The Effects of Stress on You
How the “fight or flight” response affects your body
The “fight or flight” response is your body’s natural reaction to perceived danger or stress
The “fight or flight” response is your body’s natural reaction to perceived danger or stress, triggered by the autonomic nervous system, specifically the sympathetic branch. It’s an evolutionary survival mechanism designed to prepare you to either confront a threat or escape it. When activated, a cascade of physiological changes occurs, driven by the release of stress hormones like adrenaline (epinephrine) and cortisol from the adrenal glands. Here’s a breakdown of what happens to your body:
1 Heart Rate and Blood Pressure Increase: Adrenaline signals your heart to beat faster and harder, pumping more blood to your muscles and vital organs. Blood vessels constrict in less critical areas (like your skin or digestive system) and dilate in muscles, boosting oxygen delivery for immediate action.
2 Breathing Speeds Up: Your respiratory rate increases, and airways dilate, allowing more oxygen into your lungs. This fuels your muscles and brain, heightening alertness and physical readiness.
3 Energy Surge: The liver releases stored glucose into the bloodstream, providing a quick burst of energy. Fats may also break down to supply additional fuel, ensuring your body has the resources to act fast.
4 Heightened Senses: Your pupils dilate to improve vision, and your brain sharpens focus on the threat, tuning out irrelevant details. Hearing may become more acute as you scan for danger.
5 Muscle Tension: Blood flow prioritizes large muscle groups, making them tense and primed for action—whether that’s running away or fighting back.
6 Digestion Shuts Down: Non-essential systems like digestion slow or stop. Blood is rerouted from your stomach and intestines, which is why you might feel “butterflies” or nausea during acute stress.
7 Sweating: Your body activates sweat glands to cool itself in anticipation of physical exertion, even before you start moving.
8 Immune and Repair Systems Pause: Energy-intensive processes like immune response or tissue repair are temporarily suppressed to conserve resources for immediate survival.
These changes happen almost instantly and can last until the brain—via the amygdala and hypothalamus—senses the threat is gone. The parasympathetic nervous system then kicks in to reverse the effects, calming your heart rate, restoring digestion, and bringing you back to baseline.
In modern life, though, this response can fire up over non-physical stressors—like a work deadline or argument—leading to chronic stress if it’s triggered too often. Over time, that can wear on your body, raising risks for things like heart disease, anxiety, or digestive issues. But in the moment? It’s a brilliantly tuned system to keep you alive.