The corticotropin-releasing factor (CRF)/hypothalamic-pituitary-adrenal (HPA) axis system plays an important role in the stress response. CRF is released from the hypothalamus, with stimulation of adrenocorticotropic hormone (ACTH) release from the pituitary, resulting in glucocorticoid (Cortisol in man) release from the adrenal, which in turn has a negative feedback effect on the axis at the level of the pituitary, as well as central brain sites including hypothalamus and hippocampus. Cortisol has several effects that facilitate survival. In addition to its role in triggering the HPA axis, CRF acts centrally to mediate fear-related behaviors and triggers other neurochemical responses to stress, such as the noradrenergic system via the brain stem locus coeruleus. Noradrenergic neurons release transmitters throughout the brain; this is associated with an increase in alerting and vigilance behaviors, critical for coping with acute threat.]
https://www.edutopia.org/article/understanding-trauma-informed-education 

https://www.npr.org/sections/ed/2014/06/15/320725558/how-trauma-affects-the-brain-of-a-learner