Thyroid Agents

Question 1

What is the hypothalamic-pituitary-thyroid axis?

Answer 1

hypothalamus releases thyrotropin releasing hormone (TRH); signals anterior pituitary to release thyroid stimulating hormone (TSH); thyroid releases T3 and T4 (stimulatory to peripheral tissues & inhibitory to hypothalamus/pituitary for feedback inhibition)

Question 2

**actions of thyroid hormones

Answer 2

• -increase basal metabolic rate
• -increase HR and CO
• -stim carb metabolism
• -reduce insulin sensitivity
• -stim protein synthesis for growth & development

Question 3

what is needed to make thyroid hormones

Answer 3

iodide and protein w/ a lot of tyrosine residues

Question 4

What is the significance of perchlorate?

Answer 4

an environmental contaminate that causes hypothyroidism

Question 5

What is the significance of thyroid pyroxidase?

Answer 5

it is an enzyme that catalyzes the oxidation, iodination, and coupling rxns; target of PTU/MMI that inhibit thyroid function

Question 6

How do high levels of iodide affect the release of T3/T4?

Answer 6

paradoxically inhibits the release

Question 7

Which disorder has low TSH and high T3/T4?

Answer 7

Grave’s disease (hyperthyroidism)–antibodies that activate TSH receptor and stimulate thyroid to produce T3/T4; pit and hypothalamus are inhibited; goiter present

Question 8

symptoms of Grave’s disease

Answer 8

flushed, warm skin; weak muscles; tachycardia; increased metabolic rate & increase appetite; exophthalmos

Question 9

Why are PTU and MMI slow-acting?

Answer 9

colloid is full of thyroglobulin so you have to use up stores of thyroid hormones before the medication is effective

Question 10

What is the best treatment for hyperthyroidism?

Answer 10

subtotal thyroidectomy followed by replacement therapy to treat resulting hypothyroidism

Question 11

Which disorder has high TRH/TSH and low T3/T4?

Answer 11

hypothyroidism

Question 12

types of hypothyroidism

Answer 12

primary–Hashimoto’s, starts in thyroid gland
secondary–lack of TSH
tertiary–lack of TRH
also drug-induced, congenital, or d/t iodine deficiency

Question 13

What is the most common cause of hypothyroidism?

Answer 13

iodine deficiency

Question 14

symptoms of hypothyroidism

Answer 14

drowsiness, sluggishness, hypothermia, mental & growth retardation

Question 15

What is myxedema?

Answer 15

severe hypothyroidism; leads to coma if not treated

Question 16

T3 characteristics

Answer 16

active; has 3 iodines; *more potent; shorter half-life; activates thyroid hormone receptor; good oral absorption; expensive

Question 17

T4 characteristics

Answer 17

inactive; has 4 iodines; main product of thyroid; activates receptor or is converted to T3 or reverse T3 (main source of T3); longer half-life; less expensive so *preferred

Question 18

What is thyrotoxicosis?

Answer 18

nervousness, insomnia, increased basal metabolic rate; adverse rxn to thyroid hormone replacement therapy