Problem: Cortisol, a steroid, is under strong circadian control, whereby it is secreted into the bloodstream at approximately 8:00 AM every day. Almost every cell in the body has receptors for cortisol, and its diverse actions include homeostatic maintenance of blood pressure, the immune system, metabolism of proteins, carbohydrates, and fats, water balance, and immune system regulation. Cortisol's signaling mode here is _. (hint: The signaling modes and in crine; also note that spelling counts!)