When we refer to the HPA-axis, we are referring to a complex communication system that encompasses three different regions of our body. This communication system is crucial for our survival, because it is an important part of our defense when faced with threats, and because it coordinates the re-establishment of homeostasis when the threat is over. Therefore, the activity of the HPA-axis is a part of the stressresponse, and its main function is to improve our chances of survival in the presence of threats to our physical or psychological well-being. Communication is established between the hypothalamus, the pituitary gland and the adrenal gland through the release of hormones (see figure 1). When the HPAaxis is activated due to, for example, the presence of a physical or psychological stressor, the paraventricular nucleus of the hypothalamus releases corticotropin releasing hormone (CRH) and arginine-vasopressin (AVP) into the portal circulation of the median eminence. CRH and AVP induce the pituitary gland to secrete adrenocorticotropic hormone (ACTH) into the bloodstream, which stimulates the cortex of the adrenal glands, where, finally, glucocorticoids are released into the bloodstream (Ulrich- Lai and Herman, 2009). The most notable glucocorticoid in humans is cortisol.