Final answer:
The first stage of the body's reaction to stress is known as the alarm stage, which triggers the fight-or-flight response and prepares the body for immediate physical exertion.
Step-by-step explanation:
The first stage of the body's reaction to stress is known as the alarm stage. This is part of the general adaptation syndrome (GAS), which was proposed by Hans Selye. The alarm reaction is characterized by an immediate physiological response to a threatening situation, which is also referred to as the fight-or-flight response. This stage is mediated by the hormones epinephrine and norepinephrine, which prepare the body for extreme physical exertion. Consequent stages after the alarm stage include the stage of resistance, where the body adapts to the stressor, and the stage of exhaustion, which occurs if the stress persists over a longer term and can lead to adverse health effects.