Question

Short / Long answer type questions.
A person with symptoms of hypothyroidism, for example, sluggishness and intolerance to cold, is found to have abnormally low plasma concentrations of $T_4$, $T_3$ and TSH. After an injection of TRH, the plasma concentrations of all three hormones increase. Where is the site of the defect leading to the hypothyroidism?

Answer 1

As after injecting TRH (thyrotropin-releasing hormone), the plasma concentration of all three hormones increases, this is a case of TRH deficiency. The site of the defect is hypothalamus as TRH is produced here.

Thyrotropin-releasing hormone deficiency is a condition in which the hypothalamus does not produce adequate amounts of thyrotropin-releasing hormone (TRH). After it is secreted by the hypothalamus, TRH acts on the pituitary gland to cause the release of a second hormone called thyroid stimulating hormone (TSH). TSH then acts at the thyroid gland where it causes the release of thyroid hormone. In this condition, a deficiency of TRH leads to a deficiency of thyroid hormone, which is known as hypothyroidism.