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