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13 Cards in this Set
- Front
- Back
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What are the actions of thyroid hormone?
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maintain metabolic homeostasis
important in normal development stimulates protein synthesis stimulates cholesterol metabolism increases oxygen demand regulates myocardial gene expression |
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Briefly explain the hypothalamic-pituitary-thyroid axis
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TRH is released from the hypothalamus
TRH stimulates release of TSH from the pituitary gland TSH acts on the thyroid gland to cause release of T3 and T4 (mostly T4) *T3 and T4 feed back to pituitary and hypothalamus to block release *Somatostatin decreases TSH release from the pituitary *Iodine levels affect release of thyroid hormones from thyroid gland |
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What is thyroid peroxidase?
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it catalyzes the formation of T3 and T4 by integrating iodine into thyroglobulin and coupling components
*uses H2O2 as a co-factor |
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what is 5'-deiodonase?
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enzyme that converts T4 to T3
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What is L-thyroxine?
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T4, can be made synthetically and used as a replacement to treat hypothyroidism
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Why is T4 used instead of T3 for replacement therapy in hypothyroidism?
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more physiologic
normalizes serum and tissue levels of T3 and T4 used heavily by CNS (T3 cannot cause actions) main product of thyroid gland, so bypasses fewer body mechanisms |
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What are the ADEs associated with using L-thyroxine?
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symptoms of hyperthyroidism: tachycardia, hyperactivity, polyphagia, weight loss
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What is Methimazole?
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thyroid peroxidase inhibitor
used in cats to treat hyperthyroidism *replaced Propylthiouracil, which had the same MOA plus blocked 5'-deiodonase |
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What are the ADEs of Methimazole?
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vomiting
scratching of face |
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How is radioactive iodine used to treat thyroid problems?
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emits gamma rays and beta particles that selectively destroy thyroid tissue after uptake by the thyroid gland
-acts locally, doesn't harm other tissue -MAY destroy too much, cause hypothyroidism |
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How do glucocorticoids affect thyroid function?
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decrease release of TSH, inhibit 5'-deoidonase to decrease levels of thyroid hormone
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How do anticonvulsants such as Phenobarbital affect thyroid function?
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upregulates metabolism of thyroid hormones (induces CYP450 enzymes) so they have a shorter half life, serum levels are lower
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How do NSAIDs (salicylate group) affect thyroid function?
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decrease serum levels of T3 and T4
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