Stressor

A stressor is a chemical or biological agent, environmental condition, external stimulus or an event that causes stress to an organism.

An event that triggers the stress response may include:
 * environmental stressors (elevated sound levels, over-illumination, overcrowding)
 * daily stress events (e.g. traffic, lost keys, quality and quantity of physical activity)
 * life changes (e.g. divorce, bereavement)
 * workplace stressors (e.g. high job demand v. low job control, repeated or sustained exertions, forceful exertions, extreme postures)
 * chemical stressors (e.g. tobacco, alcohol, drugs)
 * social stressor (e.g., societal and family demands)

Stressors have physical, chemical and mental responses inside of the body. Physical stressor produce mechanical stresses on skin, bones, ligaments, tendons, muscles and nerves that cause tissue deformation and in extreme cases tissue failure. Chemical stresses also produce biomechanical responses associated with metabolism and tissue repair. Physical stressors may produce pain and impair work performance. Chronic pain and impairment requiring medical attention may result from extreme physical stressor or if there is not sufficient recovery time between successive exposures.

Stressors may also affect mental function and performance. One possible mechanism involves stimulation of the hypothalamus, crf (conticotrophin release factor) -> pituitary gland releases “acth” (adrenocorticotropic hormone) ->adrenal cortex secretes various stress hormones (e.g. cortisol) ->stress hormones (30 varieties) travel in the blood stream to relevant organs e.g. glands, heart, intestines. ->flight-or-fight response. Between this flow there is an alternate path that can be taken after the stressor is transferred to the hypothalamus, which leads to the sympathetic nervous system. After which, the adrenal medulla secretes epinephrine. Mental and social stressors may affect behavior and how individuals respond to physical and chemical stressors.