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Nutrition Muscle weakness B vitamins


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Vitamin B1
common name
two things that it does
requirement for thiamin
concentrated locations
thiamin pyrophosphate
cofactor in decarboxylation(TPP in PDH, KDH, IDH)
coenzyme in carbohydrate metabolism
thiamin requirements are influenced by carbs consumed
location: muscles and CNS
beri beri
thiamin deficiency
causes the disease beriberi, in which the patient presents with muscle weakness, ataxia, footdrop, ophthalmoplegia,

Beriberi is regarded as a medical emergency because it can progress to cardiac failure. Two forms of beriberi are "wet" (edematous) or "dry" (nonedematous)
what types of eating habits induces thiamin deficiency?
not eating pork legumes and yeast
milling grains
eating some foods that may destroy dietary thiamin
thiamin may be destroyed in processing
ethanol favors thiamin def
how is it found in the body?
what are some common foods rich in niacin?
legumes cereals meat fish
what are some important roles of pyridine nucleotides(NAD)
cosubstrates for dehydrogenase
substrates for ADP ribosylation
precursors of cyclic ADP-ribose
what is niacin made from?
synthesis of niacin from trp requires B6
what does niacin deficiency cause?
excess niacin vs excess nicotinamide
niacin = excess of 1 g, acute flushing, biomedical abnoralities

nicotinamide = nothing
Folic acid, main biochemical purpose
a 1 C donor

folate easily destroyed by cooking
what is niacin clinically used for
reductions of elevated blood cholesterol
biochemical structural features of folic acid
chain of glutamate residues
absorption and transport of folate
transport system takes it up and its then reduced and some is methylated, it must be demethylated to serve any purpose
demethylation of folic acid
homocysteine + 5-methylTHF -> met + THF

note: need B12

can be trapped in the methyl stage
folate deficiency causes?
macrocytic anemia
How can a B12 deficiency be masked?
if you take a loot of folic acid, not all of it will get methylated, and so it will look like you have enough vit B12
Folate deficiency
what clinical diseases can folate decrease the risk of
homocysteineanemia -
because folate metabolizes homocysteine

inadequate folate will show a decrease of [folate] where in the body: start from what gets decreased first
serum folate decreases
RBC folate decreases
get hypersegmented neutrophils and mean corpuscular volume increases,
Hb decreases
what are the syptoms of pellagra
diarrhea dementia dermatitis
Wernicke-Korsakoff syndrome
Wernicke-Korsakoff syndrome:a genetic defect that prevents them from effectively utilizing dietary vitamin B1. TPP binding is weak, becomes manifested if thiamin intake is compromised (by alcoholism, poor diet, or malabsorption). This syndrome presents with many of the signs of beriberi, but also with memory problems, disorientation, and coma.
where does the body usually get niacin?
NADH from legumes and cereals
muscle weakness, anorexia, and skin eruptions, cracked, pigmented, and scaly skin in areas exposed to sun (hands, forearms, neck, and legs); Casal's necklace

what is this disease and what is it due to
pellagra niacin def
inhibits the synthesis of new cells, causing anemia, villous atrophy, and depapillation of the tongue. In addition to showing hypochromic, megaloblastic red cells on a blood smear, hyperhomocysteinemia
folate deficiency, could also be B12 def,
hyperhomocysteinemia because homocytseine is converted to met when demethylating THF
what else does a B12 deficiency cause?
conversion of methylmalonic acid to succinyl CoA
numbness and tingling of the extremities, weakness, and other neurological changes. Long-term effects on the nervous system can be irreversible,methylmalonic acid accumulates
what does absorption of B12 require?
gastric acid releases B12, R-proteins bind it and then binds Intrinsic Factor (IF) in the duodenum
some patients must receive B12 by injection,why?
Pernicious anemia is a pathological B12 deficiency arising from an inability to properly absorb dietary B12 (defective IF), in 3-6 months will show deficiency
where does B12 reabsorption occur
ileum, very efficient receptor mediated process
how long can B12 stores last in the body? why?
10-20 years b/c B12 is recaptured for re-use
what are dietary sources of B12
meat, fish, dairy products and eggs; plants are devoid of B12
Vitamin B12 has no toxicity (a TUL has not been determined), allowing megadoses to be used in some cases of deficiency.
what is the precursor of PLP
vitamin B6, found in various chemical forms - pyridoxine, pyridoxal, pyridoxamine
how does B6 effect homocysteine?
reducing elevated homocysteine because it is a factor in the reaction by which homocysteine is converted to cysteine
B6 is toxic?
toxic at high doses
what is the schilling test?
assess whether a deficiency is due to malabsorption of B12:
radioactive cobalamin (a chemical form of B12) is given by mouth and B12 storage sites are saturated by injected cobalamin. In a normal individual the radiolabeled cobalamin will be efficiently absorbed but excreted in the urine (since storage sites are blocked). Low urinary excretion confirms poor absorption
how do you distinguish iron deficiency anemias fromn folate/B12 anemias
blood smear and complete blood counts

see microcystic anemia(iron) vs macrocystic anemia(folate/B12)

may need to test serum folate RBC folate and serum B12
aa metabolism, glycogen breakdown, H action
B6 deficiency
rare, vitamin is widley distributed, LARGE doses however can cause irreversible peripheral neuropathy (over 500mg/day)
riboflavin is found in what?
a component of the enzyme prosthetic groups FAD FMN (oxidation reduction rxns)
uncomplicated riboflavin deficiency vs riboflavin deficiency
uncomplicated is uncommon and milder
a prosthetic group in enzymes of carboxylation
is biotin free or bound
bound is bound to epsilon-amino group of lysine(as an amide)
biotin deficiency
not really seen
describe the structure of pantothenic acid
beta-alanine in amide linkage with pantoic acid
what is pantothenic acids role in the body
effect acyl group transfer as part of Coenz A (add a mercaptoethylamine and adenine to pantothenic acid and viola)
pantothenic acid deficiency

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