The Role of Hormones and Nerves:

Throughout your body, all processes are precisely and automatically regulated by hormones and nerve activity. It is done so without conscious effort. The central nervous system acts a control unit. It evaluated all activities both inside and outside your body to monitor and adjust to changing conditions.
The stress response illustrates how the entire body reacts to anything perceived as a threat to your stability or equilibrium.
Both physical and psychological stressors elicit the body's stress response. Major physical stressors include, surgery, burns, and infections. Other major physical stressors include, an extreme hot or humid climate, toxic compounds, radiation, and pollution.
Also, chronic "little stresses" or hidden day-to-day issues can lead to real physical ailments.
Good examples are:
1. Family conflicts;
2."I hate my job";
3. Lack of time, or lack of organization;
4. Too much responsibility;
5. "No one understands why I'm stressed";
6. Rush hour traffic.

And then there are major life changes such as:
1. Death or loss of a loved one;
2. Serious illness or accident;
3. Divorce or separation;
4. Death of a close relative;
5. Getting fired or laid off from work;
6. Marriage;
7. Major personal property loss (fire, theft, vandalism);
8. New household member.

Stress response begins when your brain perceives a threat to your equilibrium. The sight of a car hurling toward you; the terror that an enemy is concealed around a nearby corner, the excitement of planning for a party, the feeling of pain; a snarled traffic jam or any other such disturbance perceived by the brain serves as an alarm signal.