Question

The secretion of TSH is directly controlled by:
(i) TRH
(ii) $T_3$
(iii) $T_4$

• A. i and ii
• B. ii and iii
• C. i and iii
• D. i, ii, and iii

Answer 1

The correct option is D i, ii, and iii

TSH or thyroid stimulating hormone is secreted by the anterior pituitary. It stimulates the thyroid gland to secrete the thyroid hormones, triiodothyronine ($T_3$) and thyroxine ($T_4$).

The secretion of TSH itself is stimulated by TRH (thyrotropin-releasing hormone) secreted by the hypothalamus.

When the levels of $T_3$ and $T_4$ in blood get too high, the seretion of both TRH from the hypothalamus and TSH from the pituitary is inhibited.