Stress Biology Learning Path

Definition of stress and stressors

Stress (physiological, biological, or psychological) is an organism’s response to a stressor—such as an environmental condition or a change in life circumstances. When stressors disrupt an organism’s equilibrium, multiple body systems respond, including in humans and most mammals the autonomic nervous system (ANS) and the hypothalamic-pituitary-adrenal (HPA) axis. Key hormones involved include adrenaline and cortisol, which help coordinate short-term adaptation and longer-term regulation of bodily functions. Stressors are the stimuli or demands that trigger these responses. They can be acute (intense but shorter-lived) or chronic (persisting over longer periods), and chronic stressors are often more harmful because they require repeated physiological activation. In psychology, stressors can contribute to anxiety, depression, and other disorders, especially when coping resources are limited. Stress is also linked to the biological need for equilibrium (homeostasis): disruptions that push the body away from its optimal functioning can be experienced as stress, while attempts to restore balance can also involve stress-related physiological demands.

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Homeostasis and equilibrium as stress framework

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