The stress response of the body is somewhat like an airplane readying for take-off. Virtually all systems (eg, the heart and blood vessels, the immune system, the lungs, the digestive system, the sensory organs, and brain) are modified to meet the perceived danger.

External and Internal Stressors

People can experience either external or internal stressors.

· External stressors include adverse physical conditions (such as pain or hot or cold temperatures) or stressful psychological environments (such as poor working conditions or abusive relationships). Humans, like animals, can experience external stressors.

· Internal stressors can also be physical (infections, inflammation) or psychological. An example of an internal psychological stressor is intense worry about a harmful event that may or may not occur. As far as anyone can tell, internal psychological stressors are rare or absent in most animals except humans.

Acute or Chronic

Stress Stressors can also be defined as short-term (acute) or long-term (chronic).

Acute Stress: Acute stress is the reaction to an immediate threat, commonly known as the fight or flight response. The threat can be any situation that is experienced, even subconsciously or falsely, as a danger.

Common acute stressors include: · noise, · crowding, · isolation, · hunger, · danger, · infection, and · imagining a threat or remembering a dangerous event. Under most circumstances, once the acute threat has passed, the response becomes inactivated and levels of stress hormones return to normal, a condition called the relaxation response.

Chronic Stress: Frequently, however, modern life poses on-going stressful situations that are not short-lived and the urge to act (to fight or to flee) must be suppressed. Stress, then, becomes chronic. Common chronic stressors include: · on-going highly pressured work, · long-term relationship problems, · loneliness, and · persistent financial worries.

WHAT IS THE EFFECT OF ACUTE STRESS?

The best way to envision the effect of acute stress is to imagine oneself in a primitive situation, such as being chased by a bear. The Brain's Response to Acute Stress In response to seeing the bear, a part of the brain called the hypothalamic-pituitary-adrenal (HPA) system is activated.

Release of Steroid Hormones. The HPA systems trigger the production and release of steroid hormones ( glucocorticoids), including the primary stress hormone cortisol. Cortisol is very important in marshaling systems throughout the body (including the heart, lungs, circulation, metabolism, immune systems, and skin) to deal quickly with the bear.

Release of Catecholamines. The HPA system also releases certain neurotransmitters (chemical messengers) called catecholamines, particularly those known as known as dopamine, norepinephrine, and epinephrine (also called adrenaline).

· Catecholamines activate an area inside the brain called the amygdala, which apparently triggers an emotional response to a stressful event. (In the case of the bear, this emotion is most likely fear.)

· Neurotransmitters then signal the hippocampus (a nearby area in the brain) to store the emotionally loaded experience in long-term memory. In primitive times, this combination of responses would have been essential for survival, when long-lasting memories of dangerous stimuli (ie, the large bear) would be critical for avoiding such threats in the future.

· During a stressful event, catecholamines also suppress activity in areas at the front of the brain concerned with short-term memory, concentration, inhibition, and rational thought. This sequence of mental events allows a person to react quickly to the bear, either to fight or to flee from it. (It also hinders the ability to handle complex social or intellectual tasks and behaviors.)

Response by the Heart, Lungs, and Circulation to Acute Stress

As the bear comes closer, the heart rate and blood pressure increase instantaneously.

· Breathing becomes rapid and the lungs take in more oxygen.

· Blood flow may actually increase 300% to 400%, priming the muscles, lungs, and brain for added demands.

· The spleen discharges red and white blood cells, allowing the blood to transport more oxygen.

The Immune System's Response to Acute Stress

The effect on the immune system from confrontation with the bear is similar to marshaling a defensive line of soldiers to potentially critical areas.

· The steroid hormones dampen parts of the immune system, so that infection fighters (including important white blood cells) or other immune molecules can be redistributed.

· These immune-boosting troops are sent to the body's front lines where injury or infection is most likely, such as the skin, the bone marrow, and the lymph nodes.

The Acute Response in the Mouth and Throat

As the bear gets closer, fluids are diverted from nonessential locations, including the mouth. This causes dryness and difficulty in talking. In addition, stress can cause spasms of the throat muscles, making it difficult to swallow.

The Skin's Response to Acute Stress

The stress effect diverts blood flow away from the skin to support the heart and muscle tissues. (This also reduces blood loss in the event that the bear catches up.) The physical effect is a cool, clammy, sweaty skin. The scalp also tightens so that the hair seems to stand up.

Metabolic Response to Acute Stress

Stress shuts down digestive activity, a nonessential body function during short-term periods of physical exertion or crisis.

The Relaxation Response: the Resolution of Acute Stress Once the threat has passed and the effect has not been harmful (ie, the bear has not eaten or seriously wounded the human), the stress hormones return to normal. This is known as the relaxation response. In turn, the body's systems also normalize.

WHAT ARE THE NEGATIVE EFFECTS OF STRESS?

In prehistoric times, the physical changes in response to stress were an essential adaptation for meeting natural threats. Even in the modern world, the stress response can be an asset for raising levels of performance during critical events such as a sports activity, an important meeting, or in situations of actual danger or crisis. If stress becomes persistent and low-level, however, all parts of the body's stress apparatus (the brain, heart, lungs, vessels, and muscles) become chronically over- or under-activated. This may produce physical or psychologic damage over time. Acute stress can also be harmful in certain situations.

Stress-related conditions that are most likely to produce negative physical effects include:

· An accumulation of persistent stressful situations, particularly those that a person cannot easily control (for example, high-pressured work plus an unhappy relationship).

· Persistent stress following a severe acute response to a traumatic event (such as an automobile accident). · An inefficient or insufficient relaxation response.

· Acute stress in people with serious illness, such as heart disease.

Psychologic Effects of Stress

Studies suggest that the inability to adapt to stress is associated with the onset of depression or anxiety. In one study, two-thirds of subjects who experienced a stressful situation had nearly six times the risk of developing depression within that month. Some evidence suggests that repeated release of stress hormone produces hyperactivity in the hypothalamus-pituitary-adrenal axis and disrupts normal levels of serotonin, the nerve chemical that is critical for feelings of well-being. Certainly, on a more obvious level, stress diminishes the quality of life by reducing feelings of pleasure and accomplishment, and relationships are often threatened.

Heart Disease

Mental stress is as major a trigger for angina as physical stress. Incidents of acute stress have been associated with a higher risk for serious cardiac events, such as heart rhythm abnormalities and heart attacks, and even death from such events in people with heart disease.

Stress activates the sympathetic nervous system (the automatic part of the nervous system that affects many organs, including the heart). Such actions and others may negatively affect the heart in several ways:

· Sudden stress increases the pumping action and rate of the heart and causes the arteries to constrict, thereby posing a risk for blocking blood flow to the heart.

· Emotional effects of stress alter the heart rhythms and pose a risk for serious arrythmias in people with existing heart rhythm disturbances.

· Stress causes blood to become stickier (possibly in preparation of potential injury), increasing the likelihood of an artery-clogging blood clot.

· Stress may signal the body to release fat into the bloodstream, raising blood-cholesterol levels, at least temporarily.

· In women, chronic stress may reduce estrogen levels, which are important for cardiac health.

· Stressful events may cause men and women who have relatively low levels of the neurotransmitter serotonin (and therefore a higher risk for depression or anger) to produce more of certain immune system proteins (called cytokines), which in high amounts cause inflammation and damage to cells, including possibly heart cells.

· Recent evidence confirms the association between stress and hypertension (high blood pressure). People who regularly experience sudden increases in blood pressure caused by mental stress may, over time, develop injuries in the inner lining of their blood vessels. In one 20-year study, for example, men who periodically measured highest on the stress scale were twice as likely to have high blood pressure as those with normal stress. The effects of stress on blood pressure in women were less clear.

More research is needed to confirm the actual harm of stress on the heart. For example, one study of people who work under demanding conditions suggested that heart disease, including high blood pressure, attributed to work stress may simply be due to the way people cope with the stress. People who are trying to deal with stress often resort to unhealthy habits including high-fat and high-salt diets, tobacco use, alcohol abuse, and a sedentary lifestyle. In one study, men were more apt to use alcohol or eat less healthily in response to stress, while women tended to have healthier ways of coping.

Stroke

One survey revealed that men who had a more intense response to stressful situations, such as waiting in line or problems at work, were more likely to have strokes than those who did not report such distress. In some people prolonged or frequent mental stress causes an exaggerated increase in blood pressure. In fact, a 2001 study has linked for the first time a higher risk for stroke in adult Caucasian men and elevated blood pressure during times of stress.

Susceptibility to Infections

Chronic stress appears to blunt the immune response and increase the risk for infections and may even impair a person's response to immunizations. A number of studies have shown that subjects under chronic stress have low white blood cell counts and are vulnerable to colds. And once any person catches a cold or flu, stress can exacerbate symptoms. People who harbor herpes or HIV viruses may be more susceptible to viral activation following exposure to stress. Even more serious, some research has found that HIV-infected men with high stress levels progress more rapidly to AIDS when compared to those with lower stress levels. (In some studies, stressful events most linked with a higher incidence of infections were interpersonal conflicts, such as those at work or in a marriage.)

Immune Disorders

The contradictory effects of stress on the immune system can have mixed effects on autoimmune diseases (which are those that are caused by inflammation and damage from immune attacks on the body). For example, eczema, lupus, and rheumatoid arthritis may demonstrate changes ranging from improvement to deterioration in response to stress. A 2001 study reported that short-term stress appears to have no negative effect on multiple sclerosis, but chronic stress is a major risk factor for flare-ups.

Cancer

Current evidence does not support the idea that stress causes cancer. Nevertheless, some animal studies suggest that lack of control over stress (not simply stress itself) had negative effects on immune function and contributed to tumor growth. And, two small studies on melanoma and breast cancer patients reported improved survival with therapies that offered emotional support. Other research has not detected similar survival benefits, but support groups still have great value in reducing stress in patients with terminal cancer.

Gastrointestinal Problems

The brain and the intestine are strongly related and mediated by many of the same hormones and nervous system. (Indeed, some research suggests that the gut itself has features of a primitive brain.) It is not surprising then that prolonged stress can disrupt the digestive system, irritating the large intestine and causing diarrhea, constipation, cramping, and bloating. Excessive production of digestive acids in the stomach may cause a painful burning.

Irritable Bowel Syndrome. Irritable bowel syndrome (or spastic colon) is strongly related to stress. With this condition, the large intestine becomes irritated, and its muscular contractions are spastic rather than smooth and wave like. The abdomen is bloated and the patient experiences cramping and alternating periods of constipation and diarrhea. Sleep disturbances due to stress can further exacerbate irritable bowel syndrome.

Peptic Ulcers. It is now well established that most peptic ulcers are either caused by the H. pylori bacteria or by the use of nonsteroidal anti-inflammatory (NSAID) medications (such as aspirin and ibuprofen). Nevertheless, studies still suggest that stress may predispose someone to ulcers or sustain existing ulcers. Some experts, in fact, estimate that social and psychologic factors play some contributing role in 30% to 60% of peptic ulcer cases, whether they are caused by H. pylori or NSAIDs. In any case, some experts believe that the anecdotal relationship between stress and ulcers is so strong that attention to psychological factors is still warranted.

Inflammatory Bowel Disease. Although stress is not a cause of inflammatory bowel disease (Crohn's disease or ulcerative colitis), there are reports of an association between stress and symptom flare-ups. One study, for example, found that while short term (past month) stress did not significantly exacerbate ulcerative colitis symptoms, long term perceived stress tripled the rate of flare-ups compared to patients who did not report feelings of stress.

Eating Problems

Stress can have varying effects on eating problems and weight.

Weight Gain. Often stress is related to weight gain and obesity. Many people develop cravings for salt, fat, and sugar to counteract tension and, thus, gain weight. Weight gain can occur even with a healthy diet, however, in some people exposed to stress. And the weight gained is often abdominal fat, a predictor of diabetes and heart problems. In a 2000 study, lean women who gained weight in response to stress tended to be less able to adapt to and manage stressful conditions. The release of cortisol, a major stress hormone, appears to promote abdominal fat and may be the primary connection between stress and weight gain in such people.

Weight Loss. Some people suffer a loss of appetite and lose weight. In rare cases, stress may trigger hyperactivity of the thyroid gland, stimulating appetite but causing the body to burn up calories at a faster than normal rate.

Eating Disorders. Anorexia nervosa and bulimia nervosa are eating disorders that are highly associated with adjustment problems in response to stress and emotional issues.

Diabetes

Chronic stress has been associated with the development of insulin-resistance, a condition in which the body is unable to use insulin effectively to regulate glucose (blood sugar). Insulin-resistance is a primary factor in diabetes. Stress can also exacerbate existing diabetes by impairing the patient's ability to manage the disease effectively.

Pain

Researchers are attempting to find the relationship between pain and emotion, but the area is complicated by many factors, including effects of personality types, fear of pain, and stress itself.

Muscular and Joint Pain. Chronic pain caused by arthritis and other conditions may be intensified by stress. (According to a study on patients with rheumatoid arthritis, however, stress management techniques do not appear to have much effect on arthritic pain.) Psychologic distress also plays a significant role in the severity of back pain. Some studies have clearly associated job dissatisfaction and depression to back problems, although it is still unclear if stress is a direct cause of the back pain.

Headaches. Tension-type headache episodes are highly associated with stress and stressful events. (Sometimes the headache doesn't even start until long after a stressful event is over.) Some research suggests that tension-type headache sufferers may actually have some biological predisposition for translating stress into muscle contraction. Among the wide range of possible migraine triggers is emotional stress (although the headaches often erupt after the stress has eased). One study suggested that women with migraines tend to have personalities that over-respond to stressful situations.

Sleep Disturbances

The tensions of unresolved stress frequently cause insomnia, generally keeping the stressed person awake or causing awakening in the middle of the night or early morning.

Sexual and Reproductive Dysfunction

Sexual Function. Stress can lead to diminished sexual desire and an inability to achieve orgasm in women. Stress response can also cause temporary impotence in men. Part of the stress response involves the release of brain chemicals that constrict the smooth muscles of the penis and its arteries. This constriction reduces the blood flow into and increases the blood flow out of the penis, which can prevent erection.

Premenstrual Syndrome. Some studies indicate that the stress response in women with premenstrual syndrome may be more intense than in those without the syndrome.

Fertility. Stress may even affect fertility. Stress hormones have an impact on the hypothalamus gland, which produces reproductive hormones. Severely elevated cortisol levels can even shut down menstruation. One interesting small study reported a significantly higher incidence of pregnancy loss in women who experienced both high stress and prolonged menstrual cycles. Another reported that women with stressful jobs had shorter periods than women with low-stress jobs.

Effects on Pregnancy. Old wives' tales about a pregnant woman's emotions affecting her baby may have some credence. Maternal stress during pregnancy has been linked to a 50% higher risk for miscarriage. It is also associated with lower birth weights and increased incidence of premature births, both of which are risk factors for infant mortality. One study suggested that stress experienced by expectant mothers can even influence the way in which the baby's brain and nervous system will react to stressful events. Stress may cause physiologic alterations, such as increased adrenal hormone levels or resistance in the arteries, that may interfere with normal blood flow to the placenta.

Memory, Concentration, and Learning

Stress has significant effects on the brain, particularly on memory. The typical victim of severe stress suffers loss of concentration at work and at home and may become inefficient and accident-prone. In children, the physiologic responses to stress can clearly inhibit learning. Although some memory loss occurs with age, stress may play an even more important role than simple aging in this process. In one study older people with low stress hormone levels tested as well as younger people in cognitive tests: those with higher stress levels tested between 20% and 50% lower.

Effect of Acute Stress on Memory. Studies indicate that the immediate effect of acute stress impairs short-term memory, particularly verbal memory. In one interesting 2000 study, subjects took pills containing either cortisone (a stress hormone) or a placebo (a dummy pill). Those taking the cortisone performed significantly worse on memorization tests than those taking the placebo pill did. In an earlier study, when individuals were subjected to four days of stress, verbal memory was also impaired. Fortunately, in such cases, memory is restored after a period of relaxation.

Effect of Chronic Stress on Memory. Studies have strongly associated prolonged exposure to cortisol (the major stress hormone) to shrinkage in the hippocampus, the center of memory. For example, two studies reported that groups who suffered from post-traumatic stress disorder (Vietnam veterans and women who suffered from sexual abuse) displayed up to 8% shrinkage in the hippocampus. It is not yet known if this shrinkage is reversible.