Which of the following hormones is a key player in regulating metabolism?

The hormone that plays a key role in regulating metabolism is insulin. Insulin is produced by the pancreas and is vital for the regulation of glucose levels in the bloodstream. It facilitates the uptake of glucose by cells, particularly in muscle and adipose tissue, allowing the cells to use glucose as an energy source or store it as glycogen. This regulation of glucose is essential for maintaining metabolic equilibrium.

Insulin also promotes the storage of fats and proteins, impacting not only energy metabolism but also the metabolism of lipids and proteins. Its influence on carbohydrate metabolism makes it a central player in overall metabolic processes within the body.

Cortisol, while important in stress response and having metabolic effects, primarily increases blood sugar levels and is involved in the body's response to stress rather than acting as a direct regulator of metabolism in the way insulin does. Growth hormone influences growth and has metabolic actions, particularly in promoting protein synthesis and fat breakdown, but its primary role isn't centralized in metabolic regulation. Thyroid-stimulating hormone (TSH) regulates the thyroid gland's production of thyroid hormones, which are critical for metabolic rate but is not directly involved in the immediate regulation of metabolic processes as insulin is.