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29 Cards in this Set
- Front
- Back
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What are the 2 main forms of vitamin D?
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D2 (ergocalciferol) and D3 (cholecalciferol)
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What structural difference is there between D2 and D3?
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D2 has a double bond the the tail (side chain) and D3 doesn't
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What foods are commonly fortified with vitamin D?
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OJ, milk, cereals
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what are dietary sources of vitamin D3
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beef liver, eggs, fatty fish and their oils ( limited foods)
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What is the main source of vitamin D?
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the sun
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what compound is found in the skin that absorbs UVB rays to produce previtamin D3?
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7-dehydrocholesterol
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What inactive metabolites are generate to prevent excess D3?
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lumisterol and tachysterol
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which inactive metabolite is produced from 7-dehydrocholesterol? from previtamin D3?
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7-dehyrdo : lumisterol
previtamin D3: tachysterol |
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Once synthesized in skin, what picks up the D3 in the blood?
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DBP ( vit D binding protein)
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how is dietary D3 absorbed?
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from a micelle that takes it to the enterocyte to be passively diffused inside
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what transports the vitamin from the enterocyte into the lymphatic system?
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chylomicrons
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What organ is DBP-bound vit D primarily taken to? what other tissues pick up some before?
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primarily liver! adipose, and muscles can pick up some too
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what reaction must happen before vit d ( from chylomicron or DBP) can begin getting converted to the active form>
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must be hydroxylated
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what enzyme hydroxylates vitamin d3 to become calcidiol?
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25-hydroxylase (mostly happens in LIVER)
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where is the major storage site of calcidiol?
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blood
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what are normal levels of calcidiol?
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30-40 ng/ml
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what organ takes up most of the calcidiol from the blood in response to increased PTH?
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the kidneys
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where is most of the calcitriol made and what enzyme is required?
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kidneys, 1-hydroxylase
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what is the active form of vitamin D? (hormonal form)
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calcitriol
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what inhibits calcitriol synthesis?
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high serum Ca (hypercalcemia) and P (hyperphosphatemia) levels
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what does calcitriol bind to in the nucleus of cells to influence gene experession?
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VDR (vitamin D receptors)
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What is the main function of calcitriol and the intestines?
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increase absorption of calcium to raise blood calcium levels
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what is the main function of calcitriol and the kidneys?
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induce calcium reabsorption in kidneys by activating proteins to reabsorb it
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how does PTH affect the kidneys?
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interacts with receptors on kidney cells to increase expression of 1-hydroxylase to and synthesis of calcitriol
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what role does calcitonin play?
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blocks ca and p mobilization from bones by inhibiting osteoclast activity
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Vitamin D diminishing the production of angiotensin II helps reduce what chronic illness?
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high blood pressure
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what is calcidiols apparent role in decreasing the risk of heart disease?
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lowers LDL and increases HDL
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what is the major end product of calcitriol breakdown?
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calcitroic acid
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what is the RDA for vitamin D?
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600 IU (15 micrograms): children 1+ and adults
800 IU (20 micrograms): adults > 70 |
