- The adrenal gland consists of two main parts: the adrenal cortex and the adrenal medulla.
- The adrenal medulla is responsible for the production and release of catecholamines, primarily epinephrine and to a lesser extent norepinephrine.
- These hormones are critical for the body's "fight or flight" response, helping to increase heart rate, blood pressure, and blood glucose levels during stressful situations.

- Epinephrine is the major hormone secreted by the adrenal medulla.
- Norepinephrine is also released but in smaller quantities compared to epinephrine.
- Hormones like aldosterone and cortisol are secreted by the adrenal cortex, not the medulla.

Therefore, the correct answer is epinephrine, as it is the primary hormone released by the adrenal medulla.

Reference: Ganong's Review of Medical Physiology, 26th Edition, Chapter 34: Adrenal Medulla and Catecholamines