Processes/Relationships

Question 1

what inhibits 5’-deiodinase and thus causes low T3?

Answer 1

Fasting, illness, Fetus, Glucocorticoids, catecholamines Drugs (PTU)

Question 2

percentage of T4 and T3 bound and free

Answer 2

T4- 99.97% bound, 0.03% free

T3-99.7% bound 0.3% free

Question 3

Thyroid binding globulin is increased by

Answer 3

Estrogens, pregnancy (stimulate the liver)

Question 4

thyroid binding globulin is decreased by

Answer 4

androgens, nephrotic syndrome

Question 5

deiodination D1 to T3 location

Answer 5

plasma membrane, released into circulation

Question 6

deiodination D2 to T3 location

Answer 6

within cell, moves to nucleus and can bind to thyroid hormone receptors to cause biological actions

Question 7

Hypothyroidism and muscle relaxation

Answer 7

slows the relaxation phase of deep tendon reflexes because slower return of calcium ions to SR and slower disengagement of actin and myosin

Question 8

metabolism of thyroid hormones

Answer 8

degradation occurs in the liver, T3 and T4 are inactivated by deamination, decarboxylation or conjugation, and excreted in the feces

Question 9

Actions of thyroid hormones

Answer 9

growth and development- facilitate protein synthesis in most cells especially in the brain, neuronal proliferation and myelination
Calorigenesis- increase BMR, oxygen consumption and heat production
cardiovascular-Increase HR, force of contractin and CO
Metabolic effects- stimulate the metabolism of cholestrol to bile acids (decrease cholestrol in the blood), enhance lipolytic actions of hormones on fat cells (increase free fatty acids in the blood), increase glucose concentrations in the blood

Question 10

peripheral deiodination occurs in?

Answer 10

liver and kidney

Question 11

Causes of decreased 24 hour Radioactive Iodine Uptake

Answer 11

hypothyroidism, ingestion of iodine containing substances (false negative), TSH deficiency states, ingestion of thyroid hormone

Question 12

causes of increased 24 hour Radioactive Iodine Uptake

Answer 12

iodine deficiency states (false positive), potent diuretics (increased renal clearance of iodine) (false positive), hyperthyroidism

Question 13

Indications for thyroid scintigraphy

Answer 13

eval of size and shape of thyroid
eval of distribution of activity
eval of function activity of dominant nodule
localization of ectopic thyroid tissue

Question 14

increased malignancy of thyroid nodule

Answer 14

cold nodules tend to be more malignant than hot nodules