Butterflies in the stomach is the physical sensation in humans of a "fluttery" feeling in the stomach, caused by a reduction of blood flow to the organ. This is as a result of the release of adrenaline and norepinephrine in the fight-or-flight response, which causes increased heart rate and blood pressure, consequently sending more blood to the muscles.
Physiology
When the brain perceives a stressful or emotionally significant situation, the sympathetic nervous system activates the fight-or-flight response, prompting the adrenal glands to release adrenaline and cortisol into the bloodstream. These hormones increase heart rate and redirect blood away from the digestive system toward the muscles and heart, causing the blood vessels surrounding the stomach and intestines to constrict. The idiom has been in widespread use for over a century to describe the unsettling sensation associated with a stressful or thrilling situation.
It can also be a symptom of social anxiety disorder. This feeling is usually experienced before doing something important or stressful.
See also
- Anxiety