Biological Systems MCAT Practice Exam

Which substance is primarily released by the adrenal medulla?

1. Cortisol

2. Aldosterone

3. Epinephrine

4. Insulin

The correct answer is: Epinephrine

The primary substance released by the adrenal medulla is epinephrine, also known as adrenaline. The adrenal medulla is part of the adrenal glands, which are located on top of the kidneys. It is responsible for producing catecholamines, which are crucial for the body's fight-or-flight response during stressful situations. Epinephrine plays a vital role in the body’s acute stress reaction by increasing heart rate, blood pressure, and glucose levels, thereby preparing the body for rapid action. This hormone enhances energy availability and increases oxygen delivery to muscles, facilitating a quick response to emergencies. In contrast, cortisol and aldosterone are hormones produced by the adrenal cortex, not the medulla. Cortisol is a glucocorticoid that helps regulate metabolism and the immune response, while aldosterone is a mineralocorticoid that regulates sodium and water balance in the body. Insulin, on the other hand, is produced by the pancreas, and its primary role is to regulate blood glucose levels. Thus, the release of epinephrine from the adrenal medulla is significant in managing immediate physiological responses to stress.