Your adrenal glands release adrenaline into your bloodstream faster than you can blink.

The adrenal glands are part of the endocrine system and sit directly above the kidneys. When the brain perceives a threat, the hypothalamus sends a signal through the sympathetic nervous system to the adrenal medulla. This pathway is incredibly fast because it uses direct nerve impulses rather than hormonal signals to initiate the release.Research shows that a human blink takes about 300 to 400 milliseconds to complete. In contrast, the adrenal glands can begin secreting epinephrine (adrenaline) into the bloodstream in under 200 milliseconds. This speed is vital for survival, allowing the body to react to physical threats before the conscious mind has fully processed the situation.Once released, adrenaline binds to adrenergic receptors throughout the body. This triggers the liver to break down glycogen into glucose for immediate energy, dilates the airways to increase oxygen intake, and redirects blood flow away from the digestive system toward large muscle groups.Physiologist Walter Bradford Cannon first described this biological mechanism in 1915 at Harvard Medical School, establishing the "fight-or-flight" response as a fundamental physiological reaction. Modern studies using high-speed imaging and blood analysis confirm that these glands are among the most responsive tissues in the human body.