From Wikipedia, the free encyclopedia.
Cortisol (hydrocortisone, C21H3O5, ), is a corticosteroid hormone synthesized in the zona fasciculata of the cortex of the adrenal glands.
The amount of cortisol present in the serum undergoes diurnal variation, with the highest levels present in the early morning, and lower levels in the evening, several hours after the onset of sleep. Serum cortisol levels fluctuate in response to a number of other variables, including ACTH levels, psychological stress, and such physiological stressors as hypoglycemia, illness, fever, trauma, surgery, fear, pain, physical exertion or extremes of temperature.
Cortisol inhibits the secretion of corticotropin releasing hormone (CRH), resulting in feedback inhibition of ACTH secretion. This normal feedback system is overridden in situations of stress.
Most serum cortisol, all but about 4 percent, is bound to proteins including corticosteroid binding globulin, CBG, and albumin. Only free cortisol is available to most receptors.
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