Stress is the body's response to physical, mental, or emotional changes, situations, and forces. Stress can result from external factors (e.g., events, environment) or from internal factors (e.g., expectations, attitudes, feelings).
Stress often occurs in response to situations that are perceived as being difficult to handle or threatening. Common causes for stress (called stressors) include illness, injury, fear, and anxiety.
Each person reacts to stress differently. A healthy response to stress begins quickly; is appropriate in degree and in length; and can improve function, motivation, and productivity.
The body's response to stress is initiated and controlled by the central nervous system (brain and spinal cord). In response to a stressful situation, the brain first signals the inner portion of the adrenal gland (called the adrenal medulla) to release hormones (e.g., adrenaline [epinephrine], norepinephrine) that initiate the "flight-or-fight" response.
Next, the brain triggers the release of other hormones, such as cortisol, to sustain this response. Effects of these hormones include the following:
- Changes in digestion (caused by increased blood flow to the muscles and reduced blood flow to the gastrointestinal tract)
- Dilation of blood vessels
- Increased breathing (respiration) rate
- Increased heart rate and blood pressure (caused by increased blood flow to the brain)
- Increased blood sugar levels (to provide more energy)
Stress can be acute (short term), episodic (frequent), or chronic (long term). Acute stress, which is the most common type, results from events, pressures, and demands of the recent past and anticipated in the near future.
Acute stress that occurs frequently is called episodic stress. This type of stress is common in people whose lives are extremely busy or disorganized, and in those who tend to worry excessively.
Chronic stress is a serious condition. This type, which occurs when a stressful situation is prolonged and continuous, often causes severe physical and emotional symptoms.
Posttraumatic stress disorder (PTSD) is a psychiatric condition that can occur following life-threatening events, such as military action, natural disasters, terrorist incidents, serious accidents, and violent personal assaults (e.g., rape).
Following severe trauma, some stress reactions do not go away and even worsen over time. People who suffer from PTSD often relive the experience through nightmares and flashbacks, have difficulty sleeping, and feel detached or estranged. These symptoms are often severe and long lasting and they can significantly impair daily life.
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