When I am stressed, I become alert and I experience a faster heartbeat and breathing than usual. There are also times that I have a headache caused by situations that makes me feel anxious. Now that I've deepen my learning about the endocrine system, I've learned that all these clinical manifestations occur as part of my stress response.
There are two kinds of stress: eustress (helpful) and distress (harmful). Stressor is defined as any stimulus that produces a stress response.
Stress response or general adaptation syndrome (GAS), which are mainly controlled by the hypothalamus, helps us cope in emergency situations or with things that worry us. It occurs in three stages: (1) an initial fight-or-flight response, (2) a slower resistance reaction, and eventually (3) exhaustion.
The Fight-or-Flight response
This stage is initiated by nerve impulses from the hypothalamus to the sympathetic division of the autonomic nervous system (ANS). It mobilizes the body’s resources for immediate physical activity and brings huge amounts of glucose and oxygen to the organs that are most active in warding off danger. In fight-or-flight response, the brain must become highly alert, the skeletal muscles fighting off an attacker, and the heart which must work vigorously to pump enough blood to the brain and muscles. During this stage, nonessential body functions such as digestive, urinary, and reproductive activities are inhibited.
Resistance reaction
When the fight-or-flight response dissipates, the resistance stage takes over in helping the body fight a stressor. This longer-lasting response is initiated in large part by hypothalamic releasing hormones. It is the reason behind why our heart still pounds even after the removal of the stressor. If this stage is successful, our bodies return to normal. However, if the resistance stage fails to combat the stressor, our next resort is the state of exhaustion.
Exhaustion
If the body cannot sustain the resistance stage, it proceeds to exhaustion. This is caused by the prolonged exposure to high levels of cortisol and other hormones in the resistance reaction which leads to wasting of muscle, suppression of the immune system, ulceration of the gastrointestinal tract, and failure of pancreatic beta cells. Pathological alterations may also emerge as a result of resistance reactions that linger after the stressor has been removed.
Reference:
Tortora, G. & Derrickson, B. (2014). Principles of Anatomy and Physiology (14th ed.). New Jersey, NJ: Wiley