Stress is difficult to define because researchers approach it in different ways. Some use the term stress to refer to circumstances that threaten well-being or to refer to the response people have to threatening circumstances. Others think of stress as the process of evaluating and coping with threatening circumstances. Yet others use the term to refer to the experience of being threatened by taxing circumstances. This chapter will use the term stress in the last sense: the experience of being threatened by taxing circumstances.
Researchers agree that stress is subjective. People don’t have the same response to the same circumstances. Instead, stress depends on how people appraise or evaluate environmental events. If people believe that a challenge will severely tax or exceed their resources, they experience stress.
Stressors are psychologically or physically demanding events or circumstances. Research links stressors to increased susceptibility to physical illnesses such as heart disease as well as to psychological problems such as anxiety and depression.
Stressors don’t always increase the risk of illness. They tend to affect health more when they are chronic, highly disruptive, or perceived as uncontrollable. Researchers who study stress usually distinguish among three types of stressors:
Exposure to difficult circumstances doesn’t produce stress by itself. Rather, stress occurs when people experience frustration, conflict, or pressure:
Example: A student worked very hard on a term paper with the hope of getting an A but ends up with a B.
Example: A student tries to decide between two interesting classes.
Example: A boy invites a girl to a party. She finds him attractive, but going to the party means she won’t have time to study for one of her final exams.
Example: Because of his financial situation, a man might have to choose whether to keep his nice-looking car, which breaks down frequently, or buy a badly dented, but reliable, used one.
Example: A high school student wants to be accepted by the popular crowd at school, so she tries hard to distance herself from her old friends because the popular crowd considers them geeky or undesirable.
The experience of stress is accompanied by many physiological changes.
Hans Selye, a pioneer in the field of stress research, proposed that stressors of many different kinds result in a nonspecific bodily response. He said the body’s stress response consists of a general adaptation syndrome, which has three stages: alarm, resistance, and exhaustion.Stage 1.
In the alarm stage, an organism recognizes a threatening situation. The sympathetic nervous system activates, giving rise to the fight-or-flight response. Digestive processes slow down, blood pressure and heart rate increase, adrenal hormones are released, and blood is drawn away from the skin to the skeletal muscles.Stage 2.
The resistance stage occurs when stress continues. Physiological arousal stabilizes at a point that is higher than normal.Stage 3.
If stress is prolonged, organisms reach the exhaustion stage. The body’s resources run out, and physiological arousal decreases. In this stage, organisms become more susceptible to disease.
In stressful situations, the brain sends signals to the rest of the body along two pathways.
In the first pathway, the hypothalamus of the brain activates the sympathetic division of the autonomic nervous system, which in turn stimulates the inner part of the adrenal glands, which is called the adrenal medulla. The adrenal medulla releases hormones called catecholamines, which include epinephrine and norepinephrine. The action of the catecholamines results in the fight-or-flight response.
In the second pathway, the hypothalamus sends signals to the pituitary gland. The pituitary releases adrenocorticotropic hormone (ACTH) , which in turn stimulates the outer part of the adrenal glands, which is called the adrenal cortex. The adrenal cortex then releases hormones called corticosteroids, which include cortisol. Corticosteroids increase blood sugar levels, providing energy. Corticosteroids also help to limit tissue inflammation in case injuries occur.