Which hormone is primarily secreted by the adrenal gland's outer layer?

The hormone primarily secreted by the adrenal gland's outer layer, known as the adrenal cortex, is cortisol. Cortisol plays a vital role in the body’s response to stress by regulating various processes, including metabolism, immune response, and blood pressure. Its secretion is controlled by the hypothalamus and pituitary gland through a negative feedback mechanism involving adrenocorticotropic hormone (ACTH).

Cortisol is often referred to as the "stress hormone" because its levels rise in response to stressors, helping to prepare the body to handle challenging situations by providing energy and modulating other bodily functions. This contrasts with the functions of the other hormones listed. For instance, insulin is produced by the pancreas, adrenaline is secreted by the adrenal medulla (the inner part of the adrenal gland), and thyroxine is produced by the thyroid gland, making these options unrelated to the adrenal cortex's primary secretions.