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PHYSIOLOGY OF STRESS

COURSE DESCRIPTION Stress is at epidemic levels in the world today. Currently, as many as 90 percent of all visits to health-care providers in the United States are considered to be stress-related. Stress affects every aspect of the body, mind, and spirit, resulting in a wide range of symptoms from headaches or stomach ailments to heart disease or death. Stress is difficult to define because it varies from individual to individual. What one person finds stressful might not bother another person at all. There are many types of stress, and each can result in many different physiological effects on the body. The goal of this course is to provide an overview of the physiology of stress, the body’s responses to stress, and how stress affects the central nervous, endocrine, and immune systems. COURSE OBJECTIVES Upon completion of this course, you will be able to do the following: 1. Compare the different definitions of stress. 2. Describe the origins and concepts of stress. 3. Identify the stages of the general adaptation syndrome (GAS). 4. Explain the fight-or-flight response. 5. Describe the three levels and two forms of stress. 6. Discuss the body’s responses to stress. 7. Describe the effects of stress on the nervous system. 8. Describe the effects of stress on the endocrine system. 9. Describe the effects of stress on the immune system. 10. Describe the relationship between stress and the cardiovascular system. 11. Explain the relationship between stress and the gastrointestinal system.


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INTRODUCTION

Since the dawn of time, all living organisms have been subjected to evolutionary pressure from the environment (stress). Their ability to respond effectively to threats from the environment, predation, or other stressors ultimately determined their ability to survive and reproduce (Segerstrom & Miller, 2004). Stress remains an integral part of life for every individual. While it may not be the same types of stressors as in earlier times, everyone has stressors in their lives as they try to juggle the demands of work, family, personal responsibilities, and environmental stressors (such as natural disasters or political upheavals). However, what may be stressful to one individual is not necessarily perceived as stressful to another individual, and that is what makes stress so difficult to define. For example, when riding a roller coaster, some people are hunched down in the back seats with their eyes shut and jaws clenched, stomach tense, skin pale, and grabbing onto the retaining bar with such fear that their knuckles are literally white. Other individuals choose to sit right up front, yelling and screaming and relishing every steep plunge and high-speed twist and turn of their wild ride. These wide-eyed thrill seekers find the ride exhilarating, and they find the “adrenaline rush” and physical sensations so enjoyable they may even choose to go on the ride again. So was the roller coaster ride a stressful event (American Institute of Stress, 2013)? It depends on which of the riders you ask. Stress research has surged in the last 50 years as interest in the topic has increased. Today the word stress has many different definitions and connotations. According to Seaward (2012), in Eastern philosophies, stress is considered to be the absence of inner peace; in Western culture, it is considered the loss of control. Serge Kahili King, a noted healer, describes stress as any change experienced by the individual. Researcher Richard Lazarus calls stress a state of anxiety produced when events and responsibilities exceed one’s ability to cope with them. Hans Selye added to this definition, stating “stress is the nonspecific response of the body to any demand placed upon it to adapt, whether that demand produces pleasure or pain” (Seaward, 2012, p. 6).


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Seaward (2012) states that a more current definition of stress is “the inability to cope with a perceived (real or imagined) threat to one’s mental, physical, emotional, and spiritual well-being, which results in a series of physiological responses and adaptations” (p. 4). According to Trivieri & Anderson (2002), stress is a reaction to any stimulus or challenge that upsets the body’s normal function and disturbs mental or physical health. Stress can be brought on by internal circumstances (such as illness, pain, or emotional upset) or by external circumstances (such as death, family or financial problems, or job challenges). Attitudes, beliefs, and emotional states ranging from love to anger can trigger chain reactions that affect blood chemistry, heart rate, and the activity of every cell and organ in the body (Seaward, 2012). A situation, circumstance, or any stimulus that is perceived to be a threat is referred to as a stressor, or that which causes or promotes stress (Seaward, 2012). While the definitions of stress vary, most experts agree that stress is not what happens to someone—those outside forces are the stressors. What matters is how a person reacts to the stressor. ORIGINS AND CONCEPTS OF STRESS The concept of the mind’s influence on health has been recognized since the time of Hippocrates (460–377 BCE). As the founder of Western medicine and the originator of the Hippocratic Oath, Hippocrates equated health to the harmonious balance between the mind, body, and environment. This philosophy changed with the writings of Rene Descartes in 1637. Descartes’ perspective led to a major paradigm shift in the Western world when he proposed the separation of the “thinking mind” from the “machine-like body.” Because of Descartes, during the next 300 years, there was a clinical distinction between medical disorders and psychiatric disorders. Health disorders originating from the mind or spirit were not considered to be connected to the body and were studied and treated as separate issues (Bhatia & Tandon, 2004). During the Renaissance, English physician Thomas Sydenham (1624–1689) helped change the Cartesian perspective by furthering the concept originally proposed by Hippocrates. Recognized as a founder of clinical medicine and epidemiology, Sydenham observed the “healing power of nature” and asserted that a person’s internal responses to external forces were a major factor in disease and health (Pelletier, 1993). Despite the advances made by Sydenham, very little was published or discussed about stress or the connection between the body and the mind for many years after he shared his insights. The word stress was used mainly in the context of physics to describe the amount of tension or force that needed to be placed on an object to bend or break it. Prior to the 1960s, it was difficult to find much of anything written on stress. During the 1960s, Selye was one of the first researchers to apply the notion of stress to human beings (Seaward, 2012). Now the term stress is as common as the term computer. GENERAL ADAPTATION SYNDROME Known as the father of stress research, Selye developed much of the research and theories that serve as the foundation for what we know today about stress. During the 1960s, he developed a theory called the general adaptation syndrome (GAS), which states that all


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organisms have a similar response when confronted with a challenge to their well-being, regardless of whether they see the challenge as positive or negative. The GAS is comprised of three stages of response:

1. The first stage is the alarm reaction, also known as the fight-or-flight response. First described during the nineteenth century by Harvard physiologist Walter B. Canon, the fight-or-flight response is the body’s internal adaptive response to a threat (Seaward, 2012). In this stage, the body “gears up” physically and psychologically for a real or perceived threat. This response was essential to survival in a time when human beings faced all types of physical threats, such as wild animals. Today, although we do not typically have the same type of threats from predators, this reaction remains a major response of the body to any real or perceive threat (Eliopoulos, 2004).

2. In the stage of resistance, the body maintains its state of readiness, but not to the

extent of the initial alarm phase. 3. If the body has to maintain the heightened state of readiness, it reaches a stage of

exhaustion. At this point, the body has no further energy reserves, is unable to sustain the workload required by constant vigilance, and fails. Illness and possibly death can ensue (Eliopoulos, 2004).

The General Adaptation Response FIGHT-OR-FLIGHT RESPONSE

When the body perceives a threat (or stressor), a series of chemical and physical responses occur. The first response is the activation of the autonomic nervous system (ANS), a part of the nervous system that is not normally under an individual’s control (Mayo Clinic, 2013). The sympathetic branch of the autonomic nervous system regulates the stress response, while the parasympathetic nervous system controls the relaxation response. When the stress response occurs, the body secretes catecholamines (stress hormones) that help prepare the person to either fight or turn from the threat and run. The most well-known of these stress hormones is epinephrine, secreted by the medulla of the adrenal glands (located on top of the kidneys), and norepinephrine, also secreted by the adrenal glands and nerve endings throughout the body (Seaward, 2012).


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The release of these hormones triggers the fight-or-flight response and a cascade of physiologic changes are set in motion. The entire body is focused on keeping the brain, heart, lungs, and major muscles ready to fight or flee. The anterior pituitary gland secretes adrenocorticotropic hormone (ACTH), which stimulates the adrenal glands to release aldosterone and cortisol. The pituitary gland also secretes vasopressin, or antidiuretic hormone.

• Aldosterone and vasopressin preserve blood volume by reducing the amount of sodium and water that the kidneys excrete (Eliopoulos, 2004; Mayo Clinic, 2013; National Cancer Institute, 2011; The American Institute of Stress, 2013). As a result,

! the heart rate rises and blood pressure increases to pump blood to the vital organs (the brain, heart, lungs, kidneys, and liver);

! the rate and depth of respiration increases (to deliver the maximum amount of oxygen to all the cells in the body);

! the liver releases glucose and glycogen (to supply the muscles

with energy for either fighting or fleeing and the brain with fuel for thinking);

! blood vessels in vital organs dilate to receive the maximum

amount of oxygen and nutrients for optimum functioning; and

! blood vessels in non-vital organs (such as the skin and the digestive tract) constrict so that blood is shunted to the vital organs.

• Cortisol is also released and serves to increase glucose production and help

break down fats and proteins to provide the body with the needed energy for


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dealing with the event. When an individual experiences stress, cortisol levels rise rapidly. High levels of cortisol inhibit the production of prostaglandins, anti-inflammatory substances that dilate blood vessels and support various functions of the immune system. Despite the fact that cortisol has anti-inflammatory properties, low levels of prostaglandin result in immune suppression and inflammation. When cortisol levels remain high for long periods of time, immune system function decreases or may shut down altogether. This can result in mild to severe or even life-threatening conditions such as allergies and autoimmune diseases, and it has even been linked to cancer (Eliopoulos, 2004; Mayo Clinic, 2013; National Cancer Institute, 2011; The American Institute of Stress, 2013).

TYPES OF STRESS

In the 1950s and early 1960s, psychiatrists Thomas Holmes and Richard Rahe at the University of Washington School of Medicine found ways to quantify the effects of stressful events. They found that events like divorce, a death in the family, a job change, pregnancy, obtaining a large mortgage, marriage, and retirement can cause stress serious enough to affect an individual’s health and well-being. The more stress people experience, the more likely they are to become sick in the months following the stressful events. When life brings many stressors at once, a prolonged, intense, and potentially dangerous reaction is even more likely (Pelletier, 1993). Scientists now know that the body responds differently to different types of stress. As a result, stress is often classified by levels (eustress, neustress, and distress) and by form (short-term and long-term). Levels of Stress There are three levels of stress—eustress, neustress, and distress.


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• Good stress, which Selye called eustress, motivates individuals, has pleasant or enjoyable effects, and keeps individuals excited about life. Examples include falling in love, the birth of a child, getting a job promotion, watching a scary movie, riding on a roller coaster, or having a surprise birthday party (Seaward, 2012). While such events may cause a short-term alarm response, the strength and duration of the stress are limited.

• Neustress describes sensory stimuli that have no consequential effects and are

considered neither good nor bad (Seaward, 2012).

• Bad stress, called distress by Selye, fully initiates the fight-or-flight response and may have a prolonged impact on a person’s life and well-being. A divorce, having a loved one involved in an accident, and a job loss are possible examples. Usually when individuals talk about stress, they are referring to distress (Eliopoulos, 2004). Signs of distress are extremely varied and can include many symptoms, such as headaches, heart palpitations, pain, a constricted throat, weariness, nausea, and diarrhea (Trivieri & Anderson, 2002).

This image was used with special permission from The American Institute of Stress (2013).

What one person considers distress can be considered eustress by another. For example, one person may consider a long commute to be a great way to unwind from a hectic day at work while another person may consider the long drive to be tiring and a barrier to time spent with family. Categories of Stress There are two forms of stress—short-term (acute) stress and long-term (chronic) stress. Short-term Stress (Acute Stress) Short-term (acute) stress is intense, disappears quickly, and is caused by events such as a near-miss on the highway or a loud noise. The body responds with the typical fight-or-flight response (Seaward, 2012).


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Short-term, or minor, stressors enable the body to respond in a mode that supports immediate survival. Short-term stress usually has a beginning and an end. Short-term stress can be beneficial. For example, if someone needs to quickly respond to a potential car accident on the highway, a short-term stress response can shut down non-essential body functions (such as digestion) and support essential body functions (like increased blood flow to the brain, allowing for improved reaction time). Once the stressor is removed, the body usually returns to normal (Contrada & Baum, 2011). Physical symptoms related to short-term stress are varied and can include the following:

• Rapid respirations • Cold hands and feet • Cool skin • Diarrhea • Headache • Dry mouth • Rapid heart rate • Headaches • Nausea • Muscle tension • Excessive perspiration

Long-term Stress (Chronic Stress) Long-term (chronic) stress occurs over an extended period of time (e.g., hours, days, weeks, months, or even years). The stress responses are prolonged, often leading to the development of illness or chronic disease. Examples include living with a horrible college roommate; looming credit card bills; dealing with a difficult boss; being in combat for an extended time, or having relationship problems with a close friend, spouse, or family member.


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With long-term stress, the immune system is often suppressed or less vigilant than normal, and the individual may experience any of the following (National Cancer Institute, 2011; Seaward, 2012):

• chronic pain • headaches • osteoporosis • gastrointestinal distress • constipation or diarrhea • weight loss or gain • immune system disturbances (ranging from mild illness, such as increased frequency

of the flu or colds, to severe disturbances such as autoimmune disorders, such as rheumatoid arthritis, lupus, scleroderma, or even cancer)

• fatigue • sleep disturbances • mood instability • hypertension • elevated blood lipid levels • changes in eating, drinking, or smoking behaviors • dizziness • irritability, depression, or restlessness • heightened sensitivity to stimuli • poor impulse control • substance abuse • muscle tension • skin disorders (such as acne or dryness) • teeth grinding • panic attacks • difficulty thinking, concentrating, or remembering things • social withdrawal • changes in the quality of relationships


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Any symptoms, or any combination of symptoms, does not necessarily mean that a person is experiencing chronic stress, but they provide individuals with an opportunity to examine their lives and see if they can make any changes that could alleviate the symptoms they are experiencing. Long-term stress plays a significant role in the development or exacerbation of chronic diseases, is harmful because the body remains in a heightened state of the stress response for a longer period of time, and can slow the healing process and increase the duration of an illness (Contrada & Baum, 2011). Stress impacts virtually every body system. However, the most pronounced physiological impacts of stress are experienced by the nervous system, the endocrine system, the immune system, the cardiovascular system, and the gastrointestinal system. STRESS AND THE NERVOUS SYSTEM

The nervous system includes the central nervous system (CNS) and peripheral nervous system (PNS). The CNS consists of the brain and spinal cord; the PNS consists of 31 pairs of spinal nerves and 12 pairs of cranial nerves that branch off from the brain and spinal cord. The PNS also includes the autonomic nervous system (ANS) or neurons that innervate the muscles and glands that automatically maintain bodily homeostasis (Medscape, 2013).


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The Brain

(Photo courtesy of the National Institute on Aging. (2012). Alzheimer’s disease: Unraveling the mystery. Retrieved May 20, 2013, from http://www.nia.nih.gov/alzheimers/publication/alzheimers-disease-unraveling-mystery )

The brain is the cognitive center of the body in which memories are stored, ideas are generated, and emotions originate (Contrada & Baum, 2011). The human brain is further divided into three levels: the vegetative level, the limbic system, and the neocortical level (Seaward, 2012).

• The vegetative level consists of both the brain stem and the reticular formation, which connects the brain to the spinal cord.

• The limbic system is the emotional center of the brain and contains the thalamus,

hypothalamus, pituitary gland, and a structure called the amygdala (Seaward, 2012). The amygdala links an individual’s emotional responses to memories and is strongly connected to the hypothalamus. The hypothalamus modulates heart activity, body temperature, blood pressure, and endocrine activity, and it also contains the centers that modulate a person’s emotional condition and basic biologic drives (sex, thirst, and hunger). When the amygdala responds to danger or stress, it signals the hypothalamus to initiate the fight-or-flight response by the sympathetic nervous system (Freeman, 2004).

• The neocortical level, the highest and most sophisticated level of the brain, is

where an individual’s sensory information is processed (decoded) as a threat or nonthreat and where cognition (thought process) takes place. The neocortex houses the neural mechanisms that allow an individual to analyze, imagine, and create and utilize intuition, memory, and cognitive organization (Seaward, 2012).

The Autonomic Nervous System The autonomic nervous system regulates visceral activities and vital organs (e.g., brain, heart, lungs, kidneys, and liver). This part of the central nervous system does not require


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conscious thought. Physiological events such as respiration, digestion, heart rate, and blood vessel dilation are involuntary and controlled by the ANS. The autonomic system conveys sensory impulses from the blood vessels, the heart and all of the organs in the chest, abdomen and pelvis through nerves to other parts of the brain. The brain then responds according to the stimuli received. The two major components of the autonomic nervous system are the sympathetic and parasympathetic nervous system. Both the sympathetic and parasympathetic nervous systems function together to maintain homeostasis in the body. However, depending on stimuli from the body’s internal or external environment, one system may take a more dominant role than the other in regulating the body’s physiological response to the stimuli (Contrada & Baum, 2011; Seaward, 2012; Streeten, 2013). The following image describes functions of the two components of the autonomic nervous system.

Parasympathetic and Sympathetic Nervous Systems

This image was used with special permission from The American Institute of Stress (2013). Sympathetic Nervous System The sympathetic nervous system is activated during what is perceived by the individual to be a threatening situation and triggers the fight-or-flight response when there is an element of a threat present. Catecholamines, specifically epinephrine and norepinephrine, are released at various neural synapses creating a series of events that occur in several organ tissues to prepare the body for metabolic change and physical movement. Energy is directed away from digestion. The stress response is activated and many physiological events occur such as pupil dilation, and an increase in heart rate, perspiration, salivation, and respiration.


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Parasympathetic Nervous System The parasympathetic nervous system (PNS) is associated with a relaxed state. The PNS helps calm and slow down the body’s reaction to stressors. When the parasympathetic system is activated, pupils contract, energy is directed to the gastrointestinal tract to assist in digestion, and the body’s heart rate, respiratory rate, and endocrine system become slower and stabilized. STRESS AND THE ENDOCRINE SYSTEM The nervous system and endocrine systems communicate very closely with each other, and the actions of one intimately affect the actions of the other. For this reason, they are often referred to as the neuroendocrine system. The endocrine system is comprised of nine specialized glands (the pituitary, the thyroid, the four parathyroid glands, the two adrenals, and the thymus), organs (pancreas, kidneys, ovaries, testicles). The hypothalamus, which is not a gland but a nerve center, is also important in the synthesis of hormonal factors released during stress. The endocrine system produces biochemical substances called hormones that monitor and/or alter almost every bodily process. Hormones are the body’s “chemical messengers” because they can alter cellular metabolism by transmitting a signal from one cell to another. Hormones include amines and amino acids, peptides, polypeptides, proteins, and steroids (Contrada & Baum, 2011; Freeman, 2004). The endocrine glands and tissues help regulate metabolic functions throughout the body. They release the hormones that attach to specific cell receptor sites to modulate cellular metabolism. The hypothalamus has direct influence over the pituitary gland, which is called the “master glad” because it manufactures hormones, which then triggers hormone release in other organs (Seaward, 2012). Endogenous opioids (those produced by the body, such as endorphins, enkepthalins) are synthesized in the pituitary gland and other parts of the central nervous system. “Opioids have a morphine like effect with receptors throughout the body. These naturally occurring hormones produce the commonly known “runner’s high,” increase a person’s pain threshold, and explain how people can “ignore” their own serious injury to save a loved one” (Bartol & Courts, 2013, p. 717). Stress affects the endocrine system in many ways (Macho, et al., 2003; Ranabir & Reetu, 2011; University of Maryland Medical Center, 2013):

• It increases plasma insulin, growth hormone, prolactin, and glucocorticoid levels (in an effort to mobilize energy sources and adapt the individual to the stressor).

• It increases the production of cortisol and catecholamines (leading to an increase in cardiac output, skeletal blood muscle flow, sodium retention, cutaneous vasoconstriction, blood glucose levels, bronchiolar dilatation, behavioral activation, and a reduction in intestinal motility).

• It increases the release of vasopressin (in an effort to constrict blood vessels and retain water in the body via the kidneys and in an effort to support social behavior, sexual motivation, bonding, and maternal responses during stress).


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• It reduces the production of gonadotropins and gonadal steroid hormones (leading to the disruption of the normal menstrual cycle and impairment of reproductive and sexual function).

• It reduces the production of thyroid-stimulating hormone (TSH).

STRESS AND THE IMMUNE SYSTEM

Stress can have a profound effect on the immune system. For a body to remain healthy, a state of balance (or homeostasis) must be maintained. Stress disrupts this balance by suppressing the body’s immune system and increasing the risk of infections, autoimmune disorders, overall inflammation, and possibly even cancer (Contrada & Baum, 2011; Ubaldo, et al., 2010). The immune system is actually a complex network of cells, tissues, and organs that work together to defend the body against attacks by “foreign” invaders, such as microbes (bacteria, parasites, and fungi) and some viruses. The immune system can prevent microbes from invading the body, and if they succeed in doing so, seek out and destroy the microbes. The immune system organs are located throughout the body and include the bone marrow, the thymus, lymphocytes, lymph nodes, spleen, and other lymphoid tissues found in the linings of the digestive tract, airways, and lungs. These tissues include the tonsils, adenoids, and appendix. The immune system has two major components (Bartol & Courts, 2013; Contrada & Baum, 2011; Levy, 2002):

• The innate (nonspecific) immune system is the body’s first line of defense against threatening organisms. Included in this system are white blood cells known as granulocytes and macrophages that recognize and destroy threatening organisms. The innate system also includes natural killer (NK) cells, which attack and destroy virally infected cells and cancer cells.

• The acquired (specific) immune system is made up of certain white blood cells (lymphocytes) and the antibodies they produce. Lymphocytes circulate throughout the blood or lymphatic tissue, patrolling the body for signs of danger. Lymphocytes known as T lymphocytes or T cells mature in the thymus and then migrate to other tissues. B lymphocytes (or B cells) become activated and mature into plasma cells that make and release antibodies used to identify and neutralize bacteria and


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viruses. Kiecolt-Glaser and Glaser (1993) explain that “all of these immunological organs have now been shown to contain networks of nerve cells, which provide a pathway for the brain and central nervous system to influence immunity” (p. 41).

The two components of the immune system interact by means of two distinct mind- or brain-mediated pathways that are activated by stress.

• The first and most direct brain pathway is the sympathetic-adrenal-medullary (SAM) axis, which activates the ANS. The motor neurons of the ANS use neurotransmitters and neuropeptides (e.g., norephinephrine and epinephrine) for information and thus communicate directly with immune cells and tissues to alter immune system responses (Freeman, 2004). Neurotransmitters are substances that transmit nerve impulses across a synapse. Neuropeptides are unique messenger hormones, produced in the brain (and other body organs) that fit into the receptor sites of lymphocytes. Immune cells have built-in receptor sites for the body’s several hundred or so neuropeptides, which can either increase or decrease the cells’ metabolic function (Seaward, 2012).

• The second and indirect brain pathway is the hypothalamic-pituitary-adrenal

(HPA) axis, which alters both the body’s physiology and immune functions by signaling the endocrine system to release hormones (corticotropin-releasing hormone [CRH], adrenocorticotropic hormone [ACTH] and glucocorticoids such as cortisol). Once the hormones are released, the physiologic and immune responses to the stressor occur.

The immune, endocrine, and nervous systems communicate via hormones, neuropeptides, neurotransmitters, and products of immune cells. The immune system shares anatomic connections and signal molecules with the nervous and endocrine systems. The nervous system has direct connections to immune system organs (thymus, bone marrow, lymph nodes, and spleen). Stress can result in many different effects on the immune system, including the following (Graham, Christian, & Kiecolt-Glaser, 2006; Marketon & Glaser, 2008; Parker & Douglas, 2010; Segerstrom & Miller, 2004):

• A reduction in natural killer cell abilities • A reduction in the ability of white blood cells to perform key functions • A suppression of lymphocyte populations • A reduction in and/or impairment of the body’s response to immunizations • A redistribution of immune cells into areas of the body where they are less effective • A reduction in cytokines (cells that activate certain types of immunity) • An increased risk of allergies • An exacerbation of the symptoms of autoimmune diseases (such as lupus, Crohn’s

disease, multiple sclerosis, rheumatoid arthritis) • An exacerbation of the symptoms of asthma • A reduction in antibody production • A reactivation of latent viral infections


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• An increased risk of pregnancy failure (due to reduction of vital hormones such as progesterone, prolactin, and glucocorticoids)

• A delay in wound healing • A possible link to the development and progression of cancer

STRESS AND THE CARDIOVASCULAR SYSTEM

The cardiovascular system has two parts:

• the heart, which pumps the blood (and beats approximately 35 million times in a year), and

• the vascular network (consisting of arteries, veins, and capillaries) through which blood is channeled.

The average individual has approximately 5 liters of blood volume. The arteries carry blood away from the heart, and the veins return blood to the heart. The miles and miles of blood vessels that distribute oxygen and nutrients to the cells and remove waste products (such as carbon dioxide) make up the vascular network (Mayo Clinic, 2011). The heart is a muscular organ that lies near the center of the thoracic cavity. It is somewhat anterior in the chest and is situated directly behind the sternum. The heart lies within a pericardial cavity, which is lined by a thin, serous membrane called the pericardium. A membrane called the epicardium surrounds the heart itself. Pericardial fluid is the lubricant between the pericardium and the epicardium. There is only about 10 cc of pericardial fluid, but it reduces friction between the surfaces of the two membranes. The heart is composed of three layers:

• the epicardium, • the myocardium or cardiac muscle, and • the endocardium that lines the inner surfaces of the heart’s chambers.

The heart is divided into four chambers: the right atrium, the right ventricle, the left atrium, and the left ventricle.


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The main function of the cardiovascular system is to maintain an adequate blood flow.

Stress produces many effects on the cardiovascular system, including the following (Groenendyk, Agellon, & Michalak, 2013; University of Maryland Medical Center, 2013; Wirtz, Ehlert, Bartschi, Redwine, & von Kanel, 2009):

• myocardial ischemia leading to coronary artery disease • ventricular fibrillation and other arrhythmias • plaque rupture • coronary thrombosis • endothelial dysfunction (a precursor of atherosclerosis) • vasoconstriction • hypertension • congestive heart failure • impaired clearance of fat molecules in the body • decreased myocardial oxygen supply • impaired exercise capacity (exercise intolerance) • cardiomyopathy (especially stress, or Takotsubo, cardiomyopathy) • increased intima-medial thickness (a measure of the arteries that signifies worsening

atherosclerosis) • increased inflammatory markers in the bloodstream • elevated plasma lipid profiles (total cholesterol [TC], low-density lipoprotein cholesterol

[LDL-C], high-density-lipoprotein cholesterol [HDL-C], and triglycerides) STRESS AND THE GASTROINTESTINAL SYSTEM The gastrointestinal (GI) system includes the oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, gallbladder, pancreas, and liver (Meiner & Lueckenotte, 2006; Meiner, 2011). The brain and the enteric (gastrointestinal) nervous system are closely connected bidirectionally by both the parasympathetic and sympathetic nervous system pathways, forming the brain-gut axis. Because there are more nerve cells in the stomach and intestines (approximately 100 million neurons) than in the entire spinal cord, many experts


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call the digestive system a “mini brain.” In addition, 95 percent of the body’s serotonin (a hormone that helps control mood) is found in the digestive system, not the brain (Woolston, 2013). There is clear evidence that thoughts and emotions related to stress have a profound influence on gastrointestinal function (Bhatia & Tandon, 2004; University of Maryland Medical Center, 2013).

Because many of the same hormones and parts of the nervous system control the gastrointestinal system, stress can result in a diverse range of effects, including the following (Bhatia & Tandon, 2004; Buret, et al., 2010; Buret, 2006; University of Maryland Medical Center, 2013):

• gastroesophageal reflux disease (GERD) • slowed gastric emptying • increased diaphragmatic contractions • dyspepsia • peptic ulcer disease • exacerbation of inflammatory bowel diseases (such as colitis, colonic carcinoma,

bowel dysfunction, bleeding) • increased intestinal permeability (affecting electrolyte absorption, water absorption,

and immune cell changes) • increased mucosal mast cells • colonic inflammation • abdominal bloating and cramping • nausea and vomiting • constipation and diarrhea • increased cortisol levels and related weight gain • increased risk of anorexia and bulimia • exacerbation of diabetes • increased susceptibility to food allergies • increased incidence of small intestine bacterial overgrowth syndrome (SIBO)


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SUMMARY Stress affects every individual uniquely. Each person’s threshold for stress can vary, and the physiological responses to acute and chronic stressors can be as unique as the individual who is experiencing the stress. Virtually every body system is affected by stress, and prolonged stress can lead to illness, chronic disease, or death.


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