Which of the following is NOT a primary component of the stress response system?

The correct answer is the respiratory system because it is not a primary component of the stress response system. The stress response is primarily governed by the role of the hypothalamus, pituitary gland, and adrenal glands, often referred to collectively as the HPA axis (hypothalamic-pituitary-adrenal axis).

The hypothalamus initiates the stress response by releasing corticotropin-releasing hormone (CRH), which signals the pituitary gland to release adrenocorticotropic hormone (ACTH). This hormone then stimulates the adrenal glands to produce cortisol and other stress hormones, which prepare the body to respond to stressors.

In contrast, while the respiratory system may react to stress—such as by increasing breathing rate during a stressful event—it is not part of the central mechanism that regulates the stress response itself. The involvement of the respiratory system is more of a physiological effect of stress rather than a core component of the stress response mechanism. Thus, highlighting the HPA axis is essential to understanding the stress response, making the respiratory system not a primary component.