The stress response system, also known as the fight-or-flight response, is the body's automatic physiological reaction to perceived threats. Hans Selye introduced the concept of General Adaptation Syndrome (GAS) to describe the predictable pattern of changes that occur in response to stress. GAS consists of three sequential stages: alarm, resistance, and exhaustion. This model helps explain how chronic stress can contribute to health problems.
Alarm stage
In the alarm stage, the body's initial reaction to a stressor involves a temporary state of shock, during which physiological resistance to stress and illness drops below normal. This stage activates the sympathetic nervous system, releasing stress hormones like adrenaline and cortisol. Although these hormones prepare the body for a quick response to the stressor, they simultaneously suppress the immune system. This suppression increases the risk of infections and makes the body more vulnerable to illnesses or injuries during this period.
Resistance stage
If the stress continues, the body transitions into the resistance stage. In this phase, the body attempts to adapt to the ongoing stress by stabilizing and boosting its defenses. Hormones are released to counteract the effects of stress and inflammation, allowing the immune system to function more effectively. During this stage, the body can fight off infections and maintain balance with relatively high efficiency despite the persistent stress.
Exhaustion stage
However, if the stress remains unresolved, the body eventually enters the exhaustion stage. In this final stage, the prolonged stress response leads to the depletion of energy reserves, resulting in physical and mental fatigue. The body's heightened vulnerability can lead to serious health consequences, such as cardiovascular diseases, immune dysfunction, or even mortality. Continuous activation of the stress response without recovery can cause irreversible damage to vital organs and systems.
Hans Selye proposed that the stress response system, which activates in reaction to perceived threats or challenges, follows a consistent pattern.
Using this idea, he introduced the general adaptation syndrome, or GAS, which describes the body's typical responses to stress through three stages: alarm, resistance, and exhaustion.
In the alarm stage, the body experiences a temporary shock, lowering its resistance to illness and stress below normal levels.
To counteract this shock, hormones are released that briefly weaken the immune system, increasing the risk of infections.
During the resistance stage, the body increases hormone production to defend against stress, allowing the immune system to combat infections effectively.
The anti-inflammatory hormone cortisol is also released to reduce the effects of physical injuries, enhancing the body's ability to cope with challenges.
If stress persists, the body enters the exhaustion stage, where prolonged exposure to stress causes wear and tear.
During exhaustion, the risk of illness increases, and severe conditions like heart attacks may occur, which can cause lasting damage or death.
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