Which hormone is secreted by the pituitary gland to regulate thyroid function?

The hormone that is secreted by the pituitary gland to regulate thyroid function is thyroid-stimulating hormone (TSH). TSH plays a critical role in the feedback loop that controls the production of thyroid hormones. When the levels of thyroid hormones (such as T3 and T4) in the bloodstream are low, the hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to secrete TSH. This, in turn, prompts the thyroid gland to produce and release more thyroid hormones, thereby regulating metabolism and other vital functions in the body.

In contrast, insulin is produced by the pancreas and regulates glucose metabolism, while growth hormone is also secreted by the pituitary gland but primarily affects growth and metabolism rather than directly influencing thyroid function. Cortisol, produced by the adrenal glands, is involved in the body's stress response and metabolism but does not regulate thyroid function. Thus, TSH is specifically and crucially involved in the regulation of the thyroid, making it the correct answer.