Thyroid Physiology

  1. Which cells of the thyroid produce thyroid hormones?
    Follicular cells (aka thyrocytes)
  2. Thyroid hormones are attached to ____ and stored in the extracellular fluid known as _____
    • Thyroglobulin
    • Colloid
  3. Which cells produce calcitonin?
    Parafollicular C cells
  4. What is the trace element required by thyroid hormone that is unique to them?
  5. Formation of thyroid hormone requiring presence of what substance in the colloid?
  6. How is iodide transported from the blood into thyrocytes?
    Sodium-iodide symporter moves iodide from blood into the thyrocyte
  7. Sodium-iodide symporter transport iodide _____ the concentration gradient.
    • Against
    • Needing energy from Na/K ATPase
  8. T/F: sodium-iodide symporter pumps both sodium and iodide from blood into the thyrocyte, but the sodium gets pumped out through Na/K ATPase in order to generate the energy required for the symporter
  9. How is iodide transported from the thyrocyte into the colloid?
    Cl-/ I- antiporter called pendrin
  10. What is pendrin?
    The Cl-/I- antiporter that transports iodide from the thyrocyte into the colloid in exchange of a Cl- from colloid into thyrocyte
  11. Dietary intake of 500 iodide, and the thyroid gland takes up ____ of it
    120 , 80 of it is used to produce T3 and T4
  12. T/F: body takes in more iodide than it excretes out
    False; body takes in 500 and excretes out 500 (480 through pee and 20 in stool)
  13. What is organificiation?
    Oxidizing iodide via peroxidase, first step
  14. What happens after iodide is oxidized?
    It combines with tyrosine within the thyroglobulin
  15. T/F: rT3 is most biologically active
    False; rT3 has no known biological activity; T3 is the most active
  16. T4, T3 and rT3 are all products of the coupling of two ________ derivatives
    • Iodinated tyrosine = MIT and DIT= monoiodotyrosine, diiodotyrosine
    • i.e. mono + di = T3, di + di = T4
  17. rT3 is formed by two ____ molecules with _____ iodine being removed from the inner benzyl ring of ____
    • DIT
    • One
    • T4
  18. The activity of Na/I pump is regulated by _____ levels, low level of it would ____ the pump
    • Iodide
    • Stimulate
  19. High levels of ___ inhibits organification and synthesis of thyroid hormone, this is the ______ effect
    • Iodide
    • Wolff-chaikoff
  20. What is the enzyme that recycles iodide and tyrosine?
    • Iodotyrosine Deiodinase
    • Congenital absence of this enzyme would have MIT and DIT appear in the urine and contribute to symptoms of iodine deficiency
  21. What are the plasma proteins that bind thyroid hormones to maintain a large poo of hormone ready for mobilization?
    • Albumin
    • Transthyretin
    • Thyroxine-binding globulin
  22. T/F: most of the T4 and T3 found in plasma are in free form
    False; they are mostly bound to thyroxine-binding globulin or albumin (T3), low amounts are in free form
  23. Human thyroid secretes mostly _____
    • T4
    • Most of the T3 and rT3 are formed from T4 deiodination in the tissues
  24. T/F: TSH is hydrophobic so it can diffuse through cell membrane and bind nuclear receptors
    False; TSH binds GPR and stimulate G alpha which raises cAMP and stimulates the synthesis of T4 and T3. T4 and T3 are hydrophobic so they can diffuse through cell membrane and bind intracellular receptors
  25. Increased TBG (thyroxine binding globulin) levels, such as in pregnancy, can _____ thyroid hormone secretion
  26. Thyroid hormones ____ metabolism, so would _____ glucose absorption, glycogenolysis, gluconeogenesis, lipolysis and protein synthesis and degradation
    • Increase
    • Increase metabolic pathways
  27. Thyroid hormones effect on CNS:
    • Maturation of CNS
    • (in hyperthyroidism, there is increased DTRs)
  28. In the nucleus, T3 interacts with the thyroid hormone receptor, which is bound as _____ with a ______ receptor
    • Heterodimer
    • Retinoid X
  29. T/F: patients with elevated or decreased concentrations of binding proteins, particularly TBG, are typically euthyroid
  30. When there is an increased in the concentration of TBG proteins in the plasma, what happens to the concentration of free thyroid hormones?
    Falls , but this is a temporary change because would then stimulate TSH production
  31. Conditions in which concentrations of thyroxine binding proteins increases:
    • Estrogens,
    • Methadone
    • Heroin,
    • Major tranquilizers,
    • Clofibrate
  32. Conditions in which concentrations of thyroxine binding protein decreases:
    • Glucocorticoids
    • Androgens
    • Danazol
    • Asparaginase
Card Set
Thyroid Physiology
Endo Exam 1