vitamins Flashcards
What are vitamins?
Don’t provide energy but some are linked to energy yielding pathways
Needed in small amounts (ug or mg/day or IU)
Can be obtained from diet or synthesised
What are vitamins diverse functions?
Coenzymes, hormones, cell signalling, antioxidants, regulators of growth and differentiation
What affects the availability and absorption of vitamins?
Properties of food
Preexisting disease
Drugs compete for sites of absorption or kill bacteria
What does RDA and NRV mean?
RDA- adequate intake to ensure the requirements of all healthy people at met
NRV- nutrient reference value, %
What are fat soluble vitamins?
Vit A, D, E and K
Stored in body fat and liver
What are water soluble vitamins?
Vit B and C
Requires steady supply
What is Vitamin A?
Retinoids (active form)
Carotenoid pigments in plants are cleaved to yield retinoids
Vit A binds to proteins (opsins) in the cells of the retina to form visual pigments
Vit A is a nuclear modulator of gene expression
~hydrophobic retinoic acid passes through cell membrane
~binds to intracellular receptor
~translocates into nucleus
~associates w DNA to influence transcription/translation
So is important for cell proliferation, differentiation and development
What happens if you have a deficiency of Vit A?
Major could cause blindness
Impaired resistance to infection (involved in differentiation and function of lymphocytes and neutrophils)
Mild could cause night blindness (poor sight in low light)
Prolonged/severe- metaplasia and keratinisation of conjunctiva epithelial cells or thickening of cornea (xerophthalmia)
What is Vitamin D?
Hormone precursor
~D3- calciol/cholecalciferol
~D2- ercalciol/ergocalciferol
Endogenous synthesis is more important than dietary
~D3- photolysis of 7-dehydrocholesterol in skin
Maintains plasma calcium conc and other hormones
Involved w steroid hormone activating nuclear receptors
How is Vit D involved in bone metabolism?
Stimulates intestinal Ca2+ and PO43- absorption and renal Ca reabsorption
Mineralisation is controlled by availability of Ava and PO4
Osteoblasts have receptors for calcitriol
If osteoclast activity/no increases, Ca stores can be mobilised
What happens if you have a deficiency of Vit D?
Bone mineralisation fails (rickets/osteomalacia)
Impaired immune function
What is Vitamin E?
Anti-oxidant- v active free radical trapping
Inactivates protein kinase C in cell signalling
What happens if you have a deficiency of Vit E?
V rare as levels need to be low for a long time- difficult due to fat stores
However fat malabsorption conditions eg. Crohns, may contribute
What is Vitamin K?
Co-enzyme in postranslational carboxylation of glutamate to y carboxyl glutamate
Permits binding of proteins to membrane phospholipids (for minerals like Ca can be incorporated)
Vit K dependent proteins involved in blood clotting
Some anticoagulants are Vit K antagonists e.g. warfarin
What happens if you have a deficiency of Vit K?
Haemorrhagic disease
~esp. newborns which is why Vit K is given at birth
What is Vitamin B1?
Co-enzyme THIAMIN involved in-
~energy yielding pathways (pyruvate/alpha-keto-glutarate dehydrogenases) to p. ATP
~nervous system- p. acetyl choline and myelin
~pentose phosphate pathway- p. NADPH for biosynthesis and ribose sugars for nucleotides
Also-
~catabolises leu, isoleu and val
~regulates nerve chloride channels
p.=produces
What happens if you have a deficiency of Vit B1?
Beriberi (peripheral neuritis)
Presents as weakness and stiffness
What is Vitamin B2?
Electron carrier RIBOFLAVIN in oxidation/reduction reactions
Bound to enzyme
FAD and FMN oxidising coenzymes accept 2 H atoms
What happens if you have a deficiency of Vit B2?
Not too big of a problem
Bacterial synthesis forms B2
Efficient conservation to reuse
What is Vitamin B3?
NIACIN
Precursor of coenzymes NAD and NADP
Electron carriers in redox reactions
Synthesised from dietary tryptophan
What happens if you have a deficiency of Vit B3?
Rare- Pellegra ~dermatitis ~diarrhoea ~dementia ~death Oral presentation- atrophic glossitis
What are the other B vitamins?
B5- PANTHOTHENIC ACID
~for RBCs and adrenal gland hormones
Deficiency rare- fatigue, insomnia
B6- PYRIDOXINE
~cofactor in transamination
Deficiency- microcytic anaemia
B9- FOLATE and B12- COBALAMIN
~coenzymes involved in DNA/myelin synthesis
Deficiency- anaemia, neurological damage
Supplements- recom. in pregnancy
What is Vitamin C?
Reducing sugar and antioxidant ASCORBIC ACID
~keeps Cu+ instead of Cu2+ for dopamine beta-hydroxylase to synthesise nor/adrenaline
~lysine/proline hydroxylases to mature c. tissue (collagen)
~keeps Fe2+ instead of Fe3+ to increase absorption (Vit C increases iron absorption)
What are some oral manifestations?
Face- malar pigmentation (B vits), nasolabial seborrhoea (Vit B2,3,6, iron), lack of colour (malnutrition)
Lips- cheilosis (Vit B2,3,6), angular fissures (Vit B2,3,6, iron)
Gingivae- spongy, bleeding, redness (Vit C)
Tongue- glossitis (Vit B3,6,9,12, iron), pale, atrophic, smooth/slick (iron, folate), magenta (riboflavin)
