Which gland produces the neurotransmitter secreted in response to stress?

The adrenal medulla is the correct answer because it is responsible for producing catecholamines, specifically adrenaline (epinephrine) and norepinephrine. These neurotransmitters are released into the bloodstream in response to stress, preparing the body for a fight-or-flight response. This rapid response system increases heart rate, blood pressure, and energy supplies, which are critical in stressful situations.

The other glands mentioned do play roles in the endocrine system but in different contexts. The pineal gland primarily produces melatonin, which regulates sleep-wake cycles. The hypothalamus is involved in a variety of functions, including hormone secretion that controls the pituitary gland, but it does not directly produce the neurotransmitters associated with immediate stress responses. The thyroid gland produces hormones that regulate metabolism but is not involved in the acute stress response like the adrenal medulla is.