A hormone, also called epinephrine, released by the adrenal glands in response to signals from the sympathetic autonomic nervous system. These signals are triggered by stress, exercise, or by an emotion such as fear. Adrenaline increases the speed and force of the heartbeat. It widens the airways to improve breathing and narrows blood vessels in the skin and intestine so that an increased flow of blood reaches the muscles. Synthetic adrenaline is sometimes given by injection as an emergency treatment for cardiac arrest or anaphylactic shock. Adrenaline eye drops may be used to treat glaucoma, but regular use can cause a burning pain in the eye.


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