Flight-or-Fight Response

The flight-or-fight response is a finely tuned, automatic response system for coping with fear, danger, or threat. It is regulated by the Sympathetic Nervous Division of the Autonomic Nervous System.

When the Flight-or-Fight response is activated the endocrine system releases the stress hormones cortisol and the catecholamines, adrenalin and nor-adrenalin.


Suppress digestion and reproduction, increases glucose utilization, and, interestingly, improves learning and memory.


The catecholamines, epinephrine and nor-epinephrine, increases glucose utilization, increases cardiovascular tone, and suppresses digestion.

Body Changes

When the flight-or-fight response is activated, here are a few of the body changes that take place:

Cardiovascular System

  • blood is channeled to the skeletal and muscular system
  • heart beat rate increases
  • blood volume and blood pressure increases


Opiod output increases. These include the neuropeptides, endorphins, enkephalins, which increase analgesia. That is they decrease sensitivity to pain.

Muscular system

There are changes in muscle tone and strength, especially the arms and legs.


Alertness increases.

Immune System

The immune system is suppressed. It takes a lot of energy for the body to maintain the highly complex immune system. So it temporarily turns it down.

Metabolic Rate

Increased metabolic rate for energy production.

Kidneys (Urinary System)

Urine output is decreased.

Flight-or-fight and stress

The prolonged activation of the flight-or-fight response leads to stress with its many negative consequences.



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