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42 Cards in this Set
- Front
- Back
where is calcium located in the body? |
99% found within the bones 1% found in extracellular fluids, intracellular structures, cell membranes |
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serum calcium exists in three fractions: |
protein bound: physiologically inactive ionized: physiologically active, functions intracellularly (better indicator of calcium tatus) complexed: complexed with small negative ion (such as citrate, lactate, phosphate), biologic role uncertain; albumin carries calcium in the blood (low albumin, low serum calcium) |
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what is the appropriate biochemical indicator for calcium? |
there are none presently largely due to the fact that calcium concentration in the body fluids is tightly controlled, little/none association between calcium intake and serum calcium concentrations urinary tends to be better than blood (more responsive to high/low intake) - still not great indicator |
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what are low serum calcium concentrations indicative of? |
metabolic issue, rather than low of high intake of calcium (although special considerations for TPN patients - calcium is going straight into the blood) |
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factors that can influence urinary calcium concentrations |
hypercalcemia - increased serum calcium time of day - increased urinary calcium concentration during the day diet - increased protein, increased urinary calcium |
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zinc functions |
zinc is a cofactor for numerous enzymes involved in many metabolic processes such as: protein synthesis, wound healing, immune function, tissue growth, tissue maintenance |
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where is zinc stored in the body? |
there is no reserve (storage) for zinc in the body; concentration is maintained by both conservation and redistribution of tissue zinc |
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are static measures, like serum zinc, reliable? |
they are available but interpretation is complicated by body's homeostatic control of zinc status and other factors that are unrelated to zinc status (stress, infection, inflammation) so serum zinc is NOT a reliable indicator of dietary zinc intake or whole body zinc status |
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what is a more reliable statis indicator of zinc status |
metallothionen may be an indicator (a little better than serum zinc); it is a static measurement; metallothionen is a protein found in the liver, pancreas, and kidney that binds zinc and copper tissue metallothionen concentrations are often proportional to zinc status (if both serum zinc and serum metallothionen are low, zinc deficiency is likely) need both serum zinc and metallothionen to determine deficiency |
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what is another way to evaluate zinc? |
hair zinc concentration - reflects zinc status over past several months gold standard in non-industrialized countries but in our country it can be contaminated by all sorts of things (must follow proper methods if used) |
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limitations to hair zinc concentration: |
its susceptibility to contamination from exogenous sources non-nutritional factors that affect assessment: hair dye, shampoos, pregnancy, age |
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vitamin A status is grouped into 5 categories: |
deficient, marginal, adequate, excessive, toxic |
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assessment of vitamin A involves ____ measures and ____ measures |
static (serum vitamin A) and functional (dose response test, dark adaptation) measures functional tests usually used in research settings |
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serum vitamin A (retinol) |
most common measure of vitamin A status typically 95% of serum vitamin A is in the form of retinol, bound to retinol binding protein (other 5% is unbound free retinyl esters) serum measures are predictive for vitamin A status when reserves are either deficiency or excessive (good at assessing at the extremes) there are guidelines generated from NHANES data for interpretation of serum vitamin A best clinical method |
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what to remember when interpreting serum vitamin A |
serum vitamin A concentrations may be within expected range despite low concentrations of vitamin A in the liver |
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relative dose response procedure |
fasting blood sample taken vitamin A administered orally as retinyl palmitate blood sample taken 5 hours later typically done in developing countries, not done clinically |
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modified dose response procedure |
dehydroretinol, a naturally occurring form of vitamin A that is not found in the diet is administered only one blood sample taken at 5 hours can tell all levels of stores |
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relative dose response/modified dose response principle: |
if stores of retinol are high, plasma retinol concentration is not affected much by oral administration if stores of retinol are low, plasma retinol concentration will increase rapidly from oral administration best research methods |
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direct measure of liver stores |
measurement of liver concentration of vitamin A can be used to assess status best method |
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dark adaptation principle |
vitamin A plays a large role in visual function when light strikes rhodopsin, the molecule will split into opsin and a trans-isomer of retinol, which generates a visual response - rhodopsin is then reformed during this process, some retinol is lost and replaced by vitamin A with vitamin A deficiency, less rhodopsin is formed and eye fails to adapt to low light levels after exposure to bright light measure rhodopsin and rate of generation |
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serum vitamin C |
most commonly used test to assess Vitamin C status highly related to recent dietary intake of Vitamin C factors that affect serum vitamin C: smoking, gender |
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what better represents cellular and total body pool of Vitamin C |
Vitamin C concentration in poly- and mono- morphonuclear leukocytes |
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what is the best test to assess vitamin D status and why? |
total 25 (OH) D level in blood ingested and cutaneously produced vitamin D is rapidly converted to 25 (OH) D, but in serum only a fraction of 25 (OH) D is converted to its active metabolite 1, 25 (OH) 2D |
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what is the method of choice for assessing Vitamin E status? |
plasma tocopherol but if available, then the ratio of alpha tocopherol to total plasma lipids because tocopherols are transported on the lipoproteins in the blood ratios usually used in research setting |
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what are two methods to assess biotin status? |
urinary biotin excretion - better indicator - static urinary 3-hydroxyisovalerate excretion - biotin is needed in two amino acid reactions and in deficiency will produce 3-hydroxyisovalerate - functional indicator |
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what is the most common way to measure vitamin B6? |
plasma PLP (pyroxidal 5'-phosphate) PLP accounts for 70-90% of total B6 in plasma fasting concentration is most accurate |
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what is vitamin B6 composed of? |
pyridoxine (PN) pyridoxal (PL) pyridoxamine (PM) within the liver, erythrocytes, and other tissues these compounds are phosphorylated into PLP and PMP |
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factors affecting plasma PLP concentration |
asthma, coronary heart disease, pregnancy these conditions decrease PLP but not due to vitamin B6 deficiency |
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what are three other methods to evaluate vitamin B6 status? |
urinary 4-pyridoxic acid (4-PA) - major urinary metabolite of B6 and is indicative of recent B6 intake functional tests: tryptophan load test, methionine load test (vitamin B6 is responsible for the metabolism of these amino acids) |
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serum folate and what affects it |
indicates recent dietary intake but does not correlate well with tissue stores non-nutritional factors affecting folate: acute renal failure, active liver disease, RBC hemolysis |
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what is the best measure of depleted tissue stores of folate? |
erythrocyte folate - correlates well with liver stores and total body stores reflects folate intake for the life of the RBC (120 days) less influenced by dietary folate |
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what is the most common way to measure vitamin B12 and what are factors that affect this measurement |
serum Vitamin B12 - however, serum levels are maintained at the expense of tissue stores factors that affect serum B12: leukemias and lymphomas, active liver disease |
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what is a functional way to assess vitamin B12 |
methylmalonic acid (MMA) - B12 is needed for the conversion of MMA to succinyl CoA MMA increases in B12 deficiency, but not folate deficiency best to use MMA test in combination with serum B12 to assess B12 status |
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what are the different groups for Vitamin K |
Vitamin K1: phylloquinone, phytonadione K2: menaquinone or MKs K3: menadione (synthetic form not used in humans) |
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how do you assess vitamin K status |
phylloquinone and menaquinoes are the most commonly measured, K1 more so because it is the primary source of dietary vitamin K serum K1 reflects recent intake and responds to changes in dietary intake within 24 hours vitamin K is variable in the diet, one serum may not reflect normal dietary intake |
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a classical measure of vitamin K deficiency can be |
increased prothrombin time - time it takes your blood to clot (vitamin K is needed to turn proteins into substances that will clot your blood) this test is no longer used much |
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other proteins that can be used to assess Vitamin K status? |
osteocalcin and matrix Gla protein (both depend on Vitamin K for carboxylation of glutamyl residues) |
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all possible ways to assess vitamin K status |
blood phylloquinone concentration (most common - clinical) prothrombin time (not used anymore) factor VII activity (not used anymore) urinary gamma-carboxyglutamyl residues (research) undercarboxylated prothrombin (research) under gamma-carboxylated osteocalcin (research) |
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three methods to indicate iodine status |
urinary iodine concentration (most used) the goiter rate blood concentrations of thyroid stimulating hormone and thyroglobulin |
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which method can assess iodine over days |
urinary iodine is a sensitive indicator of recent intake (days) spot urinary iodine concentrations are highly variable from day-to-day and should not be used to classify iodine status of individuals |
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which method can assess iodine over weeks/months? |
thyroglobulin shows an intermediate response (weeks to months) |
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which method can assess iodine over months/years? |
changes in the goiter rate reflect long term-iodine nutrition |