Environmental stresses

Physiological or biological stress is an organism's response to a stressor such as an environmental condition. Stress is the body's method of reacting to a . Stimuli that alter an organism's environment are responded to by multiple systems in the body. The autonomic nervous system and hypothalamic-pituitary-adrenal (HPA) axis are two major systems that respond to stress. The sympathoadrenal medullary (SAM) axis may activate the fight or flight response through the sympathetic nervous system, which dedicates energy to more relevant bodily systems to acute adaption to stress, while the parasympathetic nervous system returns the body to homeostasis. The second major physiological stress, the HPA axis regulates the release of cortisol, which influences many bodily functions such as metabolic, psychological and immunological functions. The SAM and HPA axes are regulated by a wide variety of brain regions, including the limbic system, prefrontal cortex, amygdala, hypothalamus, and stria terminalis. Through these mechanisms, stress can alter memory functions, reward, immune function, metabolism and susceptibility to diseases. Definitions of stress differ; however, one system proposed by Elliot and Eisdorfer suggests five types of stress. The five types of stress are labeled "acute time limited stressors", "brief naturalistic stressors", "stressful event sequence", "chronic stressors", and "distant stressors". Acute time limited stressors involve short term challenges, while, on the other hand, brief naturalistic stressors involve an event that is normal but nevertheless challenging. Stressful event sequences are a stressor that occur, and continue to yield stress into the immediate future. Chronic stressors involve exposure to a long-term stressor and a distant stressor is a stressor that isn't immediate.

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