Epinephrine and norepinephrine are the hormones underlying the body’s “fight or flight” response, or the changes that occur to a person's physiological state when he or she deals with stressful situations. These stressful situations can include life or death scenarios, like running from a predator, or the more mundane instances of stress most people experience, like intense feelings of anger, fear, or anxiety.
These hormones tend to work in tandem, and typically, when one is released, so is the other. When they reach the bloodstream, they cause increased heart rate, elevated blood pressure, deep rapid breathing, and rapid sugar metabolism to allow for bursts of strength in the skeletal muscles. They also divert resources away from other body systems, like the digestive tract, in order to maximize efficiency in dealing with the stress of the moment before returning to rest and relaxation.
What are the differences between epinephrine and norepinephrine?
Chemically, epinephrine and norepinephrine are nearly identical. The only molecular difference between them is that a methyl group is attached to the main structure of the molecule on epinephrine, whereas a hydrogen atom is in the same spot on norepinephrine.
Both hormones are produced in the medulla of the adrenal glands located above the kidneys. However, a key difference is that norepinephrine is synthesized from dopamine, a neurotransmitter. As such, it can serve as an additional neurotransmitter when the fight or flight response is activated.
Functionally, this means the largest difference between the two is that norepinephrine is able to function as a psychoactive stimulant in the brain, whereas epinephrine acts only as a hormone on cells in the body. While both chemicals contribute to increased heart rate, elevated blood pressure, deep breathing, and sensation of a “rush” experienced while in a dangerous situation, it is norepinephrine that is responsible for the sudden cognitive alertness and intense awareness of surroundings during stressful events.
How do epinephrine and norepinephrine affect the body?
Physiologically, both chemicals prepare the body to spring into action, allowing for sudden bursts of strength. Epinephrine relaxes the muscle surrounding bronchial tubes to increase oxygen intake even as it constricts blood vessels to speed up blood flow, which is why it is used to control allergic reactions which tend to constrict the airway and lower blood pressure.
It also begins breaking down large amounts of glycogen and other energy stores into glucose for short term use. Norepinephrine then redirects these resources to skeletal muscles, which is why some people experience greater physical strength than they ever have before when dealing with a threat.
