**2. The arrangement of the stress response**

The stress response is the complex process that can be initiated by immune or central nervous system. The central nervous system reacts against macroscopic threats and controls whole body response. Thus, in face of lacking of the system integrity central nervous system switches all functions over to subordinate constitutive activities to defense against the threat. The hypothalamus – pituitary – adrenal axis is activated and vasopressin, prolactin and growth hormone are released. In clinical settings corticotropin realizing hormone and vasopressin (both stimulated by adreno-cortical signals e.g. pain, fear, hypovolemia or immunologic stimuli e.g. interleukins, TNF, cytokines) (1) synergistically increase adrenocorticotropin (ACTH) secretion. ACTH induces conversion of cholesterol to cortisol which cooperates with sympathetic nervous system to prepare a body for response by mobilization of energetic substrates, increase of intravascular volume and blood pressure enhancement (Tab.1.).

The immune system reacts against microscopic threats infringing endothelial or epithelial barriers. The initial signal is amplified by cascade of lymphokines and activated cells and stimulates central stress response which eventually terminates system overstimulation. Immune response and tissue damage contribute to systemic inflammatory response syndrome (SIRS) development. These inflammatory signals are transferred to the central nervous system by vagus nerve and activate HPA axis (2).

Adaptation to chronic stress in humans is not well understood and unnatural situation. It is mostly created in the clinical settings when treatment of critical disease is implemented and it reaches chronic phase. After acute stress response when ACTH, prolactin, growth hormone, and thyroid hormone are elevated, the pulsatile, more physiologic pattern of neurohormones concentration appears. Although normal limits of plasma neurohormons levels in stress response are not known, inadequate concentrations can lead to acute failure and shock.


**Table 1.** Role of the cortisol in stress response initiation.
