Chronic stress is the response to emotional pressure suffered for a prolonged period of time in which an individual perceives they have little or no control. It involves an endocrine system response in which corticosteroids are released. While the immediate effects of stress hormones are beneficial in a particular short-term situation, long-term exposure to stress creates a high level of these hormones. This may lead to high blood pressure (and subsequently heart disease), damage to muscle tissue, inhibition of growth, suppression of the immune system, and damage to mental health.
Hans Selye (1907–1982), known as the "father of stress", is credited with first studying and identifying stress. He studied stress effects by subjecting lab mice to various physical, antigenic, and environmental stressors, including excessive exercise, starvation, and extreme temperatures. He determined that regardless of the type of stress, the mice exhibited similar physical effects, including thymus gland deterioration and the development of ulcers. Selye then developed his theory of general adaptive syndrome (GAS) in 1936, known today as "stress response". He concluded that humans exposed to prolonged stress could also experience hormonal system breakdown and subsequently develop conditions such as heart disease and elevated blood pressure. Selye considered these conditions to be "diseases of adaptation", or the effects of chronic stress caused by heightened hormonal and chemical levels. His research on acute and chronic stress responses introduced stress to the medical field.
Animals exposed to distressing events over which they have no control respond by releasing corticosteroids. The sympathetic branch of the nervous system is activated, also releasing epinephrine and norepinephrine.
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.
Different types of stressors, the timing (duration) of the stressors, and genetic inherited personal characteristics all influence the response of the hypothalamic–pituitary–adrenal axis to stressful situations. The hypothalamic–pituitary–thyroid axis and other endocrine axes are also involved in the stress response. Those with a wealthy background have a stronger response to stress than those in the lower strata.
Chronic stress causes the body to stay in a constant state of alertness, despite being in no danger. Prolonged chronic stress can lead to symptoms of skin problems, menstrual problems, anxiety, depression, social isolation, headache, abdominal pain or lack of sleep to back pain and difficulty concentrating. Other symptoms include panic attacks or a panic disorder. Chronic stress can increase an individual's risk for psychiatric disorders and some physical disorders, especially cardiovascular diseases.
Since chronic stress is due to a wide variety of environmental, nutritional, chemical, or pathological factors, a wide range of physiological systems can be damaged. Stress can cause such things as atrophy of muscles, push the body to store energy as fat, and keep blood sugar abnormally high. All of these are symptoms of diabetes. Overexposure to glucocorticoids can also cause hypertension (high blood pressure) and atherosclerosis (hardening of the arteries), which increases heart attack risk.
Chronic stress also reduces resistance of infection and inflammation, and might even cause the immune system to attack itself.
Regarding to effects on the brain, chronic stress inhibits neuron growth inside the hippocampus (which impairs memory). It also suppresses neural pathways active in cognition and decision-making, speeding up aging. Also, being chronically stressed worsens the damage caused by a stroke and can lead to sleep disorders. (Cortisol causes wakefulness, so overexposure causes stress-induced insomnia.)