Which hormone primarily influences metabolic rate and is secreted by the thyroid gland?

Thyroxine, also known as T4, is the hormone that primarily influences metabolic rate and is secreted by the thyroid gland. This hormone plays a crucial role in regulating the body's metabolism, which includes the speed at which the body converts food into energy. It affects the metabolic processes in almost every tissue in the body, elevating metabolism in cells and thereby influencing weight management, energy levels, and how the body uses carbohydrates, fats, and proteins.

Thyroxine does this by enhancing the overall energy expenditure of the body, increasing oxygen consumption, and stimulating protein synthesis. Its secretion is controlled by another hormone, Thyroid Stimulating Hormone (TSH), which is produced by the pituitary gland in response to thyrotropin-releasing hormone (TRH) from the hypothalamus.

In summary, the role of thyroxine is pivotal in maintaining metabolic balance, making it essential for growth, development, and general metabolic regulation.