Stress refers to a mentally or emotionally disruptive or disquieting influence or a state of tension or distress caused by such an influence. It can be a cause or a consequence. It can be defined as a negative emotional experience accompanied by predictable biochemical, physiological, cognitive and behavioural changes that are directed towards either altering the stressful event or accommodating its effects. This means that stress has a function.

There are three approaches to studying stress:

1. Stress as stimulus (i.e. stressor)
   This makes use of questionnaires and exposure paradigms (e.g. major life event checklist).
2. Stress as an evaluative process (i.e. stress perception)
   This includes evaluating a situation and deciding whether one can cope with the situation and deciding whether the situation is challenging.
3. Stress as response (i.e. stress response)
   This includes the response to stress such as depression or an increased heart rate.

The stress response follows stress perception which follows the stressor. Stress as an evaluative process includes two steps:

1. Primary appraisal
   This includes appraising the situation (e.g. harmful or not).
2. Secondary appraisal
   This includes assessing the resources and this determines the coping method (i.e. emotion-focused coping or problem-focused coping).

The two appraisals happen very quickly. Stressful situations consist of control (1) and social evaluation (2). The less control, the more stressful a situation is. The amount of perceived control determines how stressful a situation is.

The social self-preservation theory states that threats to the social self engender a specific set of psychological and physiological reactions. This includes feelings of low social worth (e.g. shame) and an increase in cortisol. These reactions can occur in situations of social evaluation. The stress responses are determined by social context.

Acute stress can be induced by having people do complex tasks (1) and have an amplifying component (e.g. social evaluation) (2). Acute stress lasts for 5 minutes to 2 hours. The reactivity hypothesis states that exaggerated cardiovascular responses to acute stress are a risk factor for the development of cardiovascular disease.

The fight-or-flight response includes the sympathetic branch of the autonomic nervous system (i.e. fast, first-wave response). It also includes the endocrine pathways of the HPA axis (i.e. slow, second-wave response). The SNS prepares the body for immediate action by stimulating the adrenal medulla to produce adrenaline and noradrenaline. The HPA axis activates the hypothalamus to release corticotrophin which sets other endocrine events in motion. This eventually leads to the release of cortisol. Increased cortisol in the blood leads to immune suppression (1), gluconeogenesis (2), fat metabolism (3), adrenalin production (4), more and better fear memory (5) and worse declarative memory (6).

The presence of cortisol in the bloodstream stops the hypothalamus from producing cortisol, meaning that the cortisol levels will naturally go back to baseline levels. However, after a prolonged period of stress, the HPA axis can become dysregulated and this can lead to chronically elevated levels of cortisol which has negative health effects. There are stronger physiological responses in novel (1), unpredictable (2) and uncontrollable situations (3). Attempting to obtain control in uncontrollable situations leads to more stress.

There is a two-wave defence response to stress. In the first wave of physiological responses, there are three systems that are relevant:

1. Parasympathetic nervous system
   This system is deactivated and makes use of acetylcholine as neurotransmitter.
2. Sympathetic-adreno-medullary (SAM) system
   This system is activated (e.g. increase in blood pressure). It releases adrenaline (i.e. hormone) and noradrenaline (i.e. neurotransmitter).
3. Hypothalamic-pituitary-adrenal axis (HPA-axis)
   This system is activated (e.g. increase in cortisol). It releases adrenocorticotrophic hormone (ACTH).

A substance can be both a hormone and a neurotransmitter. The way it is released determines whether it is a hormone or a neurotransmitter. A hormone can operate at a greater distance (1), has larger and sustained temporal effects (2) and can lead to systemic changes (3). It activates receptors on a distant cell whereas a neurotransmitter activates receptors on adjacent cells.

A lowered parasympathetic activity leads to a dry mouth (1), increased heart rate (2) and obstipation (3). The parasympathetic withdrawal is typically measured as heart rate variability. The more irregular the heart rate is, the more relaxed a person is. A regular and fast heart rate is associated with stress. There is parasympathetic activation with some stimuli (e.g. blood phobia; disgust; fainting).

Sympathetic activation leads to the fight or flight response. This leads to an increase in blood pressure (1), increase in heart rate (2), a blood redistribution (3), increased metabolism (4) and the level of lipids and glucose goes up (5).

However, the fight or flight response is not the only response to a stressor. The tend and befriend response refers to a response to a stressor where one tends to their offspring and seeks out others for safety and comfort. Oxytocin is at the basis of the affiliative response and in other affiliative behaviour. It is possible that the tend and befriend response to stressors could buffer against long-term negative health impacts through oxytocin.

The release of ACTH leads to an increase in cortisol. This is the second-wave of physiological response as it takes some time before cortisol starts to be released. The hypothalamus releases CRF which activates the anterior pituitary. This releases ACTH and this activates the adrenal cortex which releases cortisol. This leads to a biological response but is a short-lived response as a certain level of cortisol in the blood deactivates the system.

The response to stress depends on evaluating the demands of the situation (i.e. primary appraisal) (1), evaluating the resources and ability to cope (i.e. secondary appraisal) (2) and reappraisal (3). There is an association between stress and poor mental health.

Perceived stress predicts cardiovascular disease mortality. The function of the stress response is to restore homeostasis in the body. Homeostatic models define health as a state in which all physiological parameters operate within normal values. Allostasis defines health as a state of responsiveness and optimal predictive fluctuation to adapt to the demands of the environment.

Allostasis refers to maintaining physiological stability by adapting to demands (e.g. raise body temperature as a result of infection). Allostatic load refers to the wear and tear on the body after repeated allostatic responses.

Chronic stress refers to feelings of fatigue, lack of energy, irritability, demoralization and hostility. It is a risk factor for non-insulin-dependent diabetes. It can be exacerbated by a poor diet (1), using tobacco (2) and using alcohol (3). It can be reduced through exercise.

There are four types of allostatic load:

1. Frequent stress
2. Prolonged exposure to stress hormones as a result of a lacking adaptation to repeated stressors of the same type (e.g. public speaking remains stressful even after a long time).
3. Inability to shut off allostatic responses after stress is terminated
4. Compensatory increases in other systems as a result of inadequate responses in some allostatic systems (e.g. more cytokine secretion if cortisol secretion does not increase with stress)

The negative feedback loop of cortisol takes longer in elderly, which may be due to allostatic wear and tear over a lifetime. The glucocorticoid cascade hypothesis states that wear and tear of the hippocampal region leads to dysregulation of the HPA axis and cognitive impairment. Damage in the hippocampal region leads to impaired contextual memories.

The immune-enhancing effects of acute stress depend on adrenal secretion. Acute stress prepares the immune system for immediate threat and this response is enhanced if there is an established immunologic memory. This can be adaptive if the immunologic memory is of a tumour cell or maladaptive if the memory is an allergic reaction. The hypersensitivity response of the immune system is substantially inhibited rather than enhanced when allostatic load is increased. This leads to suppressed cellular immunity (e.g. leading to more severe forms of the common cold).

Resilience refers to people showing swift recovery from stressful events (1), having sustainability of purpose in the face of adversity (2) and growth from adversity (3). Positive emotions and positive emotional dispositions are important in resilience. People who appraise an event as challenging have smaller cortisol responses than people who appraise it as threatening.

Coping refers to any attempt to cope with a stressor. Emotion-focused coping refers to coping strategies focused on reducing distress. Problem-focused coping refers to coping strategies focused on dealing with the problem. Coping strategies that enable a person to feel in control increase positive emotions and decreases negative emotions.

Social relationships shape the way a person responds to a stressor. The presence of another person can reduce SNS and HPA axis activation but this depends on the nature of the relationship (1), culture (2) and gender (3).

A stress burnout consists of emotional exhaustion (1), depersonalization (2) and reduced personal accomplishment (3). Engagement refers to high levels of vigour, dedication and absorption. It is associated with good performance. A burnout can be conceptualized as a continuum between burnout and work engagement.

High levels of burnout are associated with poor job satisfaction (1), intention to change job (2), sick leave (3), younger age (4), being male (5) and use of addictive substances (6). The risk of burnout operates at individual level (i.e. lifestyle and coping) (1), environmental level (i.e. social support structures) (2) and organizational level (i.e. job design) (3). A burnout is more likely in a job that involves a high workload (1), a lack of control (2), insufficient rewards (3), an absence of fairness (4), value conflicts (5) and a poor sense of community (6).