Stress is the condition that results when person-environment transactions lead the individual to perceive a discrepancy, whether real or not, between the demands of a situation and the resources of the person's biological, psychological or social systems.

In medical terms, stress is the disruption of homeostasis through physical or psychological stimuli. Stressful stimuli can be mental, physiological, anatomical or physical reactions.

History

The term 'stress' in this context was coined by Austro-Canadian endocrinologist Hans Selye, who defined the General Adaptation Syndrome or GAS paradigm in 1936.

It was gradually realized that such concepts as anxiety, antagonism, exhaustion, frustration, distress, despair, overwork, pre-menstrual tension, over-focusing, confusion, mourning, and fear could all come together in a general broad term, stress.

General Adaptation Syndrome

Hans Selye researched the effects of stress on rats and other animals by exposing them to unpleasant or harmful stimuli. He found that all animals showed a very similar series of reactions, broken into three stages. He describes this universal response to the stressors as the General Adaptation Syndrome, or GAS, in 1956. According to Selye's GAS there are three stages regarding the response to a stressor.  

• Alarm is the 1st stage. When the threat or stressor is identified or realised, the body's stress response is a state of alarm. During this stage adrenaline will be produced in order to bring about the fight-or-flight response. There is also some activation of the HPA axis, producing cortisol.
• Resistance is the 2nd stage. If the stressor persists, it becomes necessary to attempt some means of coping with the stress. Although the body begins to try to adapt to the strains or demands of the environment, the body cannot keep this up indefinitely, so its resources are gradually depleted.
• Exhaustion is the 3rd stage and final stage in the GAS model. During this stage it is believed that all the body's resources are eventually depleted and the body is unable to maintain normal function. The initial autonomic nervous system symptoms may reappear (sweating, raised heart rate etc.). If the body stays in this stage for an extended period of time (as in chronic stress conditions) long term damage may result as the capacity of glands, and the immune system resulting in diseases and illnesses such as ulcers, depression or even cardiovascular problems, along with other mental illnesses.

Neurochemistry and Physiology

In response to a stressor, corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP) are secreted into the hypophyseal portal system and activate neurons of the paraventricular nuclei (PVN) of the hypothalamus. The locus ceruleus and other noradrenergic cell groups of the medulla and pons, collectively known as the LC/NE system, also become active and use brain epinephrine to execute autonomic and neuroendocrine responses, serving as a global alarm system.

The autonomic nervous system provides the rapid response to stress commonly known as the fight-or-flight response, engaging the sympathetic nervous system and withdrawing the parasympathetic nervous system, thereby enacting cardiovascular, respiratory, gastrointestinal, renal, and endocrine changes.

The hypothalamic-pituitary-adrenal axis (HPA), a major part of the neuroendocrine system involving the interactions of the hypothalamus, the pituitary gland, and the adrenal glands, is also activated by release of CRH and AVP. This results in release of adrenocorticotropic hormone (ACTH) from the pituitary into the general bloodstream, which results in secretion of cortisol and other glucocorticoids from the adrenal cortex. These corticoids involve the whole body in the organism's response to stress and ultimately contribute to the termination of the response via inhibitory feedback.

Common Factors of Stress
Both negative and positive stressors can lead to stress. Some common categories and examples of stressors include:

• Adverse experiences during development (e.g. prenatal exposure to maternal stress], poor attachment histories], sexual abuse)
• Disease
• Environmental factors: Lack of control over environmental circumstances, such as food, housing, health, freedom, or mobility
• Lifestyle factors: heavy drinking, drug abuse, insufficient sleep
• Life events: birth and deaths, marriage, and divorce
• Personal relationships: conflict, deception 
• Physical Trauma
• Responsibilities: lack of money, unemployment
• Sensory: pain, bright light
• Work/study: exams, project deadlines, and group projects
• Social factors: struggles with specific individuals and social defeat can be potent sources of chronic stresses
• Work/study: exams, project deadlines, and group projects

Signs and Symptoms of Poorly Managed Stress

Excess stress can manifest itself in a variety of emotional, behavioral, and even physical symptoms, and the symptoms of stress vary enormously among different individuals.

Common somatic (physical) symptoms often reported by those experiencing excess stress include:

• emotional and behavorial symptoms (e.g., include nervousness, anxiety, changes in eating habits including overeating, loss of enthusiasm or energy, and mood changes)
• fatigue
• gastrointestinal disturbances,
• insomnia
• muscle tension
• tension headaches

It is also known that people under stress have a greater tendency to engage in unhealthy behaviors, such as excessive use or abuse of alcohol and drugs, cigarette smoking, and making poor nutritional choices, than their less-stressed counterparts. These unhealthy behaviors can further increase the severity of symptoms related to stress, often leading to a "vicious cycle" of symptoms and unhealthy behaviors.

Stress and Disease

There is significant evidence that stress can cause or worsen various diseases or conditions. These include:

• aging
• anxiety disorders
• asthma
• cancer
• cardiovascular disease
• depression
• gastrointestinal problems
• high blood pressure
• migraines and
• fluctuations of blood sugar in diabetics.

There also is scientific evidence showing that people experiencing psychological stress are more prone to develop colds and other infections than their less-stressed peers. Overwhelming psychological stress (such as the events of 9-11) can cause both temporary (transient) and long-lasting (chronic) symptoms of a serious psychiatric illness called post traumatic stress disorder (PTSD).

Managing Stress

Stress Management is the ability to maintain control when situations, people, and events make excessive demands.  Here are just a few examples of strategies that you can use to manage some of the causes of stress:

• Exercise Regularly. Exercise is one of the best physical stress-reduction techniques available. Exercise not only improves your health and reduces stress caused by unfitness, it also relaxes tense muscles and helps you to sleep. Exercise has a number of other positive benefits you may not be aware of: (1) It improves blood flow to your brain, bringing additional sugars and oxygen that may be needed when you are thinking intensely. (2)  By exercising, you speed the flow of blood through your brain, removing bio waste products caused by our body's internal actions faster.(3) Exercise can cause release of chemicals called endorphins into your blood stream. These give you a feeling of happiness and positively affect your overall sense of well-being. (4) There is also good evidence that physically fit people have less extreme physiological responses when under pressure than those who are not. This means that fit people are more able to handle the long- term effects of stress, without suffering ill health or burnout.
• Get enough sleep. Lack of rest can aggravate stress.
• Eat well. Avoid sugars, processed foods, too much caffeine.
  
• Don't sweat the small stuff. Try to prioritize a few truly important things and let the rest slide Learn how to best relax yourself. Determine if the issue is worth stressing about? is it something that you have no control over to change?
• Be mindful. You can selectively change the way you react, by first identifying stress in its early stages. Listen to your body and feel the early signs of stress (maybe you can feel tightness in your chest, or your response starts quickening). Take these early signs as an opportunity to implement relaxation techniques like counting to ten and deep breathing, and/or use it as an opportunity to remove yourself from the stressful situation before it gets worse. Bottom line: learn to recognize stress for what it is. Increase your body's feedback and make stress self-regulating.
• Avoid extreme reactions. Why hate when a little dislike will do? Why generate anxiety when you can be nervous? Why rage when anger will do the job? Overreacting can escalate stress.
• Walk Away. Remove yourself from the stressful situation. Many people bring stress upon themselves by not walking away.
  
• Reduce brain clutter. Practice clearing your mind of disturbing thoughts.A good technique is to write down what is bothering you, then file it away, and out of your mind.
  
• Take 5 for yourself. Give yourself a break if only for a few moments daily
• Try positive thinking. Positive thinking does help bring about positive change. Negative thoughts can affect the brains thinking and result on physio-chemical changes within your body...and thought process.
  
• Try not to personalize things. Maybe the other person or situation you are dealing with is really about them and their poor coping techniques and not about you.
• Meditate. Meditation and breathing exercises have been proven to be very effective in controlling stress. 
• Prioritize. If you feel overwhelmed with a "to do list" reduce the number of events going on in your life and you may reduce the circuit overload. Set a realistic list of items to do and start prioritizing.
• Avoid self-medication or escape. This includes alcohol and drugs, as well as dietary extremes such as excess sugar and caffeine..