Kortisol

Kortisol, also known as cortisol in English, is a glucocorticoid steroid hormone produced by the zona fasciculata of the adrenal cortex. It is released into the bloodstream in response to stress and is a key part of the hypothalamic–pituitary–adrenal (HPA) axis. Secretion follows a circadian rhythm with peak levels in the early morning and a nadir at night.

Kortisol crosses cell membranes and binds to the glucocorticoid receptor (GR); the receptor-ligand complex translocates to the nucleus and modulates gene expression via glucocorticoid response elements, producing anti-inflammatory and metabolic effects. It also exerts rapid non-genomic actions.

Functions include metabolic effects such as promoting gluconeogenesis, mobilizing amino acids from muscle, and stimulating lipolysis to raise blood glucose. It helps maintain vascular responsiveness to catecholamines and modulates the immune system by suppressing inflammatory responses; it also influences brain function and mood.

Regulation and clearance: in the blood, most kortisol is bound to corticosteroid-binding globulin and albumin; a small fraction is free and active. It is metabolized primarily in the liver and excreted by the kidneys. Enzymes 11β-hydroxysteroid dehydrogenase type 1 and type 2 interconvert cortisol and its inactive form cortisone, affecting local tissue concentrations.

Clinical relevance: abnormally high levels define Cushing's syndrome; low levels define Addison's disease. Diagnosis uses morning or salivary cortisol measurements, overnight or low-dose dexamethasone suppression tests, and 24-hour urinary free cortisol. Treatments target underlying causes; exogenous steroids can cause iatrogenic hypercortisolism.