What is the initial response of the body to sudden disruptions in the external environment?

The initial response of the body to sudden disruptions in the external environment is the alarm phase. This concept is rooted in the body's stress response, often described in terms of the "fight or flight" reaction. When faced with a stressor, the body first recognizes this threat and triggers an immediate response via the autonomic nervous system and the endocrine system.

During this alarm phase, the body releases stress hormones like adrenaline and cortisol, which prepare it to either confront the danger or flee from it. This response leads to heightened awareness, increased heart rate, rapid breathing, and other physiological changes that are essential for survival in a threatening situation.

In the context of the other options, resistance refers to the body’s effort to adapt and cope with the ongoing stress once the alarm phase has been initiated, while recovery signifies a return to baseline functioning after the stressor has been managed or resolved. Homeostasis, on the other hand, represents the overall balance and stability of internal conditions in the body, which is a longer-term state rather than an immediate reaction to a sudden disruption. Thus, the alarm phase is clearly defined as the body's first response to a stressor, making it the correct answer.