Epinephrine, or adrenaline, is a hormone released by the adrenal glands as part of a “fight or flight” response. Its function is to prepare the body to flee or fight back. As such, it must affect a wide range of bodily tissues, including the muscles, circulatory system, and lungs.
The adrenal gland receives input from the nervous system, which stimulates it to release epinephrine into the bloodstream. Released in times of stress, this hormone can lead to feelings of alertness or an energetic state as it prepares the body for action. Some of the effects include increased blood sugar levels and dilated air passages.
Epinephrine also functions as a medication administered for a range of health conditions, particularly anaphylaxis, a severe allergic reaction. Epinephrine, the only immediate treatment for anaphylaxis, is also used to treat cardiac arrest, among other acute conditions. When administered to treat anaphylaxis, epinephrine functions to reduce symptoms by increasing heart rate, opening airways, and reducing swelling. These are the same effects caused by epinephrine released naturally by the body.
In either case, epinephrine functions by binding to the adrenergic receptors. These receptors, found on a variety of cell types within the body, enable the epinephrine to have a wide range of resulting effects. For example, when epinephrine binds to alpha receptors found on the walls of blood vessels, it functions to constrict the vessels, increasing blood pressure. Meanwhile, when it binds to the beta receptors in the lungs, epinephrine causes airways in the lungs to relax.