Unlike steroid hormones, thyroid hormones (T3 and T4) can be stored after synthesis. This is due to the fact that
a. thyroid hormones are not membrane-permeant molecules.
b. thyroid hormones are protein hormones, and are stored in vesicles until an elevation in intracellular calcium stimulates their release.
c. thyroid hormones are sequestered in colloid, surrounded by a wall of follicular cells, and that presents too much of a barrier for the hormones to pass through.
d. thyroid hormones remain attached to a larger protein molecule until the thyroid is stimulated to secrete them, at which point they are cleaved from the protein and diffuse from the cell into the circulation.
e. None of the above is correct.
D
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