Depressive Disorders: Mechanisms, Measurement and Management by Yiru Fang

Depressive Disorders: Mechanisms, Measurement and Management by Yiru Fang

Author:Yiru Fang
Language: eng
Format: epub, pdf
ISBN: 9789813292710
Publisher: Springer Singapore


8.2 Biology of Stress

Human being and other living organisms need to keep homeostasis, which can be threatened by external and internal, or physiological (e.g., injury, pain, infection) and psychological (can be real or perceived) stimuli, namely, stressors. In response to stressors, the organism will generate a series of physiological, psychological, and behavioral changes to maintain or re-establish its homeostasis. All of these adaptive responses are collectively called stress response, in short, namely, stress. Thus, stress is the physical, psychological, and behavioral responses evoked by the stressor to cope with it, which is a fundamental requirement for survival and well-being. Stress is an adaptive process in coping with stressors during evolution and a common experience of daily life.

During the process of stress response, autonomic nervous system and HPA axis are two primary systems being activated and functioning (Belda et al. 2015; Ulrich-Lai and Herman 2009). The activation of autonomic nervous system evokes the most immediate physiological response to stressor via its sympathetic (sympathoadrenal medullary axis) and parasympathetic branches with opposing activity, which play an important role in translating stress into a response. Excitation of sympathoadrenal medullary axis increases adrenaline and noradrenaline level in blood, heart rate, vasoconstriction, and energy dedication, representing classical fight-or-flight response, while the parasympathetic arm activation attenuates sympathetic excitation and returns the body to homeostasis. The second major physiological response under stress, HPA axis activation, causes the release of corticotropin-releasing factor (CRF) from the parvocellular part of paraventricular neurons (PVN) of hypothalamus to trigger the secretion of adrenocorticotrophic hormone (ACTH) from the pituitary, and finally lead to the liberation of glucocorticoids (GCs; named cortisol in human and corticosterone in rodent, respectively) into blood, which influence many bodily functions such as metabolic, psychological, and immunological functions. The GCs can also exert self-limiting effect through negative feedback on HPA axis to prevent the rise of GCs level, which otherwise fail in some cases like chronic stress. Normally, the activation of HPA axis and autonomic nervous system is tightly regulated, ensuring the body quickly respond to stressful events and return to homeostasis rapidly. There are much complementary actions between HPA axis and sympathetic system in bodily responses such as energy mobilization and blood pressure maintenance, as circulating GCs can potentiate sympathetically mediated effects; conversely, sympathetic nervous system can facilitate GCs release via its innervation of adrenal cortex.

Besides the activation of physiological function for survival under stress (e.g., increasing energy availability and accelerating oxygen supply), other physical functions which are not for immediate survival, including appetite, digestion, and immune, will be downregulated. Meanwhile, stressed subjects will also exhibit increased alertness, vigilance, and attention, which are thought to be good for responding to threatening situation. Moreover, stress may also affect memory, reward, and susceptibility to diseases (Aich et al. 2009; Ragen et al. 2016; Gilpin 2014; Becker 2010; Laudenslager 1987; Musić and Rossell 2016; Myruski et al. 2018; Wolf 2017). In emotion, based on the appraisal of stressor by exposed individuals as routine or challenging, gratifying or taxing, benign or harmful if taxing,



Download



Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.