Final answer:
The body's first reaction to a stressor involves the fight-or-flight response, which includes the release of adrenaline and cortisol from the adrenal glands, increasing heart rate and respiration for immediate action. The HPA axis plays a crucial role in this process. If the stress continues, the body moves into the stage of resistance, adapting but remaining alert.
Step-by-step explanation:
Understanding the Fight-or-Flight Response to Stress
When the body encounters a stressor, its initial reaction is to activate the fight-or-flight response, orchestrated by the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis. This involves the release of adrenaline from the adrenal glands, resulting in increased heart rate and respiration. Simultaneously, the HPA axis prompts the hypothalamus to release corticotropin-releasing factor, which leads to the pituitary gland secreting adrenocorticotropic hormone (ACTH). ACTH then stimulates the adrenal glands to release cortisol and other hormones, preparing the body for quick action. However, if stress persists, entering the stage of resistance, the body adapts but maintains a readiness to respond as needed, with less intensity compared to the initial alarm phase.
During the general adaptation syndrome (GAS), the stage of resistance can involve physiological adaptations, such as increased nutrient absorption if food is scarce, reflecting the body's efficiency in dealing with long-term stressors. The constant alertness, while beneficial in short durations, can lead to health implications like increased susceptibility to heart disease and weakened immune response if the stress response becomes chronic.