Rapidly taken up by thyroid gland contains most kidney Goitrogens in foods eg

Rapidly taken up by thyroid gland contains most

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Rapidly taken up by thyroid gland (contains most) & kidney - Goitrogens in foods (e.g.- thioglucoside & linamarin in cassava) may impair uptake by thyroid - Transported in blood bound to: o Thyroxine-binding globulin o Albumin o Transthyretin (TTR) which binds to & transports Vit A - Excreted in urine - Urinary iodide - Fxn’l indicators: Thyroxine (T4) & serum thyroid stimulating hormone (TSH)
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6 VITAMINS MAIN FORMS/ COENZYMES FUNCTIONS RDA & SOURCES DEFICIENCY & CLINICAL SYMPTOMS ABSORPTION ASSESMENT Biotin Food form: Biocytin (biotinllysine) - Functions as coenzyme for carboxylases (transfer of CO2 gps) o Biotinylation activates enzymes (e.g.- pyruvate carboxylase, Propionyl-CoA carboxylase for catab of AAs Ile Thr Met & Val, acetyl CoA carboxylase I & II for FA syn, B- methylcrotonyl CoA carboxylase for Leu catab) - Non-coenzyme roles: o Histone biotinylation of Lys residues for cell proliferation, gene silencing, cellular response to DNA damage o Via biotinidase & holocarboxylase synthetase AI: 30ug/d (increases during pregnancy) - Deficiency is rare o Ingestion of raw eggs o Genetic defect in biotinidase which impairs absorption or holocarboxylase synthetase o GI disorders: IBD, alcoholics SYMPTOMS Hair loss (alopecia), scaly rash, depression , hallcuinations NO UL - Free biotin = main circulating form o Imported into cells via sodium- dependent multivitamin transporter - Biotin removed via biotinidase before import - Passive diffusion at high doses - Urinary biotin excretion - Lymphocyte holo- methylcrotonyl- CoA carboxylase & holo-propionyl-CoA carboxylase** Vitamin A Food forms: Preformed retinoids- stored in animal tissue: o Retinal o Retinoic acid o Retinyl ester (RE) = storage form o all- trans- retinol typically bound to FA (e.g.- palmitate) § Retinyl palmitate**; typically bound to proteins Pro-vit A carotenoids: o β-carotene 900 µg of RAE/d 70µg of RAE/d RAE = retinol activity equivalents TOXICITY- o Hypervitaminosis A o β-carotene non-toxic; may cause skin pigmentation - Liver biopsy - Plasma retinol: only shows severe def - Relative dose response (RDR) test: magnitude of ↑ in RBP following supplementation - Conjunctival impression cytology Vitamin D Food forms: Cholecalciferol (Vit D3) - Animal form HORMONAL & TXN’L ACTIVATOR FXNs Increases Ca (and Pi) absorption - 1,25(OH) 2 D 3 binds to VDR & 15µg/ d & 20µg/d DEFICIENCY - Children = Rickets - Brought into enterocyte via NPC1L1
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7 - Cholesterol à pro-vitD à pre-vit D à Vit D3 Ergocalciferol (Vit D2) - Found in small amts in plants - Supplemental form 25(OH) 2 D 3 : status indicator; major circulating form Calcitriol 1,25(OH) 2 D 3 : metabolically active form; maintains Ca lvls 1,24,25(OH) 2 D 3 : excretory form stimulates expression of TRPV6 & PMCA1b o VDR binds to 1,25(OH) 2 D 3 and forms heterodimer with RXR o 1,25(OH) 2 D 3 -RXR complex binds to VDRE & stimulates tx of Ca handling genes TRPV6, calbindin & PMCA1b - Ca transport is a saturable process comprised of three 1,25(OH) 2 D 3 regulated steps: Entry of Ca through the membrane channel via TRPV6, located in the apical membrane of the intestinal epithelium Binding to the Ca binding protein, calbindin which shuttles Ca through the enterocyte
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  • Spring '14
  • Knutson,MitchellD
  • Vitamin, Vitamin B12, enterocytes

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