Wikipedia: Cortisol

In normal release, cortisol (like other glucocorticoid agents) has widespread actions which help restore homeostasis after stress. (These normal endogenous functions are the basis for the physiological consequences of chronic stress - prolonged cortisol secretion.) * It acts as a physiological antagonist to insulin by promoting glycogenolysis (breakdown of glycogen), breakdown of lipids (lipolysis), and proteins, and mobilization of extrahepatic amino acids and ketone bodies. This leads to increased circulating glucose concentrations (in the blood). There is a decreased glycogen formation in the liver . [2] Prolonged cortisol secretion causes hyperglycemia. * It can weaken the activity of the immune system . Cortisol prevents proliferation of T-cells by rendering the interleukin-2 producer T-cells unresponsive to interleukin-1 (IL-1), and unable to produce the T-cell growth factor.[3] It reflects leukocyte redistribution to lymph nodes, bone marrow, and skin. Acute administration of corticosterone (the endogenous Type I and Type II receptor agonist), or RU28362 (a specific Type II receptor agonist), to adrenalectomized animals induced changes in leukocyte distribution. * It lowers bone formation thus favoring development of osteoporosis in the long term. Cortisol moves potassium into cells in exchange for an equal number of sodium ions.[4] This can cause a major problem with the hyperkalemia of metabolic shock from surgery. * It helps to create memories when exposure is short-term; this is the proposed mechanism for storage of flash bulb memories. However, long-term exposure to cortisol results in damage to cells in the hippocampus. This damage results in impaired learning. * It increases blood pressure by increasing the sensitivity of the vasculature to epinephrine and norepinephrine. In the absence of cortisol, widespread vasodilation occurs. * It inhibits the secretion of corticotropin-releasing hormone (CRH), resulting in feedback inhibition of ACTH secretion. Some researchers believe that this normal feedback system may break down when animals are exposed to chronic stress. * It increases the effectiveness of catecholamines. * It allows for the kidneys to produce hypotonic urine.