Final answer:
In the long loop negative feedback regulation of thyroid hormone (TH), TH would have an inhibitory action at the level of the hypothalamus and pituitary gland.
Step-by-step explanation:
In the long loop negative feedback regulation of thyroid hormone (TH), TH would have an inhibitory action at the level of the hypothalamus and pituitary gland.
When the levels of thyroid hormones in the blood fall too low, the hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to release thyroid-stimulating hormone (TSH).
TSH then acts on the thyroid gland to stimulate the synthesis and release of thyroid hormones (T3 and T4) into the blood. Once the blood levels of thyroid hormones reach a certain threshold, they exert an inhibitory action on the hypothalamus and pituitary gland, reducing the release of TRH and TSH, respectively.