Thyroid S2M1

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  1. In using radioactive iodine with imaging, what would one see in a patient with Graves disease and Thyroditis
    • The Thyroid gland will look much darker then normal due to its over activity in Graves
    • Thyroditis will have a lighter appearence then normal
  2. On a uptake/hour assessment of radioactive iodine into the thyroid gland, what would you see in extreme stimulation of the gland
    In the first six hours the uptake is high and then in lowers to about 50%
  3. What happens if there is an increase in TBG (Thyroxin binding globulin) but not an increase in T3 or T4
    There will be less free T3 and T4
  4. Why can T4 be considered a prohormone
    Because it is the primary source of the active T3
  5. Most conversion of T4 to T3 occurs in
    Tissues with high blood flow
  6. Deiodinases
    These convert T4 to T3
  7. How does free T3 and T4 enter the target cells
    Passive Diffusion
  8. Type 1 iodenases
    These are the general class of iodenases
  9. Type 2 iodinases function where
    CNS and Brain
  10. What do Type 3 iodinases do
    They transform T4 into rT3
  11. What is the significance of rT3
    It is a competitive inhibitor and of T3
  12. What causes an increase in rT3
  13. Reverse T3 (rT3) Dominance (Wilson’s syndrome)
    Results in reduced body temperature, slowing the action of many enzymes, leading to a clinical syndrome, known as Multiple Enzyme Dysfunction, which produces the effects seen in hypothyroidism.
  14. When rT3 is high, why doesn't performing a T3/T4 test on the blood give an accurate reading
    They could be normal, a direct measurement of rT3 must be performed for an accurate assessment of what is occurring
  15. What happens to mitochondria in an animal when they are given thyroid hormones
    They increase in size and number to pump out more ATP
  16. What is the effect of an increased amount of Thyroid hormones on Na+/K+ -ATPase
    • Causes an increase in synthesis of Na+/K+ ATPase causing
    • Oxidative Phosphorilation
    • Protein synthesis and degradation
    • CO2 and heat production
  17. In relation to thyroid hormones on transcription factors, what happens when they are absent
    A co-repressor prevents gene transcription
  18. Thyroid hormones have what effect on brown adipose tissue
    • They increase metabolic rate, which increases "futile cells", which increases the heat production in brown adipose tissue
    • The higher the amount of thyroid hormone, the higher the metabolic rate
  19. What are some systematic affects of thyroid hormones
    • Increased heart rate and blood volume
    • Increases O2 release into tissues
    • Increased gut motility
    • Increased bone turnover and resorption
    • Increased muscle contraction
    • Increased Glyconeogenesis/Glycolysis/Lypolysis
    • Increased insulin, PTH, and ACTH
    • Decrease in Alpha receptors
  20. What are the different ways that thyroid secretion is inhibited
    • High T3 and T4 - Anterior Pit. makes less TSH
    • High T3 and T4 - Hypothalamus makes less TRH
    • High Temp and metabolism - Hypothalamus makes less TRH
  21. Dopamine, Somatostatin, Glucocorticoids have what affect on the Anterior pituitary in respect to TSH
    Their abundance shuts it off
  22. Primary hypothyroidism
    • There is a defect in the Thyroid for making T3 and T4
    • TSH and TRH are high as a result, trying to stimulate the thyroid to synthesize them

    Could be a result of Hashimotos Thyroiditis or an iodine deficiency
  23. What is secondary hypothyroidism affecting
    • Though the hypothalamus is releasing lots of TRH, the Anterior pituitary is damaged not making TSH and the thyroid isn't releasing much T3 and T4
    • Could be a cause of a tumor or radiation damage to the pituitary
  24. Primary Hyperthyroidism
    • The thyroid is over producing T3 an T4
    • Could be caused by a secretory tumor or Graves disease
    • (TRH and TSH are low)
  25. Secondary Hyperthyroidism
    • The anterior pituitary is pumping out lots of TSH causing the thyroid to pump out lots of T3 and T4
    • Could be caused by a tumor in the Anterior Pituitary
    • (TRH is low)
  26. Tertiary hypothyroidism
    Damage to the hypothalamus causing it to not release TRH
  27. In Graves disease, what is the difference in the effect of the antibodies in comparison to TSH
    The antibodies can trigger the release of Thyroid hormones for up to 12 hours where as TSH only triggers for an hour
  28. Is Goiter seen in hypo or hyper thyroidism
  29. What is one of the only systematic decreases in hyperthyroidism
    Serum cholesterol
  30. Levothyroxine
    • Replacement therapy in hypothyroid patients
    • Once a day dose
  31. What is the MOA of Levothyroxine (T4)
    Binds to, and circulates with Thyroxine- Binding globulin (TBG) allowing normal regulatory target tissue processes to generate appropriate T3
  32. For long term thyroid hormone replacement, what is the drug of choice
    Levothyroxine (T4)
  33. How are Levothyroxine (T4) and Triiodothyronine (T3) administered
    • Orally
    • IV administration in Myxedema coma
  34. Antithyroid drugs have what different actions
    • Inhibit Iodine uptake
    • Inhibit thyroid hormone synthesis
    • Inhibit thyroid hormone release from thyroid
  35. Radioiodine (I131)
    • Way to medically destroy thyroid tissue in treatment for thyrotoxicosis
    • Should not be taken if pregnant or lactating
  36. 123Iodine
    Used to measure iodine uptake and also for thyroid imaging
  37. Potassium iodide
    • Inhibits hormone release
    • Inhibits Organification
    • Decrease the size and vascularity of the hyperplastic gland
    • Not effective after 14 days
  38. Propylthiouracil (Thioamide)
    • Inhibits hormone synthesis
    • Inhibits organification
    • Used for mild thyrotoxicosis
    • Takes 4 weeks to start working
  39. What is the side affect of Propylthiouracil
    Agranulocytosis (low WBC)
  40. Why is Propranalol used for hyperthyroidism
    • It is a beta blocker that works on the tachycardia, tremors, and sweating (symptoms hyperthyroidism)
    • Inhibits conversion of T4-T3 (deiodination)
  41. Organification
    Oxidation of iodide by peroxide, and then binding to tyrosine residues within the thyroglobulin molecule
  42. What drugs inhibit deiodination
    • High dose Propylthiouracil
    • Corticosteroids
    • Beta blockers
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Thyroid S2M1
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