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.
Update Date 12/9/2012
Updated by: Glenn Gandelman, MD, MPH, FACC Assistant Clinical Professor of Medicine at New York Medical College; Private Practice specializing in Cardiovascular Disease in Greenwich, CT. Review provided by VeriMed Healthcare Network.