Final answer:
Thyroid hormone secretion is regulated through a negative feedback system where increasing levels of T3 and T4 suppress the secretion of TSH from the anterior pituitary, which in turn reduces the stimulation of the thyroid gland.
Step-by-step explanation:
Regulation of Thyroid Hormone Secretion
The secretion of thyroid hormones is regulated by a negative feedback mechanism involving the hypothalamus, the anterior pituitary gland, and the thyroid gland. When thyroid hormone levels in the blood are low, the hypothalamus secretes thyrotropin-releasing hormone (TRH). TRH then stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH). TSH prompts the thyroid gland to secrete thyroxine (T4) and triiodothyronine (T3). As the levels of T3 and T4 rise in the bloodstream, they exert negative feedback on the anterior pituitary and hypothalamus, thereby reducing the secretion of TSH and TRH, which in turn leads to reduced secretion of T3 and T4.
Answering the student's question, the regulation of thyroid hormones is primarily controlled through b) Suppression of the anterior pituitary by circulating thyroid hormones.