Which of the following substances is NOT primarily secreted by the adrenal cortex?

The adrenal cortex is primarily responsible for the secretion of steroid hormones, which include cortisol (a glucocorticoid), aldosterone (a mineralocorticoid), and androgens. Insulin, on the other hand, is produced by the pancreas, specifically by the beta cells in the islets of Langerhans. This hormone plays a critical role in regulating blood glucose levels but is not involved in adrenal function.

Adrenaline (also known as epinephrine) and norepinephrine (or noradrenaline) are catecholamines that are primarily secreted by the adrenal medulla, the inner part of the adrenal glands, rather than the cortex. In contrast, cortisol is indeed a hormone secreted by the adrenal cortex, emphasizing the cortex's role in producing stress-related hormones and maintaining metabolic functions.

Thus, choosing insulin highlights the distinction between the hormonal functions of the pancreas and the adrenal cortex, illustrating why it is the correct answer.