-cis-retinaldehyde. This reacts with a lysine residue in opsin, forming the holoprotein rhodopsin
  • 7. The absorption of light by rhodopsin causes isomerization of the retinaldehyde from 11-cis to all trans, and a conformational change in opsin. This results in the release of retinaldehyde from the protein and the initiation of a nerve impulse. The key to initiation of the visual cycle is the availability of 11-cis retinaldehyde, and hence vitamin A . In deficiency, both the time taken to adapt to darkness and the ability to see in poor light are impaired.
  • 8. The many different types of cells in the body perform highly specialized functions. The process whereby cells and tissues become “programmed” to carry out their special functions is called differentiation. Through the regulation of gene expression, retinoic acid plays a major role in cellular differentiation. Vitamin A is necessary for normal differentiation of epithelial cells, the cells of all tissues lining the body, such as skin, mucous membranes, blood vessel walls and the cornea In vitamin A deficiency, cells lose their ability to differentiate properly
  • 9. Retinoic acid plays an important role in reproduction and embryonic development, particularly in the development of the spinal cord and vertebrae, limbs, heart, eyes and ears
  • 10. Vitamin A is required for the normal functioning of the immune system and therefore helps to protect against infections in a number of ways. It is essential in maintaining the integrity and function of the skin and mucosal cells, which function as a mechanical barrier and defend the body against infection . Vitamin A also plays a central role in the development and differentiation of white blood cells, such as lymphocytes, killer cells and phagocytes, which play a critical role in the defense of the body against pathogens
  • 11. Absorption and body stores Vitamin A is absorbed in the upper part of the small intestine. Pro- vitamin A carotenoids can be cleaved into retinol via an enzymatic process. Preformed vitamin A occurs as retinyl esters of fatty acids. They are hydrolyzed and retinol is absorbed into intestinal mucosal cells (i.e. enterocytes). After re-esterification it is incorporated into chylomicrons, excreted into lymphatic channels, delivered to the blood and transported to the liver. Vitamin A is stored in the liver as retinyl esters; stores are enough for one to two years in most adults.
  • 12. Carotenes are not absorb 100 % 1ug of retinol is taken as equivalent to 6ug of beta carotene For vitamin A absorption, cellular retinol binding protein II is necessary Vitamin is then reestirified within the mucosal cells of the small intestine where absorb with chylomicrons Bile salts help in carotene and vitamin A absorption
  • 13. Eye changes “Xerophthalmia” bitot’s spots of cornea “Keratomalacia” cornea becomes dull and insensitive.
  • 14. Cilia are lost and respiratory tract infections take place Vitamin A increases immunity. Xerosis (dryness) and scaling of hair follicles (Hair loss with skin shedding) Growth retardation Deformed skull bones may result nerve degeneration and paralysis Defective formation of the tooth enamel takes place
  • 15. Lipocytes of liver cells store it in the form of esters Retinoic acid is transported by albumin in plasma
  • 16. Headache, nausea, vomiting, drowsiness, peeling of skin, anorexia, dry itchy skin, alopecia, cracking of the lips and painful areas over bones May be hepatomegaly, splenomegaly, hypothyroidism, leucopenia, anemia, bleeding tendency because of hypoprothrombinemia, high ALP
  • 17. Vitamin D is a fat-soluble vitamin. Vitamin D is not found in many foods. Foods that naturally contain significant amounts of vitamin D are fatty fish and eggs. To increase intake of vitamin D, foods have been fortified. Milk is the most commonly consumed products that are fortified with vitamin D. Juices, breakfast cereals, breads, and yogurt are also fortified with vitamin D. Cholecalciferol is a form of vitamin D made naturally by the body when the skin is exposed to sunlight. However, most people do not get enough sunlight to satisfy their daily recommended intake through sunlight, especially in the winter.
  • 18. 7-Dehydrocholesterol, undergoes a nonenzymic reaction on exposure to ultraviolet light, yielding previtamin D. This undergoes a further reaction over a period of hours to form the vitamin itself, Cholecalciferol, which is absorbed into the blood stream. The recommendations are 200 IU from birth to 50 years of age, 400 IUs from 51-70 years age, and 600 IUs for 71+ years of age. These recommendations meet the minimum requirements, mostly based on bone health
  • 19. In the liver, Cholecalciferol, which has been synthesized in the skin or derived from food, is hydroxylated to form the 25- hydroxy derivative calcidiol.  This is released into the circulation bound to a vitamin D binding globulin which is the main storage form of the vitamin. In the kidney, calcidiol undergoes either 1-hydroxylation to yield the active metabolite 1,25-dihy-droxyvitamin D (calcitriol) or 24-hydroxylation to yield an inactive metabolite, 24,25-dihydroxyvitamin D(24-hydroxycalcidiol). Ergocalciferol from fortified foods undergoes similar hydroxylation's to yield calcitriol.
  • 20. Fish, including salmon and tuna are excellent sources. Egg also contains vitamin D, the highest concentration is in the yolk
  • 21. The main function of vitamin D is in the control of calcium homeostasis, and in turn vitamin D metabolism is regulated by factors that respond to plasma concentrations of calcium and phosphate Calcitriol acts to reduce its own synthesis by inducing the 24-hydroxylase and repressing the 1-hydroxylase in the kidney. Its principal function is to maintain the plasma calcium concentration.
  • 22. Calcitriol achieves this in three ways: it increases intestinal absorption of calcium, reduces excretion of calcium, and mobilizes bone mineral. In addition, calcitriol is involved in insulin secretion, synthesis and secretion of parathyroid and thyroid hormones, inhibition of production of interleukin by activated T lymphocytes and of immunoglobulin by activated B lymphocytes, differentiation of monocyte precursor cells, and modulation of cell proliferation. In its actions, it behaves like a steroid hormone, binding to a nuclear receptor protein.
  • 23. The two main forms of calcium in supplements are carbonate and citrate. Calcium carbonate is more commonly available and inexpensive. Both forms are absorbed well by the body, but individuals with low levels of stomach acid may absorb citrate better. Carbonate is absorbed better when taken with food but citrate is unaffected by the presence of food.
  • 24. There are two forms available for vitamin D supplements, D2 (Ergocalciferol) and D3 (Cholecalciferol). Vitamin D2 is made by the conversion of a sterol found in plants and yeast. Unlike calcium these two forms are not equal in absorption. Vitamin D3 is metabolized differently than D2 and research shows it is more effective in raising serum concentrations of the active form of vitamin D and is also able to maintain higher levels for longer.
  • 25.  Probably the most well understood function that Vitamin D has is in the absorption of calcium from the small intestine. When vitamin D is inadequate, calcium from the diet is poorly absorbed. Another well characterized and important role of vitamin D is to maintain appropriate levels of calcium and phosphate in the blood to ensure proper bone formation, mineralization, growth, and repair. Vitamin D has other roles that have been less well characterized. It is thought to improve muscle strength and immune function and reduce inflammation.
  • 26. Deficiency (Complication) People at risk for vitamin D deficiency include breast fed infants, older adults, people with limited sun exposure, people with dark skin, and people with fat malabsorption. People age 50 and older are at increased risk of developing vitamin D deficiency because as they age the skin looses its ability to synthesize vitamin D as efficiently and the kidneys also convert less to its active form People with darker skin have more pigment melanin which reduces the skin’s ability to produce vitamin D after sun exposure.
  • 27. Prolonged inadequate intake of vitamin D will lead to impaired bone metabolism. In children, under mineralization of bone causes soft and deformed bones and can lead to the condition known as rickets. When children developed rickets, their legs were too weak to hold their weight, resulting in bowed legs, which often persisted into adulthood. Osteomalacia is the adult form of rickets, and leads to impaired mobility and bone fractures Osteoporosis, a condition that leads to weak and porous bones.
  • 28. In the vitamin D deficiency disease rickets, the bones of children are under mineralized as a result of poor absorption of calcium. Similar problems occur in adolescents who are deficient during their growth. Osteomalacia in adults results from demineralization of bone in women who have little exposure to sunlight, often after several pregnancies. Although vitamin D is essential for prevention and treatment of Osteomalacia in the elderly, there is little evidence that it is beneficial in treating osteoporosis.
  • 29. Some infants are sensitive to intakes of vitamin D as low as 50 µg/d, resulting in an elevated plasma concentration of calcium. This can lead to contraction of blood vessels, high blood pressure, and calcinosis, the calcification of soft tissues. Although excess dietary vitamin D is toxic, excessive exposure to sunlight does not lead to vitamin D poisoning because there is a limited capacity to form the precursor 7- dehydrocholesterol and to take up Cholecalciferol from the skin

Editor's Notes

  1. Alopecia areata (AA) is a condition in which hair is lost from some or all areas of the body, usually from the scalp. Because it causes bald spots on the scalp, especially in the first stages, it is sometimes called spot baldness. In 1–2% of cases, the condition can spread to the entire scalp (alopecia totalis) or to the entire epidermis (alopecia universalis). Conditions resembling AA, and having a similar cause, occur also in other species.