General Adaptation Syndrome

Stress may be defined as a threat to homeostasis or the stable internal environment. The physiologic response to stress involves activation of the central nervous system (CNS) with consequent stimulation of the hypothalamic—pituitary—adrenal (HPA) axis and the autonomic nervous system Importantly, these systems respond to hormonal stimulation from the immune system; they also interact with other endocrine systems, such as those controlling gonadal, thyroid, and growth functions. The principal central control loci of the stress system are the corticotropin releasing hormone (CRH) and locus cerulus-norepinephrinergic neurons of the hypothalamus and brainstem; these neurons regulate the HPA axis and the sympathetic nervous system, respectively. The hormone products of these systems, cortisol and the catecholamines, act to maintain cardiovascular, metabolic, and immune homeostasis during stress.