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45 Cards in this Set
- Front
- Back
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What does high TH do to the TSH levels?
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high TH supresses TSH
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What does low TH do to TSH?
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low TH allows TSH to be secreted
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What kind of feedback is TSH and TH?
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negative
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What are the steps of the mechanism of thyroid hormone action? (5)
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1) convert T4-->T3 using 5'deiodinase in peripheral tissues
2)T3 enters nucleus and binds with high affinity to nuclear receptor 3)thyroid hormone receptor homodimer or hormone receptor+9-cisretinoic acid heterdimer binds with coactivator to the thyroid response element 4) transcription is stimulated 5)induction of multiple proteins |
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What are the four molecules required to stimulate transcription?
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1) thyroid homone receptor (homodimer)
2)thyroid hormone receptor + 9-cis retinoic acid RXR receptor (heterodimer) 3) co-activator 4) thyroid response element |
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Where is the thyrotrophic releasing hormone (TRH) synthesized?
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hypothalamus
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What is the structure of TRH? (1)
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tripeptide-pyroglutamine -histadine -proline amide
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What is the action of TRH?
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stimulates TSH secretion by thyrotrophs in anterior pituitary
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How does TRH go from the hypothalamus to the anterior pituitary?
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1) TRH secreted in hypothalamus
2) secreted into hypophyseal portal circulation 3) carried to anterior pituitary |
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What is the impact of TH on TRH?
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loss of receptors for TRH on membranes of thyrotropes --> decreasing TSH
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What is the structure of TSH? (3)
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1)glycoprotein of 28,00 daltons
2)two non covalently linked subunits alpha and beta |
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What is the structure of the alpha unit?
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identical to alpha subunit of LH, FSH, hCG
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What is the structure of the B subunit?
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specificity portion
similar to TSH |
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What aspects of the TSH are required for receptor binding and hormone action?
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alpha and beta subunits
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What does TSH stimulate? (2)
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1)T3, T4 and TG synthesis
2) growth of thyroid gland |
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What is the half life of TSH in plasma? Is it fast or slow?
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1 hour, fast
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What is the plasma level of TSH?
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.5-5.0 units/mL
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What is the mechanism of TSH action? (5)
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1)TSH membrane receptor complex
2) increases adenylyl cyclase 3) increases cAMP 4) increases phosphokinases 5) biological responses |
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What is the central equations for thyroid regulation (2)?
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increase T3, T4: decrease TSH
decrease T3, T4: increase TSH |
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How can you affect the closed loop of thyroid regulation?
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remove thyroid
decrease T3, T4: increase TSH |
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What is the T/S ratio?
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thyroid hormone: serum ratio
indicates the amount of thyroid hormone |
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What are the three things that cause a hypothyroid goiter?
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1) NA-CNS sodium thiocyanate or Potassium PerClorate (HClO4-)
2) administration of polythiouracil 3) I deficiency |
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What is the mechanism on TH of CNS or HCLo4?
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block iodine pump --> iodide can not access thyroid gland
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What is the result of CNS or HlCO4 for TH?
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result: no TH formed
decrease TH, increase TSH --> goiter |
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What is the mechanism of polyuracil on thyroid?
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inhibits conversion of iodide to iodine
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What is the effect of polyuracil on thyroid?
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1) no TH formed
2) TH decreases: TSH increases--> goiter |
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What is the T/S ratio of CNS or HCLO4?
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1:1
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What is the T/S ratio of polythiouracil?
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T/S ratio becomes very hi
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What is the mechanism of iodide deficiency on thyroid?
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no Iodide
iodide is trapped little TH is made this causes increased TSH goiter forms |
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↑TRH --> ___ TSH
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↑TRH --> ↑TSH
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↑ Somatostatin --> __ TSH?
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↑ Somatostatin --> ↓ TSH
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↑TSH --> ___ leptin
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↑TSH --> ↑ leptin
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How do you get a euthyroid goiter?
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iodide deficiency because of living in goiter belts
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What is the difference between hypothyroid goiter and euthyroid goiter?
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gland gets some iodine and makes some TH where as in hypothyroid goiter you make almost no TH
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What causes a hyperthyroid goiter?
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production of Thyroid Stimulating Igs (TSIs) that ↑T3/T4
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What is the cause of all goiters?
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prolonged ↑ TSH
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What is another name for hyperthyroid goiter?
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Grave's disease
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What is the way you measure thyroid function?
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1)radioimmuno assay
2) ↑ serum TSH |
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What does hyper or hypo thyroidism do to cholesterol and LDL levels?
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1) hypo: ↑
2) hyper: ↓ |
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What are the causes of hypothyroidism?
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1*: thyroid failure
2 *: pituitary of hypothalamus failure 3*: absent/defective thyroid hormone receptors |
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What are the 10 symptoms of hypothyroidism?
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1) ↓ BMR
2) ↑ LDL + cholesterol 3) growth failure 4) weight gain 5) constipation 6) cold intolerance 7) dry, thick sin 8) depression 9) insomnia 10) myxedema |
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What is myxedema?
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mucoproteinous skin deposit
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What are the causes of hyperthyroidism?
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emotional trigger
Grave's disease |
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What are the symptoms of hyperthyroidism?
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1) ↑BMR
2) ↑ sweating, body heat 3) ↑ GI dysfunction 4) negative calcium balance, osteoporosis 5) expopthalmos 6) neuromuscular fatigue 7) negative nitrogen balance 8) psychotic behavior |
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What happens to the thyroid balance during pregnancy?
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euthyroid BUT
↑ estrogen -->↑ TBG ↑ T3 +T4 |
