Chapter 22: Stress

SELYE’S CONCEPT OF STRESS Development of the stress concept Through many experiments, Selye exposed animals to noxious agents and found that they all responded with the same syndrome of changes, or “stress triad” Definitions Stress: a state or condition of the body produced by “diverse nocuous agents” and manifested by a syndrome of changes Stressors: agents that produce stress General adaptation syndrome: group of changes that manifest the presence of stress

SELYE’S CONCEPT OF STRESS (cont.) Stressors Stressors are extreme stimuli—too much or too little of almost anything Stressors are often injurious or painful stimuli Anything an individual perceives as a threat is a stressor for that individual Stressors are different for different individuals and different for one individual at different times General adaptation syndrome Manifestations: stress triad (hypertrophied adrenals, atrophied thymus and lymph nodes, and bleeding ulcers); many other changes Stages: three successive phases: alarm reaction, stage of adaptation or resistance, and stage of exhaustion; each is characterized by a different syndrome of changes (Table 22-1)

SELYE’S CONCEPT OF STRESS (cont.) Mechanism of stress Consists of a group of responses (syndrome) to internal condition of stress; stress responses are nonspecific: the same syndrome of responses occurs regardless of kind of extreme change that produced stress Stimulus that produces stress and thereby activates stress mechanism is nonspecific; it can be any kind of extreme change in the environment Stress responses, Selye believed, were adaptive, tend to enable the body to adapt to and survive extreme change; Selye referred to this syndrome of stress responses as general adaptation syndrome

SELYE’S CONCEPT OF STRESS (cont.) Numerous factors influence stress responses: individual’s physical and mental condition, age, sex, socioeconomic status, heredity, and previous experience with similar stressors Successfully coping with stress occurs most often; results in adaptation, healthy survival, and increased resistance; sometimes, however, stress produces exhaustion or death Summary of Selye’s stress mechanism (Figure 22-4, then Figures 22-2 and 22-3)

SOME CURRENT CONCEPTS ABOUT STRESS Definitions Stress: any stimulus that directly or indirectly stimulates the hypothalamus to release corticotropin-releasing hormone Stress syndrome: also called the stress response; many diverse changes initiated by stress Stress syndrome (Figure 22-6) Stress and disease: Selye held that stress could result in disease instead of adaptation Indicators of stress Changes caused by increased sympathetic activity (e.g., faster, stronger heartbeat; higher blood pressure; sweaty palms; dilated pupils) Changes resulting from increased corticoids: eosinopenia, lymphocytopenia, increased adrenocorticoids in blood and urine

SOME CURRENT CONCEPTS ABOUT STRESS (cont.) Corticoids and resistance to stress Still controversial; not proved that increased corticoids increase an animal’s or a person’s ability to resist stress, but corticoid levels in blood do increase during stress Psychological stress Psychological stressors: anything that an individual perceives as a threat to survival or self-image (Figure 22-7) Psychological stress: a mental state characterized by a syndrome of subjective and objective responses; dominant subjective response is anxiety; some characteristic objective responses are restlessness, irritability, lying, crying

SOME CURRENT CONCEPTS ABOUT STRESS (cont.) Effects of intrauterine stress Fetus develops short- and long-term responses to stress experienced during intrauterine development (Figure 22-8) Frequent stressors include maternal malnutrition, hypoxia, and exposure to toxins such as alcohol Low birth weight and preterm delivery are common immediate responses to intrauterine stress Maternal-fetal blood levels of cortisol are important mediators of stress Influenced by endocrine secretory activity of maternal-fetoplacental unit and the shared maternal-fetal hypothalamic-pituitary-adrenal mechanism

SOME CURRENT CONCEPTS ABOUT STRESS (cont.) Effects of intrauterine stress (cont.) Fetal programming responses to stress often result in negative outcomes later in life Affect many organ systems and even life expectancy Concept of “biological tradeoffs” may be involved in fetal programming outcomes; for example, low birth weight and preterm delivery may be tradeoffs by fetus to survive the stress of maternal malnutrition in a problem pregnancy

THE BIG PICTURE: STRESS AND THE WHOLE BODY Stress affects the entire body Nervous system detects and integrates stressors that trigger stress responses Stress affects immune system Neuroimmunology studies mind-immunity link