Which hormone's primary function revolves around glucose metabolism in the human body?

Insulin plays a crucial role in glucose metabolism, making it the correct choice for this question. Its primary function is to regulate blood sugar levels by facilitating the uptake of glucose into cells, particularly in muscle and fat tissues. When you eat, the glucose level in your bloodstream rises, prompting the pancreas to release insulin. Insulin helps lower blood glucose levels by promoting the conversion of glucose into glycogen for storage in the liver and muscles and enabling cells to utilize glucose for energy.

In contrast, cortisol, while important for various metabolic functions, is more involved in the body's stress response and the regulation of metabolism of carbohydrates, proteins, and fats during times of stress, rather than specifically focusing on glucose metabolism. Estrogen and testosterone are hormones that primarily influence sexual development and reproductive functions, along with other roles in the body, but they do not directly regulate glucose metabolism to the extent that insulin does. Thus, the focus of insulin on glucose regulation makes it the essential hormone in this context.