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Schematic of the HPA axis (CRH, corticotropin-releasing hormone; ACTH, adrenocorticotropic hormone) Hypothalamus, pituitary gland, and adrenal cortex The hypothalamic–pituitary–adrenal axis (HPA axis or HTPA axis) is a complex set of direct influences and feedback interactions among three components: the hypothalamus (a part of the brain located below the thalamus), the pituitary gland (a ...
The activation of the HPG axis in both males and females during puberty also causes individuals to acquire secondary sex characteristics. This process, known as gonadarche, is preceded by adrenarche, the maturation of the adrenal glands, which contributes to the production of androgens responsible for some pubertal changes.
The HPA axis ultimately results in the release of cortisol, which generally has immunosuppressive effects. However, the effect of stress on the immune system is disputed, and various models have been proposed in an attempt to account for both the supposedly "immunodeficiency" linked diseases and diseases involving hyper activation of the immune ...
The mechanism lies in epinephrine being secreted by the adrenal medulla and activating glycogenolysis (the breakdown of glycogen into glucose, or promoting gluconeogenesis (glucose formation). While epinephrine has a greater effect in glucose production, norepinephrine can also increase glucose levels but at high concentrations.
The activation of SNS during an immune response might be aimed to localize the inflammatory response. The body's primary stress management system is the HPA axis. The HPA axis responds to physical and mental challenge to maintain homeostasis in part by controlling the body's cortisol level.
In people with MDD this often shows increased activation in depressed people, but the mechanism behind this is not yet known. [120] Increased basal cortisol levels and abnormal response to dexamethasone challenges have been observed in people with MDD. [121] Early life stress has been hypothesized as a potential cause of HPA dysfunction.
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If the amygdala perceives a match to the stimulus, i.e., if the record of experiences in the hippocampus tells the amygdala that it is a fight, flight or freeze situation, then the amygdala triggers the HPA (hypothalamic–pituitary–adrenal) axis and "hijacks" or overtakes rational brain function. [5]