How does cortisol function in the body?

Cortisol is a steroid hormone produced by the adrenal glands in response to stress and low blood glucose levels. Its primary functions include regulating metabolism and modulating the immune response. Cortisol plays a significant role in the body's ability to respond to stress by increasing glucose availability through gluconeogenesis, thereby providing the energy necessary for a 'fight or flight' response. Additionally, it helps in maintaining blood pressure and has anti-inflammatory effects, which are critical for managing immune system activity.

In contrast, the other options do not accurately capture cortisol's primary roles. Muscle growth is primarily stimulated by anabolic hormones like testosterone and growth hormone rather than cortisol, which can actually inhibit protein synthesis when present in excess. While cortisol can influence blood pressure indirectly, it does not directly control heart rate. Digestion is mainly managed by hormones such as gastrin and secretin, and cortisol does not play a central role in this process.