Cortisol is a steroid hormone released from the adrenal cortex in response to ACTH. Normally, cortisol levels rise and fall during the day repeating on a 24 hour cycle (diurnal variation); highest levels are at about 6 to 8 A.M. and lowest levels are at about midnight. Physical and emotional stress can increase serum cortisol, because a normal response to stress involves increased secretion of ACTH by the pituitary gland.
|