During periods of stress, such as preparing to run in a race, the brain signals the adrenal glands to produce epinephrine or "adrenaline". Epinephrine increases the rate in which the heart beats. The increased cardiac output supplies more oxygen to the muscles, putting the body in a heightened state to react. As a longer term response to stress, cortisol is secreted by the adrenal glands, promoting the release of energy.
Review Date 5/10/2019
Updated by: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.