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36 Cards in this Set
- Front
- Back
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What is the minimum daily requirement for iodine per day?
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150 µg per day
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What is euthyroid?
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individual with normal thyroid levels
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What is the T/S ratio? What does it mean?
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thyroid/serum ratio for iodide, it means how much iodide you have in your thyroid vs how much is in your serum (it should be alot higher in your thyroid since you are actively pushing it out)
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What are the main steps of thyroid synthesis? (9)
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1) iodide accumulation
2) TSH stimulates iodide transport 3)conversion of iodide to iodine (meanwhile) 4)thyroglobulin gets iodinated on tyrosyl residues to make MIT and DIT 5)peroxidase makes T3 and T4 6)release of T3 and T4 7) release of MIT and DIT 8) making of more I- from MIT and DIT (you can start another cycle now) |
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What are the two sources of iodide in the thyroid epithelial cell?
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1) Na-I cotransporter
2) recovery of I- from MIT and DIT |
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How id iodide transport regulated?
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TSH: stimulates iodide transport
CNS (thiocynaate) and HClO4 (perchlorate): inhibit I- transport |
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What is the enzyme involved in converting Iodide to Iodine?
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thyroid peroxidase enzyme with a cofactor of H2O2
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What drugs inhibit the conversion of iodide to iodine?
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1) propylthiouracil (PTU)
2) methimazole |
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how do you get MIT and DIT from thyroglobulin?
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thyroid peroxidase (with H2O2 cofactor) iodinates the tyrosyl residues of thyroglobulin
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How do you form T3?
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MIT + DIT
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How do you form T4?
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DIT + DIT
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How do you get the coupling reactions that make T3 and T4 from MIT and DIT?
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thyroid peroxidase with H2O2 precursor
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How do you get the release of thyroid hormone?
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proteolysis in lysosyme vesicles releases T3 and T4 as well as MIT and DIT
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What enzyme converts MIT and DIT into iodide?
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deiodinase
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What happens when you have excess iodide?
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decrease in T3 and T4 biosynthesis due to downregulation of Na-I symporter and peroxidase genes
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Between T3 and T4, which is the most potent?
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T3
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Between T3 and T4 which is present in the largest amount?
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T4
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Which has the longer half life T3 or T4?
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T4
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Which is found more in the free solubulized form in plasma? T3 or T4?
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T3 (maybe thats why it has a shorter half life)
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Which is found most in the protein bound form, T3 or T4?
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T4
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What are the two proteins that bind T3?
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1)Thyroid Binding Globulin, TBG
2) Albumin |
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What are the three hormones that bind T4?
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1) Thyroid Binding Globulin TBG
2) Thyroxine binding prealbumin (TBAPA) 3) Albumin |
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What are the three ways in which degradation of thyroid hormones occurs?
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1) T4 deiodinated to T3
2) T4 deoodinated into reverse T3 3) conugation or oxidative deamination |
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What are 5 reasons that cause an increase of peripheral T4 being converted to rT3?
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1) illness
2) starvation 3) corticosteriods 4) propranolol (beta blocker) |
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What happens during fasting to total T4 and free T4?
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concentrations remain normal
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What is the action of TH on normal growth and development? (2)
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-supports secretion of growth hormone
-supports mental development |
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What condition exemplifies the effects of TH deficiency during development?
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cretinism
1) short stature 2) mental retardation |
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What are the metabolic effects of TH? (5)
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1) calorigenic
2) thermogenic 3) carb, protein, lipid metabolism 4) muscle 5) adipose tissue |
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What is the calorigenic effect of TH?
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↑BMR
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What is the thermogenic effect of TH (2)
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acute: ↑metabolism, muscle activity, catecholamine action
chronic: ↑peripheral T3-->T4 |
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What is the effect of TH on carb, protein and fat metabolism?
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↑ metabolism
↑ absorption of nutrients |
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What is the effect of TH on muscle metabolism?
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negative nitrogen balance
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What is the effect of TH on adipose metabolism?
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↑ FA metabolism
↑ need for vitamins |
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What is the effect of TH on neural development?
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promoting
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What is the effect of TH on cardiovascular system?
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↑ rate/strength of heart beat and ventilation
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How does TH exert its effect on the cardiovascular system?
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↑Β receptors
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