Physiology of Stress
Our stress response originates in the hypothalamus, the area of the brain involved in a variety of regulatory processes. When a stressor is encountered, cells in the periventricular regions of the hypothalamus activate the ANS and HPA axis. Sympathetic neurons in the hypothalamus activate the adrenal glands to release epinephrine. Epinephrine prepares the body to respond by increasing blood flow to the heart, muscles and organs, which, in turn, results in extra bursts of oxygen to our lungs and brain, and increased glucose from our energy stores.
Once the ANS is activated, the HPA axis becomes engaged. With HPA axis activation, cells secrete corticotrophin releasing factor (CRF), a hormone which travels to the anterior lobe of the pituitary gland and binds to receptors in the anterior pituitary. These, in turn release adrencocorticotropin (ACTH), another hormone that enters general circulation and eventually activates the adrenal gland. The adrenal releases the second major stress hormone, cortisol, which travels throughout the body to produce a number of effects. Cortisol replenishes the energy stores depleted by the adrenaline rush.
The stress hormones, adrenaline and cortisol, are end points at which the HPA axis may tip out of balance. The HPA axis tries to keep the nervous system, glands and immune system in balance by adjusting the allostatic response. With repeated demands, there is gradual loss of maintenance of nromative body parameters and fluctuating neural or neuroendocrine responses.