Biology
Animals exposed to distressing events over which they have no control respond by releasing of corticosteroids. These, if prolonged, lead to structural changes in their brains. Changes happen to neurons and their synapses in the hippocampus and medial prefrontal cortex. These produce impairments in working memory and spatial memory, as well as increased aggression.
Linked to impairment of the medial prefrontal cortex are deficits in the part of the striatum with which it is linked. This can bias decision-making strategies, as affected individuals shift from flexible behavior to one dominated by habit. Changes also occur to dopaminergic activity in the prefrontal cortex.
Stress has a role in humans as a method of reacting to difficult and possibly dangerous situations. The "fight or flight" response when one perceives a threat helps the body exert energy to fight or run away to live another day. This response is noticeable when the adrenal glands release epinephrine, causing the blood vessels to constrict and heart rate to increase. In addition, cortisol is another hormone that is released under stress and its purpose is to raise the glucose level in the blood. Glucose is the main energy source for human cells and its increase during time of stress is for the purpose of having energy readily available for over active cells.
The release of these hormones is intended to be temporary. If someone is under stress for long periods of time they may have adverse health effects later on, such as hypertension and increased risk of cardiovascular disease.
Different factors may prolong this "fight or flight" reaction in the body. Chronic stress can be rooted in prolonged psychological stressors. For example, some studies have looked at the health effects of social discrimination in African Americans. This demographic has markedly higher hypertension levels that are attributed to higher levels of perceived social discrimination. This phenomenon has been coined John Henryism by sociologist James Sherman.
Read more about this topic: Chronic Stress
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