Which hormone is associated with morning wakefulness and stress?

• A. Cortisol
• B. Melatonin
• C. Dopamine
• D. Serotonin

Answer: (A)

Cortisol is the hormone tied to both morning wakefulness and the body's stress response. It is released by the adrenal cortex under stimulation from ACTH in the pituitary as part of the HPA axis. Cortisol shows a daily pattern, with levels rising soon after waking—this cortisol awakening response helps increase glucose availability, energy, and alertness to start the day. It also rises in response to stress, preparing the body to meet challenges by mobilizing energy, supporting cardiovascular function, and modulating the immune system.

Melatonin promotes sleep and is higher in darkness, so it supports sleep rather than wakefulness. Dopamine influences motivation and arousal but is not the primary hormone linked to the morning rise or the general stress response. Serotonin regulates mood and various aspects of sleep-wake regulation but, again, is not the main hormone responsible for morning wakefulness or stress.