note Right!   The Hypothalamic-Pituitary-Adrenal axis (HPA axis) is a major part of the neuroendocrine system that controls reactions to stress. Species from humans to the most ancient organisms share components of the HPA axis. It is the mechanism for a set of interactions among glands, hormones & parts of the mid-brain that mediate a general adaptation syndrome. The HPS axis also leads to puberty, not only the growth spurt but also the development of sexual characteristics.