Research1 has shown when an individual appraises a situation as being stressful, the adrenal medulla releases the hormone adrenaline, which prepares the body for a fight or flight response. This increases heart, sweating, blood pressure, and breathing rates. The hypothalamus, which is a brain structure associated with emotional reactions, such as fear responds to stress by activating the pituitary gland, which in turn secretes adrenocorticotropic hormone (ACTH) that activates the adrenal glands to release the hormone corticosteroid. Cortisol helps the body to maintain steady supplies of blood sugar.
When the stress response (flight/fight response) is activated. It is important to get it back to its baseline. Learning to relax can play a tremendous difference in alleviating stress. This can be achieved by activating the parasympathetic nervous system (PNS) of the autonomic nervous system (ANS) to elicit what Dr. Benson2 termed the relaxation response, which is a “physical state of deep rest that changes the physical and emotional responses to stress.” The relaxation response works in the opposite way of the fight-or-flight response. It lowers the stress hormone levels and lowers blood pressure.
1Gunnar, M., & Quevedo, K. (2007). The neurobiology of stress and development. Annual Review of Psychology, 58, 145-173.
2Benson, H., Kotch, J. B., Crassweller, K. D., & Greenwood, M. M. (1977). Historical and clinical considerations of the relaxation response. American Scientist, 65(4), 441-445.