In a biological context, how is stress defined?

In a biological context, stress is defined as a response to perceived threats that impact bodily functions. This definition encompasses the physiological, psychological, and behavioral changes that occur when an individual senses a challenge or threat in their environment. The response can be understood through the lens of the body's fight-or-flight mechanism, which involves the activation of the hypothalamic-pituitary-adrenal (HPA) axis and the release of stress hormones like cortisol and adrenaline. These changes prepare the body to deal with emergencies, affecting systems such as the cardiovascular, endocrine, and immune systems.

This definition distinguishes stress from other experiences or conditions that do not necessarily involve a threat perception, such as physical exercise, which rather can be a source of positive stress (eustress). Mood disorders and emotional reactions to happiness focus on different aspects of psychological well-being and do not relate directly to the stress response mechanism that occurs biologically in reaction to threats. Understanding stress in this way highlights its role in maintaining homeostasis and the impact it can have on health outcomes when experienced chronically.