The response to any stress situation is characterized by a predictable sequence of mind and body events. Broadly speaking, stress triggers the release of chemical messengers, primarily adrenaline, into the blood stream. These messengers activate the sympathetic nervous system and the endocrine (hormone) system. These 2 systems work together and trigger four mind-body changes to prepare the person for – fight or flight:
- the redirection of the blood to the brain and large-muscle group and away from the skin, internal organs and extremities.
- Increase alertness by way of improved vision, hearing, and other sensory processes through the activation of the brainstem (ancient brain)
- The release of glucose (blood sugar) and fatty acids into the blood stream to sustain the body during the stressful event
- Depression of the immune system, as well as restorative and emergent process (such as digestion)
In some cases, the stress response could be very functional; it need not be inherently bad or defensive.