Anatomy and Physiology Resource Site

9.7 - Stress Response

When the body is put under stress, the sympathetic division of the autonomic nervous system (the SNS) becomes active.

The SNS activates the secretion of hormones from the adrenal cortex, initiating the stress response.

The stress response has two main stages:

The alarm stage is short-term (seconds to hours)
The resistance stage is long-term (hours to days), but if it lasts too long it can cause the body to use all its energy reserves and start damaging organs and tissues.

Short-term stress response (alarm stage)

When the sympathetic system is activated, catecholamines are released. Catecholamines have immediate effects on the cardiovascular and respiratory systems and cell metabolism. Heart rate increases, the bronchioles dilate and glycogen is broken down to glucose to increase aerobic capacity. The rate of energy metabolism is also increased.

Long-term stress response (resistance stage)

When the sympathetic system is activated for a long period of time, glucocorticoids are released upon stimulation from ACTH.

Glucocorticoids stimulate water retention by the kidneys, increasing blood pressure. Protein and fats are also broken down and the immune system is suppressed.

All three of these effects can be potentially damaging to the body if the resistance stage lasts long enough. With a suppressed immune system and depleted energy reserves, the body becomes susceptible to infection and chronic fatigue.