The stress response, known as the general adaptation syndrome, helps us cope with situations that make us anxious and worried. It happens in three stages: the fight-or-flight response, resistance reaction, and exhaustion.
Our fight-or-flight response is initiated by the nerve impulses coming from the hypothalamus. These impulses will activate our sympathetic nervous system and the adrenal medulla. The adrenal glands will release hormones that will increase our heart rate, blood pressure, and blood sugar (resulting in a burst of energy). Overall, this response increases our blood circulation and ATP production. It will also slow down nonessential activities.
As the stress continues, we will now enter the resistance reaction. The sympathetic division will continue to release hormones from the hypothalamus that will help the body to fight off or resist the stressor. These hormones include growth hormone-releasing hormone (GHRH), corticotropin-releasing hormone (CRH), and thyrotropin-releasing hormone (TRH). This stage lasts longer because it will continue until the stressor ends or the individual has used up all their resources. This stage also accelerates the breakdown reactions of the body to provide more ATP to counteract the stress.
Exhaustion occurs when the body's resources are all used. Too much exposure to high levels of cortisol and other hormones involved in the resistance stage will cause damage to our body (e.g., muscle waste, immune system suppression, etc.). Pathological changes may also occur because resistance reactions may continue even after the stressor is long gone. Thus, it can lead to stress-related diseases, such as hypertension and a weakened immune system.
With that, interleukin-I plays a role by linking stress to immunity. Interleukin-I is produced by our macrophages and stimulates the Adrenocorticotropic hormone (ACTH) secretion, which produces cortisol. Aside from the role cortisol plays in the resistance stage, it also prevents the production of interleukin-1. Thus, the immune system will initiate the stress response, and when cortisol is produced, it will turn off one immune system mediator.
Reference:
Tortora GJ & Derrickson B. (2014). Chapter 18.14 The Stress Response. Principles of Anatomy and Physiology. John Wiley & Sons, Inc. 14 edition. Pp 713-714.