Motivation and emotion/Book/2015/Stress physiology

Stress physiology:
What are the physiological components of stress?

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Overview

Figure 1. Modern day stress

Stress has become one of society's great obsessions. What was designed as an individual's survival mechanism is now generally considered as an inescapable burden of a modern lifestyle (Seaward, 2006). When using the term stress we often use it to describe the unpleasant feelings of anxiousness, irritability, sleeplessness and the general sense of being unable to cope (Dow, 2014). Furthermore, we associate stress with an array of health implications such as cardiovascular disease, high blood pressure and immunity dysfunction (Dimsdale, 2008; Steptoe & Kivimaki, 2012).

Society's fixation on the negative impact of stress and its psychological components has led to an oversimplification of a very complex physiological response. Dr Everly, co-founder of the International Critical Incident Stress Foundation stated that: “To understand the stress response, we must possess a fundamental knowledge not only of psychology but of physiology as well.”

In order to improve our ability to reduce the negative impacts of stress on health, it is important that the physiology basis of the stress response is well understood. A holistic approach to understanding stress allows for more effective treatment of stress-related symptoms. This chapter focuses on the physiological components of stress. In light of this, this chapter aims reveal the complex and multifaceted nature of stress. The chapter should assist the reader in understanding the various causes and types of stress, relevant theoretical frameworks of stress, the physiological components of stress and techniques on how to reduce the negative impact of stress.

Stress and Illness

If you don't think your anxiety, depression, sadness and stress impact your physical health, think again. All of these emotions trigger chemical reactions in your body, which can lead to inflammation and a weakened immune system. Learn how to cope, sweet friend. There will always be dark days -Kris Carr

The notion that emotions have little to no relation to illness was widely accepted in the early days of scientific medicine. Prior to the development of behavioural medicine, all illnesses were once thought to be solely caused by structural factors such as bacteria and viruses. In the present day, it is accepted that emotions can affect illness and patterns of recovery (Kalat, 2013). Interestingly, today's leading causes of death are now attributed to lifestyle diseases, in comparison to several decades ago when causes of death were dominated by infectious diseases (Seaward, 2006). Lifestyle diseases refers to diseases that are predominately treatable and preventable by altering behaviours. While the relationship between stress and health remains debated, a review of literature supports a positive relationship between stress and illness (Arnetz & Ekman, 2006; Kalat, 2013; Salleh, 2009; Seaward, 2006). According to recent research 70 to 80 percent of disease and illness is related to stress (Seaward, 2006). These figures may not be surprising in light of reports that 91% of Australian adults report feeling stressed in at least one aspect of their lives and furthermore of those affected 50% report to be extremely stressed in a specific part of their life (Lifeline, 2013).

Stress is believed to affect illness in two ways. One way is through changes in behaviours that lead to increased risk of lifestyle diseases (Herbert & Cohen, 1994). Changes in behaviour are influenced by negative psychological states associated with stress such as anxiety and depression (Bickerstaff, 2007). The other way is through direct physiological changes that influence the susceptibility to disease (Herbert & Cohen, 1994). This chapter will further explain the relationship between health and the physiological changes in the stress response.

Defining Stress

Stress like emotions, are brain activities that are both difficult to define and quantify (Kalat, 2013). The term stress at its most basic level can be defined as any change experienced by the individual. Expanding from this definition, a psychological perspective defines stress as the conditions in which the individual's coping abilities are exceeded by his or hers environment. A physiological perspective on the other hand defines stress as the rate of exhaustion on the body (Seaward, 2006).
According to Rice, contemporary scientific literature presents three distinct definitions of stress;

stress is any external stimulus that causes arousal and tension to the individual stress is an internal mental state of arousal and tension stress is a physical response to demanding and damaging intrusions (1992).

Taking into account of all definitions of stress presented, they all share a common feature in that, the outcome of a stress response is determined by cognitive processes in the brain (Artnetz & Ekman, 2006). External stimulus is defined as a stressor based on the perceived threat by the brain. The the threat to homeostasis may be perceived or real.

Sources of stress

Stressors refer to any stimulus that signal the activation of the stress response (Elliot & Eisdorfer, 1982).

The Environment: environmental factors of stress can lead one to feel overloaded with competing demands to adjust. Environmental stressors may include factors such as air pollution, crime, traffic, weather, population, crime and poor standards of living.

Social Stressors: social factors of stress include the act of attempting to meet the standards of the different social roles we identify with for example, a student, a parent, an employee etc. Social stressors may include deadlines for assignments, financial problems and relationship issues.

Physiological: physiological factors of stress refers to the situations and circumstances that affect the body. For example the onset of puberty and menopause, giving birth, aging, poor nutrition, sleep disturbances, and lack of exercise.

Thoughts:cognitive factors of stress include whether we perceive a situation as positive or negative. Pessimistic thinking can lead to the onset of stress (Glanz & Schwartz, 2008).

Types of Stress

Is stress really all that bad? According to research the answer is no. Stress serves an important function in the body which will be further outlined in this chapter (Bickerstaff, 2007; Kalat, 2013). In order to highlight the negative and positive of stress, Hans Selye introduced the term eustress and distress to provide distinctions between positive and negative stress (Rice, 1992).

Distress: refers to stress in which results in unpleasant and damaging effects to the body. There are two types of distress, acute and chronic. The types vary in intensity and duration. Typically acute stress is typically more intense than chronic stress, it also does not last long. Chronic stress on the other hand is less intense but can last for prolonged periods of time (Seaward, 2009). Acute distress may be experienced in situations such as believing you received a fail grade for your final exam only to realise shortly that your exam marks had been mistaken for another student and you in fact had passed. Chronic stress may occur in such traumatic events such as a death of a family member, where to grieving process may time an indefinite amount of time.

Eustress: refers to positives effects of stress on the body such as heightened awareness and increased mental alertness.

Are your stress levels out of control? In order to appropriately deal with stress, it is important to be able to recognise when stress levels are out of control. Generally speaking there are three distinct responses to stress when levels exceed a beneficial outcome to the body: An agitated or angry response to stress. This includes feelings of being overly emotional and being fired up. A depressed or withdrawn response to stress. This includes feelings of having little emotion or energy, feeling solitary and having little to emotion and energy. A frozen or tense response to stress. This includes feelings of not being able to do anything; you may appear to be paralysed on the surface while having internal feelings of being agitated or angry (Salleh, 2009). If you identify with these responses to stress, you may be experiencing stress overload.

Theories of Stress

In order to effectively explain the physiological components of stress this chapter will present relevant theories in which assist in providing a framework in which the components can be understood. While there are several theories of stress, this chapter will focus on the fight or flight response and general adaption theory as they are supported by scientific research.

Theory of emotion

According to the theory, events stimulate the autonomic nervous system, which reacts in many physiological responses. From the physical reactions that occur in the body the brain will make an interpretation. The interpretation is an emotion.This theory is similar to the explanations of the “fight or flight” reaction. However, the fight or flight reaction emphasises on the initial brain interpretation of the event. Event ==> Arousal ==> Interpretation ==> Emotion

The emergency theory

In refutation of the theory of emotion proposed by James and Lange, Cannon and Brad proposed the emergency theory. According to Cannon and Bard, the cause and effect relationship of physiological changes and emotions is dismissed. Rather it is argued that the physiological changes and emotions occur simultaneously in response to a stressor. The theory is supported by Cannon’s experiments on cats, in which afferent nerves of the autonomic nervous system sympathetic branch were severed. By severing the nerves, Cannon believe he could test whether emotion could be expressed without a visceral afferent feedback as outlined in the theory proposed by James and Lange. Based on the study, Cannon had found that arousal and emotions occur simultaneously when confronted with a stressor.
Event ==> Simultaneous Arousal and Emotion

The theory of cognitive appraisal

In support of the emergency theory stance on simultaneous processing involved in the stress response, the theory of cognitive appraisal was proposed in 1984 by Richard Lazarus. According to Lazarus the stress response is comprised of two factors, the stressor in the environment and the individual response to the stressor. This concept had led the theory to the notion of cognitive appraisal. There are generally two divisions of cognitive appraisal: primary and secondary appraisal. Primary appraisal refers to determining the level of threat to the individual, while secondary appraisal refers to the assessment of resources required to minimise, tolerate or eliminate the stressor. These factors are considered to influence the individuals’ response to the stressor.
Event ==> Thinking ==> Simultaneous Arousal and Emotion

General adaption syndrome

Hans Selye is notable for his development of the General Adaptation Syndrome in 1936. This stress model was based on his observation of the homeostasis. Homeostasis refers to the tendency of organisms to maintain a stable internal state. In order to restore and maintain homeostasis when presented with a stressor, the body acts with a fight or flight response. Another observation by Selye recognised that despite the need to combat the stress, the body has limitations, noting that chronic stress compromises the body's ability to adapt to the stressful environment. These two observations are the main themes in which the general adaption syndrome is founded upon. General adaption syndrome describes the body’s response to stress in three phases.

# Alarm Stage This phase describes the initial reaction to the stressor in which is perceived as a threat to homeostasis, in turn the fight or flight response is activated. The physiological components in the fight or flight response will be outlined in detail in the following parts of the chapter.

# Resistance Stage Once the body has responded to the stressor, levels of stress should decrease or become absent. After the fight or flight response the body must repair the damage caused during the response process. While the body has transitioned from the alarm stage to the resistance stage it remains alert especially when the stressors are continuous and the body is required to continuously fight the stressors. However, it should be noted that the response is not as strong as in the first phase of the stress response.

# Exhaustion Stage This phase refers to the stage when the body begins to be unable to reduce to negative impact of the stressors due to prolonged periods of stress. This is caused by exhaustion of adaptive energy in the body, this stage may be referred to as the beginning of stress overload and burnout which have detrimental side effects on health.

The Physiological Components of Stress

This chapter addresses six systems involved in the physiology of stress. The nervous, endocrine, and immune system are directly involved whereas the respiratory, cardiovascular and digestive system play an important role in the stress response.

The Nervous System

The nervous system is comprised of two divisions: the central nervous system (CNS), which consists of the brain and spinal cord and the peripheral nervous system (PNS) which consists of subdivisions, the automatic nervous system (ANS) and the somatic nervous system. Lastly, the automatic nervous system consists of two main parts including the parasympathetic nervous system and the sympathetic nervous system. For the purposes of explaining the physiological response to stress, this chapter will focus on the brain and the automatic nervous system.

Central Nervous System

The Brain

While reading this your brain is processing great amounts of information simultaneously, when put under stressful conditions the brain establishes priorities for processing. Between every stressor and response is the brain, the activities that take place in the brain determines the response to the stressful situation. The cognitive processes that take place are influenced by the unique information stored specifically in ones’ brain; this factor can be attributed to the complex and unpredictable nature of the stress response. For the purposes of explaining the relationship between the brain and the stress response, this chapter explains the brain on three levels; the vegetative level (automatic responses), the limbic system (emotional thought processing) and the neocortical level (rational thought processing).

The Vegetative Level

The Vegetative level refers to the lowest part of the brain, that consists of the reticular formation and the brain stem. The neural fibers in the reticular formation that the link the brain to the spinal cord is referred to as the reticular activating system (RAS). The brain stem consists of pons, medulla and mesencephalon, it is responsible for involuntary functions such as breathing and heartbeats. Furthermore, the brain stem is responsible for keeping vital organs functioning at all times.

In regards to the stress response to medulla is involved in many ways, for example the respiratory center of the brain stem regulates rhythmic breathing.There is also a good balance between inhalation and exhalation (Guyton, 1977). However in a stressful situation the cerebral cortex send signals to the automatic respiratory nuclei which in turn signals the respiratory system. As a result breathing becomes imbalanced, inhalation is increased, or very deep breathing occurs. The changes in breathing result increased levels of oxygen in the blood. The change in breathing can be noted as one of the most common reactions to a stressor. When under extreme stress, anxiety hyperventilation may occur.

The sympathetic and parasympathetic are also involved in the control of the heart. The sympathetic system can be noted for increasing the heart rate when activated by the stress response. Under a normal state the heart beats at 70 beats per minute however under stress it can increase the heartbeat to 250 beats per minute. In addition the sympathetic system increases the strength of the heartbeat in stressful situations. The parasympathetic system on the other hand can be noted for its moderation of the strength and decreasing the rate of the heartbeat.

The reticular formation is a rope like structure comprised of fibers which run through the middle of the brain stem and upwards into the hypothalamus and thalamus. There are three main functions of the reticular formation;it provides a channel for communication between the brain and body, it selects the sensory information to be processed by the cerebral cortex and it controls arousal.

The reticular formation is a the main two-way path in which the brain communicates with the rest of the body, the descending pathway relays signals from the hypothalamus to organs which are controlled by the autonomic system, while the other ascending pathway relays involuntary motor impulses to voluntary muscles. In the stress response the brain sends signals down the descending pathway as well as the hypothalamic pituitary pathway to alert the body of the presence of a psychosocial stressor. In response, there are changes in the cardiovascular, glandular and immune systems.

The ascending pathway signals the brain of the presence of a physical stressor, physical stressors may be conditions such as extreme temperatures or physical injuries to the body. In response to the physical stressors the body may react in an array of emotional states which produce psychological tension and discomfort. The awareness of pain is controlled by reticular formation in conjunction with thalamic centers. Signals that aware the body of pain result in the activation of healing processes, in some cases the body can produce opiates to reduce the feeling of pain.

As the reticular formation changes the sensitivity of receptors in order to assist the flow of vital information to its target destination. As a result, an immense amount of information that was sent to the brain is lost or distorted in the process. The purpose of delivering only selective information to the brain is that it allows for the brain to operate with greater efficiency. The question at hand is what is the criteria in which the reticular formation deems information important? To put it simply changes in the motivation, emotion and attention input are deemed important information. For example, a mother may be able to sleep with the noise of the tv and radio on, however at the sound of her baby whimpering she awakens. Despite the noise of the baby being much quieter than the tv and radio. As the noise of the baby evokes higher motivational strength in comparison to the noise of the tv and radio, the reticular formation permits the signal to reach the brain.

The reticular formation third function is arousal of higher centers of the brain. The reticular formation alerts higher centers of the brain that important information is going coming their way. This notion is supported by surgical procedures in which the cortex and the reticular formation are isolated resulting in depressed cortical activity and in some cases coma.

The Limbic System

The limibic system refers to the mid level portion of the brain, this portion contains the thalamus, hypothalamus, amygdala and the pituitary gland. These four glands are responsible for the maintenance of homeostasis in the body. The hypothalamus for example controls body temperature and appetite. In addition, the hypothalamus is the center in which registers pain and pleasure. The unified actions of these glands can explain why appetite diminishes in light of extreme stressful conditions. In the stress response, when the body is in the presence of a stressor or (threat to homeostasis), the hypothalamus reacts in four ways;

1. it activates the autonomic nervous system
2. it stimulates the secretion of adrenocorticotropic hormone (ACTH)
3. it produces antidiuretic hormone (ADH)
4. it stimulates the thyroid gland to produce thyroxine

The limbic system is the part of the brain which controls emotions.

The neocortical level

The neocortex is the highest level of the brain, it processes sensory information and makes a judgement as to whether it is a threat or not.Furthermore, cognition takes place at the neocortical level, this is the most sophisticated level of the brain. This area of brain tissue is argued to separate humans from other species, in comparison to the brain stem which is thought to be the most primitive part of the human brain due to the fact that this portion of the brain is similar across all mammals.Higher levels of the brain can override lower levels of the brain, for example conscious thoughts can intervene in the functions in the vegetative level. Awareness of this fact is helpful when attempting to eliminate the stress response through coping and relaxation methods.

The Autonomic Nervous System

The autonomic nervous system is the main control for cardiac muscle, the majority of glands and all smooth muscle (Liebman 1979). The autonomic nervous system is controlled by brain stem, hypothalamus and spinal cord. This system controls several bodily functions including; blood pressure, bowel elimination and heart activity. The autonomic nervous system is comprised of two parts, the parasympathetic nervous system and the sympathetic nervous system. The systems do not work in high levels of unison, rather when one system is active the other system is passive and vice versa. The parasympathetic nervous system is active when the body is relaxed. The parasympathetic nervous system is responsible for slow and balanced breathing, a decrease in heart rate, blood pressure, temperature and muscle tension. The sympathetic nervous system on the other hand is active during emergencies. The alarm begins in the hypothalamus and once the sympathetic nervous system receives the signal it is aroused as a result there is an increase in blood pressure. The flow is increased to large muscles while decreased to internal organs such as the digestive system. Furthermore, there is an increase in blood glucose pg 126

The Endocrine System

The endocrine system is comprised of several glands which secrete hormones in the circulatory system. The adrenal gland is a major component in the stress response. The adrenal gland is divided into two divisions. The cortex and the medulla.

The cortex is the outer layer of the adrenal gland and is responsible for the secretion of cortisol and aldosterone.

The medulla is the inner part of the gland and is responsible for the secretion of epinephrine and norepinephrine.

Together the nervous system and the endocrine system form metabolic pathways. The pathways include the ACTH axis, the vasopressin asix and the thyroxine axis

The Immune System

The immune system is comprised of cells in which protect the body from pathogens.There is an optimal strength for the immune system. If it is too weak the body will become susceptible to viruses and bacteria, however if the immune system is too strong it will cause damage by attacking cells in the body. Autoimmune disease refers to when the immune system attacks normal cells. Leukocytes also known as white blood cells are the most important component of the immune system. There are several types of leukocytes, in the stress response three types are significantly effected namely; B cells, T cells and natural killer cells. B cells secrete antibodies, T cells directly attack pathogens without the use of antibodies. Some T cells assist other T cells and B cells to multiply. Natural killer cells attack all intruders unlike the B cells and T cells which only attack specific intruders. These leukocytes in conjunction with other cells produce cytokines. Cytokines are small proteins that fight infections as well as signal the brain to elicit the appropriate response. In response to the trigger the hypothalamus responds by decreasing energy, appetite and sex drive, while also producing fever and increased sleepiness. Increased sleepiness and the decrease in energy are the immune system's way of fighting illness as it allows the body to dedicate energy to immune attack but conserving energy. When stressed the immune system is effected in several ways; in response to the stressor the nervous system activates the immune system to produce more natural killer cells and secrete more cytokines which are