31: Vitamins - Perry Flashcards
define vitamins
Heterogeneous group of organic compounds required in small amounts for cellular functions; cannot be synthesized in adequate amounts
biological roles of vitamins
Essential cofactors in enzymatic reactions
Biological regulatory molecules
Antioxidants
water soluble vitamins
Water soluble (B vitamins, vitamin C) – absorbed in portal blood, circulate in free form, not stored
can have tolerable upper limits (adverse effects at high levels) but not toxic
fat soluble vitamins
Fat soluble – (A, D, E, K) absorption is 40-90% via bile salts; require carrier protein for circulation, stored to some extent by body fat
can become toxic in lg. doses (have tolerable upper limits)
describe how folate and cobalamin work together
Joint role in one-carbon transfer pathway
Necessary for production and maintenance of new cells, DNA/RNA synthesis
Folate works as a substrate for cobalamin
Deficiency of cobalamin can lead to a “methyl trap” in methylation pathway
cobalmin deficiency –>
folate deficiency –>
pernicious anemia
Megaloblastic anemia, neural tube defects
describe cobalamin structurally
Cobalamin contains a cobalt ion complexed in a ring structure (corrin ring)
R group can attach to various groups including methyl group to yield methylcobalamin
Animal sources only
most common B12 deficiency
Pernicious anemia
Parietal cells fail to secrete intrinsic factor.
Risk increases with age (occurring in up to 15% of elderly), gastrointestinal conditions/surgeries (Crohn’s, atrophic gastritis, autoimmune destruction of gastric mucosa, gastric bypass)
measures B12 and IF deficiency
schilling test
describe megaloblastic anemia
maturation of hematopoietic precursor cells is disrupted due to defect in DNA synthesis; white and red blood cells are enlarged; many cells die in bone marrow which leads to anemia
B12 low and folate normal =
normal B12 and high folate =
b12 low and folate high =
Macrocytosis, anemia,
cognitive impairment
No cognitive impairment
Odds ratio = 5 for cognitive impairment and anemia (*masks the B12 deficiency and shows up worse)
Antioxidant
refers to any molecule capable of stabilizing or deactivating free radicals before they attack cells - act as electron donors to stabilize the reactive species – different types based on solubility
describe vit D
Able to synthesize if adequate UV light
Little from diet
Can be considered a hormone – synthesized at 1 site, converted into active hormone at another site, exerts action at target tissues
functions of vit D
Kidney, bone, intestine –> maintain blood calcium
May be involved in cell differentiation
Immunity
role of B1 Thiamin
Oxidative decarboxylation of α-keto acids and 2-keto sugars
deficiency: Beriberi, muscle weakness, anorexia, tachycardia, edema
sources: east, pork, legumes
role of B2
Riboflavin
Electron (hydrogen) transfer reactions
deficiency: Cheilosis, glossitis, hyperemia and edema of pharyngeal and oral mucous membranes
sources: Liver, beef, dairy
role of B3 niacin
Electron (hydrogen) transfer reactions
deficiency: Pellagra, diarrhea, dermatitis, confusion, dementia
sources: Tuna, liver, poultry, beef, mushrooms
role of pantothenic acid
Acyl transfer reactions
deficiency: Very rare, numbness, tingling of extremities, fatigue
sources: Widespread, highest in egg yolk, liver, kidney
role of B6
Pyridoxine
Coenzyme in many transamination and decarbxylation reactions
deficiency: Dermatitis, glossitis, convulsions
sources: Liver, fish, meat
role of biotin
CO2 transfer reactions, carboxylation reactions
deficiency: Very rare, anorexia, nausea, glossitis, dermatitis
sources: Yeast, liver, kidney; synthesized by microflora
role of folic acid
One carbon methyl transfers, amino acid metabolism
deficiency: Megaloblastic anemia, fatigue, depression, confusion
sources: Brewer’s yeast, liver, green leafy vegetables, lima beans
role of B12 cobalamin
Methylation of homocysteine to methionine, conversion of methylmalonyl CoA to succinyl CoA
deficiency: Megaloblastic anemia, degeneration of peripheral nerves, glossitis
sources: Meat, fish, shellfish, poultry, milk
fole of vit C or ascorbic acid
Antioxidant, role in collagen synthesis, immune function, absorption of non-heme iron
deficiency: Scurvy, fatigue, slow wound healing, bleeding gums, rupture of capillaries
sources: Fruits and vegetables
role of beta-carotene and its derivative retinol
Vision, metabolites involved in growth failure, growth and differentiation of epithelial, nervous, and bone tissue, immune function
deficiency:Children: poor dark adaptation, xerosis, keratomalacia
Adults: night blindness, xeroderma
sources:Liver, dark green leafy vegetables, orange fruits and vegetables
role of vit D cholecalciferol
Regulator of bone metabolism, primarily calcium, other roles emerging
deficiency:Children: rickets
Adults: osteomalacia
sources:Skin synthesis, liver, fish, fortified dairy, eggs
role of vit D alpha-tocopherol
Antioxidant,
Enzymatic activities
Gene expression
Cell signaling
deficiency:Infants: anemia
Children & adults: neuropathy, myopathy
sources:Vegetable oil, nuts, green vegetables
role of vit K
Blood coagulation
Bone growth
deficiency:Children: hemorrhagic disease of newborns
Adults: defective blood clotting
sources: Gut flora, dark green leafy vegetables
