Cortisol is a glucocorticoid class steroid hormone; it is produced in humans by the zona fasciculate of the adrenal cortex within the adrenal gland. It is quantified as a marker for hypothalamic pituitary adrenal axis reactivity. In humans, cortisol levels are increased in stress, depression, and selected systemic diseases such as Cushing's syndrome as well as in response to low blood-glucose concentration as well as a response to psychosocial stress.