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Most members of the animal kingdom have three primary goals. The first is to find enough to eat. The second is to avoid becoming someone else's dinner. The third is to reproduce. To most animals, stress is a simple phenomenon. It usually wears the face of a predator or another animal competing for a mate or food source. Environmental conditions create stress as well: people, floods, and drought, for example, affect availability of nesting sites and food supplies.

Only a short while ago in geological time, our primitive ancestors were challenged by similar sources of stress. Nature favors survival of the fittest. Cavemen and women who were best able to escape predators, deal with disaster, and obtain food and mates were those who produced future generations who eventually produced us.

As you will learn in this chapter, the stress response produces physical changes that improve an organism's ability to cope with physical threats. It increases our strength and helps us run faster and farther. A strong stress response probably provided an evolutionary advantage for our prehistoric ancestors. The stronger their stress response, the better able they were to fight or flee predators, endure long journeys in search of food, and protect and provide for their children.

Civilization has changed, and the routine challenges we face rarely require a strong physical response; but human physiology is not so different from that of our ancient ancestors, and we still respond to perceived threats with the same fight-or-flight arousal. Such arousal is still quite beneficial when we must confront an attacker, rescue a child in danger, or even sprint to catch a bus. But what about the stress of feeling overloaded with work? Being consistently awakened by a noisy neighbor? Having to work with a difficult professor? By and large, your stress response is inappropriate for the challenges you face, as you rarely have an opportunity to fight or run away. This is the heart of the problem. A response that is sometimes advantageous is more often inappropriate and may ultimately cause physical strain and disease. Understanding the fight-or- flight response will enable you to better understand the health effects of chronic stress and the importance of stress management.

Students, especially those with little background in biology, have reported that this chapter causes more stress than any other chapter. Expecting this text to relieve rather than create stress, many are initially taken aback when faced with the intricacies of stress physiology. Read slowly, take notes, and then reread the chapter once again. Don't memorize anything you don't have to, but look for common themes and real life applications.

Imagine you are walking along humming your favorite song to yourself when suddenly you hear a threatening growl behind some bushes. The growl turns into angry snarling, and a raging pit bull terrier emerges from the shrubbery, dragging a broken chain. Teeth bared, he rushes toward you in a frenzy. Fortunately for you, your immediate appraisal of this threat activates your fight- or-flight response and all systems are go, either to counter the attack or beat a hasty retreat.

Some of the manifestations of the fight-or-flight response are quite obvious: a rapidly pounding heart, shallow breathing, increased sweating, muscle tension, dry mouth, and stomach butterflies. Let's take a closer look at the stress response to see how these symptoms are produced and how they help you deal with that snarling pit bull.

The fight-or-flight response is orchestrated by your brain, which activates various organs such as your muscles by sending messages of arousal. These messages are sent in two ways. The first and fastest is by the nervous system, which activates the fight-or-flight response through direct communication with target organs via the nerve cells. The second is the endocrine system, which activates the fight-or- response through the action of chemical messengers called hormones that reach target organs through the circulatory system. Let's start with the nervous system to see how the fight-or-flight response is produced.

The nervous system consists of your brain, spinal cord, and the peripheral nerves that travel from your spinal cord to all parts of the body. The brain and spinal cord make up the central nervous system (CNS) while all other nerves are considered the peripheral nervous system (see Figure 2.1). It is the job of the nervous system to coordinate all parts of the body so that they work together. The afferent nervous system consists of the nerve cells that receive information from the external and internal (inside your body) environment and conduct this information to the brain, where it is processed at both conscious and subconscious levels. In the example above, your ears send information about the dog growling, your eyes send information about the dog's movement, internal sensors (proprioceptors) send information about your body's position and muscle tension. Your brain integrates all this information, recalls past experiences and everything your mother ever told you about strange dogs, and decides what to do. Run as fast as you can! So the brain sounds the alarm and sends messages to all systems of the body via the efferent nervous system.

The efferent system is subdivided into two parts. The somatic nervous system sends impulses from the central nervous system to skeletal muscles. This is how the body produces movement. This system is considered to be at least partly under conscious control. You've decided to flee rather than fight the dog; your brain coordinates muscular contraction to produce a personal best in running time. The autonomic nervous system (ANS) sends information from the central nervous system to nonskeletal systems such as the circulatory system (heart and blood vessels), respiratory system (lungs and airways), digestive system (stomach, pancreas, liver, gallbladder, small intestine, large intestine), urinary system (kidneys, bladder), and endocrine system (glands). Scientists generally regard the activity of the ANS as outside voluntary control, although biofeedback research has shown people can learn to control many autonomic functions, including heart rate, stomach acidity, and blood pressure.

The autonomic nervous system can either speed up or slow down the activity of the organs and systems it innervates. The two branches of the ANS that perform these functions are the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS) (see Figure 2.2). In the fight-or-flight response, your brain activates the sympathetic nervous system, which speeds up those functions necessary for immediate survival. For example, the liver releases sugar into the bloodstream to fuel the working muscles, the heart beats faster and harder to circulate plenty of blood. The SNS suppresses such functions as digestion, which can be postponed. Following are some of the important physiological effects of the SNS response that help us fight or flee:

After getting safely away from the dog, you heave a sigh of relief and collapse into a chair. At this point, your brain decreases SNS activity while increasing parasympathetic output. This is the relaxation response. Heart rate and blood pressure return to normal, muscles relax, and your stomach and intestines resume the task of digesting your lunch. Some of the actions of the sympathetic and parasympathetic branches of the autonomic nervous system are listed in Table 2.1. In this table you can see that the actions of the sympathetic nervous system are balanced by the actions of the parasympathetic nervous system. For example, activation of sympathetic nerves causes the heart rate to increase, while activation of parasympathetic nerves causes the heart rate to decrease.

At this point in our discussion of the physiology of the stress response, you may already have a glimmer of understanding about how the stress response becomes harmful. As long as a balance exists between arousal and relaxation, negative health effects from stress are less likely to develop. But suppose you are chronically aroused, your body continuously geared up to fight or flee. Continuous physiological arousal unbalanced by the relaxation response can lead to negative health consequences (Dienstbier, 1991; Woods, 1987). Among the primary goals of stress management and relaxation training are developing your ability to increase parasympathetic output, cultivating the relaxation response, and reducing the sympathetic fight- or-flight response, thus bringing the two systems into a more healthful balance.

BRAIN PHYSIOLOGY: THE BODY/MIND CONNECTION

Let's go back to one of the most important components of the nervous system: the brain (see Figure 2.3). As we examine how the brain participates in the stress response, you'll see why it's impossible to separate completely the psychological and physical responses to stress. This interaction forms the basis for an area of study known as psychophysiology. Psychophysiology is the study of the relationship between psychological and physiological functions; it provides much of the basic information we have concerning the physiology of stress.

The most obvious role played by the brain in the stress response is as the seat of conscious thought and awareness. Here is where you evaluate demands placed on you and your ability to respond. Here is where purely imaginary ideas and fears can trigger a full-blown stress response. Thought, judgment, and memory of past experiences occur in the outer layer of the brain, the cerebral cortex, which is the largest area of the brain. Sensory areas in the cerebral cortex interpret sensory nerve impulses, motor areas control movement, and association areas are involved with emotional and intellectual processes.

FIGURE 2.3 The Brain

The brain coordinates the nervous and endocrine responses to stress.

Deeper areas of the brain participate in the stress response as well. An area called the diencephalon is made up of the thalamus and hypothalamus. The thalamus integrates and relays sensory information to the cerebral cortex. It helps interpret sensations of pain, temperature, and pressure; it is also involved in emotion and memory. The hypothalamus is an important control center for many physiological functions. It controls the autonomic nervous system, regulates the pituitary gland, and secretes several hormones and other chemical factors. The hypothalamus appears to be the center for the learned control of autonomic functions that occurs during relaxation and biofeedback training.

The thalamus and hypothalamus are part of an area of the brain called the limbic system, which also includes part of the cerebral cortex and other structures. It lies above and around the brain stem and is involved with motivation and emotion; it also contributes to memory. Because of its function in emotions such as pain, pleasure, anger, fear, sorrow, sexual feelings, and affection, the limbic system is sometimes refered to as the "emotional" brain (Tortora & Grabowski, 1993).

The deepest area of the brain is the brain stem. This is the "oldest" part of the brain, having been around for the longest period of our evolution. The brain stem contains structures that automatically regulate essential life functions such as breathing, heart action, and digestion through the sympathetic and parasympathetic branches of the autonomic nervous system. Although these functions are considered involuntary, psychological factors such as stress can affect them. An example is anxiety hyperventilation, in which breathing becomes very fast and interferes with the normal regulation of blood gas (oxygen and carbon dioxide) concentrations, resulting in dizziness, shortness of breath, pounding heart, and even fainting. Anxiety hyperventilation is uncomfortable and even frightening, and many experiencing this condition interpret it as an impending heart attack. Some research has suggested that breathing practice and relaxation are effective treatments for hyperventilation (Hegel et al., 1989). Rebreathing air in and out of a paper bag also works (by raising the carbon dioxide content of inspired air).

The nerve fibers of the reticular formation (RF) run through the middle of the brain stem up into the diencephalon and act as a major communication pathway between the brain and the rest of the body, an important body-mind connection. The RF scans the sensory information making its way to the brain and evaluates its importance. It alerts higher centers to critical information, thus stimulating arousal and consciousness.

The reticular formation selectively relays sensory information upward for further processing, sending on information deemed relevant and short-circuiting sensory information that seems unnecessary. This limits the amount of sensory information that actually reaches higher levels of the brain and keeps us from being overwhelmed with input. How does the RF "know" what is important? It receives information from higher brain centers responsible for emotion, motivation, and other associative processes that helps it "decide" what is relevant. For example, you may fall asleep while waiting for a friend to stop by. You snooze on, oblivious of the noise of traffic outside and the radio playing, but you awaken when you hear a knock on the door. The RF signals you that an important message is coming through. In our pit bull example, the dog's angry snarl need not be loud to be noticed above background noise such as traffic and construction. The RF knows this sound requires your attention.

An interesting application of this selectivity function of the RF is relaxation training for the treatment of chronic pain. The RF functions with the thalamus to control awareness of pain. Negative emotions associated with pain may increase sensory transmission of pain by the RF and thalamus, while relaxation training may help reduce the transmission of pain impulses, thus reducing conscious awareness of pain. Childbirth is a good example. Feeling fearful and out of control increases a woman's pain during labor. Breathing and relaxation exercises accompanied by reassuring, supportive labor coaches help reduce fear and sensations of pain. Less medication is called for in these cases and labor is generally easier (Rosen, 1991).

The brain governs and coordinates the autonomic nervous system and endocrine system. Let's take a look at how the endocrine system complements the action of the ANS in the production of the fight-or-flight response.

THE ENDOCRINE SYSTEM: RAGING HORMONES

Raging hormones. Where do they come from? Hormones are chemical messengers produced by the endocrine system that, along with the nervous system, coordinates physiological functions so that all parts of the body work together. Messages from the nervous system reach specific sets of cells via nerve cell networks and take only milliseconds to transmit. The instantaneous response of the autonomic nervous system is why the fight-or-flight response occurs so quickly. The endocrine system releases hormones into the bloodstream, from where they reach and can affect virtually every cell in the body. Messages from the endocrine system may take from a few seconds to several hours or more to bring about their specific effects.

Why two systems? Many physiological responses, such as the fight-or-flight response, are so essential to survival that back-up systems have evolved. The immediate response of the sympathetic nervous system is backed up by the longer lasting action of several hormonal pathways, as you will see in this section. As you read about the actions of these hormones, you might anticipate why long-lasting stress, and long-term activation of these hormonal pathways, can lead to negative health effects.

The nervous and endocrine systems work closely together and are linked in several ways. The nervous system can stimulate or inhibit the release of hormones, while hormones can stimulate or inhibit the transmission of nerve impulses. Hormones have many functions, including the regulation of metabolism, reproduction, and growth and development (Mills & Chir, 1985). Let's take a look now at how they help us respond to stress.

Your brain has been alerted to the rapid approach of the snarling pit bull terrier. This message came from sensory information relayed by your eyes and ears up through the reticular formation (no chance of this information getting short-circuited!) and to the cerebral cortex. The information has been processed with input from the limbic system, and a message has been sent to the hypothalamus to sound the alarm. The hypothalamus immediately initiates sympathetic nervous system arousal and the fight-or-flight response has begun. An endocrine response is initiated as well. Here are some of the pathways involved.

What a Rush: Hormones of the Adrenal Medulla

When responding to stress, the autonomic nervous system stimulates the adrenal glands, which sit on top of the kidneys like little caps (see Figure 2.4). The adrenal glands are really two glands in one. The outside layer is called the adrenal cortex while the inner portion is the adrenal medulla. The adrenal medulla is activated by direct nerve connection with the posterior (back portion) hypothalamus, and when stimulated secretes the hormones epinephrine (commonly called adrenaline) and norepinephrine (also called noradrenaline). These hormones are collectively referred to as the catecholamines; they are sympathomimetic-that is, they have effects similar to those listed for the sympathetic nervous system, as shown in the following list (Mullen et al., 1993; Tortora & Grabowski, 1993; Woods, 1987):

Increase the heart rate and contractile force of the heart, thus also increasing blood pressure. This increases blood flow to active muscles, heart, and lungs.
Dilate arteries in the heart, lungs, brain, and skeletal muscles. This increases blood flow to organs essential for fighting or fleeing.
Constrict peripheral arteries (arteries in hands and feet). This ensures good blood flow to the heart and is why, under stress, you get "cold feet." Hand temperature may also decrease.
Dilate airways. Increases air flow to lungs.
Increase blood sugar level. This is accomplished by signaling the liver to release stored sugar into the blood, which supplies more fuel for working muscles.
Increase metabolic rate (speed up cellular metabolism). This speeds up energy production to support emergency functions.
Slow digestive processes. This spares energy for essential fight-or-flight processes and avoids wasting energy on unnecessary functions.
Contract spleen. This releases stored blood, which increases blood volume Red blood cell production also increases.
Speed rate of clotting. This prevents bleeding.
Increase sweating.

FIGURE 2.4 The Adrenal Glands

The adrenal glands are composed of the adrenal medulla and the adrenal cortex; they are located on top of the kidneys.

Stressed Out: Hormones of the Adrenal Cortex

Even as it is orchestrating the autonomic nervous system response to stress and stimulating the response of the adrenal glands, the hypothalamus is secreting some hormones of its own. The anterior (front portion) hypothalamus secretes a hormone called corticotropin-releasing hormone (CRH) which stimulates the pituitary gland, located at the base of the brain, to release adrenocorticotropic hormone (ACTH). ACTH is carried in the blood stream, and soon reaches the adrenal glands. ACTH acts on the adrenal cortex, stimulating it to release two families of hormones called glucocorticoids and mineralocorticoids (see Figure 2.5). This sequence is known as the hypothalamus-pituitary-adrenal pathway.

Cortisol (hydrocortisone), corticosterone, and cortisone are three glucocorticoids involved with the-fight-or-flight response. Glucocorticoids affect several metabolic processes. Cortisol is the most abundant glucocorticoid and is responsible for about 95 percent of glucocorticoid activity (Tortora & Grabowski, 1993). Glucocorticoids do the following (Chrousos & Gold, 1992; Tortora & Grabowski, 1993):

Mobilize energy sources by increasing the rate of protein breakdown in cells, especially muscles, so that the proteins may be used for energy or to make enzymes. The glucocorticoids stimulate the liver to produce glucose from certain protein components if blood sugar is low.
Make blood vessels more sensitive to agents promoting constriction, thus helping to raise blood pressure. Since blood loss was often involved in fight or flight for our ancient ancestors, increased blood pressure was advantageous in maintaining adequate circulation despite a drop in blood volume.
Glucocorticoids inhibit the process of inflammation. Inflammation may make the inflamed area stiff. Preventing mobility limitations is helpful in the short run, but long- term effects include delayed healing.
Cortisol also causes a decrease in the number of lymphocytes released from the thymus gland, located in the upper chest, and the lymph nodes. Lymphocytes are an important component of the immune system defense against bacteria and other foreign invaders. This decrease in immune activity may be one of the " energy conservation" processes of the glucocorticoids. When facing the pit bull, you are not so worried about the cold germs in your nose. Of course, if you are under chronic stress and cortisol levels remain elevated, the negative impact of cortisol on the immune system becomes very important.

FIGURE 2.5 The Hypothalamus-Pituitary-Adrenal Pathway

The adrenal cortex also secretes mineralocorticoids. Mineralocorticoids help control fluid and salt balance. The mineralocorticoid alclosterone is responsible for about 95 percent of the action of this hormone family. Aldosterone causes the kidneys to retain sodium and water, an action that increases blood volume and consequently, blood pressure-both helpful if blood is lost.

Nervous Energy: Thyroid Hormones

There's more. The busy hypothalamus also instructs the thyroid gland in its work. The thyroid gland is located in the throat (see Figure 2.6). It produces hormones that help regulate energy expenditure, growth and development, and nervous system activity. Here's how it works. The hypothalamus secretes thyrotropin-releasing hormone (TRH), which causes the pituitary gland to release thyroid-stimulating hormone (TSH). This hormone, TSH, then tells the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3), which are functionally similar and are commonly referred to as thyroid hormones (see Figure 2.7). This sequence of events is known as the hypothalamus-pituitary-thyroid pathway.

FIGURE 2.6 Glands that Participate in the Fight-or-Flight Response

Glands are organs that secrete hormones. The glands illustrated here play important roles in the fight-or- flight response.

During the stress response, the thyroid hormones stimulate the breakdown of glycogen and fats in most cells of the body to increase production of sugar and fats to fuel metabolism. The thyroid hormones also stimulate protein synthesis. They increase the reactivity of the nervous system, heightening the autonomic nervous system stress response. Specific actions are (Greenberg, 1990; Tortora & Grabowski, 1993):

Increase resting metabolic rate.
Increase free fatty acids (FFA). These are produced from storage fat molecules called triglycerides. FFA can be used as fuel for energy production.
Increase rate at which liver converts Protein into blood sugar (glucose).
Increase heart rate and contractile force.
Increase blood pressure and blood flow.
Increase rate and depth of breathing.
Increase gastrointestinal motility (may result in diarrhea).
Increase nervousness and alertness.

FIGURE 2.7 The Hypothalamus - Pituitary Thyroid Pathway

Under Pressure: Antidiuretic Hormone

One final hormone important in the stress response and its health effects is antidiuretic hormone (ADH), also called vasopressin, which is secreted by the pituitary gland. An antidiuretic is anything that prevents urine production and water loss. This hormone, ADH, causes the kidneys to remove water from fluid destined to become urine and return it to the bloodstream-an action that increases blood volume and thus raises blood pressure. Antidiuretic hormone raises blood pressure by another mechanism as well: contraction of the smooth muscles in the artery walls. Many things influence the action of ADH. For example, alcohol inhibits ADH secretion and thus increases water loss. This helps explain why thirst accompanies a hangover.

Summary: Nervous and Endocrine Systems

Is this chapter starting to sound a little repetitious? It should be. At this point you are probably recognizing some common themes. Both the nervous and endocrine systems mobilize a person to respond to a stressor in some physically active manner. The hypothalamus activates the sympathetic nervous system response; it also stimulates the adrenal and thyroid glands through either direct innervation or stimulation of the pituitary gland to secrete epinephrine, norepinephrine, cortisol, aldosterone, and the thyroid hormones (see Figure 2.8). Sympathetic nervous system activation and the endocrine response have similar effects that reinforce each other. The combined actions of these systems increase metabolic rate and mobilize fuel for energy production; increase blood pressure, blood flow, and respiration; and inhibit systems not essential for immediate survival.

FIGURE 2.8 Pathways of the major stress hormones

STRESS RESEARCH

Hans Selye: Stress -A Response

Probably best known of the early stress research pioneers is Hans Selye. Selye's work on laboratory animals in the 1930s and 1940s was some of the first to study the physical stress response (Selye, 1936). His research described in detail the stress response of the pituitary and adrenal glands, and the shortand long-term physical effects of stress throughout the body.

Selye created the first working definition of stress, describing it as the nonspecific response of the body to any demand made upon it (Selye, 1956). He called the response nonspecific because he observed the same physical response to a wide variety of "alarming agents" including bacterial infection, trauma, heat, cold, and psychological stimuli (Feuerstein et al., 1986). Selye believed that in humans, positive stressors, which he termed eustress-such as getting admitted to college, winning a scholarship, or taking a trip- caused a physiological fight-or-flight response similar to that caused by more disturbing change, which he called distress-such as getting a bad grade in a course, having an argument, or losing your wallet. He also noted that the same response occurred whether the threat was real or imagined (Selye, 1982).

Selye devised a theory about the health effects of chronic stress which he called the General Adaptation Syndrome (GAS). When exposed to chronic stress, such as continuous exposure to loud noise, an animal exhibits three stages of adaptation. Initially, the fight-or-flight response occurs, which Selye called the alarm reaction. Physiologists link the alarm reaction to the autonomic nervous system's immediate response to stress (Tortora & Grabowski, 1993). As exposure to the stressor continues, the animal will develop some resistance to the stressor. Selye referred to this period as the stage of resistance. Physiologists have characterized this stage as being supported by the various stress hormones that circulate throughout the period of stress, sustaining a long-term stress reaction. The stage of resistance continues until the stressor stops or the animal's resistance is worn down. At this time it enters the stage of exhaustion, which, if the stressor continues, ends ultimately in the animal's death (Selye, 1982).

Selye's approach was typical of scientists working with laboratory animals in that its focus was on physiological response. Such a focus was convenient because it defined stress clearly and in a way that could be directly observed and measured in the laboratory. This early research laid the groundwork for the expanded definitions of stress to follow.

Selye continued to research and write about stress throughout his life. He theorized that each person possesses a finite amount of "adaptation energy," which he compared to "an inherited bank account from which we can make withdrawals but to which we apparently cannot make deposits" (Selye, 1982, p. 10). To Selye, eustress and distress both resulted in some degree of wear and tear, which accumulated to produce aging.

Stress researchers today have a deep respect for Selye's groundbreaking work, much of which continues to be supported by scientific investigation. Subsequent research has shown, however, that our responses to eustress and distress do differ somewhat, as do their health consequences. Psychologists also believe we probably can make deposits into our "inherited bank account" of adaptation energy, and this is what increasing one's stress resistance is all about. In modified form, however, Selye's adaptation energy theory holds much truth. We have all felt our adaptation energy run low when faced with excessive stress, and current research supports the notion that too much change increases one's likelihood of developing stress-related illnesses (Holmes & Rahe, 1967).

FIGHT OR FLIGHT: THE CARDIOVASCULAR SYSTEM RESPONDS

Now that you understand how the fight-or-flight response comes about, let's take a closer look at its effects. As you prepare to run away from that vicious pit bull terrier, your pounding heart signals that the cardiovascular system is ready far action.

The cardiovascular system includes the heart, blood vessels, and blood. This system circulates blood to every cell in the body, delivering oxygen, fuel, and hormones, and removing waste products. Physical activity dramatically increases the need for these services, which is why the cardiovascular system responds so strongly to stress.

Sympathetic stimulation causes an immediate increase in heart rate that is reinforced by the epinephrine and norepinephrine released into the bloodstream by the adrenal medulla. This response helps you retreat from the snarling dog but can be a distraction for stress that does not require a strong physical response. Perhaps you have felt your heart pound when called on in class, before giving a presentation, or when excited about a phone call. After a while, you relax, your heart calms down, and no harm is done. But in cases of extreme fright or for someone with an unhealthy heart, an overdose of catecholamines can be damaging and even fatal. The heart rate can become irregular and interfere with effective circulation; coronary arteries may spasm, cutting off blood flow to the heart muscle (Monagan, 1986; Turkkan et al., 1982). A catecholamine overdose may be responsible for heart attacks caused by cocaine, which stimulates the sympathetic nervous system (Gawin, 1991; Isner et al., 1986).

Another major effect of the nervous and endocrine systems' stress response on the cardiovascular system is an increase in blood pressure. High resting blood pressure is called hypertension, and is caused by many factors, including too much stress. Blood pressure is a measure of the force exerted by the blood against the blood vessel walls. It can be measured using a blood pressure cuff (called a sphygmomanometer) and stethoscope, and is typically measured in the arteries of the upper arm. The pressure of the blood against the arterial walls is greatest at the moment blood is ejected from the heart as it contracts. This pressure is called the systolic blood pressure. The diastolic blood pressure is the pressure in the arteries while the heart is "resting" between beats. Pressure is measured in units called millimeters of mercury (mmHg), referring to the distance a column of mercury rises in a tube for a given pressure: the greater the pressure, the higher the column will rise. It is written as systolic/ diastolic. Normal resting blood pressure varies from person to person but is usually about 120/80 for men and 110/70 for women.

During exercise, systolic blood pressure rises quickly as the amount of blood pumped by the heart increases. This is a healthy response and ensures an adequate blood supply to the working muscles. Blood pressure returns to normal after exercise. During the stress response, both systolic and diastolic blood pressures tend to rise. Diastolic pressure increases with the increased blood volume and increased peripheral resistance that results from the stress response. More fluid ejected with greater force in a smaller system means more pressure. (During exercise peripheral resistance decreases as peripheral arteries dilate to increase blood flow to the skin for cooling.)

The increase in blood pressure that occurs during the stress response does not appear to be harmful in healthy people. In fact, as you run from the pit bull terrier, it is quite helpful! You have a good supply of blood to your brain and muscles. The problem with blood pressure elevation during stress comes when you don't really need to respond physically to the stressor at hand, which is most of the time. When excess stress becomes a chronic situation, the nervous and endocrine stimulation may cause blood pressure to become chronically elevated if that stress response is not balanced with a healthy dose of the relaxation response (Benson, 1977).

THE SKELETAL MUSCLES: READY TO SPRING

The next time you watch a movie, monitor your level of muscle tension. You may find that high- energy scenes lead to a sympathetic response. As the protagonist breathlessly pursues the villain, you may brace for action as well. A loud noise and you jump!

Muscles are collections of muscle cells that are capable of contraction and relaxation. A muscle's strength of contraction is controlled by the number and type of cells that are activated, or recruited, by the nervous system. A stronger contraction is produced if more cells are recruited. Muscular contraction may or may not produce movement. Even resting muscles maintain some level of contraction. Your skeletal muscles are important actors in the fight-or- flight response. Their contraction creates the movement that enables you to fight or flee. As you prepare to respond to stress, your muscles contract in preparation for movement, much like a cat preparing to pounce. As the pit bull terrier lunges madly toward you, you might initially freeze as every muscle contracts before you spring into action.

As you relax after a successful escape from the pit bull's jaws, your muscles relax as well. But imagine an individual under chronic stress, and a muscle group that remains chronically contracted as it continually braces for action, unable to let go. This is the beginning of the muscle tension problems that commonly occur in the jaw, neck, shoulder, and back as posture muscles prepare you to face the worst. Muscle tension creates pain that creates stress and more muscle tension. Pain from muscle tension may be the result of a partially contracted muscle cutting off blood flow, leading to oxygen deprivation and a buildup of waste products in the muscle tissue. Pain may also be caused by muscle spasms that put abnormal pressure on sensitive joint areas, or lead to muscle tears from inflexibility (Girdano et al., 1997).

STUDENT STRESS

CORY'S FIGHT-OR-FLIGHT RESPONSE

As Cory slugged his way through the stress physiology chapter of his stress management text, he could feel his neck and shoulders getting tighter and tighter. The tongue-twisting terminology was so foreign, and the effects of the stress hormones all sounded alike. "I hope the professor doesn't expect us to memorize all this!" he muttered aloud. An imaginary exam question began to take shape in his mind: "Describe in detail the physiology of the stress response. List the action of each hormone. Points deducted for incorrect spelling." Even though the stressor was imaginary, he could feel his breathing become shallower, and the tension in his neck and shoulders became painful.

As he read the section on muscle bracing, he recognized his symptoms immediately. "That's me," he thought. "Ready to respond at the least provocation." He could see himself hunched over like a boxer approaching his opponent, ready to throw a punch. Cory wondered whether he could change his muscle-bracing response to stress and decided to make it the focus of his work in the stress management course.

THE DIGESTIVE SYSTEM: PUT ON HOLD

Have you ever given a presentation and had a hard time talking because your mouth was very dry? Did you ever get into an argument during a meal and suddenly lose your appetite or develop a stomachache? Have you ever been unable to eat for a week because you had just fallen in love? These symptoms are a function of the effects the stress response has on the digestive system (see Figure 2.9).

The digestive system is responsible for converting food into molecules that can be used by the body. Food is ingested through the mouth, where it begins to be broken down by chewing and saliva. It is swallowed into the esophagus, which transports it into the stomach. There is a tight band of muscle called a sphincter (in this case it's called the lower esophageal sphincter) between the esophagus and the stomach that relaxes during swallowing but then prevents stomach contents from backing up into the esophagus. Heartburn occurs when this sphincter relaxes and allows the acidic contents of the stomach to enter the esophagus and produce a burning sensation.

In the stomach a number of chemicals, including hydrochloric acid, continue the process of digestion as the stomach contracts rhythmically to churn the food. The stomach contents exit the stomach through another sphincter into the small intestine, where they are further digested. The part of the small intestine adjacent to the stomach is called the duodenum and is a favorite place for ulcers. Useful molecules are absorbed or transported from the small intestine into the blood stream for use by body cells. The leftovers are sent to the large intestine and out of the body through the anal canal. The digestive system is composed primarily of smooth muscle, which conducts the food through the system by slow rhythmic contractions known as peristalsis. Other organs considered part of the digestive system include the pancreas, liver, and gallbladder, which manufacture and secrete substances that assist in the digestive processes.

FIGURE 2.9 Major organs of the digestive system

We've seen that as you run away from the snarling dog, digestion of your lunch is put on hold as a strong cardiovascular response and contraction of skeletal muscles take priority. The normal flow of saliva decreases; stomach acidity may increase; peristaltic motion in the esophagus, stomach, and intestines may accelerate or slow down. Noticeable symptoms include a dry mouth, stomach cramps or "butterflies," nausea, abdominal cramps, and even vomiting and diarrhea. These do not actually assist you as you fight or flee but are side effects of the stress response and can be annoying. Chronic stress can open a Pandora's box of digestive complaints from gum disease and esophageal spasms to ulcers and constipation; they are discussed more fully in the next chapter.

STRESS AND YOU

FIGHT OR FLIGHT? OR SIT AND STEW?

YOUR EXPERIENCE WITH THE FIGHT-OR-FLIGHT RESPONSE

We have presented a rather generic version of the fight-or-flight response, simplified for easier learning, but of course the stress response manifests itself differently from person to person. It varies with the intensity and duration of the stressor. It may vary somewhat with fitness level (Sothman et al., 1991). And some studies suggest that there may be small differences between men and women, with men experiencing more deleterious cardiovascular responses (Johansson et al., 1989; Stoney et al., 1988). Most of all, it varies with one's degree of stress resistance (Dienstbier, 1991).

Take a moment to think about your own stress response. We have noted that the fight-or-flight response is very useful for situations requiring a physical response. This arousal is often helpful for mental activity as well. It sharpens the mind and is useful for giving good performances, writing inspired exams and papers, and energizing important conversations. It does not appear to be harmful as long as it is balanced by the relaxation response. But what about those days when you, feel continually wound up, with one thing after another going wrong? Maybe at the end of one of those days you have gone to bed but been unable to sleep because your muscles were still tense and your heart was still beating more quickly than usual.

Try to recall one or two recent occasions when you remember the fight-or-flight response as inappropriate and obstructive. It could be something as simple as the alarm going off in the morning. Try to remember your physical response to those sources of stress. For each source of stress, try to answer the following questions:

What was the source of stress?

What were your physical symptoms?

How long did they last?

What did you finally do to relax?

SUMMARY

A healthy fight-or-flight response provided an advantage to our ancient ances tors. Several physiological systems have evolved to ensure the function of this response that has, until relatively recently, been so important for survival.
The fight-or-flight response is controlled by the nervous and endocrine systems. The combined actions of these systems increase metabolic rate and mobilize fuel for energy production; increase blood pressure, blood flow, and respiration; and inhibit systems not essential for immediate survival.
The sympathetic branch of the autonomic nervous system initiates the fight-or-flight response.
Many areas of the brain coordinate our physical and psychological stress response as well as our conscious and subconscious responses to stressors. Th hypothalamus and pituitary gland are especially important in the physiological regulation of the fight-or-flight response.
The organs of the endocrine system produce chemical messengers that help regulate the fight-or-flight response.
The adrenal medulla secretes epinephrine and norepinephrine in response to sympathetic stimulation. These hormones have actions that enhance cardiac and respiratory function, increase blood sugar level, increase blood volume and speed clotting.
The hypothalamus-pituitary-adrenal pathway stimulates the adrenal cortex to release glucocorticoids and mineralocorticoids. These hormones raise blood sugar and blood pressure, and inhibit inflammation and immune function.
The hypothalamus-pituitary-thyroid pathway stimulates the thyroid gland to produce thyroid hormones. These increase resting metabolic rate, raise blood sugar, and enhance cardiac and respiratory function
The antidiuretic hormone (vasopressin) increases blood pressure.
The fight-or-flight response causes an increase in heart rate and contractile force and an increase in blood pressure. Chronic stress can contribute to hypertension.
Muscles contract during the fight-or-flight response to prepare for action Chronic muscle contraction can lead to muscle tension problems.
The fight-or-flight response inhibits digestive processes. Chronic stress can cause a number of gastrointestinal disorders.
Hans Selye defined stress as the nonspecific response of the body to any demand made on it. He believed that eustress and distress cause similar physical responses.
The General Adaptation Syndrome is composed of the alarm reaction, the stage of resistance, and the stage of exhaustion.

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