Stressors

Stress is normal and natural. It is the bodies physical and mental response to an event that makes you feel primordially threatened. We are designed to feel stress to benefit us. It helps us stay focused, motivated, and alert and can help save your life in emergency situations. Stress is kind of like our body and mind motivating itself to work hard and stay focused. Too much stress can be harmful, though. Your body can begin responding to an overload of stress in way that impacts health in a negative way.

Stressors are chemical or biological agents, environmental conditions, external stimuli, or events that induce stress on an organism. An infinitely wide range of things can be considered stressors depending on the organism and it's circumstances. When an organism becomes stressed, many things begin to happen within the body, including chemical, mental, physical responses.

Within the physical body, stressors can produce mechanical stresses on pretty much anything and everything, including the skin, bones, ligaments, tendons, muscles, and nerves. Tissue failure can occur in extreme cases and chronic pain in less severe cases. Metabolism often slows, leading to decreased tissue repair. The less time the body has to recover between stressors, the more likely the body is to have physical symptoms.

Mental health and function is also affected. Stressors can cause stimulation of the hypothalamus, which causes the pituitary gland and adrenal cortex to secrete various stress hormones, which then travel through the blood stream to the organs that are designed to respond to these specific hormones. The glands, heart, and intestines receive these hormones and use the information to process the well-known flight-or-fight response.

Drugs can also be considered stressors, and fall into the category of chemical stressors. Various drugs cause stress to different parts of the body, but in general, drugs stress the heart, brain, and nervous system.

http://en.wikipedia.org/wiki/Stressor

http://www.helpguide.org/mental/stress_signs.htm