Which hormone, produced by the thyroid gland, plays a key role in regulating metabolism?

Thyroxine, also known as T4, is produced by the thyroid gland and is crucial for regulating metabolism in the body. It influences various metabolic processes, including the rate at which the body utilizes energy, synthesizes proteins, and responds to other hormones. Thyroxine increases the metabolic rate of almost every cell in the body, thereby playing a vital role in maintaining energy levels, growth, and development.

Insulin is primarily involved in glucose metabolism and regulating blood sugar levels, but it does not directly influence overall metabolic processes like thyroxine does. Cortisol, produced by the adrenal glands, is associated with stress response and also has effects on glucose metabolism, but it does not play a significant role in broad metabolic regulation like thyroxine. Testosterone is primarily a sex hormone that impacts muscle mass and fat distribution, but it does not have a direct role in regulating metabolism across various systems in the body.

Thus, thyroxine stands out as the key hormone produced by the thyroid gland responsible for the comprehensive regulation of metabolic activities.