FAT SOLUBLE VITAMINS A & D

1. By
Dr KHALED ALGARIRI
International Medicine School – MSU
January 2018

2. INTRODUCTION
The word "vitamin" comes from the Latin word vita,
means "life".
Vitamins are chemicals found in very small amounts
in many different foods.
 “vitamins have been defined as organic
compounds which are required in minute
amounts to maintain normal health of organisms

3. INTRODUCTION
VITAMINS
FAT SOLUBLE
VITAMINS
Vitamin A, D, E and
K
WATER SOLUBLE
VITAMINS
Vitamins of B-complex
group and Vit C

4. VITAMIN A CHEMISTRY
Vitamin A occurs in two forms in food

7. 1. Active vitamin A-
The Active form of vitamin is retinol, an alcohol
which can be converted to other forms
2. Provitamin A- provitamins, substances that are
transformed into vitamins in the body
 Beta-carotene is the most abundant and
widespread provitamin A.
 One need to eat approximately six times as much
beta-carotene to get the same amount of vitamin
A as in retinol.
 Carotenoids are not toxic even at high doses for
long times.
VITAMIN A

9. SOURCES OF VITAMIN A
Liver, fish, and eggs are excellent
food sources forpreformed vitamin A;
• Vegetable sources of provitamin A
carotenoids include dark green and
deeply colored fruits and vegetables.
• Moderate cooking of vegetables
enhances carotenoid release for
uptake in the gut.
• Carotenoid absorption is also aided
by some fat in a meal

14. DIGESTION AND ABSORPTION
 Dietary Vitamin A, from animal sources is available
in the form of Retinyl esters, which is hydrolyzed to
retinol and fatty acid by pancreatic hydrolases
The absorption of retinol requires the presence of
bile salts
 In the intestinal cells, retinol is esterified back and
secreted with chylomicrons

15. β-Carotene is cleaved in the intestinal mucosa by carotene
dioxygenase, yielding retinaldehyde,which is reduced to
retinol,esterified and secreted in chylomicrons together with
esters formed from dietary retinol.
The intestinal activity of carotene dioxygenase is low, so that
are latively large proportion of ingested β -carotene may
appear in the circulation unchanged.
FATE OF CAROTENES
Transport from liver to tissue
The vitamin A from the liver is transported to peripheral tissue as
Trans retinal by RBP(retinol binding protein)

17. FUNCTIONS OF VITAMIN A
 Vitamin A is essential for vision (especially dark
adaptation)
 Immune response
 Bone growth
 Reproduction
 Maintenance of the surface linings of theeyes, epithelial
cell growth and repair, andthe epithelial integrity of the
respiratory,urinary, and intestinal tracts.
 Vitamin A is also important for embryonic development
and the regulation of adult genes.
 Antioxidants :β -carotenes

18. VITAMIN A DEFECIENCY
CAUSES
• Inadequate intake
• Impaired absorption
• Impaired storage & transport
• Increased excretion [RBP]
• Alcoholism

19. CLINICAL MANIDESTATIONS
Nightblindness : due to retinal injury -Vitamin A has a
major role in photo transduction. Vitamin A deficiency
leads to alack of visual pigments; this reduces the
absorption of various wavelengths of light, resulting in
blindness
Bitot spots :Areas of abnormal squamous cell
proliferation and keratinization of the conjunctiva can
be seen in young children with vitamin A deficiency .

20. CLINICAL MANIFESTATIONS
 Keratomalacia: In advanced deficiency; the cornea becomes
hazy and can develop erosions, which can lead to its
destruction.
 Xerophthalmia : results from keratinization of the
conjunctiva.
 Infections
 Hyperkeratosis of skin
 Growth retardation

22. LABORATORY BIOCHEMICAL
INVESTIGATIONS
 Serum retinol level-Normal range is 28 to 86 μg/dL (1 to 3 μmol/L). The level
decreases in vitamin A deficiency.
 Serum RBP level
 Serum zinc level is useful because zinc deficiency interferes with RBP
production.
 An iron panel is useful because iron deficiency can affect the metabolism of
vitamin A.
 Albumin levels are indirect measures of vitamin A levels.
 Complete blood count (CBC) with differential if anemia, infection, or sepsis is
a possibility.
 An electrolyte evaluation and liver function studies should be performed to
evaluate for nutritional and volume status.

23. VITAMIN D
Vitamin-D is a fat soluble vitamin
Vitamin – D is a sterol, it contains steroid nucleus
(Cyclopentanoperhydrophenanthrene ring)
Vitamin – D function like a hormone
Forms of vitamin D:
Vitamin D in the diet occurs in two forms
Vitamin D2 (Ergocalciferol)
Vitamin D3 (Cholecalciferol)

24. Sunlight
Ergosterol
(in plants)
7-Dehydrocholesterol
Vitamin D3
Cholecalciferol)
Sunlight
dermal tissue of animals

25. Vitamin D2
(Ergocalciferol)
Vitamin D3
Cholecalciferol

26. 1,25-dihydroxyvitamin D3
25-hydroxyvitamin D3
In the liver cholecalciferol is
hydroxylated at the 25 position
by a specific enzyme 25-
hydroxylase to form 25-
hydroxy-cholecalciferol ,requires
cyt. p450 & NADPH .
In the kidney it is further
hydroxylated at 1st position by 1-
hydroxylase present in the proximal
convoluted tubules. it requires Cyt
P450, O2 and NADPH
24-25 dihydroxy cholecalciferol may
be formed by hydroxylation of 25-
HCC at 24th position.
ACTIVATION OF VITAMIN-D

27. 24,25 – DHCC is another metabolite of vitamin D
It is synthesized in kidney by 24 - hydroxylase
Calcitriol concentration is adequate, 24 – hydroxylase acts
leading to the synthesis of a less important compound 24,25
– DHCC
To maintain calcium homeostasis, synthesis of 24,25 –
DHCC is important
24,25 - Dihydroxycholecalciferol

28. Absorption : vitamin D2 and D3 form mixed micelles
by combining with bile salts & through the mucosal
cells of small intestine they are absorbed by passive
transport
Transport: vitamin D is transported from intestine to
the liver by binding to vitamin D binding globulin
Storage: 25 – hydroxycholecalciferol is the major
storage and circulatory form of vitamin D
ABSORPTION & TRANSPORT

29.  Formation of 1,25 – DHCC is regulated by the regulation of
renal 1 α – hydroxylase
 Hypocalcaemia stimulates PTH secretion which, in turn,
increases 1 α – hydroxylase. 1 α – hydroxylase activity may
be feedback inhibited by 1,25 – DHCC
REGUALTION OF VITAMIN D ACTION

30. Calcitriol (1,25 – DHCC) acts at three different levels to
maintain plasma calcium
Action on intestine:
Calcitriol increases the intestinal absorption of calcium and
phosphate
In the intestinal cells, calcitriol leads to the synthesis of a
specific calcium binding protein
This protein increases calcium uptake by intestine
VITAMIN D FUNCTIONS

31. Action on bone:
Calcitriol is essential for bone formation.
Calcitriol along with parathyroid hormone increases the
mobilization of calcium and phosphate from the bone
Causes elevation in the plasma calcium and phosphate
Action on kidney:
Calcitriol is also involved in minimizing the excretion of
calcium and phosphate through the kidney by decreasing
their excretion and enhancing reabsorption

32. Children - 10 μgm/day
Adults - 5 μgm/day
Pregnency,lactation -1200 μ gm/day
Recommended dietary allowance (RDA)
Sources of vitamin D

33. RICKETTS in CHILDREN OSTEOMALACIA IN ADULTS
Deficiency of vitamin-D

34. LABORATORY BIOCHEMICAL
INVESTIGATIONS
 Serum Calcium level
 Serum Phosphate level
 Thyroid hormones Tests
 Serum Alkaline phosphatase
 Serum Acid phosphatase

35.  Vitamin D is stored mainly in liver .
 Vitamin D is most toxic in overdoses .
 Toxic effects include demineralization of bones and increased calcium
absorption from intestine, leading increased plasma calcium
(hypercalcemia).
 Hypercalcemia is associated with deposition of calcium in many soft
tissues such as kidney and arteries
 It leads to formation of stones (renal calculi)
 High consumption is associated with loss of appetite, nausea,
increased thirst, and loss of weight .
VITAMIN D TOXICITY