CLINICAL CASES
415
[45.2] In individuals with iodide deficiency, which one of the following is
most likely?
A. TSH levels are elevated and directly stimulate growth of the thy-
roid gland to a very large size.
B. Mono- and diiodinated thyroid hormone molecules are produced,
and elevated levels of these derivatives compensate for the
deficiency.
C. TSH levels are decreased, relieving their inhibitory effects on thy-
roid cell proliferation.
D. Synthesis of the Na+, K+-ATPase is increased.
E. Tissue utilization of oxygen is increased.
[45.3] In women taking thyroid hormone replacement pills, the dosage must
be adjusted if they start taking birth control pills. Which one of the fol-
lowing best explains this situation?
A. Thyroid hormones block the action of estrogens, so the estrogen
dose must be increased.
B. Estrogens block the action of thyroid hormones, so the dose of thy-
roid hormone must be increased.
C. Progestins block the action of thyroid hormone, so the dose of thy-
roid hormone must be increased.
D. Thyroid hormones stimulate the action of estrogens, so the estro-
gen dose must be decreased.
E. Estrogens stimulate the action of thyroid hormone, so the dose of
thyroid hormone must be decreased.
A nsw ers
[45.1]
C. The patient exhibits symptoms of hypothyroidism including goi-
ter, yet thyroid hormone levels are elevated. This pattern can only be
explained by resistance of target cells to thyroid hormone, for exam-
ple, a mutation of the receptor decreasing its binding affinity for hor-
mone. Iodide deficiency would lead to goiter but not increased
hormone levels.
[45.2]
A. Elevation of TSH is the mechanism for goiter formation.
Decreased thyroid hormone levels reduce feedback inhibition of TSH
secretion by the pituitary. TSH secretion is therefore increased. TSH
acts as a growth factor for the thyroid gland, increasing its mass and
therefore its capacity to synthesize thyroid hormones.
[45.3]
B. Estrogens partially block the action of thyroid hormones, making
them less effective.
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