Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone. It is produced in many animals, mainly by the zona fasciculata of the adrenal cortex in the adrenal gland. It is produced in other tissues in lower quantities. It is released with a diurnal cycle and its release is increased in response to stress and low blood-glucose concentration. It functions to increase blood sugar through gluconeogenesis, to suppress the immune system, and to aid in the metabolism of fat, protein, and carbohydrates. It also decreases bone formation. Health effects
Metabolic response
Metabolism of glucose
In general, cortisol stimulates gluconeogenesis (the synthesis of new glucose from non-carbohydrate sources, which occurs mainly in the liver, but also in the kidneys and small intestine under certain circumstances). The net effect is an increase in the concentration of glucose in the blood, further complemented by a decrease in the sensitivity of peripheral tissue to insulin, thus preventing this tissue from taking the glucose from the blood. Cortisol has a permissive effect on the actions of hormones that increase glucose production, such as glucagon and adrenaline.Cortisol also plays an important, but indirect, role in liver and muscle glycogenolysis (the breaking down of glycogen to glucose-1-phosphate and glucose) which occurs as a result of the action of glucagon and adrenaline. Additionally, cortisol facilitates the activation of glycogen phosphorylase, which is necessary for adrenaline to have an effect on glycogenolysis.Paradoxically, cortisol promotes not only gluconeogenesis in the liver, but also glycogenesis.
Test results should, therefore, always be interpreted using the reference range from the laboratory that produced the result. Using the molecular weight of 362.460 g/mole, the conversion factor from µg/dL to nmol/L is approximately 27.6; thus, 10 µg/dL is about 276 nmol/L. Cortisol follows a circadian rhythm, and to accurately measure cortisol levels is best to test four times per day through saliva. An individual may have normal total cortisol but have a lower than normal level during a certain period of the day and a higher than normal level during a different period. Therefore, some scholars question the clinical utility of cortisol measurement.Cortisol is lipophilic, and is transported bound to transcortin (also known as corticosteroid-binding globulin) and albumin, while only a small part of the total serum cortisol is unbound and has biological activity. Serum cortisol assays measures total cortisol, and its results may be misleading for patients with altered serum protein concentrations. The salivary cortisol test avoids this problem because only free cortisol can pass through the salivary barrier. Transcortin particles are too large to pass through this barrier.Automated immunoassays lack specificity and show significant cross-reactivity due to interactions with structural analogs of cortisol, and show differences between assays. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) can improve specificity and sensitivity.