Which endocrine organ secretes cortisol and is involved in the 'fight or flight' response?

The adrenal gland is responsible for secreting cortisol, which plays a crucial role in the body's response to stress, including the 'fight or flight' response. When faced with a stressful situation, the hypothalamus signals the adrenal glands to release cortisol and other hormones. Cortisol helps to elevate blood sugar levels, enhances the brain's use of glucose, and curbs non-essential functions in a crisis, allowing the body to respond more effectively to danger. In addition to cortisol, the adrenal glands also release adrenaline, which further aids in preparing the body to confront or escape from threats, thus embodying the 'fight or flight' response.

The other options, while important in the network of hormone regulation, do not directly secrete cortisol or play a primary role in the acute stress response. The thyroid gland is primarily involved in regulating metabolism, the pituitary gland controls various endocrine functions including some stress hormones through its signaling, and the hypothalamus coordinates the overall hormonal response but does not directly produce cortisol itself.