Question

a 41-year-old woman reports that she is feeling shaky, sweaty, and anxious. she has recently begun to lose weight without any change in her diet or lifestyle. lab work reveals increased t3/t4, decreased trh, and decreased tsh. according to the lab results where do you suspect the problem occuring?
a) posterior pituitary
b) hypothalamus
c) anterior pituitary
d) thyroid

Explanation:

To determine the problem location, we analyze the hormone feedback loop. TRH (from hypothalamus) stimulates TSH (from anterior pituitary), which stimulates T3/T4 (from thyroid). Here, T3/T4 is high, but TRH and TSH are low. In a normal negative feedback, high T3/T4 would suppress TRH and TSH. However, if the thyroid is overproducing T3/T4 (e.g., in hyperthyroidism), it would cause low TRH (hypothalamus reduces TRH due to high T3/T4) and low TSH (anterior pituitary reduces TSH due to high T3/T4). If the problem were in the anterior pituitary or hypothalamus, TSH or TRH would not follow the negative feedback properly in this pattern. The posterior pituitary is not involved in this axis. So the thyroid is overproducing, leading to these lab results.

Answer:

d) Thyroid