What initiates the release of cortisol in response to stress?

The correct answer is the hypothalamus, which plays a crucial role in the body's response to stress. When a person perceives stress, the hypothalamus releases corticotropin-releasing hormone (CRH). This hormone then stimulates the pituitary gland to secrete adrenocorticotropic hormone (ACTH) into the bloodstream. In turn, ACTH signals the adrenal cortex to produce and release cortisol, a key hormone that helps the body manage stress by increasing glucose availability, suppressing the immune system, and supporting overall metabolic functions.

Understanding this sequence is vital because it establishes the relationship between the hypothalamus and the endocrine response to stress through the hypothalamic-pituitary-adrenal (HPA) axis. Other options, such as the adrenal medulla and thyroid gland, are involved in different aspects of stress response, like the acute fight-or-flight response, primarily through adrenaline production, or metabolic regulation, respectively, but they do not initiate cortisol release directly. The pituitary gland does respond to the signals from the hypothalamus, but it is not the initial trigger for cortisol release.