Understanding FIGHT-OR-FLIGHT RESPONSE—The body's response to stress

By Noralyn Onto Dudt

CORTISOL,  the body's primary stress hormone, is a key part of the fight-or-flight response, a natural reaction to perceived threats.

Cortisol is a glucocorticoid hormone that your adrenal glands located at the top of the kidneys produce and release.

Hormones are chemicals that coordinate different functions in your body by carrying messages through your blood to your organs, skin, muscles and other tissues. These signals tell your body what to do and when to do it.

If the brain perceives something dangerous, the hypothalamus releases corticotropin-releasing hormone (CRH) which travels to the pituitary gland, triggering the release of adrenocorticotropic hormone (ACTH). This hormone travels to the adrenal glands, prompting them to release cortisol.

Glucocorticoids are a type of steroid hormone. They suppress inflammation in all of your bodily tissues and control metabolism in your muscles, fat, liver and bones. Glucocorticoids also affect sleep-wake cycles.

Cortisol is an essential hormone that affects almost every organ and tissue in your body. It plays many important roles,  including:

       * regulating the body's stress response

       * helping control the body's use of fats, proteins, and carbohydrates,  or your metabolism

       * suppressing inflammation

       *  regulating blood pressure

       * regulating blood sugar

       *  helping control sleep-wake cycle

The body continuously monitors cortisol levels to maintain steady levels ( homeostasis). Higher-than-normal or lower-than-normal levels can be harmful to your health.

Widely known as the "stress hormone", cortisol has many important effects and functions throughout the body aside from regulating the body's stress response. It's also important to remember that, biologically speaking, there are multiple different types of stress, including:

*acute stress—this occurs  when you're in a sudden danger within a short period of time. For example, barely avoiding a car accident  or being chased by an animal are situations that cause acute stress.

*chronic stress—chronic ( long term) stress when you experience ongoing situations that cause frustration or anxiety. One example is having a difficult or frustrating job or having a chronic illness can cause chronic stress.

*traumatic stress—this type of  stress happens when you experience a life-threatening event that induces fear and a feeling of helplessness. For example,  experiencing an extreme weather event such as a tornado,  or experiencing war or sexual assault. In some cases, these events can lead to post-traumatic stress disorder  (PTSD).

When experiencing any of these types of stress, the body will automatically release cortisol.

Because all tissues in the body have glucocorticoid receptors, cortisol can affect nearly every organ system in the body, including:  nervous system,  immune system,  cardiovascular system,  respiratory system,  reproductive system,  musculoskeletal system, integumentary system ( skin, hair, nails, glands, nerves).

A stressful situation—whether something environmental, such as a looming work deadline, or psychological, such as persistent worry about losing a job—can trigger a cascade of stress hormone that produce well-orchestrated physiological changes. A stressful incident can make the heart pound and breathing quicken. Muscles tense and beads of sweat appear. This combination of reactions to stress known as the fight-or-flight response evolved as a survival mechanism, enabling people and other mammals to react quickly to life-threatening situations. The carefully orchestrated yet near-instantaneous sequence of hormonal changes and physiological responses helps someone to fight the threat off, or flee to safety. Unfortunately, the body can also overreact to stressors that are not life-threatening, such as traffic jams, work pressure, and family difficulties.

Over the years, researchers have learned not only how and why these reactions occur, but have also gained insight into the long term effects that chronic stress has on physical and psychological health. Over time, repeated activation of the stress response takes a toll on the body. Research suggests that chronic stress contributes to high blood pressure, promotes the formation of artery-clogging deposits, and causes brain changes that may contribute to anxiety, depression, and addiction. More preliminary research suggests that chronic stress may also contribute to obesity, both direct mechanisms (causing people to eat more) or indirectly  (decreasing sleep and exercise).

The stress response begins in the brain. When someone confronts an oncoming car or other danger, the eyes or ears ( or both) send the information to the amygdala, an area of the brain that contributes to emotional processing. The amygdala interprets the images and sounds. When it perceives danger, it instantly sends a distress signal to the hypothalamus. This area of the brain functions like a command center, communicating with the rest of the body through the nervous system so that the person has the energy to fight or flee.

The hypothalamus as the "command center"  communicates with the rest of the body through the autonomic nervous system, which controls such involuntary functions as breathing, blood pressure, heartbeat, and the dilation or constriction of key blood vessels and small airways in the lungs called bronchioles. The autonomic nervous system has two components, the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system functions like a gas pedal in a car. It triggers the fight-or-flight response, providing the body with a burst of energy so that it can respond to perceived dangers. The parasympathetic nervous system acts like a brake. It promotes the "rest and digest" response that calms the body down after the danger has passed.

After the amygdala sends a distress signal, the hypothalamus activates the sympathetic nervous system by sending signals through the autonomic nerves to the adrenal glands. These glands respond by pumping hormone epinephrine ( also known as adrenaline) into the bloodstream.  As epinephrine circulates through the body, it brings ln a number of physiological changes. The heart beats faster than normal, pushing blood to the muscles, heart, and other vital organs. Pulse rate and blood pressure go up. The person undergoing these changes also starts to breathe more rapidly. Small airways in the lungs open wide. This way, the lungs take in as much oxygen as possible with each breath. Extra oxygen is sent to the brain, increasing alertness. Sight,  hearing, and other senses become sharper. Meanwhile, epinephrine triggers the release of blood sugar (glucose) and fats from temporary storage sites in the body. These nutrients flood into the bloodstream, supplying energy to all parts of the body.

All of these changes happen so quickly that people aren't aware of them. In fact,  the wiring is so efficient that the amygdala and  hypothalamus start this cascade even before the brain's visual centers have had a chance to fully process what is happening. That explains why people are able to jump out of the path of an oncoming car even before they think about what they are doing.

As the initial surge of epinephrine subsides, the hypothalamus activates the second component of the stress response system  - known as HPA axis. The network consists of the hypothalamus, the pituitary gland, and the adrenal glands. The HPA axis relies of hormonal signals to keep the sympathetic nervous system -- the "gas pedal" --- pressed down. If the brain continues to perceive something as dangerous,  the hypothalamus releases corticotropin-releasing hormone (CRH), which travels to the pituitary gland, triggering the release of adrenocorticotropic hormone ( ACTH). This hormone travels to the adrenal glands, prompting them to release cortisol. The body thus stays revved up and on high alert. When the threat passes, cortisol levels fall. The parasympathetic nervous system—the "brake"—then dampens the stress response.

Unfortunately, many people are unable to find a way to put the brakes on stress. Chronic low-level stress keeps the HPA axis activated, much like a motor idling too high for too long. After a while, this has an effect on the body that contributes to the health problems- associated with chronic stress. Persistent epinephrine surges can damage blood vessels and arteries, increasing blood pressure and raising risk of heart attacks or strokes. Elevated cortisol levels create physiological changes that help to replenish the body's energy stores that are depleted during the stress response. But they inadvertently contribute to the buildup of fat tissue and  weight gain. For example,  cortisol increases appetite,  so that people will want to eat more to obtain extra energy. It also increases storage of unused nutrients as fat.

Fortunately, there are techniques that people can learn to counter stress response:

Physical activity—exercise such as taking a brisk walk shortly after feeling stressed,  not only deepens breathing but also helps relieve muscle tension. Movement therapies such as yoga and tai chi combine fluid movements with deep breathing and mental focus can induce calm.

Social support—confidants, friends, acquaintances, co-workers, relatives,  spouses, and companions all provide a life-enhancing social net—and may increase longevity. It's not clear why, but the buffering theory holds that people who enjoy close relationships with family and friends receive emotional support that indirectly helps sustain them at times of chronic stress and crisis.

Doing physical activities, staying connected, getting enough sleep, and eating a well-balanced meal act as counters to a body that is prone to staying revved up and on high alert.