Final answer:
The hormone that inhibits immune system function in times of stress is cortisol, a corticosteroid produced by the adrenal cortex. It is involved in long-term stress response, opposing the short-term effects of epinephrine and norepinephrine.
Step-by-step explanation:
The hormone released in times of stress that directly inhibits the function of the immune system is a corticosteroid, specifically cortisol. Cortisol is a glucocorticoid produced in response to stress and has anti-inflammatory properties, which include the suppression of the immune system. This hormone is released by the adrenal cortex during long-term stress and apart from its effects on the immune system, also facilitates the breakdown of fat into fatty acids and stimulates glucose synthesis in the body.
The gland that secretes cortisol is the adrenal cortex, which is stimulated by ACTH (adrenocorticotropic hormone) released from the anterior pituitary gland. The long-term stress response involving cortisol is distinctly different from the short-term stress response mediated by epinephrine and norepinephrine, which are released by the adrenal medulla.