AQA Biopsychology Practice Exam — Prep, Practice Test & Study Guide

In the fight or flight response, the first step involves the hypothalamus sending a signal to the adrenal gland. This is a crucial part of the body's neuroendocrine system, which coordinates the immediate reaction to a perceived threat.

When an individual identifies a threat, the hypothalamus activates the autonomic nervous system (ANS) and signals the adrenal medulla, leading to the release of adrenaline (epinephrine) into the bloodstream. This release then triggers various physiological changes in the body, such as increased heart rate, heightened alertness, and energy mobilization.

Identifying the threat initiates the whole response, but it is the signaling from the hypothalamus that specifically activates the adrenal glands to produce adrenaline, marking the first biological event in this acute stress response. Consequently, understanding this sequence is key to grasping how the body prepares for immediate action in threatening situations.